A P P L I C AT I O N A N D I N S TA L L AT I O N G U I D E
Double Conversion UPS
®
Contents
Key factors in UPS installations .....................................................1
Introduction................................................................................1
Growing needs for high-quality
and high-availability power..........................................1
Using this guide.........................................................................1
Structure of this document...........................................1
UPS in electrical installations ...................................................2
Component functions and parameters........................2
Sources of information in setting
up installation specifications........................................3
Basic notions on installations with UPS ..................................5
Supply systems with UPS...................................................5
Purpose of UPS .............................................................5
Types of UPS..................................................................5
Double-conversion static UPS......................................5
The Operating Principle (Figure 2) ...............................5
Power quality of UPS ..........................................................6
Power quality of double-conversion UPS ...................6
Voltage quality for linear loads ....................................6
Voltage quality for non-linear loads ............................7
UPS power availability ......................................................10
What is meant by availability? ...................................10
How can availability be improved? ............................11
Key factors to the availability of installations
with UPS .......................................................................11
Selection of the configuration ..........................................13
Prerequisite step in establishing installation
specifications ...............................................................13
Power calculations...................................................................14
Elements required for power calculations ......................14
Installation considerations..........................................14
Power of a UPS............................................................14
UPS percent load.........................................................16
UPS efficiency..............................................................16
Ratings of single-UPS configurations ..............................17
Single-UPS configurations .........................................17
Power levels under steady-state conditions .............17
Power levels under transient conditions ...................18
Ratings of parallel-UPS configurations ...........................21
Parallel-UPS configurations........................................21
Power levels in redundant parallel
configurations..............................................................22
Control of upstream harmonics .............................................24
UPS and upstream harmonics .........................................24
Role of the input rectifier ............................................24
Standard rectifiers.......................................................24
PFC-type transitor-based controlled
active rectifiers ............................................................24
Filtering of upstream harmonics
for UPS with Graetz bridge rectifiers ...............................25
Goals of harmonic filtering.........................................25
Types of harmonics filters ..........................................26
Filtering and parallel connection ...............................26
Combination of LC filters and generator...................26
Selection of a filter ............................................................28
Selection parameters for a filter ................................28
Comparison table of solutions ...................................28
System earthing arrangements ..............................................31
Background information on system earthing
arrangements.....................................................................31
Protection of persons against electrical contact.......31
Types of system earthing arrangements (SEA) ........32
System earthing arrangements (SEA) .......................33
Comparison of system earthing arrangements
(SEA).............................................................................35
Applications in UPS installations .....................................36
Specific aspects in systems with UPS .......................36
Protection against direct contact................................36
Protection against indirect contact ............................36
Types of systems for UPS...........................................37
Protection .................................................................................39
Protection using circuit breakers......................................39
Trip units ......................................................................39
Discrimination, cascading, current limiting ..............41
Selection of circuit breakers .............................................42
Rating ...........................................................................42
Breaking capacity ........................................................42
Ir and Im thresholds ....................................................42
Special case of generator short-circuits ....................43
Example .......................................................................43
Calculation of CB1 and CB2 ratings
and breaking capacities ..............................................44
Characteristics of the most power circuit
breaker CB3 possible ..................................................47
Cables .......................................................................................49
Selection of cable sizes .....................................................49
Cable temperature rise and voltage drops................49
Temperature rise .........................................................49
Voltage drops...............................................................49
Special case for neutral conductors ..........................51
Calculation example....................................................51
Example of an installation ................................................51
Energy storage.........................................................................52
Storage technologies ........................................................52
Energy storage in UPS................................................52
Available technologies ................................................52
Comparison of technologies ......................................52
Selection of a battery ........................................................54
Types of batteries ........................................................54
Backup time .................................................................54
Service life....................................................................54
Comparison between types of batteries ...................55
Battery monitoring ............................................................55
Battery monitoring on UPS ........................................55
Detection and prevention of battery
failure for UPSs ...........................................................55
Human-machine interface and communication....................56
Human-machine interface (HMI) ......................................56
General characteristics................................................56
Example .......................................................................56
Communication .................................................................56
High availability for critical applications
requires communicating protection equipment.......56
Solutions ......................................................................57
Preliminary work......................................................................58
Installation considerations................................................58
Dimensions ..................................................................58
Ventilation, air-conditioning .......................................58
IP degree of protection and noise level.....................59
Battery room ......................................................................59
Battery installation method ........................................59
Battery room features .................................................59
Selection of possible configurations ...........................................62
Types of possible configurations............................................62
Basic diagrams ..................................................................62
Single source ...............................................................62
Multi-source.................................................................62
UPS configurations ...........................................................62
Single UPS ...................................................................62
Parallel UPS .................................................................62
Parallel connection with redundancy ........................64
Redundant distribution with an STS..........................65
Selection table and corresponding ranges............................66
Criteria for comparison .....................................................66
Availability ...................................................................66
Maintainability.............................................................66
Upgradeability .............................................................66
Discrimination and non-propagation of faults..........66
Installation operation and management ...................66
Diagram no. 1. Single UPS......................................................68
Diagram no. 2. Active redundancy
with two integrated parallel UPS units ..................................69
Diagram no. 3. Active redundancy with integrated
parallel UPS units and external maintenance bypass ..........70
Diagram no. 4. Isolated redundancy with two UPS units ....71
Diagram no. 5. Active redundancy with parallel
units and centralised static-switch cubicle (SSC)..................72
Diagram no. 6. Active redundancy with parallel
UPS units and total isolation, single busbar .........................73
Diagram no. 7. Active redundancy with parallel
UPS units and total isolation, double busbar........................74
Diagram no. 8. Active redundancy with parallel UPS
units, double SSC and total isolation, single busbar............75
Diagram no. 9. Active redundancy with parallel UPS
units, double SSC and total isolation, double busbar ..........77
Diagram no. 10. Isolated redundancy N + 1 ..........................79
Diagram no. 11. Redundant distribution with STS ................81
Diagram no. 12 . Active redundancy with parallel
UPS and a common battery....................................................83
Elimination of harmonics in installations....................................85
Harmonics ................................................................................85
Definition, origin and types of harmonics.......................85
Harmonics....................................................................85
Non-linear loads are the cause ..................................85
Linear and non-linear loads........................................86
Types of harmonics and specific aspects of zerosequence harmonics ...................................................87
Characteristic harmonic values ........................................89
Rms value of harmonics .............................................89
Total rms current .........................................................89
Individual harmonics ..................................................89
Voltage and current harmonic distortion ..................90
Crest factor...................................................................90
Spectrum of the harmonic current ............................91
Power factor.................................................................91
Power............................................................................91
Non-linear load............................................................92
Effects of harmonics..........................................................92
Loss of apparent power ..............................................92
Temperature rise in cables .........................................92
Current in the neutral ..................................................93
Self-polluting loads .....................................................93
Risk of capacitor breakdown ......................................94
Derating of transformers ............................................95
Risk of disturbing generators .....................................96
Losses in asynchronous motors ................................96
Effects on other equipment ........................................96
Effect on recent UPS systems ....................................96
Conclusion ...................................................................96
Elimination of harmonics........................................................97
Strategies against harmonics...........................................97
Living with harmonics.......................................................97
Oversizing of equipment ............................................97
Solutions to eliminate harmonics ....................................98
Passive filters...............................................................98
Active filters / active harmonic conditioners ............98
Active harmonic conditioners ..............................................100
Active harmonic conditioners ........................................100
Characteristics ...........................................................100
Advantages of active harmonic conditioning .........100
Operating principle....................................................101
Operating modes .......................................................101
Installation modes .....................................................102
Position in the installation ........................................104
Position of current transformers upstream
or downstream ..........................................................105
Advantages ................................................................107
Procedure for implementing active conditioning .........108
Conclusion on active conditioning...........................108
New installations .......................................................108
Existing installations .................................................108
Methodology..............................................................109
1. Site audit.................................................................109
2. Determination of the most suitable solution......110
3. System installation and checks ............................110
Theoretical review ........................................................................111
Supplying sensitive loads ......................................................111
Types of electrical disturbances ......................................111
Origins of disturbances..............................................111
Types of disturbances................................................112
UPS..........................................................................................114
UPS....................................................................................114
Components of a UPS ...............................................114
UPS applications ..............................................................116
Types of UPS ..........................................................................118
Static or rotary UPS .........................................................118
Static or rotary UPS solutions ..................................118
Comparison ................................................................119
Static solution.............................................................119
Types of static UPS..........................................................120
Standards ...................................................................120
UPS operating in passive-standby mode................121
UPS operating in line-interactive mode ..................122
Double-conversion UPS............................................123
Conclusion .................................................................125
UPS components and operation ..........................................126
Components of a UPS.....................................................126
General diagram of a UPS........................................126
Power sources and UPS inputs ................................127
Components of a UPS...............................................127
Main characteristics of UPS components......................130
AC input power..........................................................130
Rectifier/charger.........................................................130
Battery (* energy storage means)............................131
Inverter .......................................................................133
Output voltage Un .....................................................134
Summary diagram for main characteristics..................136
Normal AC input: .......................................................136
Bypass AC input:........................................................136
Rectifier/charger:........................................................136
Battery: .......................................................................136
Inverter: ......................................................................136
UPS operating modes .....................................................137
Normal mode (on utility power, see figure 76) .......137
Backup mode (on battery power,
see figure 76) .............................................................137
Bypass mode (on static-bypass line,
see figure 77) .............................................................138
Maintenance mode (on maintenance
bypass, see figure 77) ...............................................139
UPS configurations..........................................................140
Parallel UPS with redundancy..................................140
Electromagnetic compatibility (EMC) ..................................142
Electromagnetic disturbances ........................................142
Electromagnetic disturbances ..................................142
Examples....................................................................142
EMC standards and recommendations .........................143
Disturbances ..............................................................143
Measured values .......................................................143
UPS standards........................................................................145
Scope and observance of standards..............................145
Scope of standards....................................................145
Observance of standards and certification..............145
CE marking.................................................................145
Main standards governing UPS .....................................146
Safety................................................................................146
Electrical environment, harmonics and
electromagnetic compatibility (EMC) ......................146
Quality ........................................................................146
Ecological environment ............................................146
Acoustic noise............................................................146
Tables on harmonic-compatibility levels.................147
Energy storage .......................................................................148
Possible technologies......................................................148
Energy storage in UPS ..............................................148
Batteries............................................................................148
The battery solution ..................................................148
Types of industrial batteries .....................................149
Installation modes .....................................................149
Constraints on batteries ..................................................150
Atmospheric constraints...........................................150
Access ........................................................................150
Main battery parameters ..........................................150
Recharge mode..........................................................151
Battery management.................................................151
UPS / generator-set combination .........................................153
Use of a generator...........................................................153
Long backup times ....................................................153
UPS / generator-set compatibility ............................154
Review of inrush currents.........................................155
Motors ........................................................................155
LV/LV transformers ....................................................155
Computer loads ...............................................................156
Harmonics ..............................................................................157
Harmonics ........................................................................157
Origin of harmonics ..................................................157
Consequences of harmonics ....................................157
Precautions ................................................................158
Characteristic harmonic values ......................................159
Current values............................................................159
Example .....................................................................161
Voltage values............................................................161
Power values..............................................................162
Non-linear loads and PWM technology ...............................164
Non-linear load performance of UPS
using PWM technology ...................................................164
Importance of the UPS output impedance..............164
UPS operating principle............................................165
PWM inverters ...........................................................167
Comparison of different sources....................................169
Output impedance of various sources ....................169
Conclusion .................................................................169
Free-frequency chopping ................................................170
Free-frequency chopping ..........................................170
PFC Rectifiers .........................................................................172
Standard and PFC rectifiers ............................................172
Standard rectifiers.....................................................172
“Clean” PFC (Power Factor Correction) rectifier.....172
PFC rectifiers..............................................................172
Implementation .........................................................173
Glossary and bibliography ..........................................................176
Glossary..................................................................................176
Bibliography ...........................................................................186
Standards ...................................................................186
Foreword
This section of the Application and Installation Guide generally describes
Caterpillar Double Conversion UPS. Additional engine systems, components
and dynamics are addressed in other Application and Installation Guides.
Engine-specific information and data are available from a variety of sources.
Refer to LEBW4950 and the Introduction section (LEBW4951) for additional
references.
Information contained in this publication may be considered confidential.
Discretion is recommended when distributing. Materials and specifications
are subject to change without notice.
CAT, CATERPILLAR, their respective logos, “Caterpillar Yellow,” the “Power
Edge” trade dress as well as corporate and product identity used herein,
are trademarks of Caterpillar and may not be used without permission.
Battery UPS
Application and Installation Guide
Key factors in UPS installations
Introduction
Using this guide
Growing needs for high-quality
and high-availability power
Structure of this document
Problems related to the quality and
availability of electrical power have
become vitally important due to the
key role of computers and electronics
in the development of many critical
applications.
Disturbances in distribution systems
(micro-outages, outages, voltage sags,
etc.) can result in major losses or
safety hazards in a number of activities
such as:
• Sensitive process industries
where a malfunction in the
control/monitoring systems can
result in production losses.
• Airports and hospitals where
faulty operation of equipment can
represent a serious danger.
• Information and communication
technologies where the necessary
level of reliability and dependability
is even higher. Data centers require
high-quality, “no-break” power
24/365, year after year and without
halts for maintenance.
UPS protection systems are now an
integral part of the value chain of many
companies. Their level of availability
and power quality have a direct effect
on the service continuity of operations.
Productivity, the quality of products and
services, the competitiveness of the
company and site security depend on
the smooth operation of the UPS.
Failure is not an option.
©2010 Caterpillar
All rights reserved.
Finding information
Information may be located in the
general contents at the start of the guide.
Sections
1. Key factors in UPS installations
presents the role of UPS in electrical
installations and indicates the main
parameters that must be taken into
account. The remainder of the
section guides you through the
selection process for a solution by
determining the main elements of
an installation with a UPS.
2. Selection of the UPS configuration
presents a number of practical
examples in view of selecting a
configuration, from a simple, singleUPS unit through to installations
offering exceptionally high levels
of availability.
3. Elimination of harmonics in
installations presents solutions to
eliminate harmonic currents in
installations.
4. Theoretical review provides
background technical information
for devices and notions mentioned
in other parts of the guide.
Finally, to facilitate the preparation
of projects:
5. Glossary and bibliography defines
the main terms used in this guide
and provides a list of standards and
documents dealing with topics
related to UPS.
Page 1
Application and Installation Guide
Battery UPS
UPS in electrical installations
Component functions and parameters
Figure 1: Functions of the components in installations with UPS..
Page 2
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Battery UPS
Sources of information in setting
up installation specifications
The diagram on the previous page
provides a general overview of the
components and various parameters
in installations with UPS.
Application and Installation Guide
Table 1 indicates:
• The order in which the subjects
are presented in this section,
• The choices that must be made,
• The purpose of each decision
with the indication of the pages
concerning the relevant elements
in this section,
• Where additional information on
each subject may be found
in the other sections of this
design guide.
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Page 3
Application and Installation Guide
Choices
Mono or
multisource
architecture and
configuration of
UPS sources
Purpose
Determine the installation
architecture and UPS
configuration best suited to
your requirements in terms of
energy availability, upgrades,
operation and budget.
Determine the rating of the
UPS unit or parallel units (for
redundancy or capacity)
UPS power rating
required, taking into account
the distribution system and
load characteristics.
Battery UPS
See
Sec. 2
Supplying sensitive loads.
Pages
17-21
Reduce voltage distortion on
the upstream busbars to
acceptable levels, depending
on the power sources likely to
supply the UPS system.
Page 24
System earthing
arrangements
Ensure installation compliance
with applicable standards for
the protection of life and
property and correct operation
of devices. Which system
earthing arrangements are
required for which
applications?
Page 31
Connections
Battery
Communication
Preliminary work
(if any)
Standards
Determine the breaking
capacity and the ratings of the
circuit breakers upstream and
downstream of the UPS, solve
any discrimination problems.
Limit voltage drops and
temperature rise in the cables,
as well as harmonic distortion
at the load inputs.
Operation on battery power
(backup time) must last long
enough to meet user
requirements.
Define UPS communication
with the electrical and
computer environment.
Construction work and
ventilation must be planned,
notably if there is a special
battery room.
Be aware of the main
applicable UPS standards.
See
Page 67
Page 111
UPS configurations.
Page 140
Engine generator sets.
Page 153
UPS make-up and
operation.
Page 14
Elimination of harmonics
in installations.
Control of
upstream
harmonics
Upstream and
downstream
protection using
circuit breakers
Additional information
Examples and comparison
of 12 typical installations,
from single-UPS units to
high-availability
architectures.
Sec. 3
Harmonics.
Page 157
Energy-storage solutions
and batteries.
Page 148
Electromagnetic
compatibility.
Page 142
Page 39
Page 49
Page 54
Page 56
Page 58
Table 1..
Page 4
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Battery UPS
Application and Installation Guide
Basic notions on installations with UPS
Supply systems with UPS
Purpose of UPS
First launched in the 1970s, UPS
importance has grown in step with the
development of digital technologies.
UPS are electrical devices that are
positioned between the distribution
system and sensitive loads. They
supply power that is much more
reliable than the distribution system
and corresponds to the needs of
sensitive loads in terms of quality and
availability.
Rotary UPS (with rotating mechanical
parts, e.g. flywheels) are not included
in the standards and remain marginal
on the market.
Types of UPS, see page 118 “Types
of static UPS”.
Double-conversion static UPS
This is the market leading technology
used in high-power installations due
to their unique advantages over the
other technologies.
Types of UPS
• Complete regeneration of the
power supplied at the output,
The term UPS covers products with
apparent power ratings from a few
hundred VA up to several MVA,
implementing different technologies.
• Total isolation of the load from
the distribution system and its
disturbances,
That is why standard IEC 62040-3 and
its European equivalent ENV 62040-3
define three standard types
(topologies) of UPS.
UPS technologies include:
• Passive standby,
• Line interactive,
• Double conversion.
For the low power ratings (< 2 kVA),
the three technologies coexist. For
higher ratings, the industry leading
technology is double conversion with
line interactive being used primarily
where efficiency is a concern for the
customer.
• No-break transfer (where
applicable) to a bypass line.
The Operating Principle (Figure 2)
• During normal operation, a
rectifier/charger turns the ACinput power into DC power to
supply an inverter and float
charge the stored energy source,
• The inverter completely
regenerates a sinusoidal signal,
turning the DC power back into
AC power that is free of all
disturbances and within strict
amplitude and frequency
tolerances,
• If the AC-input power fails, the
stored energy source supplies the
power required by the inverter for
a specified backup time
• A static bypass can transfer the
load without a break in the supply
of power to a bypass line to
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Page 5
Application and Installation Guide
Battery UPS
continue supplying the load if
need be due to an internal fault,
short circuit downstream, or
maintenance. This “fault-tolerant”
design makes it possible to
continue supplying power to the
load in “downgraded mode” (the
power does not transit the
inverter) during the time required
to re-establish normal conditions.
Double-conversion UPS, see page
126 “Components and operation”.
Figure 2: Double-conversion static UPS..
Power quality of UPS
Voltage quality for linear loads
Power quality of doubleconversion UPS
What is a linear load?
A linear load supplied with a sinusoidal
voltage draws a sinusoidal current
having the same frequency as the
voltage. The current may be displaced
(angle φ) with respect to the voltage
(figure 3).
By design, double-conversion solidstate UPS supply to the connected
loads a sinusoidal signal that is:
• High quality because it is
continuously regenerated and
regulated (amplitude ± 1%,
frequency ± 0.5%),
• Free of all disturbances from the
distribution system (due to the
double conversion) and in
particular from micro-outages
and outages (due to the battery).
This level of quality must be ensured,
whatever the type of load.
Page 6
Examples of linear loads
Many loads are linear, including
standard light bulbs, heating units,
resistive loads, motors, transformers,
etc. They do not contain any active
electronic components, only resistors
(R), inductors (L) and capacitors (C).
UPS and linear loads
For this type of load, the UPS output
signal is very high quality, i.e. the
voltage and current are perfectly
sinusoidal, 50 or 60 Hz.
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Battery UPS
Application and Installation Guide
Figure 3: Voltage and current for linear loads..
Voltage quality for non-linear
loads
What is a non-linear load?
A non-linear (or distorting) load
supplied with a sinusoidal voltage
draws periodic current that has the
same frequency as the voltage but is
not sinusoidal.
The current drawn by the load is, in
fact, the combination (figure 4) of:
• A sinusoidal current called the
fundamental, at the 50 or 60 Hz
frequency,
• Harmonics, which are sinusoidal
currents with an amplitude less
than that of the fundamental, but
a frequency that is a multiple
of the fundamental and which
defines the harmonic order (e.g.
the third order harmonic has a
frequency 3 x 50 Hz [or 60 Hz]
and the fifth order harmonic has
a frequency 5 x 50 Hz [or 60 Hz]).
The harmonic currents are caused by
the presence of power-electronic
components (e.g. diodes, SCRs,
IGBTs) which switch the input current.
Examples of non-linear loads
Non-linear loads include all those that
have a switch-mode power supply at
their input to supply the electronics
(e.g. computers, variable-speed
drives, etc.).
Figure 4: The current drawn by non-linear loads is distorted by the harmonics..
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Page 7
Application and Installation Guide
Battery UPS
Harmonic spectrum of the current
drawn by a non-linear load
The harmonic analysis of a non-linear
current consists in determining
(figure 5):
• the harmonic orders present in
the current,
• the relative importance of each
order, measured as the
percentage of the order.
Hk% = distortion of harmonic k =
rms value of harmonic k
rms value of the fundamental
Voltage and current harmonic
distortion
Non-linear loads cause both current
and voltage harmonics. This is
because for each current harmonic,
there is a voltage harmonic with the
same frequency. The 50 Hz (or 60 Hz)
sinusoidal voltage of the UPS is
therefore distorted by the harmonics.
The distortion of a sine wave is
presented as a percentage:
THD* % = total distortion =
rms value of all the harmonic k
rms value of the fundamental
* Total Harmonic Distortion.
The following values are defined:
• TDHU % for the voltage, based
on the voltage harmonics,
• TDHI % for the current, based on
the current harmonics (figure 5).
The higher the harmonic content, the
greater the distortion.
Practically speaking, the distortion in
the current drawn by the load is much
higher (THDI approximately 30%) than
that of the voltage at the input (THDU
approximately 5%).
Page 8
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Battery UPS
Application and Installation Guide
.Figure 5: Example of the harmonic spectrum of the current drawn by a non-linear load..
Non-linear loads, see the section
“Elimination of harmonics in
installations” and page 85
“Harmonics”.
UPS and non-linear loads
Harmonics affect the sinusoidal
voltage at the UPS output. Excessive
distortion can disturb the linear loads
connected in parallel on the output,
notably by increasing the current they
draw (temperature rise).
To maintain the quality of the UPS
output voltage, it is necessary to limit
its distortion (THDU), i.e. limit the
current harmonics that produce
voltage distortion.
In particular, it is necessary that the
impedance (at the UPS output and in
the cables supplying the load) remain
low.
Limiting the distortion of the output
voltage
Due to the free-frequency chopping
technique employed, the impedance at
the output of a double conversion UPS
is very low, whatever the frequency
(i.e. whatever the harmonic order). This
technique virtually eliminates all
distortion in the output voltage when
supplying non-linear loads. The quality
of the output voltage is thus constant,
even for non-linear loads.
Practically speaking, installation
designers must:
• check UPS output values for nonlinear loads and, in particular,
make sure that the announced
level of distortion, measured for
standardised non-linear loads as
per standard IEC 62040-3, is very
low (THDU < 2 to 3%),
• limit the length (impedance) of
the output cables supplying the
loads.
UPS performance for non-linear
loads, see page 164.
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Page 9
Application and Installation Guide
UPS power availability
What is meant by availability?
Availability of an electrical installation
Availability is the probability that the
installation will be capable of
supplying energy with the level of
quality required by the supplied loads.
It is expressed as a percentage.
Availability (%) = (1-
MTTR
) x 100
MTBF
The MTTR is the mean time to repair
the supply system following a failure
(including the time to detect the cause
of the failure, repair it and start the
system up again).
The MTBF is the mean time between
failures, i.e. the time the supply
system is capable of ensuring correct
operation of the loads.
Example
An availability of 99.9% (called thee
nines) corresponds to a 99.9% chance
that the system will effectively carry
out the required functions at any given
time. The difference between this
probability and 1 (i.e. 1 - 0.999 = 0.001)
indicates the level of non-availability
(i.e. one chance out of 1000 that the
system will not carry out the required
functions at any given time).
What is the practical signification
of availability?
Down-time costs for critical
applications are very high.
These applications must obviously
remain in operation as long as
possible.
The same is true for their electrical
supply.
Page 10
Battery UPS
The availability of the energy supplied
by an electrical installation
corresponds to a statistical
measurement (in the form of a
percentage) of its operating time.
The MTBF and MTTR values are
calculated or measured (on the basis
of sufficiently long observations) for
the components. They can then be
used to determine the availability of
the installation over the period.
What are the factors contributing
to availability?
Availability depends on the MTBF and
the MTTR.
• Availability would be equal to
100% if the MTTR is equal to zero
(instantaneous repair) or if the
MTBF is infinite (operation with
no breakdowns). This is
statistically impossible;
• Practically speaking, the lower
the MTTR and the higher the
MTBF, the greater the availability.
From “3 nines” to “6 nines”
The critical nature of many
applications has created the need for
much higher levels of availability for
electrical power.
• The “traditional” economy uses
power from the public utility. An
average-quality distribution
system with HV backup offers
99.9% availability (3 nines), which
corresponds to eight hours of
non-availability per year.
• Sensitive loads require an
electrical supply capable of
providing 99.99% availability
(4 nines), which corresponds to
50 minutes of non-availability
per year.
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Battery UPS
Application and Installation Guide
• The computer and communication equipment in data centres
requires 99.9999% availability
(6 nines), which corresponds to
30 seconds of non-availability
per year. This level is the means
to ensure, without risk of major
financial loss, operation of
infrastructures 24/365, without
shutdown for maintenance. It is a
step toward a continuous supply.
.Figure 6: Evolution in the level of availability required by applications...
How can availability be
improved?
Key factors to the availability of
installations with UPS
To improve availability, it is necessary
to reduce the MTTR and increase the
MTBF.
A few years ago, most installations
were made up of single-UPS units,
and the number of parallel systems
was small. The applications requiring
this type of installation still exist.
Reduce the MTTR
Real-time fault detection, analysis by
experts to ensure a precise diagnosis
and rapid repair all contribute to
reducing the MTTR.
These efforts depend on the key
factors listed next.
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However, the shift toward high
availability requires use of
configurations offering redundancy at
a number of levels in the installation
(see figure 7).
Page 11
Application and Installation Guide
Battery UPS
Figure 7: The required levels of availability have resulted in the.
use of redundancy on a number of levels in the installation.
This trend has led designers,
depending on the criticality of the
loads and the operating requirements,
to take into account some or all of the
key factors listed below.
Reliability and availability
Propose a configuration corresponding to the level of availability
required by the load, comprising
components with proven levels of
reliability and backed up by a suitable
level of service quality.
Maintainability
Ensure easy maintenance of the
equipment under safe conditions for
personnel and without interrupting
operation.
Page 12
Upgradeability
It must be possible to upgrade the
installation over time, taking into
account both the need to expand the
installation gradually and operating
requirements.
Discrimination and non-propagation
of faults
It must be possible to limit faults to as
small a part of the installation as
possible, while enabling servicing
without stopping operations.
Installation operation and
management
Make operations easier by providing
the means to anticipate events via
installation supervision and
management systems.
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Battery UPS
Application and Installation Guide
Selection of the
configuration
Prerequisite step in establishing
installation specifications
The selection of a configuration
determines the level of availability
that will be created for the load. It also
determines the possible solutions for
most of the factors listed previously.
The configuration may be single or
multi-source, with single or parallel
UPS units and with or without
redundancy.
Selection of the configuration is the
initial step in establishing installation
specifications. To assist in making the
right decision, section 2 is entirely
devoted to this subject. It compares the
various configurations in terms of
availability, protection of the loads,
maintainability, upgradeability and cost.
Configuration selection based on
typical installations corresponding
to different levels of availability.
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Page 13
Application and Installation Guide
Battery UPS
Power calculations
Elements required for
power calculations
Installation considerations
Type of load supplied
Linear loads (cos φ) or non-linear
loads (power factor).
These characteristics determine the
power factor at the UPS output.
Maximum power drawn by the load
under steady-state conditions
For a load, this is the power rating.
If a number of loads are connected
in parallel on the UPS output, it is
necessary to calculate the total load
when all the loads operate at the same
time. Otherwise, it is necessary to use
diversity to calculate the most
unfavourable operation in terms of the
power drawn.
In-rush currents under transient
conditions or for a short-circuit
downstream
The overload capacity of a UPS
system depends on the time the
overload lasts. If this time limit is
exceeded, the UPS transfers the load
to the Bypass AC input, if its voltage
characteristics are within tolerances.
In this case, the load is no longer
protected against disturbances on
the distribution system.
Depending on the quality of the
Bypass AC power, it is possible to:
• Use the Bypass AC input to
handle current spikes due to
switching of devices or
downstream short-circuits. This
avoids oversizing the system;
Page 14
• Disable automatic transfer
(except for internal faults), while
maintaining the possibility of
manual transfers (e.g. for
maintenance).
Power of a UPS
Rated power of a UPS
This rating, indicated in the
catalogues, is in the output power. It
is indicated as an apparent power Sn
in kVA, with the corresponding active
power Pn in kW, for a:
• Linear load,
• Load with a cos φ = 0.8.
However, last-generation UPS
can supply loads with a
cos φ = 0.9 leading.
Calculation of the rated power
Pn (kW) = 0.8 Sn (kVA) rated active
power
This calculation depends on the
output voltage of the UPS and the
current drawn by the load, where:
Sn (kVA) = UnIn √3 in three-phase
systems
Sn (kVA) = VnIn in single-phase
systems
For a three-phase UPS, U and I are
rms line values, for a single-phase
UPS, V is a phase-to-neutral voltage,
where:
Un = phase-to-phase voltage
Vn = phase-to-neutral voltage
Un = Vn √3
For example, if Un = 400 volts, Vn =
230 volts.
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Battery UPS
Application and Installation Guide
• The corresponding rms values
U and I,
Power and type of load
Table 2 presents the equations linking
the power, voltage and current,
depending on the type of load (linear
or non-linear).
• ω = angular frequency = 2 π f
where f is the frequency (50 or
60 Hz),
The following symbols are used:
• φ = displacement between the
voltage and the current under
sinusoidal conditions.
• Instantaneous voltage u(t) and
current i(t) values,
Linear loads
Three-phase
Sinusoidal voltage
u(t) = U √2 sin ωt
Single-phase
v(t) = V √2 sin ωt
between phases
phase to neutral
U = V √3
i(t) = I √2 sin (ωt - φ)
Displaced sinusoidal
current
Apparent power
Active power
Reactive power
phase current
Current crest factor √2
S (kVA) = VI
S (kVA) = UI √3 cos φ
P (kW) = UI √3 cos φ = S (kVA) cos φ
P (kW) = VI cos φ = S (kVA) cos φ
Q (kvar) = UI √3 sin φ = S (kVA) sin φ
Q (kvar) = VI sin φ = S (kVA) sin φ
S = √P2 + Q2
Non-linear loads
Sinusoidal voltage
u(t) = U √2 sin ωt
between phases
The regulated UPS voltage
remains sinusoidal (low THDU),
whatever the type of load.
Current with harmonics
v(t) = V √2 sin ωt
U = V √3
i(t) = i1(t) + ∑ihk(t) total phase current
i1(t) = I1 √2 sin (ωt - φ1) fundamental current
ik(t) = Ihk √2 sin (kωt - φk) k-order harmonic
I = √I 12 + I22 + I32 + I42 + .... rms value of the total current
Fc = peak current value / rms value
THDI = √I 12 + I22 + I32 + I42 + ....
I1
Apparent power
Active power
Power factor
phase to neutral
Current crest factor
Current total harmonic distortion
S (kVA) = UI √3
S (kVA) = VI
P (kW) = λ UI √3 = λ S (kVA)
P (kW) = λ VI = λ S (kVA)
λ = P(kW)
S(kVA)
Table 2..
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Page 15
Application and Installation Guide
UPS percent load
This is the percentage of the rated
power that is effectively drawn by the
load.
Load (%) =
Sload (kVA)
Sn (kVA)
Recommendation: take into
account growth in loads
It is advised to leave a margin (excess
power) when setting the rated power,
particularly if a site expansion is
planned. In this case, make sure the
percent load on the UPS is still
acceptable after the expansion.
UPS efficiency
This factor determines the power
drawn by the UPS on the upstream
distribution system, i.e. the
consumption. It may be calculated as:
η (%) =
PUPSoutput (kW)
PUPSinput (kW)
For a given power rating, a high level
of efficiency:
• Reduces power bills,
• Reduces heat losses and,
consequently, ventilation
requirements.
It is possible to calculate the efficiency
at full rated load, i.e. with a 100% load.
ηn (%) =
Pn (kW)
PUPSinput (kW)
The rated active power of the UPS is
obtained by multiplying the rated
apparent power Sn (kVA) by 0.8 (if λ >
0.8) or by λ (if λ< 0.8).
The efficiency can vary significantly
depending on the percent load and
the type of load.
Page 16
Battery UPS
The installation designer must
therefore pay attention to two aspects
of efficiency.
Recommendation 1: check the
efficiency for non-linear loads
The presence of non-linear loads
tends to reduce the power factor to
values below 0.8. It is therefore
necessary to check the efficiency value
for standardised non-linear loads. This
check is recommended by standards
IEC 62040-3 / EN 62040-3.
Recommendation 2: check the
efficiency at the planned percent
load
Manufacturers generally indicate the
efficiency at full rated load. However,
its value may drop if the percent load
is lower (1). Attention must therefore
be paid to UPS operating in an activeredundancy configuration, where the
units share the total load and often
operate at 50% of their full rated load,
or less.
(1) A UPS is optimised to operate at
full rated load. Even though losses are
at their maximum at full rated load,
the efficiency is also at its maximum.
In a standard UPS, losses are not
proportional to the percent load and
the efficiency drops sharply when the
percent load drops. This is because a
part of the losses is constant and the
relative percentage of this part
increases when the load decreases.
To obtain high efficiency at low load
levels, the constant losses must be
very low.
UPS efficiency, see page 133.
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Battery UPS
Ratings of single-UPS
configurations
Single-UPS configurations
These configurations comprise a
single, double-conversion UPS unit
(see figure 8). The overload capacity at
the UPS output is indicated by a
diagram.
In the event of an internal fault or an
overload exceeding UPS capacity, the
system automatically transfers to the
Application and Installation Guide
Bypass AC input. If transfer is not
possible, many UPS current limit for
overloads greater than the maximum
value (e.g. 2.33 In peak for one
second, which corresponds to a
maximum sine wave with an rms
value of 2.33 / √2 = 1.65 In). Beyond
one second, the UPS shuts down.
A set of disconnection switches is
available to isolate the UPS for
maintenance in complete safety.
Figure 8: Single double conversion static UPS unit and example of an overload curve...
Power levels under steady-state
conditions
A UPS is sized using the apparent
rated output power Sn (kVA) and an
output power factor of 0.8. These
conditions correspond to an active
rated power of Pn (kW) = 0.8 Sn (kVA).
In real-life situations, a UPS supplies a
number of loads with an overall power
factor λ that is often not 0.8 due to the
presence of non-linear loads and
means to improve the power factor;
• If λ ≥ 0.8, the UPS is still limited
to Pn (kW),
Consequently, selection of the power
rating in kVA must take into account
the active power supplied to the
loads.
The active power is determined by
following the following four steps.
1. Apparent and active power drawn
by the loads
The first step is to evaluate the power
requirements of the load.
Table 3 must be drawn up for the k
loads to be supplied.
• If λ < 0.8, the UPS is limited to
Sn (kW) < Pn (kW).
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Page 17
Application and Installation Guide
Battery UPS
Load
Apparent rated power (kVA)
Input power factor λ (or cos φ)
Active rated power (kW)
Load 1
S1
λ1
P1 = λ1 S1
Load 2
S2
λ2
P2 = λ2 S2
Si
λi
Pi = λi Si
Load k
Sk
λk
Pk = λk Sk
Total
S
λ
P=λS
(1) S is not the sum of Si
(2) λ must be measured
or calculated
(3) P = λ S = ∑ λi Si
…
Load i
…
(1) S is not the sum of Si because:
• it would be necessary to calculate the vectoral sum if all loads were linear, using the angles of the different cos φ,
• some of the loads are not linear.
(2) λ must be measured on site or evaluated on the basis of past experience.
(3) P = λ S = ∑ λi Si because the active power is added (no displacement).
Table 3..
2. Rated apparent power of the UPS
(Sn)
The second step is to select a UPS
with an apparent-power rating
sufficient to cover the load
requirements (in kVA).
Under the given conditions, the
suitable rated apparent power for the
UPS is:
Sn (kVA) > S. where S = P / λ.
In the UPS range, select the UPS with
a rated power Sn (kVA) just above S. If
reserve power is required and the
selected rating is too close to S, select
the next highest rating.
3. Check on the active power
The third step is a check to ensure that
the selected power rating can cover
the load requirements in kW under
the stipulated operating conditions.
For the selected rating, the UPS will
supply the rated active power:
Pn (kW) = 0.8 Sn (kVA)
• If ≥ 0.8, make sure that
Pn (kW) > P, i.e. that the UPS
can supply the additional
Page 18
power required, otherwise
select the next highest rating.
• If λ < 0.8, the power supplied by
the UPS is sufficient because Pn
(kW) > λ Sn (kVA), i.e. the
selection is correct.
4. Percent load
The fourth step is a check to ensure
that the percent load is acceptable
now and in the future, given the
desired operating conditions.
The percent load is:
Load = S / Sn(kVA).
It must be sufficient to cover any
increases in the load or if there are
plans to expand the system to become
redundant.
Power levels under transient
conditions
Load in-rush currents
It is necessary to know the in-rush
current of each load and the duration
of the transient conditions. If a
number of loads risk being turned on
at the same time, it is necessary to
sum the in-rush currents.
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Battery UPS
Necessary checks
It is then necessary to check that the
planned UPS power rating can handle
the in-rush currents. Note that the
UPS can operate for a few periods in
current-limiting mode (e.g. 2.33 In for
one second for some manufactures. If
the UPS cannot handle the in-rush
currents, it is necessary to decide
whether it is acceptable to transfer to
the Bypass AC input when the
transient conditions occur. If transfer
is not acceptable, it is necessary to
increase the power rating.
Review of in-rush currents, see
page 159.
Application and Installation Guide
Example
The following example is simply to
illustrate the point and does not
correspond to a real situation. The
purpose is to indicate the required
steps. The installation is made up of
three 400 V three-phase loads
connected in parallel:
• Computer system - S1 = 4 x 10
kVA (4 identical 10 kVA loads), λ
= 0.6 for all the loads, in-rush
current 8 In over four periods 50
Hz (80 ms) for each load,
• Variable-speed drive - S2 = 20
kVA, λ = 0.7, in-rush current 4 In
over five periods (100 ms),
• Isolation transformer - S3 = 20
kVA, λ = cos φ = 0.8, in-rush
current 10 In over six periods
(120 ms).
Figure 9: Example of an installation...
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Page 19
Application and Installation Guide
Battery UPS
Power levels under steady-state
conditions
1. Apparent and active power drawn
by the loads
Table 4 should be drawn up.
Load
Rated apparent power
(kVA)
Input power factor
Rated active power
(kW)
Computer system
40
0.8*
32*
Variable-speed drive
20
0.7
14
LV/LV transformer
20
0.8
16
Total
S
λ = 0.68 measured or
estimated
P = 54 kW
* average of new top of the range systems with power factor 0.9 and older equipment with power factor between 0.7 and 0.8.
Table 4..
2. Rated apparent power of the UPS
S = 54 / 0.68 = 79.4 kVA
An 80 kVA rating would not be
sufficient, i.e. a 100 kVA rating should
be selected or higher if a site
extension is planned.
3. Check on the active power
• The UPS can supply the loads
100 x 0.68 = 68 kW > 54 kW.
4 . Check on the percent load and
rated current
• The percent load is, therefore,
79.4 / 100 = 79.4%.
• Rated current of the UPS Sn (kVA) = UI √3 , i.e. I = 100 /
(400 x 1.732) = 144 A.
In-rush currents under transient
conditions
The loads should be started up one
after the other to avoid combining the
in-rush currents. It is necessary to
check that the UPS can handle the
in-rush currents.
Page 20
The rated currents are calculated as S
(kVA) = UI √3 , i.e.:
• Computer system - In = 10 /
(400 x 1.732) = 14.4 A, i.e. 8 In ≈
115 A for 80 ms,
• Variable-speed drive - In = 20 /
(400 x 1.732) = 28.8 A, i.e. 4 In ≈
115 A for 100 ms,
• Transformer - In = 20 /
(400 x 1.732) = 28.8 A, i.e. 10 In =
288 A for 120 ms,
• A 100 kVA UPS with an overload
capacity of 120%, i.e. 151 A x
1.2 = 173 A for 1 minute and
150%, i.e. 151 A x 1.5 = 216 A for
1 minute,
• Operation in current-limiting
mode at 2.33 In, i.e. 335 A for one
second.
If the four computer loads (10 kVA
each) are started one after the other,
the 20% overload capacity of the
UPS is sufficient (173 A -1mn > 115 A 80 ms).
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Battery UPS
If the four loads are started
simultaneously, the in-rush current
would be 4 x 115 = 460 A > 335 A. The
system would current limit for 80 ms.
For the variable-speed drive, the overload capacity is sufficient. For the
isolation transformer (288 A for 120 ms),
the overload capacity is again sufficient.
Ratings of parallel-UPS
configurations
Parallel-UPS configurations
Purpose of parallel connection
Parallel connection of a number of
identical units is the means to:
• Increase the power rating,
• Establish redundancy that increases the MTBF and availability:
Types of parallel connection
Two types of UPS units can be
connected in parallel.
• Integrated parallel UPS units:
each UPS unit includes an automatic bypass and a manual
maintenance bypass. The manual
bypass may be common to the
entire system (in an external
cubicle);
• Parallel UPS units with an SSC:
the static-switch cubicle
Application and Installation Guide
comprises an automatic bypass
and a maintenance bypass that
are common for a number of
parallel units without bypasses
(see figure 10).
True modular parallel systems are also
available, made up of dedicated and
redundant modules-power, intelligence,
battery and bypass, all engineered into
a design that is easily and efficiently
serviceable. Power modules can be
easily added as demand grows or as
higher levels of availability are required.
There are two types of parallel
configurations:
• Without redundancy: all the UPS
units are required to supply the
load. Failure of one unit means
the entire system shuts down
(not recommended);
• With redundancy N + 1, N + 2,
etc.: the number of UPS units
required for the load is equal to
N. All the UPS units (N + 1, N + 2,
etc.) share the load. If one UPS
unit shuts down, the remaining
units (at least equal in number to
N) continue to share the load.
Typical configurations and
characteristics, see section 2.
Figure 10: UPS system with parallel-connected units and a static-switch cubicle (SSC)..
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Page 21
Application and Installation Guide
Power levels in redundant
parallel configurations
In a redundant parallel configuration
made up of identical units, the units
share the load. The power rating of
each unit does not depend on the level
of redundancy, but must be calculated
to continue supplying the load even if
redundancy is completely lost.
Active redundancy:
• Improves availability,
• Increases the overload capacity,
• Reduces the percent load on
each UPS unit.
The power level is determined by
following the same four steps as for a
single-UPS configuration.
Battery UPS
Select in the UPS range the power
rating Sn (kVA) just above S/N. If
reserve power is required or the
selected rating is too close to S, select
the next highest rating.
3. Check on the active power
For the selected rating, the UPS will
supply the active rated power
Pn (kW) = 0.8 Sn (kVA)
• If λ ≥ 0.8, make sure that Pn (kW)
> P, i.e. that the UPS can supply
the additional power required,
otherwise select the next highest
rating.
• If λ < 0.8, the power supplied by
the UPS is sufficient because Pn
(kW) > λ Sn (kVA), i.e. the
selection is correct.
1. Apparent and active power drawn
by the loads
4. Percent load
The same type of table is used as that
for a single UPS (see page 20).
With redundancy, the UPS units share
the load according to the equation
The result is the apparent power S
that must be supplied to the load.
S / (N+K).
2. Rated apparent power of the UPS
units (Sn) in the configuration
Consider a level of redundancy N + K
(e.g. 2 + 1), which means:
- N units (e.g. 2) are required to
supply the load,
- K units (e.g. 1 extra unit) ensure
redundancy.
Each UPS unit must be sized to enable
the system as a whole to operate without redundancy, i.e. with N operational
units and K units shut down.
In this case, the N units must each
have an apparent power rating Sn
(kVA) such that:
Sn(kVA) > S / N.
Page 22
The percent load for each unit when
there is redundancy is therefore:
TL = S / (N + k) Sn (kVA).
In a non-redundant system, it is
calculated as:
TL = S / N Sn (kVA).
It must be sufficient to cover any
increases in the load.
Example
This example will use the results from
the last example, and we will suppose
that the loads are critical, i.e.
redundancy is required.
• The total load is 54 kW with an
overall power factor for all the
loads of 0.68, i.e. S = 54 / 0.68
= 79.4 kVA;
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Battery UPS
• If 2+1 redundancy is used, two
units must be capable of supplying the load. Each must will have
to supply S / 2 = 79.4 / 2 = 39.7
kVA;
• A 40 kVA rating would not be
sufficient, i.e. a 50 kVA rating
should be selected or higher if a
site extension is planned;
• If redundancy is not available,
the two UPS units must be
capable of supplying the load;
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Application and Installation Guide
• This is the case because 2 x 50 x
0.68 = 68 kW > 54 kW;
• During operation, the percent
load will be:
- with redundancy, i.e. with 3
UPS units sharing the load:
79.4 / 3 x 50 = 52.9%;
- without redundancy, i.e. with
only 2 UPS units sharing the
load: 79.4 / 2 x 50 = 79.4%.
Page 23
Application and Installation Guide
Battery UPS
Control of upstream harmonics
UPS and upstream
harmonics
Role of the input rectifier
UPS units draw power from the AC
distribution system via a rectifier/
charger. With respect to the upstream
system, the rectifier is a non-linear
load that causes harmonics. In terms
of harmonics, there are two types of
rectifiers.
Standard rectifiers
These are three-phase rectifiers
incorporating SCRs and using a sixphase bridge (Graetz bridge) with
standard chopping of the current.
This type of bridge draws harmonic
currents with orders of n = 6 k ± 1
(where k is a whole number), mainly
H5 and H7, and to a lesser degree H11
and H13.
Harmonics are controlled by using
a filter (see figure 11).
PFC-type transitor-based
controlled active rectifiers
These transistor-based active rectifiers
have a regulation system that adjusts
the input voltage and current to a
reference sine wave. This technique
ensures an input voltage and current
that are:
• Perfectly sinusoidal, i.e. free of
harmonics,
• In phase, i.e. with a power factor
close to 1.
With this type of rectifier, no filters are
required.
Clean transitor-based rectifiers.
Figure 11: Input rectifier and harmonics..
Page 24
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Battery UPS
Filtering of upstream
harmonics for UPS with
Graetz bridge rectifiers
Goals of harmonic filtering
This section concerns only a UPS with
conventional Graetz bridge rectifiers.
A “clean” upstream system
The goal is to ensure a level of voltage
distortion (THDU) on the busbars
supplying the UPS that is compatible
with the other connected loads.
The UTE recommends limiting the
THDU to:
• 5% when the source is a
generator,
• 3% when the source is a
transformer to take into account
1 to 2% of THDU which may
already be present on the HV
distribution system.
This recommendation may differ for
each country.
Practically speaking, solutions for
voltage distortion (THDU) must be
implemented in a manner specific to
the country where the installation is
located.
Easy combination with an engine
generator set
The goal is to make possible a
UPS/engine generator set
combination with no risk of increasing
the level of harmonics when the load
is transferred to the generator. This
risk exists because the generator has
a source impedance lower than that
of a transformer, which increases the
effects of harmonics.
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Application and Installation Guide
High power factor at the rectifier input
The goal is to increase the input
power factor (generally to a level
higher than 0.94). This reduces the
consumption of kVA and avoids
oversizing the sources.
Installation complying with standards
The goal is to comply with standards
concerning harmonic disturbances
and with the recommendations issued
by power utilities.
• Standards on harmonic
disturbances (see table 5):
- IEC 61000-3-2 / EN 61000-3-2
for devices with an input
current ≤ 16 A/ph,
- IEC 61000-3-4 / EN 61000-3-4
for devices with an input
current > 16 A/ph.
• Standards and recommendations
on the quality of distribution
systems, notably:
- IEC 61000-3-5 / EN 61000-3-5,
- EN 50160 (Europe),
- IEEE 519-2 (United States),
- ASE 3600 (Switzerland),
- G5/3 (U.K.), etc.
Standards on harmonics, see “UPS
standards” in page 145.
Table 5. Example of harmonic-current
limitations as per guide IEC 61000-3-4
/ EN 61000-3-4 for devices with an
input current > 16 A/ph (stage 1,
simplified connection).
Page 25
Application and Installation Guide
Battery UPS
% of H1 (fundamental)
Filtering and parallel connection
H3
21.6%
H5
10.7%
H7
7.2%
H9
3.8%
When a number of UPS units are
connected in parallel and depending
on the type of filter used, it is possible
to install:
H11
3.1%
H13
2.0%
H15
0.7%
H17
1.2%
H19
1.1%
H21
≤ 0.6%
H23
0.9%
Harmonic
H25
0.8%
H27
≤ 0.6%
H29
0.7%
H31
0.7%
≥ H33
≤ 0.6%
Even orders
≤ 0.6% or ≤ 8/n
(n even order)
Table 5..
Types of harmonics filters
Harmonics filters eliminate certain
orders or all orders, depending on
their technology. The following types
are available.
Passive LC filters:
• Non-compensated,
• Compensated,
• Non-compensated with contactor.
Double-bridge rectifier
Phase-shift filter
THM active filter (Active 12-pulse
technology)
Page 26
• an individual filter on each UPS
unit,
• a common filter for the entire
parallel configuration.
The goal is to achieve a balance
between cost and effectiveness, taking
into account the acceptable levels of
harmonic distortion.
The comparison tables for the various
solutions (page 29) are helpful in
making a selection.
Combination of LC filters and
generator
The generator can supply only
relatively low capacitive currents
(10 to 30% of In). When an LC filter is
installed, the main difficulty lies in the
gradual start-up of the rectifier on
generator power, when active power
is equal to zero and the generator
supplies only the capacitive current
for the filter. Consequently, the use of
LC filters must be correctly analysed
to ensure that operation complies with
manufacturer specifications. Below is
a method for selection of LC filters,
using as an example a generator
derating curve, similar to those
provided by manufacturers.
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Battery UPS
Application and Installation Guide
Figure 12: Derating curve for a generator, as a function of the installation power factor..
The curve in figure 12, provided as
one example among many, shows the
power derating as a function of the
operating point, for a given generator.
For a purely capacitive load λ = 0), the
power available is equal to only 30%
of the rated power (point A). If we
assume an apparent power rating
such that Pn generator = Pn rectifier,
the meaning of points A, B, C, D, E
and F is the following:
F: operating point at the rated load, without a filter or with a phase-shift filter.
A: reactive power corresponding to
the capacitive current of a noncompensated filter,
The capacitive current of the noncompensated filter is 230 x 30% (1) =
69 kVA.
B: reactive power corresponding to
the capacitive current of a
compensated filter,
The reactive power that the generator
can handle (point A) is 300 x 0.3 =
90 kVA.
C: operating point at start-up with a
non-compensated filter with
contactor,
The filter is therefore compatible with
the generator.
D: operating point at the rated load
with a non-compensated filter,
Example
Consider a non-compensated filter
with a 300 kVA generator and a
200 kVA UPS.
The power rating of the rectifier,
taking 87% as the efficiency value
(1 / 0.87 = 1.15), is 1.15 times that of
the inverter, i.e. 200 x 1.15 = 230 kVA.
(1) The value of 30% has been
determined experimentally.
E: operating point at the rated load
with a compensated filter,
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Page 27
Application and Installation Guide
Selection of a filter
Selection parameters for a filter
Overall effectiveness - reduction in
distortion (THDI and THDU)
The effectiveness depends on the
harmonic orders filtered and the
degree to which they are attenuated or
eliminated. It is measured by the THDI
at the rectifier input. The impact on the
THDI determines the level of the
THDU. It is necessary to check the
performance at the planned percent
load, given that many UPS systems
operate at percent loads between 50
and 75%.
Improvement in the power factor λ
The filter improves the power factor
(generally to a level higher than 0.92).
Compatibility with an engine
generator set
It is also necessary to check the
performance with the planned
source(s), either a transformer or an
engine generator set. This is because
the generator has an output
impedance lower than that of a
transformer, which increases the
effects of harmonics.
Suitable for parallel-UPS
configurations
Depending on the type of filter, it is
possible to install one on each UPS
unit or set up a single filter for overall
elimination of harmonics.
Battery UPS
Efficiency
Consumption of the filters can slightly
modify the efficiency of the installation as a whole.
Flexibility for set-up and upgrades
Filters are generally specific to a UPS
and may be factory-mounted or
installed after installation. The
conditioner provides overall
elimination of harmonics and great
flexibility in the configuration.
Dimensions
It is necessary to check whether the
filter can be installed in the UPS
cabinet or in a second cabinet.
Cost
It impacts on the effectiveness of the
filter and must be weighed against the
advantages obtained.
Compliance with standards
It is necessary to determine
compliance with standards, in
particular IEC 61000-3-4, in terms of
the individual harmonic levels
indicated in the texts.
Comparison table of solutions
The following tables list the elements
for comparison, with a general
comment on use of each type of
solution.
Table 6 presents individual solutions
for single-UPS configurations. These
solutions may also be used in parallel
configurations.
Table 7 presents overall solutions for
entire configurations.
Page 28
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Battery UPS
Application and Installation Guide
Type of filter
Criterion
LC noncompensated
LC
compensated
LC with
contactor
AC input
AC input
Double ridge
AC input
AC input
Built-in THM
AC input
THM
C
C
L
L
C
L
Diagram
Rectifier Rectifier
UPS
Load
UPS
UPS
Inverter
Load
Load
Load
UPS
Load
Figure A
Figure B
Figure C
Figure D
Figure E
7 to 8%
10%
7 to 8%
10%
7 to 8%
10%
10%
15%
4%
5%
H5, H7
H5, H7
H5, H7
H5, H7,
H17, H19
H2 to H25
0.95
1
0.95
1
0.95
1
0.85
0.8
0.94
0.94
*
**
**
**
***
***
***
***
*
**
*
*
*
*
***
Cost
***
***
***
*
**
Dimensions
***
***
***
*
***
*
*
*
*
**
Reduction in
distortion
THDI at 100% load
THDI at 50% load
Harmonics
eliminated
Power factor
λ at 100% load
λ at 50% load
Compatibility
with generator
Efficiency of filter
Flexibility,
upgradeability
Connection in
parallel with UPS
Rectifier Rectifier Rectifier Rectifier
UPS
UPS
UPS
UPS
Compliance with
guide IEC 61000-3-4
UPS
Inverter
Inverter
Figure G
Figure H
Figure I
Figure J
no
no
no
no
yes
General comment
** Good
UPS
Figure F
Solution suitable
for installations
without an engine
generator set.
*** Excellent
UPS
Solution suitable
for installations
with an engine
generator set.
The added
inductor load
reduces the
capacitive power
that must be
supplied by the
engine-generator
set.
Solution suitable
for installations
comprising an
engine generator
set with a power
rating lower than
that of the UPS. The
LC line is switched
in by the contactor
at a preset value
corresponding to
an inverter percent
load that is
acceptable for the
engine generator
set.
Solution suitable
for installations
with gensets
Solution suited
to sensitive
installations or
with changing load
levels. The most
effective and the
most flexible
solution. Does not
depend on the
percent load
or the type of
upstream source.
*Sufficient
Table 6: Comparison of individual harmonic-filtering solutions..
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Page 29
Application and Installation Guide
Type of filter
Criterion
Battery UPS
SineWave
AC input
Phase-shift filter
AC input
AC input
AC input
SW
Diagram
Load
Load
Load
Load
Figure AA
Figure BB
Figure CC
Figure DD
< 10%
35% with 1 UPS
shut down
< 5%
19% with 1 UPS
shut down
< 4%
12% with
1 UPS shut down
Reduction in
distortion
THDI at 100% load
THDI at 50% load
Harmonics
eliminated
4%
5%
H2 to H25
Power factor
λ at 100% load
λ at 50% load
0.95
1
0.8
0.8
Compatibility
with generator
***
**
Efficiency of filter
***
**
Flexibility,
upgradeability
***
*
Cost
***
***
Dimensions
***
*
Compliance with
guide IEC 61000-3-4
yes
yes
General comment
*** Excellent
** Good
Solution suited to sensitive
installations or with changing
load levels. The most effective
and the most flexible solution.
Does not depend on the
percent load or the type of
upstream source.
Solution cannot be modified. Suited to installations with more than
two parallel-connected UPS units.
* Sufficient
Table 7: Comparison of overall solutions..
Page 30
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Battery UPS
Application and Installation Guide
System earthing arrangements
Background information
on system earthing
arrangements
Protection of persons against
electrical contact
International standards require that
electrical installations implement two
types of protection of persons against
the dangers of electrical currents.
Protection against direct contacts
The purpose of this form of protection
is to avoid “direct” contact between
persons and intentionally live parts
(see figure 13).
It includes the points listed below.
• Isolation of live parts using
barriers or enclosures offering a
degree of protection at least
equal to IP2X or IPXXB.
• Opening of the enclosure (doors,
racks, etc.) must be possible only
using a key or a tool, or
following de-energising of the
live parts or automatic
installation of a screen.
• Connection of the metal
enclosure to a protective
conductor.
Protection against indirect contacts
and system earthing arrangements
The purpose of this form of protection
is to avoid “indirect” contact between
persons and exposed conductive
parts (ECP) that have become live
accidentally due to an insulation fault.
The fault current creates in the
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exposed conductive parts (ECP) a
potential that may be sufficient to
cause a dangerous current to flow
through the body of the person in
contact with the exposed conductive
parts (see figure 13).
This protection includes the points
listed below.
• Mandatory earthing of all
exposed conductive parts (ECP)
that may be accessed by the
user.
The protective conductor is used for
connection to the earth. It must never
be interrupted (no breaking devices on
the protective conductor).
The interconnection and earthing
techniques for the exposed conductive
parts (ECP) determine the system
earthing arrangement (SEA) for the
installation.
• Disconnection of the supply
when the potential of the ECPs
risks reaching dangerous levels.
Interruption is carried out by a
protection device that depends
on the selected system earthing
arrangement (SEA). It often
requires residual-current devices
(RCD) because the insulationfault currents are generally too
low to be detected by standard
overcurrent protection devices.
Page 31
Application and Installation Guide
Battery UPS
Figure 13: Direct and indirect contacts..
Types of system earthing
arrangements (SEA)
There are three types of system
earthing arrangements (SEA):
• Isolated neutral (IT),
• Earthed neutral (TT),
• Exposed conductive parts
connected to the neutral (TN
with TN-C and TN-S). The first
two letters indicate how the
neutral and the ECPs of the loads
are connected.
First letter
Second letter
Third letter (for TN)
Connection of the neutral
Connection of the ECPs
Type of protective conductor
T = earthed neutral
T = exposed conductive parts
earthed
C = Common neutral and
protective conductor (PEN)
I = isolated neutral
N = exposed conductive parts
connected to the neutral
S = Separate neutral (N) and
protective conductor (PE)
IT, TT or TN systems
TN-C or TN-S
Table 8..
Page 32
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Battery UPS
Application and Installation Guide
System earthing arrangements
(SEA)
Isolated neutral (IT)
Figure 14: IT system..
Earthed neutral (TT)
Figure 15: TT system..
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Page 33
Application and Installation Guide
Battery UPS
Exposed conductive parts connected
to the neutral (TN)
Figure 16: TN-S system (the basic principle is identical for the TN-C system)..
Page 34
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Battery UPS
Application and Installation Guide
Comparison of system earthing arrangements (SEA)
Type of SEA
Operation
Protection
of persons
Specific
equipment
Advantages
and
disadvantages
EMC
Use
IT (isolated neutral)
TT (earthed
neutral)
TN-S (ECP to
neutral)
TN-C (ECP to
neutral)
• Signalling of first
insulation fault.
• Location and
elimination of the
first fault.
• Disconnection for
the second fault.
• Disconnection
for the first
insulation fault.
• Disconnection
• Disconnection
for the first
for the first
insulation fault
insulation fault.
occurs.
• Common neutral
• Separate neutral
and protective
(N) and protective
conductor (PEN).
conductor (PE).
• Interconnection and
earthing of ECPs.
• First fault:
- very low current,
- monitoring/indication
by an IMD.
• Second fault:
- potentially
dangerous current,
- interruption by
overcurrent
protection devices
(e.g. circuit breaker).
• Earthing of ECPs
combined with
use of residualcurrent devices
(RCD).
• First fault:
- leakage current
is dangerous,
but too low to be
detected by the
overcurrent
protection devices,
- detection by the
RCDs combined
with breaking
devices.
• Interconnection
and earthing of
ECPs and neutral
imperative.
• First fault:
- fault current,
- interruption
by overcurrent
protection devices
(e.g. circuit
breaker).
Insulation-monitoring
device (IMD) and
fault-locating device.
Residual-current
devices (RCD).
For long distances,
RCDs must be used.
• Solution offering the
best continuity of
service (the first
fault is signalled).
• Requires competent
surveillance
personnel (location
of the first fault).
• High EMC
performance, very
low currents in the
earth cable.
• Easiest solution
to design and
install.
• Mandatory use
of RCDs.
• Different earth
electrodes
(distant sources).
• Highly sensitive
to lightning
strikes.
• High installation
costs for high
power ratings.
• Difficult to design
(calculation of the
loop impedances).
• Flow of high fault
currents.
• High EMC
performance, low
current in the PE
during normal
operation.
• Installations
• Commercial
requiring continuity
and residential
of service, e.g.
premises, public
hospitals, airports,
lighting, schools,
industrial processes,
etc.
ships.
• Installations and
premises where
there is a risk of fire
or explosion, i.e.
mines, etc.
• Interconnection
and earthing of
ECPs and neutral
imperative.
• First fault:
- fault current,
- interruption
by overcurrent
protection devices
(e.g. circuit
breaker).
• Reduced
installation costs
(one less
conductor).
• Difficult to design
(calculation of the
loop impedances).
• Flow of high fault
currents.
• Low EMC
performance, high
currents in the
PEN (connections
between ECPs).
• Large commercial • Large commercial
premises, tall
premises, tall
buildings, etc.
buildings, etc.
• Industries without • Industries without
continuous
continuous
processes
processes
(IT system).
(IT system).
• Supply of
• Supply of
computer systems. computer
systems.
Table 9..
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Application and Installation Guide
Applications in UPS
installations
Specific aspects in systems
with UPS
Implementation of the aforementioned protection systems
in installations comprising a UPS
requires a number of precautions for
a number of reasons:
• The UPS plays two roles:
- a load for the upstream system,
- a power source for the
downstream system,
• When the battery is not installed
in a cabinet, an insulation fault
on the DC system can lead to the
flow of a residual DC component.
This component can disturb
operation of certain protection
devices, notably RCDs used for
the protection of persons.
Protection against direct contact
When the battery is not installed in a
cabinet (generally in a special room),
the measures presented at the end of
this section should be implemented.
Protection against indirect
contact
Selection of a system earthing
arrangement
A basic protection measure required
by the standards is the creation of a
standardised system earthing
arrangement both upstream and
downstream of the UPS. The two
systems can be the same or different
if certain precautions are taken. In an
existing installation to which the UPS
is added, the upstream system is
already determined. Selection of the
Page 36
Battery UPS
downstream system, either the same
or a different one, depends on its
compatibility with sensitive loads.
Table 9 provides the necessary
elements to compare the various
standardised system earthing
arrangements.
Caution, local regulations may
prohibit certain types of system
earthing arrangements.
Selection of the breaking devices
Above and beyond the interconnection and earthing of the
exposed conductive parts in
compliance with a standardised
system earthing arrangement, the
protection of persons must be
ensured by breaking devices selected
according to the system earthing
arrangement. These devices must
cause tripping of the overcurrent
protection devices in the event of an
insulation fault.
Tripping may:
• be directly provoked by suitable
settings on the overprotection
devices (circuit breakers, fuses),
• or require (mandatory for the IT
system) use of residual-current
devices (RCD) that may or may
not be built into the circuit
breaker.
The RCDs are required to detect the
insulation-fault currents that are often
too low to trip standard overcurrent
protection devices.
Check local requirements
concerning the safety of electrical
installations.
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Battery UPS
Types of systems for UPS
The possible systems depend on:
• The existing or selected system
upstream of the UPS,
• The system downstream of the
UPS for which selection may be
determined by:
- reuse of the same system as
upstream,
- the presence of isolation
transformers upstream or
downstream which make it
possible to change the system
earthing arrangement,
- the loads (e.g. computer
systems require a TN-C or
TN-s system),
- the organisation of the
downstream distribution
system, with static transfer
switches (STS),
• Certain requirements imposed by
standards, e.g. the protective
conductor PE or PEN must never
be interrupted to ensure flow of
the fault current. A TN-C system
(non-interrupted PEN) can be
installed upstream of a TN-S
system (separate N and PE
conductors), but not the contrary.
Application and Installation Guide
UPS are increasingly designed
without transformers, offering
advantages in terms of weight, size
and efficiency. Transformerless
technology also makes it possible to
modulate the voltage for improved
adapatation to all types of loads, in
particular nonlinear loads with
harmonics.
Transformerless technology has an
impact on the use of system earthing
arrangements. For more information
see White Paper - WP 98: “The
Elimination of Isolation Transformers
in Data Center Power Systems”).
Many different cases may be
encountered depending on the
upstream and downstream earthing
arrangements and the type of UPS.
Your Caterpillar representative has
a complete set of diagrams for all
system earthing arrangements and
UPS ranges concerned.
The ranges are designed with isolation transformers. All the other ranges
use transformless technology with the
neutral recreated electronically.
The following pages show some
examples, contact your Caterpillar
representative to obtain the applicable
diagram.
Figure 17: Standard diagrams..
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Page 37
Application and Installation Guide
Battery UPS
Identical systems upstream
and downstream
Figure 18: A few examples with the same system upstream and downstream..
Different systems upstream
and downstream
Figure 19: A few examples with different systems downstream..
Page 38
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Battery UPS
Application and Installation Guide
Protection
Protection using circuit
breakers
The protection system for installations
with UPS units presented here will
implement circuit breakers. Below
is a presentation of the main
characteristics of circuit breakers
and their trip units.
Trip units
Technology
There are two types of trip units:
• Thermal-magnetic,
• Electronic.
Construction
• Built-in (thermal-magnetic only),
• Interchangeable.
Protection
Symb.
Comparison
Thermal-magnetic trip units are
simple and inexpensive.
Electronic trip units offer more precise
and comprehensive settings for better
adaptation to installations and their
requirements.
Table 10 sums up the characteristics
of both types of trip units for circuitbreakers from 1 to 630 A and should
enable you to solve most of the
problems commonly encountered
(from 1 to 400 kVA).
Figure 20 presents the characteristic
curves for the trip units.
Definition
Availability
Overload protection
(thermal or long delay) (1)
Ir
Overload current setting.
All trip units.
Long delay (2)
tr
Applies a long tripping delay
(e.g. for motor starting).
Electronic trip units
(e.g. Micrologic 2, 5, 6).
Short-circuit protection
(magnetic or short delay) (3)
Im or Isd
Short-circuit current setting.
On electronic trip units, Isd is a
function of Ir (generally 2 to 10 Ir).
All trip units.
Short delay (4)
tm or tsd
Applies a short tripping delay
(e.g. for time discrimination with
downstream circuit breaker).
Electronic trip units
(e.g. Micrologic 5, 6).
Ii
Instantaneous short-circuit
setting. Depends exclusively on
trip-unit rating (e.g. protection of
static switches).
Electronic trip units
(e.g. Micrologic 5, 6).
Short-circuit protection,
instantaneous trip (5)
(1) Ir is the thermal protection threshold (sometimes written Ith) of thermal-magnetic trip units or the long-delay protection
threshold of electronic trip units. These thresholds are defined by an inverse time curve that depends on the selected setting.
(2) tr is the time delay of the long-delay thermal protection for a given value of Ir.
(3) Im is the magnetic threshold of thermal-magnetic trip units and Isd the short-delay threshold of electronic trip units.
(4) tm is the time delay (adjustable or fixed) of the magnetic protection of thermal-magnetic trip units and tsd the time delay
(generally adjustable) of the short-delay protection of electronic trip units.
(5) Ii is the instantaneous tripping threshold.
Table 10..
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Page 39
Application and Installation Guide
Battery UPS
Figure 20: Circuit-breaker time/current curves (Icu is the ultimate breaking capacity)..
Page 40
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Battery UPS
Application and Installation Guide
Discrimination, cascading,
current limiting
Discrimination
Discrimination results from correct
circuit-breaker selection and setting
such that, if a fault occurs, it trips only
the first upstream circuit breaker.
Discrimination thus limits the part of
the installation affected by the fault to
a strict minimum. There are a number
of types of discrimination summed up
in table 11 and illustrated in figure 20.
Discrimination
Current limiting
When a high fault current hits the
circuit breaker, the breaker contacts
separate under the electrodynamic
forces, an arc is created and its
resistance limits the shortcircuit
energy.
Cascading
When a short-circuit occurs downstream of the installation (see figure 21),
the fault current also flows through
the upstream circuit breaker which
current limits, thus attenuating the
current applied to the downstream
circuit breaker. The breaking capacity
of the latter is thus reinforced.
Concerns
Principle
Current
discrimination
All types of trip units.
The fault current is lower than the
upstream threshold setting.
Ir upstream > Ir downstream and
Im or Isd upstream > Im or Isd
downstream.
Time
discrimination
Electronic trip units only (e.g. Micrologic).
Delays upstream tripping by the longtime (Ir) and short-time (Im or Isd) delay.
Energy
discrimination
Compact NSX and NS.
Arc pressure upstream is not sufficient
to trip the upstream circuit breaker, but
it is sufficient to trip the downstream
circuit breaker.
Zone-selective
interlocking
Compact NSX 100 to Masterpact with
Micrologic trip units.
Delays upstream tripping if the shortcircuit is also detected downstream. A
pilot wire connects the upstream and
downstream trip units.
Table 11..
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Page 41
Application and Installation Guide
Battery UPS
Breaking capacity
The breaking capacity must be
selected just above the short-circuit
current that can occur at the point of
installation.
Ir and Im thresholds
Table 12 indicates how to determine
the Ir and Im thresholds to ensure
discrimination, depending on the
upstream and downstream trip units.
Remark: Time discrimination must be
implemented by qualified personnel
because time delays before tripping
increase the thermal stress (I2t)
downstream (cables, semiconductors,
etc.). Caution is required if tripping of
CB2 is delayed using the Im threshold
time delay.
Figure 21: Upstream/downstream.
discrimination and cascading.
Selection of circuit
breakers
Rating
The selected rating (rated current) for
the circuit breaker must be the one
just above the rated current of the
protected downstream cable.
Energy discrimination does not
depend on the trip unit, only on the
circuit breaker.
Ir and Im thresholds depending on the
upstream and downstream trip units
Type of downstream circuit
Ir upstream / Ir
downstream ratio
Im upstream / Im
downstream ratio
Im upstream / Im
downstream ratio
Downstream trip unit
all types
magnetic
electronic
Distribution
> 1.6
>2
> 1.5
Asynchronous motor
>3
>2
> 1.5
Table 12..
Page 42
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Battery UPS
Special case of generator shortcircuits
Figure 22 shows the reaction of a
generator to a short-circuit.
To avoid any uncertainty concerning
the type of excitation, we will trip at
the first peak (3 to 5 In as per X"d)
using the Im protection setting
without a time delay.
Application and Installation Guide
Example
Consider the example used to
determine the UPS power rating
(page 17) with a number of parallelconnected 400 V three-phase loads,
namely:
• Computer system - S1 = 4 x 10
kVA, λ = 0.6, in-rush current 8 In
over four periods (80 ms),
• Variable-speed drive - S2 = 20
kVA, λ = 0.7, in-rush current 4 In
over five periods (100 ms),
• Isolation transformer - S3 = 20
kVA UPS was selected, λ = 0.8,
in-rush current 10 In over six
periods (120 ms).
The three loads represent 54 kW with
a power factor of 0.68.
On page 20, 100 kVA UPS was
selected, I = 100 / (400 x √3) = 144 A.
Figure 22: Generator during a short-circuit..
Figure 23: Example of an installation..
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Page 43
Application and Installation Guide
The goal is to select circuit breakers
CB1 and CB2, and the most powerful
circuit breaker CB3 compatible with
discrimination requirements, given
that the upstream installation includes
the following:
• 20 kV / 400 V transformer with
a power rating of 630 kVA,
• 400 V engine generator set with
a power rating of 400 kVA,
• Transformer to MLVS link, five
meters of aluminium cable
4 x 240 mm2 per phase,
• Busbars to circuit breaker link,
four meters using three copper
bars 400 mm2 per phase.
Battery UPS
Calculation of CB1 and CB2
ratings and breaking capacities
The breaking capacity depends on the
short-circuit currents downstream of
CB1 and CB2 at the level of the main
low-voltage switchboard (MLVS). Most
often, this upstream short-circuit value
is supplied by the utility. It can also be
calculated. It is necessary to determine
the sum R of the resistances upstream
and the sum X of the reactances
upstream of the considered point.
The three-phase short-circuit current
is calculated as:
U
Isc 3-ph =
√3 √R2 + X2
U is the phase-to-phase no-load
voltage (load voltage + 3 to 5%).
R = Σ Rupstream and X = Σ Xupstream
In this example, we simply indicate
the general method with a number
of simplifications to shorten the
calculations.
Figure 24: Calculation of short-circuit current for CB1 and CB2..
It is necessary to calculate the
resistances and reactances upstream
of CB1 and CB2 in figure 23.
Page 44
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Battery UPS
Application and Installation Guide
Distribution system upstream of the transformer
• Psc = upstream short-circuit power = 500 MVA = 500 x 106 VA
• U20 = phase-to-phase no-load voltage on the transformer secondary
winding = 400 V, + 3%, i.e. 410 V
• Rup = resistance upstream ≈ 15% Xup, negligible given Xup
• Xup = reactance upstream with respect to transformer secondary winding
Xup =
U202
Psc
4102
=
= 0.288 mΩ
500 x 106
Rup ≈ 0 and Xup = 0.33 mΩ.
Transformer
• Sn = rated apparent power 630 kVA
• In = rated current = 630 / U √3 = 630 103 / (400 x √3) = 909 A
• Usc = transformer short-circuit voltage = 4%
• Pcu = transformer copper losses in VA
Pcu
Rtr = transformer resistance =
≈ 20% Xtr, negligible given Ztr
3 In2
Xtr ≈ Ztr = transformer impedance =
U202
x Usc = 4102 x 0.04 / 630 103 = 10.7 mΩ
Sn
Rtr ≈ 0 and Xtr = 10.7 mΩ.
Cables linking the transformer to the MLVS
• Length 5 meters
• Cross-section 240 mm²
• ρ = resistivity at the normal temperature of the conductors copper:
ρ = 22.5 mΩ.mm2/m, aluminium: ρ = 36 mΩ.mm2/m
• Xc = conductor reactance (typically 0.08 mΩ/m) = 0.08 x 5 = 0.4 mΩ
Rc = cable resistance (copper) = ρ
L
= 22.5 x 5 / (4 x 240) = 0.12 mΩ
S
Rc = 0.12 mΩ and Xc = 0.4 mΩ.
General circuit breaker
Typical values
Rd ≈ 0 et Xd = 0.15 mΩ.
Busbars
• Xb = busbar reactance (typically 0.15 mΩ/m) = 0.15 x 4 = 0.6 mΩ
• Rb = busbar resistance = ρ L / S= 22.5 x 4 / (3 x 400) = 0.075 mΩ (negligible)
Rb ≈ 0 and Xb = 0.6 mΩ.
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Page 45
Application and Installation Guide
Battery UPS
Transformer Isc at the level of CB1 and CB2
• R = Total upstream resistance = 0.12 mΩ
• X = Total upstream reactance = 0.33 + 10.7 + 0.4 + 0.15 + 0.6 =12.18 mΩ
R can be neglected, given X.
Isc 3-ph =
U
√3 √R2 + X2
≈
U
410 = 19.4 kA
√3 X √3 x 12.18 x 10-3
Note: A rough estimate is provided by the short-circuit current on the transformer
terminals, assuming that the upstream short-circuit power is infinite.
ISCT = on transformer terminals = In / Usc = 20 In = 20 x 909 = 18.2 kA
Generator Isc at the level of CB1 and CB2
• Rated apparent power of the generator = 400 kVA
• Rated current of the generator = 400 / U √3 = 400 103 / (400 x √3) = 577 A
• X"d = short-circuit voltage of the generator = 10%
It is decided to trip at 5 In (figure 22).
ISCG = on the generator terminals = 5 In = 5 x 577 = 2.9 kA
Continuous current of CB1
This is the current at the UPS input. It is necessary to multiply the UPS rating by
1.2 to take into account the efficiency, i.e. 120 kVA.
Iinput = 120 / U √3 = 120 103 / (400 x √3) = 173 A
Continuous current of CB2
This is the continuous current of the loads supplied via the bypass, i.e. 54 kW
with a power factor of 0.68 for an apparent power S = 54 / 0.68 = 67.5 kVA.
Iload = 67.5 / U √3 = 120 103 / (400 x √3) = 97 A
Energising current of the largest load
The loads must be energised at different times. The highest inrush current is that
of the 20 kVA transformer, i.e. In = 28.8 A and 10 In = 288 A - 120 ms.
Calculation of the maximum static-switch current
This is the short-circuit current at the level of CB3, which is practically that of CB2.
Selection parameters
Table 13 sums up the various values calculated.
Page 46
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Battery UPS
Application and Installation Guide
Parameter
Value
Transformer short-circuit current
19.4 kA
Generator short-circuit current
2.9 kA
Rectifier current (UPS input)
173 A
Continuous load current downstream of the UPS
97 A
Energizing current of the largest load
288 A - 120 ms
Maximum static-switch current
19.4 kA
Characteristics of CB1 and CB2
Characteristic
D1
D2
Breaking capacity
> 19.4 kA, i.e. 25 kA
> 19.4 kA, i.e. 25 kA
Continuous current
> 173 A, i.e. 200 A
> 97 A, i.e. 125 A
Ir threshold
> 173 A +20%
> 97 A + 20%
Im threshold
> 173 A + 20% and
< 2.9 kA - 20%
> 288 A +20% and
< 2.9 kA - 20%
20% represents here the typical tolerance range of circuit-breaker settings.
Table 13..
Characteristics of the most power
circuit breaker CB3 possible
Figure 25: Calculation of the short-circuit current at CB3..
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Page 47
Application and Installation Guide
Operation with bypass power
• Breaking capacity
The highest short-circuit current
downstream of CB3 is virtually
that of CB2 because it is assumed
that the outgoing circuits are
near the UPS.
Consequently, the breaking
capacity of CB3 is also 25 kA.
• The rating is determined by the
largest load, i.e. the 4 x 10 kVA
of the computer system with a
continuous current of:
Battery UPS
• Settings
A majority of the loads is of the
distribution type, i.e. the Ir
threshold of CB3 must be less
than 97 A / 1.6, i.e. < 61 A.
The Im threshold must be less
than 1847 / 2, i.e. < 900 A.
Operation without bypass power
In this case, the short-circuited UPS
limits its current to 2.33 In for one
second.
Iload = 40 / U √3 = 40 103 /
(400 x √3) = 57 A
A 60 A device should be selected.
Page 48
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Battery UPS
Application and Installation Guide
Cables
Selection of cable sizes
Voltage drops
Cable temperature rise and
voltage drops
Maximum values
The maximum permissible voltage
drops are:
The cross section of cables depends on:
• Permissible temperature rise,
• 3% for AC circuits (50 or 60 Hz),
• Permissible voltage drop.
• 1% for DC circuits.
For a given load, each of these
parameters results in a minimum
permissible cross section. The larger
of the two must be used.
When routing cables, care must be
taken to maintain the required
distances between control circuits and
power circuits, to avoid any
disturbances caused by HF currents.
Temperature rise
Permissible temperature rise in cables
is limited by the withstand capacity of
cable insulation.
Temperature rise in cables depends on:
• The type of core (Cu or Al),
• The installation method,
Selection tables
Table 14 indicates the voltage drop in
percent for a circuit made up of 100
meters of copper cable. To calculate
the voltage drop in a circuit with a
length L, multiply the value in the
table by L/100.
If the voltage drop exceeds 3% on a
three-phase circuit or 1% on a DC
circuit, increase the cross section of
the conductors until the value is
within tolerances.
Voltage drop for 100-meter cables
• Sph - the cross section of the
conductors,
• In - rated current of the protection
devices on the circuit.
• The number of touching cables.
Standards stipulate, for each type of
cable, the maximum permissible
current.
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Page 49
Application and Installation Guide
Battery UPS
Three-phase circuit (copper conductors)
50-60 Hz - 400 V three-phase, cos φ = 0.8, balanced 3-ph + N system
Sph (mm2)
In (A)
10
16
25
35
50
70
95
120
150
185
240
300
10
0.9
16
1.2
20
1.6
1.1
25
2.0
1.3
0.9
32
2.6
1.7
1.1
40
3.3
2.1
1.4
1.0
50
4.1
2.6
1.7
1.3
1.0
63
5.1
3.3
2.2
1.6
1.2
0.9
70
5.7
3.7
2.4
1.7
1.3
1.0
0.8
80
6.5
4.2
2.7
2.1
1.5
1.2
0.9
0.7
100
8.2
5.3
3.4
2.6
2.0
2.0
1.1
0.9
0.8
6.6
4.3
3.2
2.4
2.4
1.4
1.1
1.0
0.8
5.5
4.3
3.2
3.2
1.8
1.5
1.2
1.1
0.9
5.3
3.9
3.9
2.2
1.8
1.6
1.3
1.2
0.9
4.9
4.9
2.8
2.3
1.9
1.7
1.4
1.2
320
3.5
2.9
2.5
2.1
1.9
1.5
400
4.4
3.6
3.1
2.7
2.3
1.9
4.5
3.9
3.4
2.9
2.4
4.9
4.2
3.6
3.0
5.3
4.4
3.8
6.5
4.7
125
160
200
250
500
600
800
1000
For a three-phase 230 V circuit, multiply the result by √3.
For a single-phase 208/230 V circuit, multiply the result by 2.
DC Circuit (Copper Conductors)
Sph (mm2)
In (A)
25
35
50
70
95
120
150
185
240
300
5.1
3.6
2.6
1.9
1.3
1.0
0.8
0.7
0.5
0.4
4.5
3.2
2.3
1.6
1.3
1.0
0.8
0.6
0.5
4.0
2.9
2.2
1.6
1.2
1.1
0.6
0.7
3.6
2.7
2.2
1.6
1.3
1.0
0.8
3.3
2.7
2.2
1.7
1.3
1.0
3.4
2.7
2.1
1.6
1.3
3.4
2.8
2.1
1.6
500
3.4
2.6
2.1
600
4.3
3.3
2.7
800
4.2
3.4
1000
5.3
4.2
100
125
160
200
250
320
400
1250
5.3
Table 14..
Page 50
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Battery UPS
Special case for neutral
conductors
Application and Installation Guide
Example of an installation
In three-phase systems, the thirdorder harmonics (and their multiples)
of single phase loads add up in the
neutral conductor (sum of the currents
on the three phases).
For this reason, the following rule
is applied - neutral cross section =
1.5 x phase cross section.
Calculation example
Consider a 70-meter 400 V three-phase
circuit, with copper conductors and a
rated current of 600 A.
Standard IEC 60364 indicates,
depending on the installation method
and the load, a minimum cross
section. We shall assume that the
minimum cross section is 95 mm2.
Figure 26: Connection of cables..
It is first necessary to check that the
voltage drop does not exceed 3%.
The table for three-phase circuits
indicates, for a 600 A current flowing
in a 300 mm2 cable, a voltage drop of
3% for 100 meters of cable, i.e. for 70
meters:
3 x 70/100 = 2.1%, less than the 3%
limit.
A identical calculation can be run for
a DC current of 1000 A in a 10-meter
cable with a cross section of 240 mm².
The voltage drop for 100 meters is
5.3%, i.e. for ten meters:
5.3 x 10/100 = 0.53%, less than the 1%
limit.
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Page 51
Application and Installation Guide
Battery UPS
Energy storage
Storage technologies
Energy storage in UPS
Available technologies
A UPS requires an energy-storage
system to supply the inverter with
power if utility power fails or is no
longer within tolerances.
The various technologies currently
available are the following:
The stored energy must have the
following characteristics:
• Electricity that is immediately
available to ride through microbreaks, short voltage drops and
utility outages,
• Sufficient power level to supply
the entire load, i.e. a rating
equivalent to that of the UPS
system itself,
• Backup time, generally about ten
minutes, suited to the needs of
the loads and to any other
sources available (e.g. an engine
generator set for long backup
times).
• Batteries:
- sealed lead-acid,
- vented lead-acid,
- nickel cadmium,
• Ultracapacitors,
• Flywheels:
- traditional units turning at
low speeds (1500 rmp) and
combined with engine
generator sets,
- medium-speed (7000 rpm) or
high-speed (30 to 100 000 rpm)
units.
Comparison of technologies
Batteries are by far the most
commonly employed solution today.
They are the dominant solution due
to low cost, proven effectiveness and
storage capacity, but nonetheless
have a number of disadvantages in
terms of size, maintenance and the
environment.
Ultracapacitors do not yet offer the
necessary performance levels.
Figure 27: Simplified diagram of a.
UPS with backup energy storage.
Flywheels operating at high speeds
constitute a possible technology in
terms of their power ratings (40 to
500 kW), for short backup times
(12 seconds to 1 minute).
Figure 28 shows the fields of
application for the different
technologies.
Page 52
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Battery UPS
Application and Installation Guide
Figure 28: Characteristics in terms of power ratings and backup times..
Table 15 compares the different solutions
in terms of their capacity to meet the energystorage requirements of static UPS.
Criteria for comparison
Technology
Sealed lead- Vented leadacid batteries acid batteries
Power
Backup time
****
***
5 minutes up
to several
hours
****
Ni/Cad
batteries
Ultracapacitors
Flywheels
****
*
***
*
a few seconds
**
a few dozen
seconds
****
*
5 minutes up 5 minutes up
to several
to several
hours
dozen
minutes
****
low
***
low to
medium
**
medium
*
high
*
high
Implementation /
installation / start-up
Requires a special
room
***
no
**
yes
*
yes
****
no
**
no
Temperature
*
*
**
****
***
Service life
**
**
***
****
***
Footprint
**
**
**
****
***
Maintenance
Frequency / time
required
**
medium
**
medium
*
high
****
none
***
low
****
****
****
**
***
Purchase price
Maturity of the
technology for UPS
**** Excellent
*** Good
** Fair
* Poor
Table 15,.
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Page 53
Application and Installation Guide
Selection of a battery
Types of batteries
The batteries most frequently used in
a UPS are:
• Sealed lead-acid, also called gasrecombination batteries,
• Vented lead-acid,
• Nickel cadmium.
Lithium-polymer batteries are currently
being studied for use in also. Solutions
using this technology should be
available in two to three years.
Types of batteries, see page 149
“Energy storage - Types of
batteries”.
Selection of a battery depends on the
following factors:
• Operating conditions and
requirements (special room,
battery cabinet, racks, etc.),
• Required backup time,
• Cost considerations.
Backup time
Manufactures typically offer:
• Standard backup times of 5, 10,
15 or 30 minutes,
• Custom backup times that can
reach a number of hours.
Selection depends on:
• The average duration of powersystem failures,
• Any available sources offering
long backup times (engine
generator set, etc.),
• The type of application.
Battery UPS
The following general rules apply.
• Computer systems
Battery backup time must be
sufficient to cover file-saving and
system-shutdown procedures
required to ensure a controlled
shutdown of the computer
system. Generally speaking, the
computer department determines
the necessary backup time,
depending on its specific
requirements.
• Industrial processes
The backup-time calculation
should take into account the
economic cost incurred by an
interruption in the process and
the time required to restart.
• Applications requiring long
backup times
An engine generator set can back
up a battery if long outages
occur, thus avoiding the need for
very large batteries. Generally
speaking, use of an engine
generator set becomes feasible
for backup times greater than
30 minutes to one hour. The
combination must be carefully
studied to optimise the generator
rating and ensure correct
operation.
Combination with an engine
generator set, see page 153
“Engine generator set”.
Service life
Battery manufactures provide
batteries with service lives of 5 or 10
years or longer.
Battery service life, see page 150.
Page 54
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Battery UPS
Comparison between types
of batteries
Sealed lead-acid batteries (gasrecombination)
These are the most commonly used
batteries for the following reasons:
• No maintenance,
• Easy implementation,
• Installation in all types of rooms
(computer rooms, technical
rooms not specifically intended
for batteries, etc.).
Vented batteries
This type of battery (lead-acid or
Ni/Cad) offers certain advantages:
• Long service life,
• Long backup times,
• High power ratings.
Vented batteries must be installed in
special rooms complying with precise
regulations (see page 58 “Preliminary
work”) and require appropriate
maintenance.
Battery monitoring
Battery monitoring on UPS
DigiBatTM
The DigiBatTM battery-monitoring
system is an assembly of hardware
and software, which offers the
following functions:
• Automatic entry of battery
parameters,
• Optimised battery service life,
• Protection against excessive
discharges,
Application and Installation Guide
• Limitation of the battery current,
• Continuous evaluation of
available power taking into
account the battery age, the
temperature and the percent load,
• Forecast of battery service life,
• Periodic, automatic tests on the
battery, including a check on the
battery circuit, an open-circuit
test, a partial-discharge test, etc.
DigiBat, see page 151 “Battery
Management”.
Environment sensor unit
Battery operating parameters and
particularly the temperature affect
battery life. The Environment Sensor,
easy to install and combined with a
Network Management card
(SNMP/Web), makes possible
monitoring of temperature/humidity
and the status of two contacts via
SNMP or the web. It also initiates
equipment shutdown if necessary.
Detection and prevention of
battery failure for UPSs
In spite of the advantages of sealed
lead-acid batteries, over time, all
batteries will fail due to aging. Without
rigorous monitoring, the true integrity
and capacity of a battery remains
unknown.
Battery-monitoring techniques have a
major impact on reliability and can be
used to define the best strategy for
replacement, resulting in a better level
of protection.
• Regulation of the battery floating
voltage depending on the
temperature,
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Page 55
Application and Installation Guide
Battery UPS
Human-machine interface and communication
Human-machine interface
(HMI)
General characteristics
The human-machine interface on the
UPS must be user-friendly, easy to use
and multi-lingual (adjustable to the
user's language).
It is generally made up of a mimic
panel, a status and control panel, and
an alphanumeric display. A passwordprotected personalisation menu may
be available for entry of installation
parameters and access to detailed
information.
Example
The HMI typically offers the following
functions:
On and Off buttons:
• Delayed to avoid erroneous
operations,
• With an option for a remote EPO
(emergency power off),
• Independent with respect to the
rest of the display.
Status LEDs that clearly identify:
• Normal operation (load protected),
• Downgraded operating mode
(malfunction),
• Dangerous situations for the load
(load not protected),
• Operation on battery power.
Alarms:
• Alarm buzzer and buzzer reset
button,
• Battery shutdown warning,
• General alarm,
A screen providing:
• Access to measurements:
- input power (voltage, current,
frequency),
- battery (voltage, charge and
discharge currents, remaining
backup time, temperature),
- inverter output (phase-toneutral voltage, current,
frequency, active and apparent
power, crest factor),
• Access to history logs:
- log containing time-stamped
events,
- curves and bargraphs of the
measured values.
Communication
High availability for critical
applications requires communicating protection equipment
The UPS system, essential for
mission-critical equipment, must
include communication features that
keep operators continously informed,
wherever they may be, of any risk of
compromising the operating security
of the system so that they can take
immediate action.
To ensure power availability, the UPS
communication features provide the
following four essential functions:
Supervision / monitoring of all
installed UPS via software.
Notification via the network and
the Internet.
Controlled shutdown (local or
remote, automatic or manual) of
protected applications.
• Battery fault.
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Battery UPS
Solutions
Communication cards
• Network management card
(Ethernet)
- web monitoring
- email notification
- SNMP MIB and Traps
- server protection with Network
Shutdown Module
- supervision with Enterprise
Power Manager or ISX Central
- environment monitoring with
Environment Sensor (T°, H%,
Inputs)
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Application and Installation Guide
• Modbus – Jbus card (RS232 and
RS485)
- monitoring
• Relay card (Contacts)
- indications
Page 57
Application and Installation Guide
Battery UPS
Preliminary work
Installation considerations
Ventilation, air-conditioning
The main elements that must be taken
into account for the UPS installation
are the following:
Ventilation requirements
UPS are designed to operate within a
given temperature range (typically 0
to 40°C) that is sufficient for most
operating conditions without
modifications.
• Plans for site modifications, any
preliminary work (notably for a
battery room), taking into account:
- the dimensions of equipment,
- operating and maintenance
conditions (accessibility,
clearances, etc.),
- temperature conditions that
must be respected,
- safety considerations,
- applicable standards and
regulations,
• Ventilation or air-conditioning
of rooms,
• Creation of a battery room.
Dimensions
Layout of UPS cabinets and enclosures
should be based on precise plans.
For each range:
• The dimensions and weights of:
- UPS and centralised-bypass
cabinets;
- battery cabinets,
- any auxiliary cabinets
(autotransformers,
transformers, filters, etc.),
• Minimum clearances required for
cabinets and enclosures to
ensure optimal ventilation and
sufficient access.
However, UPS and their auxiliary
equipment produce heat losses that
can, if no steps are taken, increase the
temperature of a poorly ventilated
room.
What is more, the service life of a
battery is heavily dependent on the
ambient temperature. The service life is
optimal for temperatures between 15°
C and 25° C. This factor must be taken
into account if the battery is installed in
the same room as the UPS.
A further consideration is the fact that
a UPS may be installed in the same
room as computer equipment which
often has more severe requirements
concerning operating-temperature
ranges.
Selecting a type of ventilation
For all the above reasons, a minimum
amount of ventilation is required, and
where applicable air-conditioning, to
avoid any risk of excessive temperature rise in the room due to the heat
losses.
Ventilation can be by:
• Natural convection,
• Forced exchange by a ventilation
system,
• Installation of an air-conditioning
unit.
Page 58
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Battery UPS
Selection depends on:
• The heat losses that must be
evacuated,
• The size of the room.
The thermal characteristics of a UPS
may be used to calculate ventilation
needs. They mention for each range:
• The heat losses of cabinets and
any filters installed,
• The volume of air output by a
ventilation system.
IP degree of protection and
noise level
Degree of protection (IP)
A UPS must operate in an environment
that is compatible with their degree of
protection (IP 20 for a UPS from
Caterpillar), defined by standard IEC
60529/EN 60529. The presence of dust,
water and corrosive substances must
be avoided.
Noise level
A UPS must produce a low level of
noise, suited to the room where they
are installed. Measurement conditions
for the level of noise indicated by the
manufacturer must comply with standard ISO 3746 (measurement of noise).
Battery room
Where possible and if desired, the
battery should be installed in a cabinet.
Battery-cabinet dimensions are
indicated for each UPS range,
depending on the rated power.
However, for very high-power UPS,
batteries are generally installed in
special rooms (electrical room).
Application and Installation Guide
Battery installation method
The criteria determining the batteryinstallation method are the following:
• Available floor space,
• The weight that the floor can
handle (kg/m2),
• Ease of access and maintenance.
The following three methods are used.
Battery installed directly on floor
This is the most simple arrangement.
However, a large battery room is
required, given:
• The large amount of floor space
occupied by the battery,
• The insulated flooring (duck
board), which is mandatory if
the voltage exceeds 150 volts.
Battery on racks
The battery cells are installed on a
number of different levels, off the floor.
When determining the height between
each rack, it is necessary to take into
account the space required to check
battery levels and fill the battery cells
easily. A minimum height of 450 mm
is recommended.
Battery on tiers
This installation method is similar
to the preceding. It is the most
convenient method for checking
battery levels.
Battery room features
Whatever the installation method
selected, the battery installation
must comply with the following
requirements (the numbers indicate
the elements shown in figure 29).
Batteries must be installed in compliance with international standards, local
regulations and standard IEC 60364.
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Page 59
Application and Installation Guide
Floor and walls (1)
• The floor must slope to an
evacuation trough which leads
to a holding tank,
• Protection coating against acid
on the floor and walls, up to a
height of at least 0.5 meters.
For example, asphalt for lead-acid
batteries, PVC or chlorine-based paint
for alkaline batteries.
Ventilation (2)
• Calculation of throughput
The volume of air to be
evacuated depends on the
maximum load current and the
type of battery. In installations
comprising a number of batteries,
the quantities of air that must be
evacuated are cumulative.
- vented batteries
d = 0.05 x N x Im, where
d - throughput in cubic meters
per hour,
N - number of battery cells,
Im - maximum load current in
amperes.
- sealed battery
The ventilation conditions in a
general-purpose room are sufficient.
• Safety
An automatic device must stop
battery charging if the ventilation
system fails.
Battery UPS
Layout of cells (3)
Layout must inhibit simultaneous
contact with two bare parts presenting
a voltage greater than or equal to 150 V.
If the condition listed before cannot be
met, terminal shields must be installed
and connections must be made using
insulated cables.
Service flooring (4)
If the voltage exceeds 150 V, special
flooring is required. It must offer sure
footing, be insulated from the floor
and offer at least one meter of
walkway around the battery.
Battery connection (5)
Connections must be as short a
possible.
Battery-protection circuit breaker (6)
The circuit breaker is generally
installed in a wall-mounted enclosure.
Fire-fighting equipment (7)
Authorized fire extinguishers include
power, CO2 or sand.
Safety equipment (8)
The safety equipment must include
protective glasses, gloves and a
source of water.
Inspection equipment (9)
• Hydrometer,
• Filling device,
• Thermometer.
Sensors (10)
• Hydrogen detector,
• Temperature sensor.
• Location
Air must be drawn out from the
top of the battery room.
Page 60
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Battery UPS
Application and Installation Guide
Figure 29: Layout of battery room..
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Page 61
Application and Installation Guide
Battery UPS
Selection of possible configurations
Types of possible configurations
Basic diagrams
Single source
Multi-source
The load is supplied by a single set
of UPS.
The load is supplied by more than one
set of UPS.
Figure 30: Basic diagrams..
UPS configurations
Parallel UPS
Single UPS
Purpose of parallel connection
Parallel connection of a number of
identical UPS units is the means to:
This is the standard double-conversion
UPS (see figure 31). A single UPS can
be used to form redundant configurations as shown in diagrams 4 and 11.
Single UPS, see page 5 and page
126 “UPS components and
operation”.
Standard diagrams (see table 16):
No. 1
No. 4
No. 11
• Increase the power rating,
• Establish redundancy that
increases MTBF and availability,
• Make the installation scalable.
Two types of UPS units can be
connected in parallel:
• Integrated parallel UPS units:
each UPS unit includes an
automatic bypass and a manual
maintenance bypass (figure 31).
The manual bypass may be
common to the entire system
and located in an external
cubicle (e.g. figure 32);
• Parallel UPS units with a
centralised static-switch cubicle
(SSC) (e.g. figure 33).
Figure 31: Double-conversion single UPS..
Page 62
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Battery UPS
Application and Installation Guide
Integrated parallel UPS
This configuration is upgradeable,
starting for instance with one
integrated parallel UPS unit equipped
with an automatic bypass and a
manual maintenance bypass. When
starting with two units or when
expanding to two units or more, a
common maintenance bypass is
installed in an external enclosure
(see figure 32).
Standard diagrams (see table 16):
No. 2
No. 3
Figure 32: Installation with three integrated parallel UPS.
units and a common maintenance bypass.
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Page 63
Application and Installation Guide
Parallel UPS units with a centralised
static-switch cubicle (SSC)
The static-switch cubicle comprises an
automatic bypass and a maintenance
bypass that are common for a number
of modules without a bypass (see
figure 33). It is possible to have two
redundant SSCs.
Battery UPS
Upgrading of this configuration
depends on the rating of the static
switch. It offers the highest level of
reliability (SSC with independent UPS
units).
Standard diagrams (see table 16):
No. 5
No. 6
No. 7
No. 8
No. 9
Figure 33: Three parallel UPS units with a centralised static-switch cubicle (SSC)..
Parallel connection with
redundancy
The parallel configurations presented
earlier may or may not be redundant.
Without redundancy
All the UPS units are required to
supply the load. Failure of one unit
means the entire system shuts down.
Page 64
With active redundancy (N + 1, N + 2,
etc.)
Only N UPS units are required to
supply the load, even though N + 1,
N + 2 or more units are installed. This
ensures a secure supply of power to
the load even if one (for N + 1
redundancy) or two (for N + 2
redundancy) UPS units fail or require
maintenance.
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Battery UPS
Optimum redundancy of non-modular
UPS
For non-modular systems, differences
in the lengths or tightening torques of
cables connecting the different units
can lead to problems concerning the
impedance upstream and downstream
of each UPS. For this reason, the highest MTBF is obtained for redundant
systems with just two UPS (figure 34).
For modular UPS systems, module
interconnections are an integral part of
the system, thereby eliminating
installation problems that can lower
the MTBF as more units are added.
Application and Installation Guide
Power distribution units (PDUs) can be
used to complete this distribution
configuration, offering:
• Load management,
• Multi-channel supply of power
to the loads (dual attach),
• Isolation of parts of the installation
for maintenance or upgrading.
This type of configuration ensures a
very high degree of availability and
offers a number of installationupgrade possibilities.
Standard diagrams (see table 16):
No. 11
No. 12
Figure 34: For non-modular redundant UPS systems,.
the best MTBF is obtained with two units.
Redundant distribution with
an STS
All the loads are supplied by more than
one UPS source (two single UPS units).
Each source can be made up of a
number of parallel-connected units
offering active redundancy. Use of a
static transfer switch (STS) ensures
transfer of the load between the sources
in the event of a downstream fault
(while avoiding any risk of fault
propagation) or for maintenance.
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Figure 35: Redundant distribution with an STS..
Page 65
Application and Installation Guide
Battery UPS
Selection table and corresponding ranges
Criteria for comparison
Upgradeability
Table 16 compares the standard diagrams of this section, mainly related
to UPS, according to the following
criteria.
It must be possible to upgrade the
installation over time, taking into
account both the need to expand the
installation gradually and operating
requirements.
Availability
A level of availability meeting the
needs of the application. Figures are
based on:
• An estimated level of utilitypower availability of 99.9%
(the European average),
• An MTTR of ten hours as per
standard MIL-HDB-217-F level 2
(U.S. military) and IEEE.
Maintainability
Ensure easy maintenance of the
equipment under safe conditions for
personnel and without interrupting
operation.
Page 66
Discrimination and
non-propagation of faults
It must be possible to limit faults to
as small a part of the installation as
possible, while enabling servicing
without stopping operations.
Installation operation
and management
Make operations easier by providing
the means to anticipate events via
installation supervision and
management systems.
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Battery UPS
Application and Installation Guide
Single-source configurations
Standard
diagram
number
Criteria for comparison
Availability
MTBF
Maintainability
Upgradeability
Comment
1. Single UPS
99.99790%
M1 = 475 000 h
*
4-parallelconnected UPS
units
Reference for
calculations
2. 2 integrated
parallel UPS
units
99.99947%
up to 4 x M1
**
4-parallelconnected UPS
units
3. Integrated
parallel units
and external
maintenance
bypass
99.99947%
up to 4 x M1
**
4-parallelconnected UPS
units
4. Isolated
redundancy
99.99970%
6.8 x M1
**
5. Centralised
SSC
99.99968%
6.5 x M1
**
6-parallelconnected UPS
units
6. Total
isolation,
single
busbar
99.99968%
6.5 x M1
***
6-parallelconnected UPS
units
7. Total
isolation,
double
busbar
99.99968%
6.5 x M1
***
6-parallelconnected UPS
units
8. Total
isolation,
single
busbar
99.99968%
6.5 x M1
****
6-parallelconnected UPS
units
9. Total
isolation,
double
busbar
99.99968%
6.5 x M1
****
6-parallelconnected UPS
units
Flexible
Multi-source configurations
Standard
diagram
number
Criteria for comparison
Availability
MTBF
Maintainability
Upgradeability
10. Isolated
redundancy
99.99970%
7 x M1
**
No limit
11. With STS
99.99970%
7 x M1
****
No limit to the
power rating
No propagation
of faults
12. STS + PDU
99.99930%
The highest
level of
availability
****
No limit to the
power rating
+ load
management
**** Excellent
*** Good
** Fair
Comment
* Poor
Table 16..
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Page 67
Application and Installation Guide
Battery UPS
Diagram no. 1. Single UPS
Figure 36: Double-conversion single-UPS unit..
This is the basic solution for UPS
installations. The double-conversion
UPS unit supplies high-quality voltage,
whatever the level of disturbances in
the utility power.
Availability of power for the load
99.99790% and an MTBF of 475 000
hours, compared to a utility MTBF of
96 hours.
UPS maintenance
Made easy due to the built-in bypass
for supply of power to the load during
servicing.
Possible upgrades
On site by connecting several identical
UPS units in parallel.
Page 68
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Battery UPS
Application and Installation Guide
Diagram no. 2. Active redundancy with two integrated
parallel UPS units
Figure 37: Active redundancy with two integrated parallel UPS units..
A simple solution where the UPS
units share the load.
Availability of power for the load
99.99947% and an MTBF up to four
times higher than that for a single
UPS.
UPS maintenance
During maintenance on one unit, the
load remains protected by the other.
Possible upgrades
Several identical UPS units can be
connected in parallel and equipped
with an external maintenance bypass.
Special characteristics:
• The automatic-bypass function is
ensured by managing the static
switches,
• Centralised monitoring of the
various modules,
• Can be used only with two
identical units.
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Page 69
Application and Installation Guide
Battery UPS
Diagram no. 3. Active redundancy with integrated
parallel UPS units and external maintenance bypass
Figure 38: Active redundancy with integrated parallel.
UPS units and external maintenance bypass.
An upgradeable solution where the
power rating can be increased up to
4000 kVA*.
Availability
99.99947% and an MTBF up to four
times higher than that for a single
UPS.
UPS maintenance
During maintenance on one unit, the
load remains protected by the other
units.
Easy upgrades
Several identical UPS units can be
connected in parallel for a low cost
solution with small dimensions.
Special characteristics
• The UPS units share the load,
• The automatic-bypass function is
ensured by managing the static
switches,
• Centralised monitoring of the
various modules,
• Identical modules must be used.
Page 70
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Battery UPS
Application and Installation Guide
Diagram no. 4. Isolated redundancy with two UPS units
Figure 39: Isolated redundancy with two UPS units..
An extremely flexible solution that can
combine heterogeneous and distant
UPS units. It also offers improved
backup time and is perfectly suited
to the technology implemented by
Caterpillar which provide excellent
withstand capacity for load step
changes.
Availability
99.99970% and an MTBF 6.8 times
higher than that of a single UPS.
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UPS maintenance
During maintenance on one unit,
the load remains protected.
Special characteristics
• For a single load, the two UPS
units have the same power
rating, but if there is a second
load (possible load), the rating
of the backup UPS unit must be
adapted correspondingly;
• No control wires between the
UPS units.
Page 71
Application and Installation Guide
Battery UPS
Diagram no. 5. Active redundancy with parallel units
and centralised static-switch cubicle (SSC)
Figure 40: Active redundancy with parallel units and centralised static-switch cubicle (SSC)..
The solution for centralised installations up to 4 MVA*. Excellent
reliability due to the independence
between the units and the staticswitch cubicle (SSC).
Availability
99.99968% and an MTBF up to 6.5
times higher than that for a single
UPS.
UPS maintenance
During maintenance on one unit,
the load remains protected by the
other units and the SSC. During
maintenance on the SSC, redundancy
of the UPS units is maintained.
Easy upgrades
Up to eight UPS units.
Special characteristics
The UPS units share the load.
* Power rating for N + 1 reduncancy.
Page 72
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Battery UPS
Application and Installation Guide
Diagram no. 6. Active redundancy with parallel UPS
units and total isolation, single busbar
Figure 41: Active redundancy with parallel UPS units and total isolation, single busbar..
A solution that can evolve with needs
up to 4 MVA*. Excellent reliability and
improved maintainability due to the
total independence between the UPS
units and the static-switch cubicle
(SSC).
Availability
99.99968% and an MTBF up to 6.5
times higher than that for a single
UPS.
UPS maintenance
During maintenance on one unit,
the load remains protected by the
other units and the SSC. During
maintenance on the SSC, redundancy
of the UPS units is maintained.
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Easy upgrades
Up to eight UPS units.
Special characteristics:
• Total isolation of the UPS units
or the SSC for maintenance,
• The UPS units can be tested
using a test load,
• Isolation of each UPS unit and
the SSC, thus eliminating the
single point of failure in the SSC.
* Power rating for N + 1 redundancy.
Page 73
Application and Installation Guide
Battery UPS
Diagram no. 7. Active redundancy with parallel UPS
units and total isolation, double busbar
Figure 42: Active redundancy with parallel UPS units, double SSC and total isolation, double busbar..
A solution that can evolve with needs
up to 4 MVA*. Excellent reliability and
improved maintainability due to the
total independence between the UPS
units, the static-switch cubicle (SSC)
and the busbars.
Availability
99.99968% and an MTBF up to 6.5
times higher than that for a single
UPS.
UPS maintenance
During maintenance on the UPS units
and one busbar, the load remains
protected by the other units and the
SSC, which are parallel-connected to
the second busbar. During
maintenance on the SSC, redundancy
of the UPS units is maintained.
Page 74
Easy upgrades
Up to eight UPS units.
Special characteristics:
• Transfer from one busbar to the
other without disturbing the
load,
• Total isolation of the UPS units
or the SSC for maintenance,
• Isolation of each UPS unit and
the SSC, thus eliminating the
single point of failure in the SSC.
* Power rating for N + 1 redundancy.
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Battery UPS
Application and Installation Guide
Diagram no. 8. Active redundancy with parallel UPS
units, double SSC and total isolation, single busbar
Figure 43: Active redundancy with parallel UPS units, double SSC and total isolation, single busbar..
An upgradeable solution offering
improved maintainability due to the
total redundancy of the UPS units and
the static-switch cubicles (SSC).
Availability
99.99968% and an MTBF up to 6.5
times higher than that for a single UPS.
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UPS maintenance
During maintenance on the UPS
units and one SSC, the load remains
protected by the other units and the
second SSC. During maintenance on
one SSC, redundancy of the UPS
units is maintained.
Page 75
Application and Installation Guide
Battery UPS
Easy upgrades
Up to eight UPS units.
• Total isolation of each SSC for
maintenance,
Special characteristics:
• Only one SSC is active, the other
is on stand-by and transfer of the
UPS units from one to the other
takes place without disturbing
the load,
• Parallel connection of the UPS
units in the output cabinet
eliminates the single point of
failure in an SSC,
• During operation on the bypass,
the load is split 50/50 between
the two SSCs,
Page 76
• The possibility of installing the
SSCs in two separate rooms
increases system availability in
the event of fire or other
problems.
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Battery UPS
Application and Installation Guide
Diagram no. 9. Active redundancy with parallel UPS
units, double SSC and total isolation, double busbar
Figure 44: Active redundancy with parallel UPS units, double SSC and total isolation, single busbar..
A solution for two evolving loads with
different needs in terms of power
ratings and redundancy.
Availability
99.99968% and an MTBF up to 6.5
times higher than that for a single
UPS.
UPS maintenance
During maintenance on one UPS
unit and one SSC, the load remains
protected by the other units and the
second SSC. During maintenance on
one SSC, redundancy of the UPS units
is maintained.
Easy upgrades
Up to eight UPS units.
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Page 77
Application and Installation Guide
Special characteristics:
• During operation of only one
load, only one SSC is active, the
other is on stand-by and transfer
of the UPS units from one to the
other takes place without
disturbing the load,
• During operation of the two
different loads, both SSCs are
active, each with a number of
assigned UPS units,
Page 78
Battery UPS
• Parallel connection of the UPS
units in the output cabinet
eliminates the single point of
failure in an SSC,
• The possibility of installing the
SSCs in two separate rooms
increases system availability
in the event of fire or other
problems.
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Battery UPS
Application and Installation Guide
Diagram no. 10. Isolated redundancy N + 1
Figure 45: Isolated redundancy N + 1..
Solution combining heterogeneous
and distant UPS units to protect a
number of independent loads.
Availability of power for the load
Greater than 99.99970% and an MTBF
up to seven times higher than that for
a single UPS.
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UPS maintenance
During maintenance on one UPS unit,
the load remains protected. However,
the UPS units are not totally isolated
(servicing under energised
conditions).
Possible upgrades
No limit to the power rating.
Page 79
Application and Installation Guide
Short-circuit propagation
Impossible between the sources.
Special characteristics:
• Short-circuit capacity is lower
than in a configuration with
parallel UPS units,
• (Isc, discrimination, crest factor,
etc.),
Battery UPS
UPS units downstream, their
power ratings and their criticality,
as well as any future plans for
the installation (generally
speaking, the backup UPS
has a parallel configuration),
• All the advantages of isolated
redundancy (diagram no. 4).
• Sizing of the backup UPS must
take into account the number of
Page 80
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Battery UPS
Application and Installation Guide
Diagram no. 11. Redundant distribution with STS
Figure 46: Redundant distribution with STS units..
The best solution in terms of
availability, site operation and safety.
It is the only solution that deals with
power distribution through to the
loads. It is particularly flexible and
makes for easy adaptation of
redundancy to the needs of the load.
Availability of power for the load
Greater than 99.9999%, the highest
level of availability!
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UPS maintenance
Total distribution redundancy and
servicing under no-load conditions
make for maximum safety during
maintenance.
Easy upgrades
Using single-UPS units and with no
limit to the total power rating, upgrading is made easy by the capacity
to partially isolate distribution
subassemblies.
Page 81
Application and Installation Guide
Fault propagation
Load segmenting and the technology
employed in STS units (breakbeforemake source transfer with no
interruption to the loads) ensures
isolation of loads from disturbances
caused by other, faulty loads.
Easy operation
Automatic or manual source transfer.
Continuous monitoring of the sources
(11 parameters and internal circuits).
Battery UPS
Special characteristics:
• The synchronisation module
ensures perfect source
synchronisation under all
conditions (long outages, etc.),
• Selection of the load distribution
for the UPS units,
• The UPS units can be heterogeneous and remote from the
load.
Secure transfer of desynchronised
sources.
Page 82
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Battery UPS
Application and Installation Guide
Diagram no. 12 . Active redundancy with parallel UPS
and a common battery
Figure 47: Redundant distribution with STS units and PDU..
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Page 83
Application and Installation Guide
Redundancy is built into each level,
including the PDUs, the STS units, the
UPS units and the synchronisation
modules.
Battery UPS
Same advantages as diagram no. 11,
plus:
• Capacity to enhance the
reliability of a particular point
in the installation,
• Four different supply channels
to dual-attach servers.
Page 84
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Battery UPS
Application and Installation Guide
Elimination of harmonics in installations
Harmonics
Definition, origin and types
of harmonics
Harmonics
Harmonics are sinusoidal currents or
voltages with a frequency that is a
whole multiple (k) of the frequency of
the distribution system, called the
fundamental frequency (50 or 60 Hz).
When combined with the sinusoidal
fundamental current or voltage
respectively, harmonics distort the
current or voltage waveform (see
figure 48).
Harmonics are generally identified as
Hk, where k is the harmonic order.
• IHk or UHk indicate the type of
harmonic (current or voltage).
• IH1 or UH1 designates the
sinusoidal current or voltage at
50 or 60 Hz that exists when
there are no harmonics (the
fundamental current or voltage).
Figure 48: Distortion of H1 (the fundamental) by H3 (third-order harmonic)..
Non-linear loads are the cause
Equipment implementing power
electronics is the main cause of
harmonics. To supply the electronics
with DC power, the equipment has a
switch-mode power supply with a
rectifier at the input that draws
harmonic currents.
Examples are computers, variablespeed drives, etc.
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Other loads distort the current due
to their operating principle and also
cause harmonics.
Examples are fluorescent lamps,
discharge lamps, welding machines
and devices with a magnetic core that
can be saturated.
All the loads that distort the normal
sinusoidal current cause harmonics
and are called non-linear loads.
Page 85
Application and Installation Guide
Battery UPS
Figure 49: Examples of non-linear loads that cause harmonics..
Linear and non-linear loads
Utility power supplies 50/60 Hz
sinusoidal voltage to loads. The
current waveform supplied by the
source in response to the needs of the
load depends on the type of load.
Linear loads
The current drawn is sinusoidal with
the same frequency as the voltage.
The current may be displaced (angle
φ) with respect to the voltage.
• Ohm's law defines a linear relation
between the voltage and the
current (U = ZI) with a constant
coefficient, the load impedance.
The relation between the current
and the voltage is linear.
Examples are standard light bulbs,
heating units, resistive loads, motors,
transformers.
• This type of load does not
contain any active electronic
components, only resistors (R),
inductors (L) and capacitors (C).
Page 86
Non-linear loads
• The current drawn by the load is
periodic, but not sinusoidal. The
current waveform is distorted by
the harmonic currents.
• Ohm's law defining the relation
between the total voltage and
current (1) is no longer valid
because the impedance of the
load varies over one period (see
figure 50). The relation between
the current and the voltage is not
linear.
• The current drawn by the load is,
in fact, the combination of:
- a sinusoidal current called the
fundamental, at the 50 or 60 Hz
frequency,
- harmonics, which are
sinusoidal currents with an
amplitude less than that of the
fundamental, but a frequency
that is a multiple of the
fundamental and which defines
the harmonic order (e.g. the
third order harmonic has a
frequency 3 x 50 Hz [or 60 Hz]).
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Battery UPS
Application and Installation Guide
(1) Ohm's law applies to each
voltage and current of the same
harmonic order, Uk = Zk Ik, where
Zk is the load impedance for the
given order, but is no longer valid
for the total voltage and current.
Linear loads, non-linear loads, see
page 6 “Power quality of UPS”.
Figure 50: Voltage and current for non-linear loads..
Types of harmonics and specific
aspects of zero-sequence
harmonics
Types of harmonics
Non-linear loads cause three types of
harmonic currents, all in odd orders
(because the sinusoidal is an “odd”
function).
• Harmonics H7 - H13 - …. :
positive sequence,
• Harmonics H5 - H11 - …. :
negative sequence,
• Harmonics H3 - H9 - …. :
zero sequence.
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Page 87
Application and Installation Guide
Battery UPS
Specific aspects of zero-sequence
harmonics (H3 and multiples)
Zero-sequence harmonic currents (H3
and odd multiples, written 3(2k + 1)
where k is an integer) in three-phase
systems add up in the neutral
conductor.
This is because their order 3(2k + 1) is
a multiple of the number of phases
(3), which means they coincide with
the displacement (one third of a
period) of the phase currents.
Figure 51 illustrated this phenomenon
over one period. The currents of the
three phases are displaced one third
of a period (T/3), i.e. the respective IH3
harmonics are in phase and the
instantaneous values add up.
Consequently:
• When there are no harmonics,
the current in the neutral is equal
to zero:
IN = I1 + I2+ I3 = 0
• When there are harmonics, the
current in the neutral is equal to:
I1 + I2 + I3 = 3 IH3.
It is therefore necessary to pay
particular attention to this type of
harmonics in installations with a
distributed neutral (commercial
and infrastructure applications).
Page 88
Figure 51: The third-order harmonics and.
their multiples add up in the neutral.
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Application and Installation Guide
Figure 52: When there are H3 harmonics and their odd multiples, the current in the.
neutral is no longer equal to zero, it is the sum of the zero-sequence harmonics.
Characteristic harmonic
values
• IH1 is the fundamental component
(50 or 60 Hz),
The harmonic analysis of a non-linear
current consists in determining:
• IHk is the harmonic component
where k is the harmonic order
(k times 50 or 60 Hz).
• The harmonic orders present in
the current,
• The relative importance of each
harmonic order.
Below are a few characteristic
harmonic values and fundamental
relations used in harmonic analysis.
Further information on harmonics,
see the explanations in White Paper
no. 17 “Understanding Power
Factor, Crest Factor and Surge
Factor”.
Rms value of harmonics
Harmonic analysis is used to
determine the values.
Total rms current
Irms √IH12 + IH22 + IH32 + ... IHk2 + ...
Individual harmonics
Each harmonic is expressed as a
percentage, i.e. the ratio of its rms
value to the rms value of the
fundamental. This ratio is the level
of the individual harmonic.
Hk% = distortion of harmonic k =
100 IHk
IH1
It is possible to measure the rms value
of each harmonic order because the
various harmonic currents are
sinusoidal, but with different
frequencies that are multiples
of the fundamental frequency.
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Page 89
Application and Installation Guide
Battery UPS
Voltage and current harmonic
distortion
Non-linear loads cause both current
and voltage harmonics. This is because
for each load current harmonic, there
is a supply voltage harmonic with the
same frequency. As a result, the
voltage is also distorted by harmonics.
The distortion of a sine wave is
presented as a percentage:
THD* % = total distortion =
100 rms value of all harmonics
rms value of fundamental
* Total Harmonic Distortion.
The following values are defined:
• TDHU % for the voltage, based
on the voltage harmonics,
• TDHI % for the current, based
on the current harmonics.
The THDI (or the THDU using the UHk
values) is measured using the equation:
THDI% = 100
√IH22 + IH32 + IH42 + ... + Hk2 + ...
IH1
Crest factor
The crest factor (Fc), used to characterise
the form of the signal (current or voltage),
is the ratio between the peak value and
the rms value.
Fc =
peak value
rms value
Below are typical values for different loads:
• Linear load: Fc = √2 = 1.414,
• Main frame: Fc = 2 to 2.5,
• Microcomputers: Fc = 2 to 3.
Page 90
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Application and Installation Guide
Spectrum of the harmonic
current
Defining the spectrum of a harmonic
current consists in determining the
current waveform and the individual
harmonics, as well as certain values
such as the THDI and Fc.
Figure 53: Harmonic spectrum of the current drawn by a non-linear load..
Power factor
Power factor
The power factor is the ratio between
the active power (kW) and the
apparent power S (kVA) across the
terminals of a given non-linear load.
λ=
P (kW)
S (kVA)
It is not the phase displacement
between the voltage and the current,
because they are no longer sinusoidal.
Displacement between the
fundamental current and voltage
The phase displacement φ1 between
the fundamental current and voltage,
both sinusoidal, can be defined as:
P (kW)
cos φ1 = 1
S1 (kVA)
where P1 and S1 are the active and
apparent power, respectively, of the
fundamental.
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Distortion factor
The distortion factor is defined as:
ν = √THDI2 =
λ
(as defined by IEC 60146).
cos φ1
When there are no harmonics, this factor
is equal to 1 and the power factor is
simply the cos φ.
Power
Linear load
Across the terminals of a balanced, threephase linear load, supplied with a
phase-to-phase voltage U and a current I,
where the displacement between U and
I is φ, the power values are:
• P apparent = S = UI, in kVA,
• P active = S cos φ, in kW,
• P reactive = Q = S sin φ, in kVAr,
S = √P2 + Q2
Page 91
Application and Installation Guide
Non-linear load
Across the terminals of a non-linear
load, the equation for P is much more
complex because U and I contain
harmonics. It can however be
expressed simply as:
• P = S ( = power factor)
For the fundamentals U1 and I1,
displaced by φ1:
Battery UPS
pulsating torque exists, creating
vibrations,
• The only active power present
during a voltage drop is the
heating produced by the
harmonic current (Ihk) in a
conductor with a resistance r
(r IHk2).
• P apparent fundamental =
S1 = U1I1í3
• P active fundamental = P1 =
S1 cos 1
• P reactive fundamental Q1 =
S1 sin 1
S = √P12 + Q12 + D2 where D is the
distortion power, due to the
harmonics.
Effects of harmonics
In electrical devices, harmonics
produce neither active nor
reactivepower, only losses through
the Joule effect (ri2).
Loss of apparent power
Figure 54 shows that the product of a
voltage at the fundamental frequency
without harmonics multiplied by a
third-harmonic current is zero at
the end of one period. This is true
whatever the phase and order of the
harmonic.
This is expressed by the relation
S = √P12 + Q12 + D2
Figure 54: U x I products for fundamentals (top)
and for fundamentals with harmonics (bottom).
A part of the apparent power is
consumed by the harmonics, to no
effect.
Temperature rise in cables
• In rotating machines, the
resulting motor torque is equal
to zero and only a parasitic
Page 92
Temperature rise due to harmonic
currents adds to the temperature
rise due to the fundamental
current.
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Application and Installation Guide
Temperature rise in cables is
expressed as:
∞
Losses = r + Σ IHn2
n=1
Current in the neutral
The neutral must be oversized to
take into account the third-order
harmonic currents and their
multiples.
All third-order harmonic currents and
their odd multiples add up in the
neutral (see figure 55). The current in
the neutral can reach 1.7 times that in
the phases.
Consequences
Significant losses in the neutral
r Ineutral2 = temperature rise in the
neutral.
Figure 55: The third-order harmonics and.
their multiples add up in the neutral.
Self-polluting loads
Voltage distortion mirrors that of
the current and increases in step
with the sum of the impedances
upstream of the non-linear load.
Current distortion THDI, caused by the
load, results in voltage distortion THDU
caused by the harmonic currents flowing
through the various impedances from
the source on down. Figure 56 shows the
various forms of distortion throughout a
common electrical installation.
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Page 93
Application and Installation Guide
Battery UPS
Figure 56: Effects of harmonics throughout the installation..
Risk of capacitor breakdown
In conclusion, the higher the
content of high-order components
in the voltage, the worse the
situation for the capacitor. It is
often necessary to use reinforced
capacitors.
The value of a current in a capacitor
is equal to:
.I = U C ω
For a harmonic current of order k, the
angular frequency is equal to ω = 2π k
f, and the current is equal to:
.I = 2 π k f U C
where f = the fundamental frequency
and k = the harmonic order.
What is more, for a harmonic
frequency, there can also be
resonance (1) of the capacitor
(capacitance C) with the equivalent
inductance (L) of the source
(transformer, essentially inductive) in
parallel with that of the other supplied
loads.
This resonant circuit (see figure 57)
significantly amplifies the harmonic
current of the corresponding order,
thus worsening the situation for the
capacitor.
(1) This is the case if, for a harmonic
order k, with a frequency fk = k x 50
(or 60) Hz, LCωk2 - 1, where ω = 2 π fk.
It follows that the value of the current
increases with k.
Page 94
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Application and Installation Guide
Figure 57: Effects of harmonics with capacitors, risk of resonance..
Consequences
• Risk of capacitor breakdown,
• Risk of resonance due to the
presence of the inductors.
Certain limitations must be respected:
Consequences
In compliance with standard NFC
52-114, transformers must be
derated by applying a coefficient k
to their rated power, such that:
• U max = 1.1 Un,
• I max = 1.3 In,
• THDU max = 8%,
• Selection of capacitor type,
depending on the situation, i.e.
standard, class h (reinforced
isolation), with harmonic
inductors.
Derating of transformers
Generally speaking, harmonics
result in source derating that is
inversely proportional to the load
power factor, i.e. the lower the
power factor, the more the source
must be derated.
A number of effects are combined:
• Due to the skin effect, the
resistance of a transformer
winding increases with the order
of the harmonics,
k=
√
1
n= ∞
1 + 0,1Σ H2nn1,6
n=2
This is an empirical equation.
Other national standards recommend
derating using a similar k factor that
depends on the country (e.g. BS 7821
Part 4, IEE 1100-1992).
Example
A 1000 kVA transformer supplies a sixpulse rectifier bridge drawing the
following harmonics:
H5 = 25%, H7 = 14%, H11 = 9%, H13 = 8%.
The derating coefficient is k = 0.91.
The apparent power of the
transformer is therefore 910 kVA.
• Losses due to hysteresis are
proportional to the frequency,
• Losses due to Foucault currents
are proportional to the square of
the frequency.
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Application and Installation Guide
Battery UPS
Risk of disturbing generators
• Automatic telephone exchanges,
Practically speaking, the THDI of
the current in the generator must
not exceed 20%. Above, derating is
necessary.
• Alarms,
Similar to transformers, generators
suffer greater losses due to hysteresis
and Foucault currents.
• The subtransient reactance X"d
increases as a function of the
frequency,
• The “harmonic” rotating field
sweeps the rotor at a frequency
other than the synchronism
frequency (50 or 60 Hz).
Consequences
• Creation of parasitic torque
resulting in lower efficiency of
the mechanical to electrical
conversion,
• Additional losses in the inductor
windings and the rotor damper,
• Presence of vibration and
abnormal noise.
Losses in asynchronous motors
Harmonics produce the following
effects in asynchronous motors:
• Increases in Joule and iron
losses (stator losses),
• Pulsating torque (rotor losses
with a drop in mechanical
efficiency).
The THDU must be less than 10%
to limit these phenomena.
Effects on other equipment
Harmonics can disturb operation of
the following equipment as well:
• Sensitive electronic equipment,
• Remote-control systems.
Effect on recent UPS systems
Modern UPS systems have high
chopping frequencies (PWM) and very
low output impedance (equivalent to
a transformer five times more
powerful).
When confronted with non-linear
loads, these UPS offer:
• Limited losses,
• Current-limiting operation,
• Very low voltage distortion
(THDU < 3%).
UPS are an excellent means
to supply non-linear loads.
Conclusion
Harmonics may have damaging
effects on electrical installations and
on the quality of operation.
That is why international standards
stipulate increasingly precise
harmonic-compatibility levels for
equipment and set limits for the
harmonic content on public
distribution systems.
Standards on harmonics, see page
145 “UPS standards”.
On the following pages are a
presentation of the various strategies
concerning harmonics and the
usefulness of active harmonic
conditioners.
• Non-rms trip units, resulting
in nuisance tripping of circuit
breakers,
Page 96
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Application and Installation Guide
Elimination of harmonics
Strategies against
harmonics
There are two strategies:
• Accept and live equipment to take,
• Eliminate the harmonics,
conditioners.
Living with harmonics
Oversizing of equipment
Given that the negative effects of
harmonic currents increase with the
cumulative impedance of cables and
sources, the obvious solution is to
limit the total impedance in order to
reduce both voltage distortion and
temperature rise.
Figure 59 shows that for the strongest
harmonic currents (H3 to H7), the L /R
ratio is equal to 1 for cables with a
cross-section of 36 mm².
Consequently, above 36 mm², it is
necessary to reduce the impedance
by using multicore cable to create
parallel impedances.
For Data Centers, see “Harmonic
Currents in the Data Center: A Case
Study”.
Figure 58 shows the results when
cable cross-sections and the power
rating of the source are doubled.
Given that the THDU depends primarily
on the inductive component and thus
on the length of the cables, it is clear
that this solution is not very effective
and results simply in limiting
temperature rise.
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Figure 58: Increased cable cross-sections.
to limit distortion and losses.
Page 97
Application and Installation Guide
Battery UPS
Figure 59: Influence of cable cross-section on L /R..
Solutions to eliminate
harmonics
There are different types of solutions
to eliminate harmonics.
Filters, see page 28 “Selection of
a filter”.
Passive filters
LC passive filters are tuned to the
frequency requiring elimination or
attenuate a band of frequencies.
Harmonic recombination systems
(double bridge, phase shifting) can
also be grouped in this category.
Passive filters have two major
disadvantages:
• Elimination of harmonics is
effective only for a specific
installation, i.e. the addition
or removal of loads can disrupt
the filtering system,
Active filters / active harmonic
conditioners
Active filters, also called active
harmonic conditioners, cancel
harmonics by injecting exactly equal
harmonic currents where they arise.
This type of filter reacts in real time
(i.e. actively) to the existing harmonics
in order to eliminate them. More
effective and flexible than passive
filters, they avoid their disadvantages
and, in comparison, constitute a
solution that:
• offers greater performance (total
elimination of all harmonics is
possible, up to the 50th order),
• is flexible, adaptable (action can
be configured) and reusable.
• it is often difficult to implement
them in an existing installation.
Page 98
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Application and Installation Guide
Table summing up the possible strategies against harmonics
Strategy
Advantages
Disadvantages
Solutions
Live with harmonics
Increase the
ratings of sources
and/or the crosssections of cables.
Difficult in existing solutions. Costly
solution limited to reducing the
Reduction in
resistive component for small crosssupply THDU by
sections (the inductance remains
reducing the
constant). Requires parallel cables
source impedance.
for large cross-sections. Does not
Reduction in Joule
avoid disturbances upstream of the
losses.
installation. Does not comply with
standards.
Special supply for
non-linear loads.
Limits disturbances
to neighboring
Same as above.
loads through
decoupling.
Partially eliminate harmonics
Tuned passive
filters.
Simple solution.
Only for one or two harmonic
orders. Wide-band filters are not
very effective. Possibility of
resonance. Costly design work is
required.
Range of passive filters
Including double-bridge
and phase-shifting
solutions.
Reduction in
Inductors upstream harmonic currents.
Increase in THDU across the
Limits the effects of
of the non-linear
terminals of the load.
transient
loads.
overvoltages.
Special
transformers.
Elimination of only certain
harmonic orders. Non-standard
construction.
Completely eliminate harmonics
Active harmonic
conditioners.
Total elimination of all harmonics
Simple and flexible is possible (up to the 25th order),
adaptable (action configured) and
solution.
reusable system.
Active conditioners
Table 17.
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Page 99
Application and Installation Guide
Battery UPS
Active harmonic conditioners
Active harmonic conditioners
Characteristics
Active harmonic conditioners
Active harmonic conditioners
constitute a more general approach
to the problem of harmonics. These
active filters are not only for a UPS
unit, but are designed to eliminate
harmonics throughout the installation.
Range
Active
harmonic
conditioner
Power level
20 to 480 A
50/60 Hz
systems
Active harmonic conditioners are
particularly well suited to mediumpower industrial and infrastructure
applications, offering conditioning
currents from 20 to 480 A in threephase systems with a neutral.
These solutions are presented in
the following section.
Table 18 sums up the main
characteristics.
Main characteristics
• Filtering up to H25
• Digital active
conditioning with:
- analysis and
380 to 415 V
conditioning of
3 Ph+N and 3 Ph
individual orders,
- response time 40 ms
for load fluctuations.
Applications
Filtering of medium-power
commercial, infrastructure
and industrial systems,
3Ph+N and 3 Ph, singlephase loads.
Table 18..
Advantages of active harmonic
conditioning
• Wide-band solution from H2 to
H25 with individual conditioning
of each phase,
• It is possible to select individual
harmonic orders for conditioning,
• No risk of overloads, conditioning limits to the maximum power
rating, even if the load power
exceeds the rating,
• Automatically adapts to all types
of loads, single-phase and threephase,
Page 100
• Compatible with all system
earthing arrangements,
• Power factor correction,
• Economic, when harmonics are
cut in half, losses are reduced by
four,
• Can be reused in other
installations,
• Upgradeable with parallelconnected units,
• Very compact,
• Simple installation, with current
transformers upstream or
downstream.
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Battery UPS
Application and Installation Guide
Operating principle
The source supplies exclusively the
fundamental component (IF) of the
load current.
The active conditioner measures in
real time the harmonics (IH) drawn
by the load and supplies them.
Upstream of point A, where the
conditioner is connected, the
fundamental current IF is not altered,
downstream the load draws the nonlinear current IF + IH.
Figure 60: Harmonic conditioning..
Operating modes
Digital mode, conditioning of
individual orders
The basic operating mode is digital,
with a current sensor, analogue/digital
conversion of the current measurements and real-time calculation of the
harmonic spectrum. This information
is supplied to the inverter for
compensation of the individual
harmonic orders.
The response time to load fluctuations
is 40 ms (two cycles).
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Operating diagram
The power required for conditioning is
drawn on the three-phase distribution
system and stored in the inductor L
and the capacitors charged to +Vm
and -Vm respectively (see figure 61).
Depending on the sign of the
harmonic current required, the pulse
width of one capacitor or the other is
modulated. This means the same
connection to the supply system can
be used to draw power and inject the
harmonics.
Page 101
Application and Installation Guide
The power sent to the load depends on:
• The harmonic values measured,
• User requirements, set during
system configuration: harmonic
orders to be eliminated and
power-factor correction (yes
or no).
Battery UPS
selecting program, a processor
prepares the commands for the
inverter, for execution one phase after
the measurements.
Power factor correction is obtained by
generating a fundamental current +90°
out of phase with the voltage
The current transformer, combined
with an analogue/digital converter,
determines the spectrum
(fundamental and harmonics)
of the current supplying the load.
Depending on these values and the
Figure 61: Operation..
Options
On 3Ph or 3 ph+N systems, the user
can decide to condition:
• All or only certain harmonics
up to H25,
• The power factor
Installation modes
Parallel mode
Up to four active harmonic conditioners
can be connected in parallel at the
same point of installation. This the
means to increase harmonic
conditioning capacity and/or system
availability.
Page 102
For parallel installations, a single
set of sensors is required on the
conditioned circuit and a wire link
is used to send the load-current
measurements to the various
conditioners. If one conditioner shuts
down, the remaining conditioners
continue to condition the harmonics,
within the limits of their rated
conditioning capacity.
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Battery UPS
Figure 62: Parallel operation of three.
active harmonic conditioners.
Cascade or in-series mode
“Cascade” or “in-series” operation is
possible, but simply requires special
settings to avoid any interaction
between the different conditioners.
The downstream conditioner
generally conditions a high-power
load. The upstream device conditions
other low-power outgoing circuits
and, where applicable, any residual
harmonics not conditioned by the first
conditioner.
Application and Installation Guide
Figure 63: Active harmonic conditioners.
in cascade mode.
Multi-circuit mode
In this mode, a single conditioner
can condition up to three outgoing
circuits. A set of sensors is required
for each circuit conditioned and all
are connected to active harmonic
conditioners . This configuration is
very useful when the harmonics are
concentrated on a small number of
circuits.
Figure 64: One active conditioner for several circuits..
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Application and Installation Guide
Battery UPS
Position in the installation
Total (or centralised) conditioning
The active harmonic conditioner is
connected just downstream of the
sources, generally at the main lowvoltage switchboard (MLVS) level.
Partial conditioning
The active harmonic conditioner is
connected at the main or secondary
switchboard level and conditions a set
of loads.
Local conditioning
The active harmonic conditioner is
connected directly to the terminals of
each load
Figure 65: Three possible installation points,
depending on user requirements.
Page 104
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Battery UPS
Application and Installation Guide
Comparison of installation possibilities
Type of conditioning
Total
(MLVS level)
Advantages
• Economical.
• Relieves generators
(transformers,
generators).
Disadvantages
• Harmonics remain in
the downstream part
of the installation.
• Cables must be
oversized.
Applications
• Compliance with utility
requirements.
• Avoid injecting
harmonics upstream
of the installation.
• Avoids oversizing the
• Harmonics remain
• Large buildings.
cables between the
between the secondary • Conditioning regularly
main and secondary
switchboard and the
spaced on each floor
Partial
switchboards.
non-linear load.
or set of floors.
(secondary-switchboard • Recombination of
• Outgoing cable to the • Several circuits
level)
certain harmonics may
load must be
supplying non-linear
make it possible to
oversized.
loads.
reduce conditioner
rating.
• Eliminates harmonics
where they occur.
• Reduces losses in all
cables, up to the
source.
Local
(load level)
Costly when a number
of conditioners are
required.
• For installations where
non-linear loads are
few in number and
high-powered iwth
respect to the other
loads (example: large
variable-speed drives,
high-power UPS):
- Examples: server
bays, lighting, highpower UPS,
fluorescent lighting
systems.
Table 19..
Practically speaking
• Total conditioning does not pose
any calculation problems,
• Partial conditioning requires a
few precautions,
• For all non-compensated RCD
loads (high-power variablespeed drives without inductors
for variable-torque applications),
local conditioning can guarantee
only a THDU not exceeding
certain limits to ensure proper
load operation.
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Position of current transformers
upstream or downstream
In most of the installation modes,
previously listed, two different types
of current-transformer (CT) installation
can be used with active harmonic
conditioners.
Page 105
Application and Installation Guide
Battery UPS
CT upstream of the load
This is the most common situation.
Figure 66: Installation with one CT upstream of the load..
Installation with one CT upstream of
the active harmonic conditioners and
one CT on the switchboard incomer
This configuration simplifies matters
when it is difficult to install a CT on
the line just upstream of the load. The
two CTs must have compatible and
complementary characteristics. The
difference between the measured
currents determines the necessary
compensation current.
Figure 67: Installation with two CTs, one on the switchboard.
incomer and the other upstream of the conditioner.
Page 106
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Battery UPS
Advantages
Elimination of the conditioned
harmonic currents
For the selected harmonics, active
harmonic conditioners are designed
to provide a path for the harmonic
currents with virtually zero impedance
with respect to that of the source.
This eliminates their flow upstream
towards the source.
Figure 68 shows active harmonic
conditioners between two line
sections ZL1 and ZL2, supplying a
standard RCD load that can be either
single or three-phase (switch-mode
power supply or variable-speed drive).
Application and Installation Guide
The harmonic currents IHn that
previously flowed through impedances
Zs and ZL1 upstream of the active
harmonic conditioners point of
installation, are eliminated.
The source now supplies exclusively
the fundamental current If.
It is the active harmonic conditioners
that supplies the harmonic currents
IHn to the load, by continuously
measuring the harmonics drawn
by the load.
Figure 68: Modifies the current upstream of its point of installation..
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Page 107
Application and Installation Guide
Reduction in THDU at the point
of installation
Upstream of active harmonic
conditioners, the selected harmonic
currents IHn (all or only some of the
harmonics up to the 25th) are
eliminated.
Total harmonic distortion upstream of
the point of installation is calculated
as (see page 158, figure 94):
√Σ
∞
THDU% = 100
n=2
UHn2
UH1
where UHn is the voltage drop
corresponding to harmonic IHn.
Elimination of the harmonic current for
a given order eliminates the harmonic
voltage for the same order (1).
The result is a major reduction in the
THDU, by selecting the most
significant harmonics.
Given that above the 25th order,
individual harmonics are negligible,
the THDU is practically equal to zero
and distortion is totally eliminated if it
is decided to condition all harmonics
up to the 25th.
(1) In that UHn and IHn are sinusoidal
components at frequency nf (where f
is the frequency of the fundamental),
they are related by the Ohm law,
taking into account the value of the
concerned impedances (Zs and ZL1)
with an angular frequency nω.
Therefore:
Battery UPS
Procedure for implementing
active conditioning
Conclusion on active
conditioning
Precise conditioning calculations
require:
• Precise and in-depth knowledge
on the installation (sources, lines
and installation method),
• Precise knowledge on the loads
(harmonic and displacement
curves depending on the source
impedance),
• Special calculation tools,
• Analysis and simulation.
New installations
The standard rules governing
electrical installations remain valid,
but an evaluation of the voltage
distortion (THDU) is required where
harmonic currents flow.
This evaluation is very complex and
requires special calculation software
as well as in-depth knowledge of the
non-linear loads, in particular the
harmonic distribution as a function of
the upstream impedance.
Existing installations
For existing installations, a precise
evaluation of the site is the
indispensable prerequisite to any
corrective action. The mathematical
relationship between current and
voltage distortion is complex and
depends on the various components
of the installation.
UHn = (Zs(nω) + ZL1(nω)) IHn.
For all the conditioned harmonics, IHn
= 0 and consequently, UHn = 0.
Page 108
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Battery UPS
Control over harmonic phenomena
requires know-how and experience, as
well as specialised tools and software
(spectrum analyser, calculation
software for distortion in cables,
simulation software, etc.).
However, even if each solution is
specific to a given site, proper
professional techniques and rigorous
methods ensure maximum probability
that the installation will operate
correctly.
Methodology
Three-step approach:
1. Site audit,
2. Determination of the most suitable
solution,
3. System installation and checks.
1. Site audit
Installation diagram
Before initiating a series of
measurements, we suggest you draft
a simplified diagram of the
installation, indicating the following.
• Types of equipment:
- generators: type, power rating,
voltage, Usc, X"d (engine
generator set),
- isolation transformers: voltage,
power rating, type, Usc,
coupling,
- distribution: type of cables,
length, cross-section,
installation method,
- loads: power rating, type,
- system earthing arrangements
at the various points in the
installation.
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Application and Installation Guide
• Operating modes:
- on utility power,
- on engine generator sets
(standby power or
cogeneration),
- on UPS.
• Downgraded operating modes:
- without redundancy,
- on engine generator set power.
This diagram should enable you to
locate the different measurement
points and identify critical operating
phases (for evaluation by simulation
or calculation).
Measurements
Following the previous indispensable
step, the measurement phase can
begin, starting preferably at the source
and working downstream toward the
loads drawing the harmonics, in order
to limit the number of measurements.
The quality of measurements is more
important than their quantity and
makes the next step easier.
Preliminary installation study
This first step ends with a preliminary
study of the installation:
• Point(s) of installation of the
conditioner(s),
• Installation conditions for the
protection circuit breakers,
• Installation of sensors (energised
conditions or not),
• Possibility of shutting down
the load,
• Available space,
• Evacuation of losses (ventilation,
air-conditioning, etc.),
• Environmental constraints
(noise, EMC, etc.).
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Application and Installation Guide
Battery UPS
2. Determination of the most
suitable solution
3. System installation
and checks
The previous elements are used to
determine the optimum solution
through:
This last step includes:
• Analysis of the measurement
results,
• Simulation of different solutions
for the problem encountered,
• Determination of the most
suitable solution,
• Implementation of the selected
solutions,
• Checks on performance levels
with respect to the guaranteed
results,
• Drafting of a system start-up
report.
• Drafting of a summary report
with the proposed solutions.
Page 110
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Application and Installation Guide
Theoretical review
Supplying sensitive loads
Types of electrical
disturbances
Power distribution systems, both
public and private, theoretically
supply electrical equipment with a
sinusoidal voltage of fixed amplitude
and frequency (e.g. 400 volts rms,
50 Hz, on low-voltage systems).
In real-life conditions however, utilities
indicate the degree of fluctuation
around the rated values. Standard EN
50160 defines the normal fluctuations
in the LV supply voltage on European
distribution systems as follows:
• Voltage +10% to -15% (average
rms values over 10-minute
intervals), of which 95% must be
in the +10% range each week,
• Frequency +4 to 6% over one
year with ±1% for 99.5% of the
time (synchronous connections
in an interconnected system).
Practically speaking, however, in
addition to the indicated fluctuations,
the voltage sine-wave is always
distorted to some degree by various
disturbances that occur on the system.
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Origins of disturbances
Utility power
Utility power can be disturbed or even
cut by the following phenomena:
• Atmospheric phenomena
affecting overhead lines or
buried cables:
- lightning which can produce a
sudden voltage surge in the
system,
- frost which can accumulate on
overhead lines and cause them
to break,
• Accidents:
- a branch falling on a line, which
may produce a short-circuit or
break the line,
- cutting of a cable, for example
during trench digging or other
construction work,
- a fault on the utility power
system,
• Phase unbalance,
• Switching of protection or
control devices in the utility
power system, for load shedding
or maintenance purposes.
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Application and Installation Guide
User equipment
Some equipment can disturb the
utility power system, e.g.:
• Industrial equipment:
- motors, which can cause
voltage drops due to inrush
currents when starting,
- equipment such as arc furnaces
and welding machines, which
can cause voltage drops and
high-frequency interference,
Battery UPS
Types of disturbances
Disturbances that are due to the
previously listed causes are summed
up in the following table, according to
the definitions contained in standards
EN 50160 and ANSI 1100-1992.
• Power electronics equipment
(switch-mode power supplies,
variable speed drives, electronic
ballasts, etc.), which often cause
harmonics,
• Building facilities such as lifts
which provoke inrush currents or
fluorescent lighting which causes
harmonics.
Page 112
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Battery UPS
Disturbances
Application and Installation Guide
Characteristics
Main causes
Main consequences
Power outages
Micro-outages
Total absence of voltage ≤ 10 ms.
Atmospheric conditions, switching,
faults, work on the utility.
Faulty operation and loss of
data (computer systems) or
interrupted production
(continuous processes).
Outages
Total absence of voltage for more
than one period:
• short outage: < 3 minutes (70% of
outages last less than 1 s)
• long outage: > 3 minutes
Atmospheric conditions, switching,
faults, incidents, line breaks, work
on the utility.
Depending on the duration,
shutdown of machines and risks
for people (e.g. lifts), loss of data
(computer systems) or
interrupted production
(continuous processes).
Voltage variations
Voltage sags
Reduction in the rms value of
voltage to less than 90% of the rated
value (but greater than 0%), with
return to a value greater than 90%
within 10 ms to 1 minute.
Atmospheric phenomena, load
fluctuations, short-circuit on a
neighboring circuit.
Shutdown of machines,
malfunctions, damage to
equipment and loss of data.
Overvoltage
Temporary increase to more than
10% over the rated voltage, for a
duration of 10 ms to a few seconds.
• Quality of utility generators and
transmission systems.
• Interaction between generators
and load fluctuations on the utility
power system.
• Switching on the utility power
system.
• Stopping of high-power loads (e.g.
motors, capacitor banks).
• For computer systems:
corruption of data, processing
errors, system shutdown,
stress on components.
• Temperature rise and
premature aging of equipment.
Undervoltage
Drop in voltage lasting from a few
minutes to days.
Peak in consumption, when the utility
cannot meet demand and must
reduce its voltage to limit power.
• Shutdown of computer systems.
• Corruption or loss of data.
• Temperature rise.
• Premature aging of equipment.
Voltage spike
Sudden major jump in voltage (e.g.
6 kV).
Close lightning strikes, static
discharges.
• Processing errors, corruption
of data system shutdown.
• Damage to computers,
electronic boards.
Condition where the rms value of the
phase voltages or the unbalances
between phases are not equal.
• Induction furnaces.
• Unbalanced single-phase loads.
• Temperature rise.
• Disconnection of a phase.
Voltage unbalance
(in three-phase systems)
Frequency variations
Frequency fluctuations
Flicker
Instability in the frequency. Typically
+5%, -6% (average for ten-second
time intervals).
• Regulation of generators.
• Irregular operation of generators.
• Unstable frequency source.
--These variations exceed the
tolerances of certain instruments
and computer hardware (often
±1%) and can therefore result in
the loss or corruption of data.
Flicker in lighting systems due to a
drop in voltage and frequency (< 35
Hz).
Welding machines, motors, arc
furnaces, X-ray machines, lasers,
capacitor banks.
Physiological disturbances.
Other disturbances
HF transients
Sudden major and very short jump
in voltage. Similar to a voltage spike.
Atmospheric phenomena (lightning)
and switching.
Short duration
< 1 μs.
Amplitude < 1 to 2 kV at frequencies
of several tens of MHz.
Starting of small inductive loads,
repeated opening and closing of
low-voltage relays and contactors.
Medium duration
< 1 μs and ≤ 100 μs.
Peak value 8 to 10 times higher than
the rated value up to several MHz.
Faults (lightning) or high-voltage
switching transmitted to the lowvoltage by electromagnetic coupling.
Long duration
> 100 μs.
Peak value 5 to 6 times higher than
the rated value up to several
hundred MHz.
Stopping of inductive loads or highvoltage faults transmitted to the
low-voltage system by
electromagnetic coupling.
Harmonic distortion
Distortion of the current and voltage
sine-waves due to the harmonic
currents drawn by non-linear loads.
The effect of harmonics above the
25th order is negligible.
Electric machines with magnetic
cores (motors, off-load transformers,
etc.), switch-mode power supplies,
arc furnaces, variable speed drives.
Oversizing of equipment,
temperature rise, resonance
phenomena with capacitors,
destruction of equipment
(transformers).
Electromagnetic
compatibility (EMC)
Electromagnetic or electrostatic
conducted or radiated disturbances.
The goal is to ensure low emission
and high immunity levels.
Switching of electronic components
(transistors, thyristors, diodes),
electrostatic discharges.
Malfunctions of sensitive
electronic devices.
Destruction of equipment,
accelerated aging, breakdown
of components or insulators.
Table 20..
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Application and Installation Guide
Battery UPS
UPS
UPS
A UPS (uninterruptible power system)
is used to supply sensitive
applications with secure power.
A UPS is an electric device positioned
between the utility and the sensitive
loads that supplies voltage offering:
• High quality: the output sinewave is free of any and all
disturbances in utility power
and within strict amplitude and
frequency tolerances,
• High availability: the continuous
supply of voltage, within the
specified tolerances, is ensured
by a backup supply of power.
The backup supply is generally
a battery that, if necessary, steps
in without a break in the supply
to replace utility power and
provide the backup time required
by the application.
These characteristics make UPSs the
ideal power supply for all sensitive
applications because they ensure
power quality and availability,
whatever the state of utility power.
Components of a UPS
A UPS generally comprises the main
components listed as follows.
Rectifier/charger
It draws utility power and produces a
DC current to supply the inverter and
charge or recharge the battery.
Page 114
Inverter
It completely regenerates a highquality voltage output sine-wave:
• Free of all utility-power disturbances, notably micro-outages,
• Within tolerances compatible
with the requirements of
sensitive electronic devices
(e.g. tolerances in amplitude
± 0.5% and frequency ± 1%,
compared to ± 10% and ± 5%
in utility power systems, which
correspond to improvement
factors of 20 and 5, respectively.
Note: The term inverter is sometimes
used to designate a UPS, when in
reality it is only a part of the UPS.
Energy Storage
The energy storage provides sufficient
operating backup time (seconds to
a number of hours) by stepping in to
replace utility power as needed.
Static bypass
The static bypass ensures no-break
transfer of the load from the inverter
to direct utility power and back. Nobreak transfer is carried out by a
device implementing SCRs
(sometimes called a static switch).
The static bypass makes it possible to
continue supplying the load even if an
internal fault occurs or during
maintenance on the rectifier/charger
and inverter modules. It can also serve
for transfers to call on the full power
available upstream in the event of
overloads (e.g. short circuits)
exceeding UPS capacity.
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Battery UPS
Application and Installation Guide
During operation on the static bypass,
the load is supplied directly by utility
power and is no longer protected
(operation in downgraded mode).
Maintenance bypass
This bypass may be used to supply
the load directly with utility power,
without calling on the inverter or
the static switch. Transfer to the
maintenance bypass is user initiated
with switches. By actuating the
necessary switches, it is the means
to isolate the static bypass and the
inverter for maintenance, while
continuing to supply the load in
downgraded mode.
Figure 69: The UPS solution..
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Application and Installation Guide
UPS applications
UPS are used for a wide range of
applications requiring electrical power
that is available at all times and not
affected by disturbances on the utility
power system. Table 21 presents a
number of applications.
For each, it indicates the sensitivity of
the application to disturbances.
Battery UPS
The applications requiring this type
of installation are:
• Computer systems,
• Telecommunications,
• Industry and instruments,
• Other applications.
The required UPS typologies are
presented on page 5, “Types of static
UPS”.They include static UPS
implementing the following typologies:
• Passive standby,
• Line interactive,
• Double conversion.
Page 116
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Application and Installation Guide
UPS Applications
Protection required against
Application
Protected devices
Microoutages
Outages
Voltage Frequency
variations variations
Other
Computer systems
Data centers
• Large bays for rack-mounted
servers
• Internet data centers
*****
*****
*****
*****
*****
Company networks
• Sets of computers with
terminals and peripheral
devices (tape storage units,
disk drives, etc).
*****
*****
*****
*****
*****
****
****
***
***
**
**
**
*
*
**
*****
*****
*****
*****
Small networks
and servers
• Networks made up of PCs
or workstations, server
networks (WAN, LAN)
• PCs, workstations
Stand-alone computers • Peripheral devices: printers,
plotters, voice mail
Telecommunications
Telecommunications
*****
• Digital PABXs
Industry and instruments
Industrial processes
Medical and
laboratories
Industrial equipment
Lighting systems
• Process control
• PLCs
• Numerical control systems
• Control systems
• Robot control/monitoring
systems
• Automatic machines
***
*****
***
***
****
• Instrumentation
• Scanners (60 Hz)
****
*****
****
****
***
• Machine-tools
• Welding robots
• Plastic-injection presses
• Precise regulation devices
(textile, paper, etc.)
• Heating equipment for
manufacture of semiconductors, glass, pure
materials
***
****
***
***
***
**
****
***
***
**
****
****
*****
***
• Public buildings (elevators,
safety equipment)
• Tunnels
• Runway lighting in airports
Other applications
Special frequencies
• Frequency conversion
• Power supplies for aircraft
(400 Hz)
****
*
low sensitivity to disturbances
***** high sensitivity to disturbances
Table 21..
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Application and Installation Guide
Battery UPS
Types of UPS
Static or rotary UPS
Static or rotary UPS solutions
There are two main types of UPS
which basically differ in the way the
UPS inverter function is implemented.
Static solution
These UPS use only electronic
components to perform the inverter
function. A “static-inverter function”
is obtained.
The inverter filters out utility-power
disturbances and regulates only
the frequency of its output voltage
(generally in “square-wave” form),
which supplies a regulated
motor/generator set that is sometimes
combined with a flywheel.
The motor/generator set generates an
output voltage sine-wave, taking the
inverter output frequency as the
reference.
Rotary solution
These UPS use rotary machines to
perform the inverter function.
These UPS in fact combine a motor
and a generator with a highly
simplified static inverter.
Figure 70: Static and rotary UPS..
Page 118
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Battery UPS
Comparison
Rotary solution
The arguments often put forward in
favour of this solution are as follows:
• High generator short-circuit
current on the order of 10 In (ten
times the rated current) that
makes setting of protection
devices easier,
• 150% overload capacity (of the
rated current) over a longer period
(two minutes instead of one),
• Downstream installation
galvanically isolated from
upstream AC source due to the
motor/generator set,
• Internal impedance providing
high tolerance to the non-linear
loads frequently encountered
with the switch-mode power
supplies used by computer
systems.
Static solution
Compared to the advantages of rotary
solutions
The static UPS offers the advantages
listed below.
• Operation in current-limiting mode
with discrimination ensured for
circuits rated up to In/2.
These features, which are more
than sufficient in practice,
prevent the disadvantages of
rotary systems:
- overheating of cables,
- the effects of an excessive
short-circuit current and the
corresponding voltage drop on
sensitive devices, during the
time taken by protective
devices to clear the fault.
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Application and Installation Guide
• 150% overload capacity (of the
rated current) for one minute.
The two-minute overload capacity is
of no practical use because most
overloads are very short (less than
one second, e.g. in-rush currents of
motors, transformers and power
electronics).
• Galvanic isolation, when
required, by means of an
isolating transformer,
• Double-conversion operation
which completely isolates the
load from utility power and
regenerates the output voltage
with precise regulation of the
voltage amplitude and the
frequency,
• Very low internal impedance for
higher performance with nonlinear loads due to the use of
power-transistor technologies.
Other advantages
Static solutions provide many other
advantages as well, due to powertransistor technology combined
with a PWM chopping technique.
• Simplified overall design, with a
reduction in the number of parts
and connections, and in the
number of possible causes of
failure;
• Capacity to react instantaneously
to utility-power amplitude and
frequency fluctuations by means
of microprocessor-controlled
switching regulation based on
digital sampling techniques. The
voltage amplitude returns to
regulated conditions (± 0.5% or
± 1% depending on the model) in
less than 10 milliseconds for load
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Application and Installation Guide
Battery UPS
step changes up to 100%. Within
the indicated time interval, such
a load step change produces a
load voltage variation of less
than for example ± 2%;
Conclusion
Given the advantages just presented,
static UPS are used in the vast
majority of cases, and for high-power
applications in particular.
• High, constant efficiency whatever the percent load, which is a
major advantage for redundant
UPS units with low percent loads.
A static UPS unit with a 50% load
maintains high efficiency (94%),
whereas the efficiency of a rotary
UPS drops to the 88-90% range
(typical value), which directly
impacts on operating costs;
In the following pages, the term
uninterruptible power supply
(UPS) is taken to mean the static
solution.
Types of static UPS
Standards
• Redundant configurations
providing high availability in the
framework of ultrareliable supply
systems (e.g. for data centres);
UPS
Due to the vast increase in the number
of sensitive loads, the term “UPS”
now includes devices ranging from a
few hundred VA for desktop
computers up to several MVA for data
centres and telecommunications sites.
• Possible integration in redundant
architectures with separate
functions that facilitate
maintenance by isolating parts
of the installation.
At the same time, different typologies
have been developed and the names
used for the products on the market
are not always clear (or even
misleading) for end users.
Rotary systems integrate the UPS, the
backup power and the generator as a
single component, thus making it
impossible to separate the functions.
Consider also the following nonnegligible advantages:
• No wear on rotating parts, hence
easier and faster maintenance.
For example, rotary systems
require checks on the alignment
of the rotating parts and the
replacement of the bearings after
2 to 6 years is a major operation
(lifting equipment, heating and
cooling of the bearings during
the replacement).
Page 120
That is why the IEC (International
Electrotechnical Commission)
established standards governing the
types of UPS and the techniques used
to measure their performance levels,
and those criteria were adopted by
Cenelec (European standardisation
commission).
Standard IEC 62040-3 and its
European equivalent EN 62040-3
define three standard types
(topologies) of UPS and their
performance levels.
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Battery UPS
UPS technologies include:
• Passive standby,
• Line interactive,
• Double conversion.
AC input power
These definitions concern UPS
operation with respect to the power
source including the distribution
system upstream of the UPS.
The standards define the following
terms:
• Primary power: power normally
continuously available which is
usually supplied by an electrical
utility company, but sometimes
by the user's own generation,
• Standby power: power intended
to replace the primary power in
the event of primary-power
failure.
Practically speaking, a UPS has one or
two inputs:
• Normal AC input (or Mains 1),
supplied by primary power,
• Bypass AC input (or Mains 2),
supplied by standby power
(generally speaking via a
separate cable from the same
main low-voltage switchboard
(MLVS).
UPS operating in passivestandby mode
The UPS is installed in parallel
to the utility and backs it up. The
battery is charged by a charger that
is separate from the inverter.
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Application and Installation Guide
Operating principle
• Normal mode:
- The inverter operates in
passive standby mode,
- The load is supplied by utility
power via a filter which
eliminates certain disturbances
and provides some degree of
voltage regulation,
- The standards do not mention
this filter and speak simply of a
“UPS switch”.They also indicate
that “additional devices may be
incorporated to provide power
conditioning, e.g. ferroresonant
transformer or automatic tapchanging transformer”.
• Battery backup mode:
- When the AC input voltage is
outside specified tolerances for
the UPS or the utility power
fails, the inverter and the
battery step in to ensure a
continuous supply of power to
the load following a very short
transfer time (generally less
than 10 ms). The standards do
not stipulate a time, but do
indicate that “the load [is]
transferred to the inverter
directly or via the UPS switch
(which may be electronic or
electromechanical)“,
- The UPS continues to operate
on battery power until the end
of battery backup time or utility
power returns to normal, which
provokes transfer of the load
back to the AC input (normal
mode).
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Application and Installation Guide
Battery UPS
Usage
This configuration is in fact a
compromise between an acceptable
level of protection against
disturbances and cost.
The mentioned disadvantages mean
that, practically speaking, this type of
UPS can be used only for low power
ratings (< 2 kVA) and cannot be used
as a frequency converter.
UPS operating in line-interactive
mode
Figure 71: UPS operating in..
passive-standby mode.
Advantages
• Simple diagram,
• Reduced cost.
Disadvantages
• No real isolation of the load
with respect to the upstream
distribution system,
• Transfer time. It operates without
a real static switch, so a certain
time is required to transfer the
load to the inverter. This time is
acceptable for certain individual
applications, but incompatible
with the performance required
by more sophisticated, sensitive
systems (large computer centres,
telephone exchanges, etc.),
• No regulation of the output
frequency, which is simply that
of the utility power.
Page 122
The inverter is connected in
parallel with the AC input in a
standby configuration, and also
charges the energy storage. It thus
interacts (reversible operation)
with the AC-input source.
Operating principle
• Normal mode
The load is supplied with
conditioned power via a parallel
connection of the AC input and
the inverter. As long as the input
power is within tolerances, the
inverter regulates fluctuations in
the input voltage. Otherwise
(reversible operation), it charges
the battery. The output frequency
depends on the AC-input
frequency.
• Backup mode
- When the AC input voltage is
outside specified tolerances for
the UPS or the input power
fails, the inverter and the
energy storage step in to
ensure a continuous supply of
power to the load. The power
switch (e.g. static switch) also
disconnects the AC input to
prevent power from the
inverter from flowing
upstream.
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Battery UPS
- The UPS continues to operate
on backup power until the end
of energy storage backup time
or input power returns to
within tolerance, which
provokes transfer of the load
back to the AC input (normal
mode).
• Bypass mode
This type of UPS may be equipped
with a bypass. If one of the UPS
functions fails, the load can be
transferred to the bypass AC input
via the maintenance bypass.
Application and Installation Guide
Disadvantages
• No real isolation of the load with
respect to the upstream
distribution system, thus:
- sensitivity to variations in the
utility voltage and frequent
demands placed on the
inverter;
- influence of downstream nonlinear loads on the upstream
input voltage;
Usage
This product is primarily used where
efficiency is a driving factor in the
product purchase.
Double-conversion UPS
The inverter is connected in series
between the AC input and the
application. The power supplied
to the load continuously flows
through the inverter.
Operating principle
• Normal mode
Figure 72: UPS operating in.
line-interactive mode.
Advantages
• The product has improved
efficiencies due the fact that not
all power is being broken down
and rebuilt as with a double
conversion UPS.
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During normal operation, all
the power supplied to the load
passes through the
rectifier/charger and inverter
which together perform a double
conversion (AC-DCAC), hence the
name. The voltage is continuously
regenerated and regulated.
• Backup mode
- When the AC-input voltage is
outside specified tolerances for
the UPS or the input power
fails, the inverter and the
energy storage step in to
ensure a continuous supply of
power to the load.
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Application and Installation Guide
- The UPS continues to operate
on backup power until the end
of energy storage backup time
or input power returns to
normal, which provokes
transfer of the load back to the
AC input (normal mode).
• Bypass mode
This type of UPS comprises a
static bypass (sometimes called
a static switch) that ensures nobreak transfer of the load from
the inverter to direct utility power
and back.
The load is transferred to the
static bypass in the event of the
following:
Battery UPS
The presence of a static bypass
assumes that the input and output
frequencies are identical, which
means it cannot be used as a
frequency converter. If the voltage
levels are not the same, a bypass
transformer is required.
The UPS is synchronised with the
bypass AC input to ensure no-break
transfers from the inverter to the
bypass line.
Note. Another bypass line, often called
the maintenance bypass, is available
for maintenance purposes. It is closed
by a manual switch.
- UPS failure,
- load-current transients (inrush
or fault currents),
- overloads,
- end of energy storage backup
time.
Figure 73: Double-conversion UPS..
Page 124
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Battery UPS
Advantages
• Complete regeneration of the
output power, whether it comes
from the utility or the battery,
• Total isolation of the load from
the distribution system and its
disturbances,
• Very wide input-voltage range,
yet precise regulation of the
output voltage,
• Independence of the input and
output frequencies, thus ensuring
an output frequency within strict
tolerances. Capacity to operate as
a frequency converter (if planned
as such), by disabling the static
switch,
• Much higher performance levels
under steady-state and transient
conditions,
• Instantaneous shift to backup
mode if input power fails,
Application and Installation Guide
Disadvantages
• Reduced efficiency driving higher
owning and operating cost and
increased heat rejection.
Usage
This configuration is the most
complete in terms of load protection,
regulation possibilities and
performance levels. It notably ensures
independence of the output voltage
and frequency with respect to the
input voltage and frequency.
Conclusion
Double-conversion UPSs represent
the vast majority of the medium
to high-power systems sold (90% of
the overall UPS market). This is due to
their numerous strong points in
meeting the needs of sensitive loads
at these power ratings and is largely
the result of the inverter positioned in
series with the AC input.
• No-break transfer to a bypass
line (bypass mode),
• Manual bypass (generally
standard) to facilitate maintenance.
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Page 125
Application and Installation Guide
Battery UPS
UPS components and operation
Components of a UPS
The information that follows concerns
the double-conversion UPS, the
technology most commonly used for
power ratings greater than 10 kVA.
General diagram of a UPS
The various items in figure 74 have
been assigned numbers that
correspond to the sections on the
following pages.
Figure 74: Components of a UPS..
Page 126
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Battery UPS
Application and Installation Guide
Power sources and UPS inputs
Components of a UPS
Practically speaking, a UPS has one or
two inputs:
Rectifier/charger (1)
Transforms the AC power from the
primary-power source into DC voltage
and current used to:
• Normal AC input (or Mains 1),
supplied by primary power,
• Bypass AC input (or Mains 2),
supplied by standby power
(generally speaking via a separate
cable from the same main lowvoltage switchboard (MLVS).
AC Input Power, see page 121
UPS connection to both the primary
and standby-power sources (UPS
inputs supplied by two separate
circuits from the MLVS) is
recommended because overall system
reliability is increased. However, if two
separate circuits from the MLVS are not
available, it is possible to have both AC
inputs (normal and bypass) supplied
by primary power (second cable).
Management of transfers between the
two input lines is organised as follows.
• The UPS synchronises the
inverter output voltage with that
of the bypass line as long as the
latter is within tolerances. It is
thus possible, if necessary, for
the static switch to transfer the
load to the bypass AC input,
without a break (because the two
voltages are synchronised and in
phase) or disturbances (because
the standby power is within
tolerances) for the load;
• When standby power is not
within tolerances, the inverter
desynchronises and transfer is
disabled. It can, however, by
carried out manually.
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• Supply the inverter,
• Charge and float charge the
battery.
Inverter (2)
Using the DC power supplied by the:
• Rectifier during normal
operation,
• Battery during autonomous
operation, the inverter
completely regenerates a
sinusoidal output signal, within
strict amplitude and frequency
tolerances.
Battery (3)
Makes the UPS autonomous with
respect to the utility in the event of:
• A utility outage,
• Utility-power characteristics
outside specified tolerances for
the UPS.
Battery backup times range from 6 to
30 minutes as standard and can be
extended on request. Depending on
the duration of the backup time, the
battery is housed in the UPS cabinet
or in a separate cabinet.
Static bypass (4)
A static switch is used to transfer the
load from the inverter to the bypass
without any interruption* in the
supply of power to the load (no break
because the transfer is performed by
electronic rather than mechanical
components). The switch is possible
when the frequencies upstream and
downstream of the UPS are identical.
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Application and Installation Guide
Battery UPS
Transfer takes place automatically for
any of the following reasons:
Upstream isolating transformer (10)
(optional equipment)
• Voluntary shutdown of the UPS,
Provides UPS input/output isolation
when the downstream installation is
supplied via the bypass.
• An overload exceeding the
limiting capacity of the inverter
(this transfer can be disabled),
• An internal fault.
It can also be carried out manually.
* No-break transfer is possible when
the voltages at the inverter output and
on the bypass AC input are
synchronised. The UPS maintains
synchronisation as long as the
standby power is within tolerances.
Manual bypass (5)
A manual switch is used to transfer the
load to the bypass for maintenance
purposes. The switch is possible when
the frequencies upstream and
downstream of the UPS are identical.
The shift to manual-bypass mode is
carried out using manual switches.
Manual switches (6, 7, 8)
These devices isolate the
rectifier/charger and inverter modules
and/or the bypass line for servicing or
maintenance.
Battery circuit breaker (9)
The battery circuit breaker protects the
battery against excessive discharge,
and the rectifier/charger and inverter
against a battery short-circuit.
It is particularly useful when the
upstream and downstream system
earthing arrangements are different.
Voltage-matching transformer (11)
(optional equipment)
Adapts the voltage to the desired
value.
Filters (12)
(optional equipment)
• Upstream of the rectifier/charger,
when it is of the thyristor-based
Graetz bridge type, a harmonic
filter (see page 25) reduces the
current harmonics resulting from
the switching of the rectifier
thyristors. This reduces the
voltage distortion on the
upstream busbars resulting from
the flow of harmonic currents
(the level required is generally
<5%). What is more, these UPS
from Caterpillar are equipped
with an oversized neutral
conductor installed as standard
to overcome the consequences
of third-order harmonics and
their multiples which flow in the
neutral conductor;
• Downstream, UPS implementing
new PWM-chopping techniques
may be directly connected to
non-linear loads. This technique
makes it possible for UPS from
Caterpillar to maintain the THDU
below 3%.
Page 128
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Battery UPS
Built-in communication (13) (14)
In addition to the need for a userfriendly human/machine interface for
effective monitoring of UPS operation,
it is today increasingly important for
UPS to communicate with their
electrical and computing environment
(supervision systems, building
management systems (BMS),
computer management systems, etc.).
UPS from Caterpillar are designed
with built-in capacity for total
communication and include:
• A user-friendly human/machine
interface (HMI) with an advanced
graphic display and mimic panel.
The interface is built up around
self-monitoring and selfdiagnostic systems that
continuously indicate the status
of the various UPS components,
in particular the batteries.
For example:
- the Digibat system
continuously monitors the
status of the battery with full
battery management features,
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Application and Installation Guide
• A large selection of
communication cards compatible
with market standards:
- Network Management Card
(Ethernet);
- Modbus – Jbus card (RS232
and RS485);
- Relay card (dry contacts) for
indications;
These cards can be used to implement
supervision, notification, controlled
shutdown and Teleservice functions.
Human-machine interface and
Communication: see page 56.
Upstream and/or downstream
distribution and protection devices
(15) (16)
(optional equipment)
The UPS can be supplied with the
following equipment:
• Upstream LV circuit-breakers for
the AC inputs (normal and
bypass),
• Upstream LV switchboard with
circuit-breaker protection for the
AC inputs (normal and bypass),
• Downstream LV switchboard
with circuit-breaker protection
for the different outgoing
circuits.
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Application and Installation Guide
Main characteristics of UPS
components
These characteristics are based on
the main technical specifications
presented in the IEC 62040-3 /
EN 62040-3 standards on UPS
performance requirements.
Certain terms used here differ from the
common jargon and a number of new
features have not yet been assimilated
by manufacturers. New terms or
characteristics used by the standard
are indicated between parentheses
and preceded by an asterisk.
For example, the title of a section
“input current during battery float
charging”, a commonly used term, is
followed by (*rated input current), the
term used in the standard.
Note that a number of numerical
values are indicated as examples.
They are, for the most part, drawn
from the technical characteristics of
the corresponding UPS or indicated
simply for the purposes of the
example.
AC input power
Number of phases and system
earthing arrangement
The AC-input supply (primary power)
is three-phase + neutral. Single-phase
inputs are not used for the power
levels dealt with here.
The system earthing arrangement is
generally imposed by standards (IT,
TT, TNS or TNC).
Normal AC input
The normal AC input is supplied with
utility power for the rectifier/charger,
within the specified tolerances.
Page 130
Battery UPS
• Example: 400 V rms ± 15% at a
frequency of 50 or 60 Hz ± 5%,
three-phase.
Bypass AC input
The bypass AC input is supplied with
standby power. Practically speaking,
this a cable connected to a utility
feeder in the MLVS other than the
one supplying the normal AC input.
In general, it supplies voltage with the
same characteristics as that of the
primary power.
• Example: 400 V rms ± 15% at a
frequency of 50 or 60 Hz ± 5%,
and a short-circuit current Isc2 =
12.5 kA. The short-circuit current
is important information for the
downstream protection devices
in the event of operation via the
static or maintenance bypass.
Supply of separate primary and
standby power is recommended
because it increases overall system
reliability, but is not mandatory.
However, if two separate circuits
from the MLVS are not available,
it is possible to have both AC inputs
(normal and bypass) supplied by
primary power (second cable).
Rectifier/charger
Floating voltage
This is the voltage supplied by the
rectifier/charger which keeps the
battery fully charged.
It depends on the batteries used and
the manufacturer's recommendations.
Input current during battery float
charging (* rated input current)
This is the current, under normal
operating conditions, required to
supply the inverter at its rated power
while float charging the battery.
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Battery UPS
Example: for a 100 kVA UPS with a
battery backup time of 10 minutes,
this current is
I input float = 166 A while float
charging the battery.
Input current during battery charging
This corresponds to the current
required to supply the inverter at its
rated power while charging the
battery. It is consequently higher than
the previous current and is used to
size the charger input cables.
Example: for the same UPS as
above, the input current is I input
float = 182 A, i.e. higher than
above because it is necessary to
charge the battery.
Maximum input current
This is the input current with the UPS
operating under worst-case conditions
of permitted overload, with the battery
discharged. It is higher than the above
input current during battery charging
(due to the overload current) but is
limited in time (as is the overload).
Example: for the same UPS as
above, can accept a 25% overload
for ten minutes and a 50%
overload for one minute. In the
worst-case situation with the
battery charging, the input current
can reach:
I input max. = 182 A x 1.25 = 227.5 A
for ten minutes,
I input max. = 182 A x 1.5 = 273 A for
one minute.
Beyond the above limits, the UPS
initiates no-break transfer of the load
to the bypass line and automatically
transfers back when the overload has
ended or been cleared by the
corresponding protection devices.
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Application and Installation Guide
Battery (* energy storage means)
Type
A battery is characterised by its type
(vented or sealed lead acid, or
nickel/cadmium) and how it is
installed. Caterpillar proposes sealed
lead-acid batteries mounted in
cabinets.
Service life
This is defined as the operating
period, under normal usage
conditions, for which the battery
supplies at least 50% of the initial
backup time.
For example, if a UPS is supplied
as standard with sealed lead-acid
batteries with a service life of ten
years or more. This type of battery,
rated for 30 minutes of backup
time, will contractually supply
only 15 minutes at the end of the
specified service life.
It may supply more if it has been
used under optimum conditions
(notably concerning the temperature).
However, it is contractually
guaranteed not to supply less, unless
used improperly.
Operating modes
The battery may be:
• Charging. It draws a charge
current (I1 charge) supplied by
the rectifier/charger,
• Float charging.The battery draws
a low, so-called floating current
(I1 floating), supplied by the
rectifier/charger, which maintains
its charge by compensating for
open-circuit losses,
• Discharging.The battery supplies
the inverter until its shutdown
voltage is reached.
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Application and Installation Guide
When this voltage, set by the battery
manufacturer, is reached, the battery
is automatically disconnected to avoid
damage by deep discharge.
Rated voltage
This is the DC output voltage that the
battery supplies to the inverter.
Example: 450 V DC.
Capacity
Battery capacity is expressed in
ampere/hours.
Example: for a 100 kVA UPS
equipped with a battery offering
ten minutes of backup time and a
service life of five years, the
capacity is 85 A/h.
Number of cells
Number of single battery cells making
up the entire battery string.
Example: the battery of a 100 kVA
UPS comprises, for a given type of
battery, 33 cells providing 13.6 V
each, for a backup time of ten
minutes.
Floating voltage
This is the DC voltage used to
maintain the battery charge, supplied
by the rectifier/charger.
Example: for a 100 kVA UPS, the
floating voltage is between 423
and 463 V DC.
Backup time (* stored energy time)
This is the time, specified at the
beginning of the battery service life,
that the battery can supply the inverter
operating at full rated load, in the
absence of the AC-input supply.
This time depends on the UPS percent
load.
Page 132
Battery UPS
• For a UPS operating at full rated
load (100% of rated power), the
end of the battery backup time is
reached when the battery voltage
drops to the shutdown voltage
specified by the manufacturer. This
provokes automatic shutdown of
the UPS.
• For a UPS operating at a lower
percent load (e.g. 75%), the
actual backup time may be
longer. However, it always ends
when the battery shutdown
voltage is reached.
Recharge time (* rated restored
energy time)
This is the time required by the battery
to recover 80% of its backup time (90%
of its capacity), starting from the
battery shutdown voltage. The
rectifier/charger supplies the power.
Example: for a 100 kVA UPS, the
recharge time is eight to ten
hours, depending on the battery
and the backup time. Note that the
probability of the battery being
called on to supply power twice
within such a short period
is low. This means the indicated
recharge time is representative
of actual performance.
Maximum battery current (Ib)
When discharging, the battery
supplies the inverter with a current Ib
which reaches its maximum value at
the end of discharging. This value
determines battery protection and
cable dimensions.
Example: for a 100 kVA UPS, this
current is Ib max = 257 A.
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Battery UPS
Application and Installation Guide
Inverter
This value is a fraction of the rated
power, depending on the percent load.
Rated power (Sn)
(* rated output apparent power)
This is the maximum apparent power
Sn (kVA) that the inverter can deliver
to a linear load at a power factor of
0.8, during normal operation under
steady-state conditions.
The standards also define this
parameter for operation on battery
power.
Theoretically speaking, it is the same
if the battery is correctly sized.
Active output power (Pa)
(* rated output active power for
linear or reference non-linear load)
This is the active power Pa (kW)
corresponding to the apparent
output power Sn (kVA), under the
measurement conditions mentioned
above. This value may also be
indicated for a standardised reference
non-linear load.
Example: the previous UPS, with a
rated power of 100 kVA supplies an
active power of Pa = Sn x 0.8 = 80
kW.
Rated current (In)
This is the current corresponding to
the rated power.
Example: again for a 100 kVA UPS
and an output voltage of 400 V,
this current is:
Sn
100000
=
= 144.3 A
In =
Un √3
400 x 1,732
Apparent load power (Su) and percent
load
This is the apparent power Sn (kVA)
actually supplied by the inverter to the
load, under the selected operating
conditions.
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Su ≤ Sn. and
Tc = Percent load (%) = Su / Sn.
Example: for the UPS mentioned
above, if the inverter supplies 3/4
of its rated power (75% load), it
delivers an apparent power of
75 kVA, which under standard
operating conditions (PF = 0.8)
corresponds to an active load
power of
Pa = Su x PF = 75 x 0.8 = 60 kW.
Load current (Iu)
This is the current corresponding to
the load power, that is, to the percent
load in question. It is calculated from
Pu as for the rated current, where the
voltage is the rated voltage Un (value
regulated by the inverter).
Example: for the UPS mentioned
above (75% load)
lu =
Su
75000
=
= 108.2 A
Un √3
400 x 1,732
which is the same as:
Iu = In x Tc = 144.3 x 0.75 = 108.2 A
Efficiency (η)
This is the ratio of active power Pu
(kW) supplied by the UPS to the load
to the power Pin (kW) that it draws at
its input, either by the rectifier or from
the battery.
η= Pu / Pin.
For most UPS, efficiency is optimum
at full rated load and drops sharply
with lower percent loads. Due to their
low output impedance and no-load
losses.
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Application and Installation Guide
Output voltage Un
Number of phases
The output can be three-phase (3ph3ph UPS) or single-phase (3ph-1ph
UPS), depending on the situation.
Note that the upstream and
downstream system earthing
arrangements may be different.
Rated output voltage
In general, it is the same as that of
the AC input. However, a voltagematching transformer may be
installed.
Static characteristics
These are the tolerances (maximum
permissible variations) for the
amplitude and frequency of the output
voltage under steady-state conditions.
Stricter than those applying to utility
power, they are measured for normal
operation on AC-input power and for
operation in battery backup mode.
• Output voltage variation
The amplitude tolerance is expressed
as a percentage of the nominal rms
value and may be adjustable.
Example: for a 100 kVA UPS, the
voltage 400 V rms ± 1% may be
adjusted to ± 3%.
The standards also stipulate a rated
peak output voltage and the tolerance
with respect to the rated value.
• Output frequency variation
The tolerance is expressed as a
percentage of the rated frequency.
Example: for a 100 kVA UPS, 50 or
60 Hz ± 0.1% during normal
operation on primary power and
± 0.5% in battery backup mode.
Page 134
Battery UPS
Frequency synchronisation with
primary power
The inverter supplies an output voltage
within the previously mentioned
tolerances, regardless of the disturbances affecting the upstream power.
To that end, the UPS:
• Monitors the voltage parameters
(amplitude, frequency, phase) for
the primarypower source to
determine whether they are
within specified tolerances,
• Reacts to any drift in parameters
so as to:
- readjust the inverter (phase and
frequency) to the standby power,
as long as the drift remains within tolerances, in view of load
transfer, if necessary,
- transfer the load to battery
power as soon as the drift goes
outside tolerances.
The new IGBT and PWM chopping
technologies used in UPS allow an
excellent adaptation to these
variations.
Example: for UPSs, the maximum
variation in frequency
corresponding to the tolerance is
50 Hz x 0.5% = 0.25 Hz.
Frequency synchronisation with
bypass AC power is possible from 0.25
to 2 Hz, in 0.25 Hz steps. Practically
speaking, this signifies that frequency
variations may be monitored at dF/dt
= 0.25 Hz/s and readjustment carried
out within 0.25 to 1 second.
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Battery UPS
Dynamic characteristics
These are the tolerances under
transient load conditions.
Some UPSs are capable of
withstanding the following conditions.
• Load unbalance
For unbalance in the load voltage
(phase-to-neutral or phase-tophase) of:
- 30%, the output voltage
variation is less than 0.1%,
- 100% (one phase at Pn and the
others at 0), the output voltage
does not vary more than 0.2%.
• Load step changes (voltage
transients)
For load steps from 0 to 100% or
from 100 to 0% of the rated load,
the voltage does not vary more
than:
± 2% on utility power;
+ 2% to -4 % on battery power.
Overload and short-circuit capacity
• Overloads
Application and Installation Guide
Beyond this value, the inverter
transfers the load to standby power or
performs a static shutdown (selfprotection feature).
Total output-voltage distortion
UPSs must guarantee performance
levels for all types of loads, including
non-linear loads.
Example: some UPSs limit the
voltage total harmonic distortion
(THDU) in output power to the
following levels for:
• 100% linear loads:
- THDU ph/ph < 1.5 %,
- THDU ph/N < 2%,
• 100% non-linear loads:
- THDU ph/ph < 2 %,
- THDU ph/N < 3%.
General note.The standard specifies
certain of the previously mentioned
performance levels for output power
during normal operation and
operation on backup power. In
general, they are identical.
- 1.1 In for 2 hours,
- 1.5 In for 1 minute,
with no change in the output
tolerances.
• Short-circuits
Beyond 1.65 In, inverters may
operate in current-limiting mode
up to 2.33 In for 1 second,
corresponding to:
I peak max. = √2 x 1.65 In = 2.33 In.
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Page 135
Application and Installation Guide
Battery UPS
Summary diagram for main
characteristics
Figure 75: Diagram showing the main characteristics (see the following list)..
Normal AC input:
• Voltage Un + 10% to - 15%,
• Frequency f + 4% to - 6%.
Bypass AC input:
• Voltage Un + 10% to - 15%,
• Frequency f + 4% to - 6%,
• Short-circuit current Isc2
(withstand capacity of the static
bypass).
Rectifier/charger:
• Floating voltage,
• Input currents:
- rated (battery float charging),
- maximum (battery charging).
Battery:
• Backup time: standard 5, 6, 8, 10,
15, 20, 30, 60 minutes, longer
times on request),
• Service life: 10 years or longer,
• Maximum current Ib max.
Page 136
Inverter:
• Apparent output power:
- rated: Sn (kVA),
- load power: Su (kVA) = Sn x Tc%.
• UPS percent load Tc% = Su / Sn,
• Active output power:
- rated: Pn (kW) = Sn (kVA) x 0.8,
- load power: Pu (kW) = Su (kVA)
x PF = Sn x Tc% x PF = Un Iu PF,
• Efficiency: η Pu / Pn = 93%,
• Static characteristics (outputvoltage tolerances under
steady-state conditions):
- amplitude: Un ± 1% adjustable
to ± 3%,
- frequency: f ± 1% during normal
operation, f ± 0.5% in battery
backup mode,
- inverter output voltage
synchronised (frequency and
phase) with that of the standby
power as long as the latter is
within tolerances,
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Battery UPS
• Dynamic characteristics
(tolerances under transient
conditions):
- maximum voltage and
frequency variations for load
step changes from 0% to
100% or 100% to 0%: Un ± 2%,
f ± 0.5%,
• Output voltage distortion:
- 100% non-linear loads
THDU < 2%,
• Overload and short circuit
capacity:
- overloads: 1.5 In for 1 minute,
- short-circuits: current limiting
to 2.33 In for 1 second.
Load:
• Load current (Iu),
• Power factor PF.
Application and Installation Guide
The remaining current is supplied to
the inverter with generates an outputvoltage sine-wave within the specified
amplitude and frequency tolerances.
Backup mode (on battery power,
see figure 76)
The energy storage steps in to replace
primary power and supplies the
power required by the inverter for the
load, with the same tolerances as in
normal mode.
This takes place through immediate
transfer (the energy storage is parallel
connected) in the event of:
• Normal AC-input failure
(utility-power outage),
• Normal AC input outside
tolerances (degradation
of utility-power voltage).
UPS operating modes
Normal mode (on utility power,
see figure 76)
The UPS draws the AC utility power
required to operate via the rectifier/
charger which provides DC current.
Part of the utility power drawn is used
to charge or float charge the battery:
• I1 floating, if the battery is
already fully charged,
• I1 charge if the battery is not fully
charged (i.e. charging following a
recent discharge).
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Page 137
Application and Installation Guide
Battery UPS
Figure 76: Normal mode and battery backup mode..
Bypass mode (on static-bypass
line, see figure 77)
A static switch (SS) ensures no-break
transfer of the load to the bypass AC
input for direct supply of the load by
standby power.
Transfer is automatic in the event of:
• An overload downstream of the
UPS exceeding its overload
capacity,
• An internal fault in the rectifier/
charger and inverter modules.
Transfer always takes place for
internal faults, but otherwise is
possible only if the voltage of the
standby power is within tolerances
and in phase with the inverter.
To that end:
• The UPS synchronises the
inverter output voltage with that
of the bypass line as long as the
latter is within tolerances.
Transfer is then possible:
Page 138
- without a break in the supply of
power. Because the voltages
are in phase, the SCRs on the
two channels of the static
switch have zero voltage at the
same time,
- without disturbing the load. The
load is transferred to a bypass
line that is within tolerances.
• When standby power is not
within tolerances, the inverter
desynchronises and operates
autonomously with its own
frequency. Transfer is disabled.
It can, however, by carried out
manually.
Note 1. This function greatly
increases reliability due to the very
small probability of a downstream
overload and a standby-power failure
occurring at the same time.
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Battery UPS
Note 2. To ensure correct operation
of the bypass line, discrimination
must be ensured between the
protection device upstream of the
bypass AC input (on the MLVS
outgoer) and those on the UPS
outgoing circuits (see information
on discrimination that follows).
Application and Installation Guide
Maintenance mode
(on maintenance bypass,
see figure 77)
Maintenance is possible without
interrupting load operation. The load
is supplied with standby power via the
maintenance bypass. Transfer to the
maintenance bypass is carried out
using manual switches.
The rectifier/charger, inverter and
static switch are shut down and
isolated from power sources. The
battery is isolated by its protection
circuit breaker.
Figure 77: Bypass mode and maintenance mode..
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Page 139
Application and Installation Guide
UPS configurations
Parallel UPS with redundancy
“Types of possible configurations” is
entirely devoted to a presentation of
the various configurations. Below is
some additional information on
parallel connection for redundancy.
Configurations, see “Types of
possible configurations”.
Types of parallel configurations
There are two types of parallel
configurations.
• Integrated parallel UPS units
This upgradeable configuration
can be started using a single UPS
unit with an integrated static
bypass and manual maintenance
bypass. For configurations with
more than two UPS units, a
common maintenance bypass is
housed in an external cubicle
(see figure 78).
• Parallel UPS units with a
centralised static-switch cubicle
(SSC)
The static-switch cubicle
comprises an automatic bypass
and a maintenance bypass that
are common for a number of
UPS units without a bypass
(see figure 79).
This configuration, less
upgradeable than the previous
due to the rating of the bypass,
offers greater reliability (SSC and
UPS units are independent).
Page 140
Battery UPS
• Modular UPSs
UPSs of the modular range are
made up of dedicated and
redundant modules (power,
intelligence, battery and bypass).
Modular design with plug-in
power modules improves
dependability, in particular
maintainability and availability,
as well the upgradeability of the
installation.
Redundancy
Redundancy in parallel configurations
can be N + 1, N + 2, etc.
This means that N UPS units are
required to supply the load, but N + 1
or N + 2 are installed and they all
share the load.
See the following example.
Example
• Consider a critical load with
a 100 kVA rating,
• 2+1 redundancy:
- 2 UPS units must be capable
of fully supplying the load if
redundancy is lost,
- each UPS unit must therefore
have a 50 kVA rating,
- 3 UPS units normally share the
100 kVA load, i.e. each supplies
33.3 kVA,
- the 3 UPS units normally
operate at a percent load of
33.3 / 50 = 66.6%,
- integrated parallel UPS units
are each equipped with a static
bypass. Transfer is managed
such that the three UPS units
transfer to the bypass
simultaneously, if necessary.
©2010 Caterpillar
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Battery UPS
Application and Installation Guide
Figure 78: Integrated parallel UPS units with common maintenance bypass.
and 2+1 redundancy. Operation with all units OK (redundancy available).
• Loss of redundancy:
- one UPS unit shuts down, the two
remaining units operate at 100%,
- the faulty UPS unit can be serviced
due to the maintenance bypass.
Figure 79: Integrated parallel UPS units with common maintenance bypass.
and 2 + 1 redundancy. Operation following loss of redundancy.
©2010 Caterpillar
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Page 141
Application and Installation Guide
Battery UPS
Electromagnetic compatibility (EMC)
Electromagnetic
disturbances
Electromagnetic disturbances
All electromagnetic disturbances
involve three elements.
A source
A natural source (atmosphere, earth,
sun, etc.) or, more often, an industrial
source (electrical and electronic
devices).
The source generates disturbances
through sudden (pulse) variations in
electrical values (voltage or current),
defined by:
• A wave form,
• A wave amplitude (peak value),
• A spectrum of frequencies,
• A level of energy.
A coupling mode
Coupling enables transmission of
disturbances and may be:
• Capacitive (or galvanic), for
example via transformer
windings,
• Inductive, by a radiating
magnetic field,
• Conducted, by a common
impedance, via an earthing
connection.
A victim
This is any device likely to be
disturbed, and which malfunctions
due to the presence of the
disturbances.
Page 142
Examples
Sources
In low-voltage installations, sources
include suddenly varying currents
resulting from:
• Faults or short-circuits,
• Electronic switching,
• High-order harmonics,
• Lightning or transformer
breakdown.
Frequencies may be low (< 1 MHz)
for power frequencies and their
harmonics or high (> 1 MHz) for
lightning.
Coupling
• Capacitive: transmission of a
lightning wave via a transformer.
• Inductive: radiation of a
magnetic field created by one
of the previously mentioned
currents. Radiation creates an
induced electromotive force, that
is an induced disturbing current,
in the loops of conductors made
up of the cables supplying
devices and the earthing
conductors of the devices.
As in indication, a radiation of 0.7 A/m
can disturb a video monitor.
That corresponds to the field created
2.2 m around a conductor carrying a
current of 10 A.
• Conducted (common
impedance): increase in the
potential of an earthing
connection.
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Battery UPS
EMC standards and
recommendations
Disturbances
Emission, immunity, susceptibility
An electric device is installed in an
environment that may be more or less
disturbed electromagnetically. It must
be seen as both a source and possible
victim of electromagnetic
disturbances.
Depending on the point of view, on
may speak of:
• The emission level for a source,
• The compatibility level for an
environment,
Application and Installation Guide
- Sources, limits (emission
levels) must be set for
disturbances emitted by
devices to avoid reaching
compatibility levels,
- Victims, they must also
withstand disturbance levels
higher than the compatibility
levels, if they are exceeded,
which is permissible on a
transient basis. These higher
levels are the immunity levels.
EMC standards set these levels.
List of EMC standards, see the
section on page 146 on EMC
standards.
• The immunity and susceptibility
levels for a victim.
These notions are discussed on
the next page in the section on
disturbance levels defined by the
standards.
Disturbance levels
Standard IEC 6100-2-4 defines a
number of disturbance levels for EMC:
• Level 0: no disturbance,
• Emission level: maximum level
authorised for a user on a public
utility or for a device,
• Compatibility level: maximum
disturbance level expected in a
given environment,
• Immunity level: level of
disturbance that a device can
withstand,
• Susceptibility level: level starting
at which a device or system
malfunctions. Consequently, for
devices and equipment that are
considered:
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Figure 80: EMC disturbance levels for.
disturbing/disturbed devices.
Measured values
Devices are subjected to tests.
Five major values are measured:
• CE - conducted emissions,
• RE - radiated emissions,
• ESD - electrostatic discharges,
• CS - conducted susceptibility,
• RS - radiated susceptibility.
Page 143
Application and Installation Guide
Battery UPS
The tests require major resources,
namely a Faraday cage for conducted
emissions and susceptibility and an
anechoic chamber for radiated
emissions.
Figure 81: Five major measurement values..
Page 144
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Battery UPS
Application and Installation Guide
UPS standards
Scope and observance
of standards
It is mandatory for free circulation
of goods in the EU.
Scope of standards
Its purpose is to guarantee, through
respect of the corresponding
European directives:
Standards cover the following
aspects:
• UPS design,
• Safety of persons,
• Performance levels,
• Electrical environment (notably
harmonic disturbances and
EMC),
• Ecological environment.
• That the product is not
dangerous (Low-voltage
Directive),
• That it does not pollute
(Environment Directive) and its
electromagnetic compatibility
(EMC Directive).
Standards on UPS have become much
more precise, notably with the
creation of the European EN standards
and their harmonisation with a part of
the previously existing IEC standards.
Before placing the CE marking on a
product, the manufacturer must run
or have run checks and tests which
ensure conformity of the product with
the requirements in the applicable
directive(s).
Observance of standards and
certification
It is NOT a certification standard or
mark of conformity.
Observance of standards guarantees
the reliability and the quality of a
UPS, its compatibility with the loads
supplied as well as with the technical,
human and natural environment.
It does not signify that the product
complies with national or international
standards.
Statement by a manufacturer of
conformity with standards is not, in
itself, a sufficient indication of quality.
Only certification by recognised
organisations is a true guarantee of
conformity.
What is more, the CE marking is
placed on a product under the
exclusive responsibility of the
manufacturer or the importer. It does
not imply inspection by a certified
external organisation.
To that end, performance levels of
UPSs from Caterpillar with respect
to standards are certified by
organisations such as TÜV and Veritas.
Not all labels carry the same
implications for manufacturers.
CE marking
CE marking was created by European
legislation.
©2010 Caterpillar
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It is not a certification as defined by
French law (law dated 3 June 1994).
Conformity with standards and
specified levels of performance must
be certifiable by an organisation. This
is not the case for CE marking which
authorises selfcertification.
Page 145
Application and Installation Guide
Main standards governing
UPS
UPS from Caterpillar comply (certified
by TÜV and Veritas) with the main
applicable international standards.
Safety
• IEC 60950-1 / EN 60950-1
Information technology
equipment - Safety - Part:
General requirements
• IEC 62040-1/ EN 62040-1
Uninterruptible power systems
(UPS) - General and safety
requirements for UPS.
• IEC 62040-3 / EN 1000-3
Uninterruptible power systems
(UPS) - Method of specifying the
test and performance
requirements.
• IEC 60439
Low-voltage switchgear and
controlgear assemblies.
• LV directive: 2006/95/EC
Electrical environment,
harmonics and electromagnetic
compatibility (EMC)
Harmonics
• IEC 61000-2-2 / EN 61000-2-2
Compatibility levels for lowfrequency conducted disturbances
and signalling in public lowvoltage power supply systems.
(see table 22)
• IEC 61000-3-2 / EN 61000-3-2
Limits for harmonic current
emissions (equipment input
current ≤ 16 A/ph).
Battery UPS
• IEC 61000-3-5 / EN 61000-3-5
Limitation of voltage fluctuations
and flicker.
• EN 50160
Voltage characteristics of public
networks (see table 23).
• IEEE 519
Recommended practices and
requirements for harmonic
control in electrical power
systems.
EMC
• EN 50091-2
UPS - EMC.
• IEC 62040-2/ EN 62040-2
Uninterruptible power systems
(UPS) - Electromagnetic
compatibility (EMC)
requirements.
• EMC Directive 2004/108/EC
For equipment liable to cause or
be affected by electromagnetic
disturbances.
Quality
• Design , production and servicing
in compliance with standard ISO
9001 - quality organisation.
Ecological environment
• Manufacturing in compliance
with standard ISO 14001.
Acoustic noise
• ISO 3746
Sound power levels.
• ISO 7779 / EN 27779
Measurement of airborne noise
emitted by computer and
business equipment.
• IEC 61000-3-4 / EN 61000-3-4
Limits for harmonic current
emissions (equipment input
current > 16 A/ph).
Page 146
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Battery UPS
Application and Installation Guide
Tables on harmoniccompatibility levels
Compatibility levels for individual harmonic voltages in low voltage networks
as indicated in standard IEC 61000-2-2 / EN 61000-2-2.
Odd harmonics
non-multiple of 3
Harmonic order
n
Odd harmonics
multiple of 3
Even harmonics
Harmonic
Harmonic
Harmonic
Harmonic order
Harmonic order
voltage as a %
voltage as a %
voltage as a %
n
n
of fundamental
of fundamental
of fundamental
5
6
3
5
2
2
7
5
9
1.5
4
1
11
3.5
15
0.3
6
0.5
13
3
21
0.2
8
0.5
17
19
23
25
>25
2
1.5
1.5
1.5
0.2 + 0.5 x 25/n
>21
0.2
10
12
>12
0.5
0.5
0.2
0.2
Resulting THDU < 8% (for all harmonics encountered among those indicated)
Table 22..
Compatibility levels for harmonic voltages according to the type of equipment
as indicated in standard EN 50160.
Order of the voltage
harmonic generated
Class 1
(sensitive systems and
equipment) % of
fundamental
Class 2 (1)
(industrial and public
networks) % of
fundamental
Class 1
(for connection of
major polluters) % of
fundamental
2
2
2
3
3
3
5
6
4
1
1
1.5
5
3
6
8
6
0.5
0.5
1
7
3
5
7
8
0.5
0.5
1
9
1.5
1.5
2.5
10
0.5
0.5
1
11
3
3.5
5
12
0.2
0.2
1
13
3
3
4.5
TDHU
5%
8%
10%
(1)
Class 2 corresponds to the limits of Table A of standard IEC 61000-2-2 / EN 61000-2-2
Table 23..
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Page 147
Application and Installation Guide
Battery UPS
Energy storage
Possible technologies
Batteries
Energy storage in UPS
The battery solution
The energy-storage systems used by
UPSs to backup the primary source
must have the following
characteristics:
Batteries are by far the most commonly
employed solution today for energy
storage in UPSs. They are the dominant
solution due to low cost, proven
effectiveness and storage capacity,
but nonetheless have a number of
disadvantages in terms of size,
maintenance and the environment. At
the power ratings under consideration,
they offer backup times in the tenminute range, enough to ride through
long outages and wait for start-up of an
engine generator set for extended
runtime.
• Immediate availability of
electrical power,
• Sufficient power rating to supply
the load,
• Sufficient backup time and/or
compatibility with systems
providing long backup times
(e.g. an engine generator set
or fuel cells).
Electrochemical energy storage
using batteries, where applicable
backed up by a thermal engine
generator set, is the commonly
used solution to protect critical
loads using a UPS.
Figure 82: Energy storage using a battery and an engine generator set for long backup times..
Page 148
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Battery UPS
Types of industrial batteries
Battery families
A battery is a set of interconnected cells.
Depending on the type of cell, there
are two main families of batteries:
• Lead-acid batteries,
• Nickel cadmium batteries.
Cells may also be of the:
• Recombination type sealed
batteries.
The gas recombination rate is at least
95% and they therefore do not require
water to be added during service life
(hence the term “sealed”),
• Vented type vented batteries
They are equipped with ports to:
- release to the atmosphere the
oxygen and hydrogen produced
during the different chemical
reactions,
- top off the electrolyte by adding
distilled or demineralised water.
Batteries used in a UPS
The main types of batteries used in
conjunction with UPSs are:
• Sealed lead-acid batteries, used
95% of the time because they are
easy to maintain and do not
require a special room, these
batteries can be installed in office
environments and in any position,
• Vented lead-acid batteries,
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Application and Installation Guide
• Vented nickel-cadmium batteries.
Vented batteries impose greater
constraints in terms of
maintenance (checks on the
electrolyte level) and their
position (only in the vertical
position).
Lithium-polymer batteries are currently
being studied for use in UPSs.
Battery selection, see page 54.
Installation modes
Depending on the UPS range, the
battery capacity and backup time, the
battery is:
• Sealed type and housed in the
UPS cabinet,
• Sealed type and housed in one
to three cabinets,
• Vented or sealed type and rackmounted.
Cabinet mounting
This installation method (see figure 83)
is suitable for sealed batteries. It is easy
to implement and offers maximum
safety.
Batteries installed on racks:
• On shelves (figure 84). This installation method is possible for
sealed batteries or maintenancefree vented batteries which do not
require topping up of their
electrolyte,
• Tier mounting (figure 85). This
installation method is suitable
for all types of batteries and for
vented batteries in particular, as
level checking and filling are
made easy.
Page 149
Application and Installation Guide
Battery UPS
Access
Access must be provided for testing
operations.
• Battery installed in UPS cabinet
or other cabinet: comply with the
clearances indicated in the
“Dimensions and weights”.
Figure 83: Cabinet mounting..
• Battery installed on racks: select
an installation method suited to
the type of battery.
• Preliminary work: this aspect is
important as it involves safety.
It is discussed in page 58.
Main battery parameters
Figure 84: Mounting on shelves..
Backup time
For a given battery, the backup time
depends on:
• The power that must be
supplied, a low value increases
the available autonomy,
Figure 85: Tier mounting..
Constraints on batteries
Atmospheric constraints
The batteries supplied with UPSs are
typically designed to operate under
the following conditions:
• Optimum temperature range:
15°C to 25°C,
• Optimum relative humidity
range: 5% to 95%,
• Atmospheric pressure: 700 to
1060 hPa (0.7 to 1.06 bars).
For other operating conditions, please
consult us.
Page 150
• The discharge conditions, a high
discharge rate makes possible a
lower shutdown voltage and thus
increases the backup time,
• Temperature, within the
recommended operating limits,
the backup time increases with
increasing temperature. Note,
however, that a high temperature
adversely affects battery service
life,
• Aging, battery backup time
decreases with the age of the
battery.
Service life
A battery is considered to reach the
end of its service life when its real
backup time has fallen to 50% of
the specified backup time.
©2010 Caterpillar
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Battery UPS
The service life of a battery is basically
enhanced by:
• Providing protection against
deep discharge,
• Correct charger settings, in
particular the ripple factor of
the charge or float current,
• An optimum operating
temperature, maintained
between 15°C and 25°C.
Application and Installation Guide
Recharge mode
The charge cycle takes place in two
steps:
• Step 1, a constant current limited
to 0.1 C10 (one tenth of the
battery capacity for a ten-hour
discharge),
• Step 2, a constant voltage, at the
maximum permissible value.
The charge current regularly
decreases and reaches the
floating value.
Figure 86: Battery charge cycle..
Battery management
DigibatTM
To manage the previously mentioned
parameters, all UPS from Caterpillar
come as standard with the
microprocessor-based DigibatTM
battery-monitoring system (dedicated
DSP for real-time processing).
DigibatTM, an easy-to-use system, offers
advanced and flexible functions as well
as physical and computer-aided
protection for the battery. It provides a
high level of safety, true measurement
of the backup time and optimises
battery service life. Some functions
included are:
• Measurement of the real backup
time remaining, taking into
account the age of the battery, the
temperature and the load level,
• Estimate of remaining battery
life,
• Battery test to preventively
detect battery-function faults,
• Regulation of battery voltage
with respect to the temperature
to optimise battery life,
• Automatic battery-discharge test
at adjustable time intervals.
• Automatic entry of battery
parameters,
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Page 151
Application and Installation Guide
Battery UPS
Protection includes:
• Protection against deep discharge
(depending on the discharge rate)
and battery isolation using a
circuit breaker which automatically opens when the backup
time, multiplied by two plus two
hours, has elapsed,
• Limiting of the recharge current in
the battery (0.05 C10 to 0.1 C10),
• Progressive audio alarm
signalling the end of the backup
time,
• Numerous automatic tests.
Figure 87: Digibat TM.
Temperature monitoring
UPS can also be equipped with the
Temperature Monitoring module used
to:
• Optimise the charger voltage
depending on the temperature
in the battery room,
Natural ventilation of battery cabinets
avoids battery temperature rise.
Environment Sensor is also a simple
means to monitor temperature and
humidity. It can be used to launch
shutdown when combined with
software running the module.
• Warn the user if preset
permissible temperature limits
are exceeded,
• Refine the estimate on battery
backup time carried out by the
standard system $.
Page 152
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Battery UPS
Application and Installation Guide
UPS / generator-set combination
Use of a generator
Long backup times
An engine generator set is made up
of an internal-combustion engine
driving a generator that supplies the
distribution system. The backup time
of an enginegenerator set depends on
the quantity of fuel available.
In some installations, the required
backup time in the event of a utility
outage is such that it is preferable to
use an engine generator set to back
up utility power (figure 88).
This solution avoids using large
batteries with very long backup times.
Though there is no general rule in the
matter, a generator is often used for
backup times exceeding 30 minutes.
Critical installations requiring very
high availability levels and with high
down-time costs (e.g. data centres)
systematically combine UPS and
engine generator sets.
The battery backup time of the UPS
must be sufficient for generator startup and connection to the electrical
installation. Connection is generally
carried out on the main LV
switchboard using an automatic
source-changeover system. The time
required for changeover depends on
the specific characteristics of each
installation, notably the start-up
sequence, load shedding, etc.
Figure 88: UPS / generator-set combination..
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Page 153
Application and Installation Guide
UPS / generator-set
compatibility
A number of factors must be taken
into account when using an engine
generator set to provide long backuptime power to a UPS.
Load step changes
In the event of emergency conditions
requiring connection of the
installation to the generator set,
heavy loads can result in high inrush
currents which can cause serious
generator-set operating problems.
Battery UPS
To avoid such phenomena, UPSs from
Caterpillar are equipped with a system
ensuring gradual start-up of the charger.
The walk-in lasts approximately ten
seconds. What is more, when utility
power returns, the charger may be
stopped gradually via an auxiliary
switch in order to avoid disturbing
the other loads.
Figure 89: Gradual start of the UPS rectifier during operation on generator power..
Capacitive currents
The generator can supply only
relatively low capacitive currents
(10 to 30 % of In). When an LC filter is
installed, the main difficulty lies in the
gradual start-up of the rectifier on
generator power, when active power
is equal to zero and the generator
supplies only the capacitive current for
the filter. Consequently, the use of LC
filters must be correctly analysed to
ensure that operation complies with
manufacturer specifications.
Use of compensated LC filters with a
contactor solves this problem. For
UPSs with a PFC rectifier, compatibility
is total.
Respective UPS and generator power
ratings
A UPS equipped with a PFC rectifier
has a high input power factor (greater
than 0.9).
The engine generator set can therefore
be used to maximum effectiveness.
For LC filters, compensated filters
with a contactor solve the problem
concerning capacitive currents.
Compatibility of power ratings
between modern UPSs and
engine generator sets avoids
all problems of derating.
LC filters and generators, see
page 26.
Page 154
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Battery UPS
Stability of generator frequency
During operation on engine generator
set power, fluctuation in the generator
frequency may occur due to variations
in the speed of the thermal motor for
which the regulation functions are not
instantaneous. These variations are
due to changes in the load. Examples
are start-up of the engine generator
set itself (until it reaches its rated
speed), start-up of other loads
supplied by the engine generator set
(elevators, air-conditioning systems),
or shedding of loads.
This may create problems with a lineinteractive UPS whose output
frequency is identical to that of the
input. Generator frequency variations
may lead to multiple transfers to the
energy storage (frequency outside
tolerances) and returns to input power
(when the inverter has stabilised the
frequency, but the generator itself has
not yet stabilised), resulting in
“hunting” phenomena (instability
around the frequency setpoint).
With a double-conversion UPS, the
regulation of the output power by the
inverter avoids this problem.
Double-conversion UPS are totally
compatible with the frequency
fluctuations of engine generator
sets. This is lesser so with lineinteractive UPS.
Harmonics
The subtransient reactance X"d of a
generator is generally higher than the
short-circuit voltage Uscx of a
transformer (two to four times higher).
Any harmonic currents drawn by the
UPS rectifier may have greater impact
on the voltage harmonic distortion on
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Application and Installation Guide
the upstream busbars. With PFC
rectifier technology, the absence of
upstream harmonics avoids this
problem.
Review of inrush currents
On start-up, a number of loads cause
major inrush currents (switching
surges, startup peaks), which last
a certain time.
For the UPS, these currents represent
an apparent load Sa (kVA) that is
greater than Sn (kVA), which can
be supplied under steady-state
conditions.
The value of Sa to be taken into
account in sizing UPS power is
calculated on the basis of these
inrush currents.
Below are indications on these
currents caused by common load
devices.
Motors
Motors are generally of the threephase asynchronous type (95% of all
motors). The additional power
requirement corresponds to the startup current defined by (figure 90):
• Id (5 to 8 In, rated rms value) for
a time td (1 to 10 seconds),
• Imax = 8 to 12 In, for 20 to 30
milliseconds.
The power drawn that must be taken
into account (neglecting the peak
effect of Imax) is:
Sa (kVA) = Un Id √3 during td.
LV/LV transformers
Transformer switching produces current
peaks with amplitudes that are damped
Page 155
Application and Installation Guide
according to an exponential decay
with a time constant (see figure 91).
• i = I1st peak exp -t/τ where τ is a
few cycles (30 to 300 ms),
Battery UPS
half wave of approximately 2 In.
However, it is generally much lower
than this and can be neglected.
• I1st peak = k In (where k is given,
generally 10 to 20).
Indications generally include the
number of cycles the phenomenon
lasts and the value of the various
peaks as a percentage of I1st peak.
The corresponding inrush current is
generally calculated on the basis of
(see example):
Figure 90: Curve for direct online starting.
of a three-phase asynchronous motor.
• Sa (kVA) = Un I1st peak √3 , i.e.
Sa (kVA) = k Un In √3 during the
number of cycles,
• Example of an inrush current
damped in four cycles with:
- 1st peak (100%): k In (k from
10 to 20),
- 2nd peak 30 %: 0.3 k In,
Figure 91: LV/LV transformer..
switching current.
- 3rd peak 15 %: 0.15 k In.
The total of the rms values of the
currents corresponding to the various
peaks (Ipeak / √2) (1) is:
k ln (1 + 0,3 + 0,15) = K ln 1,45
≈ k ln
√2
√2
This is roughly equivalent to the value
of the first peak alone.
Figure 92: Computer load starting current...
(1) Considering the current peaks
as sine waves; note that some
manufacturers indicate an rms value
of Ipeak / 2.
Computer loads
Switch-mode power supplies are
non-linear loads. The current for a
single-phase load has a wave form
similar to that shown in figure 95.
There can be a peak during the first
Page 156
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Battery UPS
Application and Installation Guide
Harmonics
Harmonics
Origin of harmonics
The increasing use of computing,
telecommunications and powerelectronics devices have multiplied
the number of non-linear loads
connected to power systems.
These applications require switchmode power supplies which transform
the voltage sine wave into periodic
signals of different wave forms. All
these periodic signals of frequency f
are the product of superimposed
sinusoidal signals with frequencies
that are multiples of f, known as
harmonics (see the section
“Characteristic harmonic values”
dealing with the Fourier theorem on
page 159). Figure 93 illustrates this
showing the initial current (the
fundamental) and the third-order
harmonic.
Figure 93: Example of harmonics...
The increased presence of harmonics
is a phenomenon that concerns all
electrical installations, commercial
and industrial, as well as residential.
No modern electrical environment is
exempt from these disturbances
caused by devices such as PCs,
servers, fluorescent tubes, airconditioners, variable-speed drives,
discharge lamps, rectifiers, static
power supplies, microwave ovens,
televisions, halogen lamps, etc. All
these loads are termed “non-linear”.
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Consequences of harmonics
Harmonics disturb, increasingly
severely, all sorts of activities, ranging
from factories producing electronic
components and data-processing
systems to pumping stations,
telecommunications systems,
television studios, etc., because they
represent a significant part of the
current drawn.
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Application and Installation Guide
There are three types of negative
consequences for users:
Impact on the electrical installation
Harmonics increase the value of the
rms current with respect to that of
the rated sinusoidal current. The
result is temperature rise (sometimes
significant) in lines, transformers,
generators, capacitors, cables, etc.
The hidden costs of accelerated aging
in such devices can be very high.
Impact on applications
Harmonic currents circulate in the
source and line impedances, thus
generating voltage harmonics which
lead to voltage distortion on the
busbars upstream of the non-linear
loads (figure 94).
The distortion of the supply voltage
(upstream THDU - Total harmonic
distortion in voltage) may disturb the
operation of certain sensitive devices
connected to the these busbars.
What is more, for TNC systems where
N and PE conductors are combined
to form a PEN conductor, the zerosequence third-order harmonics
cumulate in the neutral conductor.
This unbalance current in the neutral
can disturb circuits interconnecting
low-current devices and may require
oversizing of the neutral.
Battery UPS
Impact on the available electrical power
Harmonics represent an outright loss
of current (up to 30% more current
consumed). The user must pay more
for less available power.
Precautions
General
There are a number of traditional
solutions to limit harmonics:
• Installation of tuned passive filters,
• Installation in parallel of several
cables with medium-sized cross
sections,
• Separation of non-linear loads
and sensitive loads behind
isolating transformers.
However, these solutions have two
major disadvantages:
• Limitation of harmonics is effective
only in the existing installation (the
addition or removal of loads can
render it ineffective),
• Implementation is difficult in
existing installations.
Active harmonic conditioners (see
page 98) avoid these disadvantages.
Much more effective than other
solutions, they may be used with all
types of loads and can selectively
eliminate harmonics ranging from the
2nd to the 25th order.
UPS
• Due to the rectifier/charger, a UPS
is a non-linear load for its power
source. UPS from Caterpillar offer
perfect control over upstream
harmonics by using “clean” PFC
rectifiers or filters.
Figure 94: Voltage distortion due to reinjection
of harmonic currents by non-linear loads.
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Upstream of the UPS, the total voltage
distortion remains within limits that
are acceptable for the other devices
connected to the same busbars.
Characteristic harmonic
values
Current values
Harmonic expansion of a periodic
current
The Fourier theorem indicates that
any periodic function with a frequency
f may be represented as the sum of
terms (series) composed of:
• A sinusoidal term with frequency
f, called the fundamental
frequency,
• Sinusoidal terms with frequencies
that are whole multiples of the
fundamental frequency, i.e. the
harmonics,
• A DC component, where
applicable.
Application of the Fourier theorem to
the currents of non-linear loads
indicates that a periodic current I(t), of
whatever form at frequency f (50 or 60
Hz), is the sum of harmonic sinusoidal
currents defined by:
• IHn is the rms value of the nth
harmonic, at frequency nf,
• φn is the phase displacement
between the nth harmonic current
and the voltage.
It is important to evaluate the
harmonics (n ≥ 2) with regards to the
fundamental (n = 1) to determine to
what degree the function differs from
the fundamental.
To that end, the values shown next are
taken into account.
Current individual harmonic content
This value expresses the ratio in
percent between of the rms value of
the given harmonic and that of the
fundamental.
Ihn% = 100
IHn
IH1
All the harmonics present in a given
current with the indication of their
relative importance (Ihn values)
constitute the harmonic spectrum of
the current. Generally speaking, the
influence of the orders above the 25th
is negligible.
∞
I(t) = IH1√2 sin(ωt + φ1) + Σ IHn√2 sin(nωt+φn)
n=2
where
• IH1 is the rms value of the
fundamental current at frequency
f (50 or 60 Hz),
• ω = 2 π f is the angular frequency
of the fundamental,
• φ1 is the phase displacement
between the fundamental current
and the voltage,
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Battery UPS
Current total harmonic distortion
This distortion is called THDI (Total
Harmonic Distortion where I is for the
current). It expresses the ratio between
the rms value of all harmonics (n ≥ 2)
and that of the fundamental. The THDI
is also expressed in terms of the
individual harmonics.
√
THDI%=100
∞
Σ IH
n=2
IH1
2
n
=100
∞
√Σ
n=2
IHn 2 =
IH1
Note. Harmonic contents are
sometimes expressed with respect to
the complete signal Irms, and not the
fundamental (IEC documents). Here,
we use the definition of the CIGREE,
which uses the fundamental.
For the low harmonic contents
analysed in the following pages,
the two definitions produce virtually
identical results.
Rms value of a current with harmonics
The rms value of an alternating
current with a period T is:
1 T l(t)2dt
Irms =
T O
After calculation and using harmonic
representation, this can be expressed
as:
√
∫
√Σ
∞
Irms =
IHn2
n=1
where IHn = rms value of the
harmonic.
nth
∞
√Σ
(Ihn%)2
n=2
The rms value is also expressed as:
Irms =
∞
√
Ieff = IH1
IH12 + Σ IHn2 or:
n=2
√
Irms = IH1
∞
2
1+ Σ IHn hence:
n=2 IH1
√
∞
1+ Σ Ihn2 = IH1 √ 1+THDI2
n=2
• Ihn = Ihn% / 100 (individual level
expressed as a value and not as
a percentage),
• THDI = THDI% / 100 (distortion
expressed as a value and not as
a percentage).
The rms value of the current is that of
the fundamental, multiplied by a
coefficient which is due to the
harmonics and is a function of the
distortion.
One effect of harmonics is
therefore to increase the rms
value of the current, which can
lead to temperature rise and
therefore require oversizing of
conductors.
The lower the distortion, the less need
for oversizing.
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Example
Input current of a three-phase rectifier.
Figure 95: Example of the spectrum of a harmonic current..
THDI%=
√
∞
Σ (Ihn%)2
n=2
The value under the square root sign
is:
332 + 2.72 + 7.32 + 1.62 + 2.62 + 1.12 +
1.52 + 1.32 = 1164
consequently THDI% ≈ 34% and THDI =
0.34.
Ieff = IH1√1 + THDI2 = IH1 √1 + 0.342 =
1.056 x I1
The rms value of this current is
therefore 5.6% higher than the rms
value of the fundamental, i.e. than
the rated current containing no
harmonics, with a corresponding
temperature rise.
Voltage values
At the terminals of a non-linear load,
through which a distorted periodic AC
current flows, the voltage is also
periodic with a frequency f and it is
also distorted with respect to the
theoretical sinusoidal wave. The
relation between voltage and current
is no longer governed by Ohm's linear
law, because it is applicable only for
sinusoidal voltage and current. It is
possible, however, to use a Fourier
expansion for the voltage and to
define, similar to the current and with
the same results, the following values:
Voltage individual harmonic content
UHn% =
100UHn
Uh1
The harmonic spectrum can also be
calculated for the voltage.
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Battery UPS
Voltage total harmonic distortion
THDU%=100
√
∞
Σ UH
n=2
IH1
2
n
=100
√
∞
Σ
n=2
UHn
UH1
THDU for Total Harmonic Distortion,
where U is for the voltage.
Rms value of a voltage with harmonics
Irms =
√
ΣIHn2
√
∞
1+ΣUh = IH1√ 1+THDU
2
n
2
n=2
The rms value of the voltage
is that of the fundamental,
multiplied by a coefficient
which is due to the harmonics.
Power values
Power factor in the presence of
harmonics
On the basis of the active power at the
terminals of a non-linear load P (kW)
and the apparent power supplied S
(kVA), the power factor is defined by:
P(kW)
S(kVA)
This power factor does not express
the phase displacement between the
voltage and the current because they
are not sinusoidal. However, it is
possible to define the displacement
between the voltage fundamental
and the current fundamental (both
sinusoidal), by:
Page 162
√
∞
Σ (Uh )
n=2
n
2
where P1 and S1 are the active
and reactive power, respectively,
corresponding to the fundamentals.
n=1
Urms =UH1
cos φ1 =
=
Standard IEC 146-1 defines the
distortion factor:
∞
Which, similar to the current, can also
be expressed as:
λ=
2
P1(kW)
S1(kVA)
ν=
λ
cos φ1
When there are no harmonics, this
factor is equal to 1 and the power
factor is simply the cos φ.
Power in the presence of harmonics
• Across the terminals of a
balanced, three-phase linear
load, supplied with a phase-tophase voltage u(t) and a current
I(t), where the displacement
between u and i is φ, the apparent
power in kVA, depending on the
rms values U and I, is:
S = UI√3
The active power in kW is: P = S cos φ
The reactive power in kvar is: Q = S
sin φ
Where:
S = √P2 + Q2
• At the terminals of a non-linear
load, the mathematical definition
of P is much more complex
because U and I contain
harmonics. It can however
be expressed simply as:
P = S λ (λ = power factor)
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If U1 and I1 are the fundamentals
displaced by φ1, it is possible to
calculate the corresponding apparent,
active and reactive power by:
S1 = U1I1√3 P1 = S1 cos φ1 and Q1 =
S1 sin φ1. The total apparent power is:
S = √P12 + Q12 + D2
where D is the distortion power, due
to the harmonics.
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Battery UPS
Non-linear loads and PWM technology
Non-linear load
performance of UPS using
PWM technology
Importance of the UPS output
impedance
Equivalent diagram of an inverter
output
With respect to the load, an inverter is
a perfect source of sinusoidal voltage
V0 in series with an output impedance
Zs. Figure 96 shows the equivalent
diagram of the inverter output when
a load is present.
Figure 96: Equivalent diagram of an inverter output..
Effects of different load types
• For a linear load, the impedances
Zs, ZL, Zc are considered at the
angular frequency ω = 2 π f
corresponding to the distribution
frequency (f = 50 or 60 Hz),
giving V0 = (Zs + ZL + Zc) I,
• For a non-linear load, the
harmonic currents drawn by the
load flow through the
impedances. For the fundamental
and each individual harmonic, the
rms values of the current and the
voltage are related similarly and
can be expressed as:
- for the fundamental:
U1 = (Zs + ZL + Zc) I1
- for each harmonic order k:
UK = [Zs(kf) + ZL(kf) + Zc(kf)] IK
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Battery UPS
The impedance values are considered
at the frequency kf of the given order.
Voltage distortion decreases with the
individual levels of the voltage
harmonics UK / U1.
These levels are related to those of the
harmonic currents IK/ I1 by the equation:
[Zs(kf) + ZL(kf) + Zc(kf)] / (Zs + ZL + Zc).
Consequently, for a given load
current spectrum, the individual
voltage harmonic levels and the
total distortion (THDU) decrease
with the impedance of the source
and the cables at the given
frequencies.
Consequences of non-linear loads
To reduce the effects of the harmonic
currents (THDU at B and C), it is
necessary, to the greatest extent
possible, to:
• reduce the line impedance,
• ensure a low source impedance at
the various harmonic frequencies.
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Application and Installation Guide
Good behaviour on the part of a
UPS supplying non-linear loads
requires a low output impedance at
the various harmonic frequencies.
Below is a presentation of the
advantages of the PWM (pulse width
modulation) chopping technique in this
respect.
UPS operating principle
Chopping of the DC voltage by the
inverter with filtering
An inverter is made up of a converter
that transforms the DC power supplied
by the rectifier/charger or the battery
into AC power. For example, on a
single-phase UPS, there are two ways
to convert the DC power, using either
a half bridge (see figure 97) or a full
bridge (see figure 98).
The square-wave voltage obtained
between A and B is then filtered to
produce a sinusoidal voltage with a
low level of distortion at the output.
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Battery UPS
Figure 97: Half-bridge DC/AC converter. Figure 98: Full-bridge DC/AC converter..
Practically speaking, the switches
shown in figures 97 and 98 are IGBTs
for which it is possible to control the
relative on and off times.
By controlling the on and off times, it
is possible to “distribute” the voltage
over the reference sinusoidal wave.
This principle is known as PWM (pulse
width modulation). It is shown in a
simplified manner, with five squarewave pulses, in figure 99. The area of
the voltage sinusoidal wave is equal
to that of the square-wave pulses used
to generate it. These areas represent
the power supplied by the inverter to
the load
over a given time, i.e.
Page 166
∫
The higher the chopping frequency
(the higher the number of squarewave pulses), the better the regulation
with respect to the reference wave.
Chopping also reduces the size of the
internal filter required on the LC
output (see figure 100).
Figure 99: DC/AC converter output voltage with.
five square-wave pulses per half-wave.
T
VIdt
0
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Comparison with the reference
voltage wave makes it possible
to maintain the inverter output
voltage within strict distortion
tolerances, even for highly
distorted currents.
Figure 100: Inverter output filter..
PWM inverters
PWM chopping
The PWM (pulse width modulation)
chopping technique combines highfrequency chopping (a few kHz) of
the DC voltage by the inverter and
regulation of the pulse width for the
inverter output, to comply with a
reference sinusoidal wave.
This technique uses IGBTs (insulated
gate bipolar transistors) offering the
advantages of voltage control and
very short commutation times. Due
to the high frequency, the regulation
system can react quickly (e.g. 333
nanoseconds for a frequency of 3 kHz)
to modify the pulse widths within a
given period.
Functional diagram of a PWM inverter
Figure 101 shows the functional
diagram of a PWM inverter.
The output voltage is continuously
compared to the reference voltage
Vref which is a sinusoidal wave with
a very low level of distortion (< 1%).
The difference in the voltage ε is
processed by a corrector, according
to a transfer function C(p), intended to
ensure the performance and stability
of control.
The voltage from the corrector is then
amplified by the DC/AC converter and
its control system with a gain A. The
Vm voltage supplied by the converter
is filtered by the LC filter to supply the
output voltage Vs.
Practically speaking, it is necessary
to take into account the impedance of
the output transformer when it exists,
to obtain the total inductance L. Often,
the inductance is built into the transformer, which is why it is not included
in diagrams.
Figure 101: Functional diagram of a PWM inverter..
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Output impedance of a PWM inverter
It is possible to represent the above
DC/AC converter and filter as a series
impedance Z1 and a parallel
impedance Z2 (see the left-hand
side of figure 102).
The diagram can be modified to
display the output impedance Zs.
Battery UPS
The equivalent diagram (right-hand
side of figure 110) shows:
• V'm = voltage measured under
no-load conditions, i.e.:
Z2
V'm = Vm
Z1 + Z2
• Zs = impedance measured at the
output with V'm short-circuited, i.e.:
ZZ
Zs = 1 2
Z1 + Z2
Figure 102: Equivalent diagram of an inverter as seen from the output..
The ratio
Z2
is the transfer
Z1 + Z2
function of the filter, noted H(p).
To simplify, C(p) x A is replaced by
μ(p) which represents the transfer
function of the correction and
amplification.
Figure 103: Transformed functional diagram of a PWM-chopping inverter equipped.
with an output-voltage regulation system with modulated chopping frequency.
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Battery UPS
It is possible to show that the inverter
output impedance Zs in this case is
equal to:
Z' s ≈
Z1
μ (p)
This means that in the regulation pass
band, the inverter output impedance is
equal to the filter series impedance
divided by the correction and
amplification gain.
Given the high gain in the regulation
pass band, the output impedance is
significantly reduced compared to
impedance Z1 of an inverter without
this type of regulation.
Outside the regulation pass band, the
inverter output impedance is equal to
that of the filter, but remains low
because it corresponds to the
impedance of a highfrequency
capacitor.
Consequently, the output impedance
is a function of the frequency (see
figure 104).
The free-frequency PWM (pulse
width modulation) technique
considerably limits the output
impedance.
Comparison of different
sources
Output impedance of various
sources
Application and Installation Guide
• Transformers and generators the curve is a straight line
corresponding to the effect of
the inductance L (the term which
rapidly becomes dominant in the
reactance with respect to the
resistance and which increases
linearly as a function of the
frequency).
• Modern inverters implementing
the PWM chopping technique
with modulated chopping
frequency - at all harmonic
frequencies, the Zs/Zc ratio is:
- less than that noted for other
sources,
- low and virtually constant.
Conclusion
The PWM inverter is the source
offering by far the lowest output
impedance in the presence of
harmonics. It is clearly the best source
on the market in terms of its aptitude
to minimise the voltage distortion
caused by non-linear loads. It is five
to six times better than a transformer
with an identical power rating.
The new generation of UPS
implementing IGBTs and the
PWM chopping technique with
frequency modulation are the best
sources of sinusoidal voltage,
whatever the type of current
drawn by the load.
The curves in figure 104 show the
output impedances for various
sources with equal output ratings as
a function of the AC frequency. The
impedances are plotted as a percent
of the load impedance Zc.
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Battery UPS
Figure 104: Output impedance of different sources depending on the frequency..
Free-frequency chopping
Free-frequency chopping
Free frequency is an improvement to
the PWM technique.
PWM chopping can use either of two
techniques (figure 105).
Fixed-frequency chopping
The chopping fronts occur at fixed,
regular intervals corresponding to the
choppingfrequency over one period.
The width of the pulses (square-wave
pulses) can be modulated to conform
to the reference within the fixed time
interval.
The two sine waves shown in the
diagram correspond to the tolerance
(< 1%) around the reference sine wave.
Page 170
Free-frequency chopping
The chopping fronts do not necessarily
occur at fixed intervals. Chopping
adapts to the requirements of the
regulation, i.e. the rate of change of
the reference. The width of the
commutation fronts decreases (the
chopping frequency increases) as the
rate of change of the reference sine
wave increases. Conversely, the width
of the commutation fronts increases
(the chopping frequency decreases)
as the rate of change of the reference
decreases. On the whole, the average
chopping frequency is the same as
that for the fixed-frequency technique
(approximately 3 kHz). But regulation
is better because the commutation
accelerates in the zones where the rate
of change is high (see figure 106).
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It can reach eight commutations per
millisecond, i.e. a regulation time as
low as 125 nanoseconds (compared
to 300 ns for the fixed-frequency
technique).
The free-frequency technique
increases the precision of the
voltage regulation in PWM
inverters compared to the fixedfrequency technique.
Figure 105: PWM chopping with fixed-frequency and free-frequency regulation..
Figure 106: Regulation employing free-frequency commutation..
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Battery UPS
PFC Rectifiers
Standard and PFC rectifiers
PFC rectifiers
UPS units draw power from
the AC distribution system via a
rectifier/charger. With respect to the
upstream system, the rectifier is a
non-linear load drawing harmonics.
In terms of harmonics, there are two
types of rectifiers.
Operating principle
The principle behind PFC rectifiers
consists in forcing the current drawn
to remain sinusoidal. To that end, they
use the PWM technique presented
earlier.
Standard rectifiers
These are three-phase rectifiers
incorporating SCRs and using a sixphase bridge with standard chopping
of the current.
This type of bridge draws harmonic
currents with orders of n = 6 k ± 1
(where k is a whole number), mainly
H5 and H7, and to a lesser degree H11
and H13.
Harmonics are controlled by using
a filter.
“Clean” PFC (Power Factor
Correction) rectifier
This type of rectifier comprises built-in
IGBTs and a regulation system that
adjusts the input voltage and current
to a reference sine wave. This
technique ensures an input voltage
and current that are:
• Perfectly sinusoidal, i.e. free of
harmonics,
The principle is that of a “voltage
source” converter (see figure 107),
whereas the active harmonic
conditioner uses a “current source”
converter.
The converter acts as a backelectromotive force (a “sinusoidal
voltage generator”) on the distribution
system and the sinusoidal current is
obtained by inserting an inductor
between the utility power and the
voltage source.
Even if other non-linear loads
increase the voltage distortion on the
distribution system, the regulation can
adapt to draw a sinusoidal current.
The frequency of low residual
harmonic currents is the frequency of
the modulation and of its multiples.
Frequency depends on the
possibilities of the semiconductors
used.
• In phase, i.e. an input power
factor close to 1.
With this type of rectifier, no filters
are required.
Page 172
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Figure 107: Operating principle of a clean “voltage generator” converter..
Implementation
Single-phase rectifier
Figure 108 shows the operation of
a single-phase rectifier.
Voltage modulation is obtained by a
controller that forces the current to
follow a sinusoidal current reference.
Transistor T and diode D make up the
voltage modulator. The voltage u thus
changes between 0 and Vs according
to whether transistor T is in the on or
off state. When transistor T conducts,
the current in inductor L can only
increase as the voltage is positive and
u = 0.
Therefore:
di e 0
= >
dt L
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When transistor T is off, the current
in L decreases, provided that Vs is
greater than V, so that:
di=e-VS>0
dt L
For this condition to be fulfilled,
voltage Vs must be greater than the
peak voltage of V, i.e. the rms value of
the AC voltage multiplied by √2.
If this condition is fulfilled, the current
in L can be increased or decreased at
any time. The variation of the current
in L with time can be forced by
monitoring the respective on and off
times of transistor T. Figure 109 shows
the evolution of current IL with respect
to a reference value.
Page 173
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Battery UPS
Figure 108: Diagram of a clean, single-phase rectifier drawing a sinusoidal signal..
Figure 109: Evolution of current IL with respect to the reference..
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Three-phase rectifier/charger
The basic circuit arrangement is
shown in figure 110. It is similar to that
in figure 108, with the inductor placed
upstream of the rectifiers; the
operating principle is also the same.
The monitoring system controls each
power leg and forces the current
drawn on each phase to follow the
sinusoidal reference.
Figure 110: Diagram of a clean, three-phase rectifier drawing a sinusoidal signal..
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Glossary and bibliography
Glossary
Active harmonic conditioner
Active harmonic conditioners (AHC)
are used to eliminate the harmonic
currents flowing in an electrical
installation and consequently limit
voltage and current distortion (THDU
and THDI respectively) to a given
percentage. The conditioner
continuously analyses the harmonic
current drawn by the load and injects,
on a realtime basis, an identical
current with the appropriate phase.
The current supplied by the source
remains virtually sinusoidal, whatever
the operating conditions. The
conditioner automatically adapts to
changes in the installation and covers
the entire low-frequency harmonic
spectrum (H2 through to H25). Active
harmonic conditioners are also called
active filters.
ANSI (American National Standards
Institute)
U.S. organisation in charge of
standardisation. Traditionally, it is
assisted in this task by scientific
organisations such as the IEEE (Institute
of Electronics and Electrical Engineers).
Availability of an electrical installation
Availability is the probability that
the installation will be capable of
supplying energy with the level of
quality required by the supplied loads.
Availability (%) = (1-
MTTR
) x 100
MTBF
Practically speaking, the lower the
MTTR (fast repair) and the higher the
MTBF (time without failure), the
higher the availability.
Page 176
Backup time
Time during which the UPS can
supply the rated load with power from
its energy storage under nominal
conditions when the normal AC
source fails. This time depends on the
battery. Typical backup times are 6, 8,
10, 15 or 30 minutes.
Battery circuit breaker
DC circuit breaker that protects the
battery circuit of a UPS.
Battery, recombination
Battery with a gas recombination rate
at least equal to 95%. No water need
be added over battery life, which is
why such batteries are commonly
referred to as “maintenance free”
batteries.
BMS (Building Management System)
System used to control and monitor
all building utilities and systems from
a central location. It is generally
composed of sensors, actuators and
programmable controllers connected
to a central computer (or several
computers) equipped with specific
software.
Charger
Device associated with the rectifier
and used to supply the battery with
the electrical power (DC current)
required to recharge and/or float
charge the battery, thus ensuring the
availability of backup power.
Cos φ
A measure of the phase displacement
between the current wave and the
voltage wave observed at the
terminals of a linear load.
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Battery UPS
Cos φ1
A measure of the phase displacement
between the fundamental current
wave and the fundamental voltage
wave observed at the terminals of a
non-linear load.
Crest factor (Fc)
The ratio between the peak value of a
current and its rms value.
Fc =
Ipeak
Irms
Discrimination
System whereby a fault trips the
protection device of the faulty load
circuit only. Protection devices on
neighbouring circuits and upstream
are not tripped.
Distortion factor (ν)
Factor measuring the effect of
harmonics on the power factor at the
terminals of a load supplied with AC
power.
ν=
λ
cosφ1
λ : power factor
cos φ1 : cos φ of the fundamental
EMC (Electromagnetic compatibility)
Possibility of a device to operate
normally when installed near other
devices, given the disturbances
emitted by each device and their
mutual sensitivities.
EN (European Normalisation)
Label used for European standards.
These standards are issued by
CENELEC. Following acceptance by
the member countries, these
standards enter into force and replace
the national standards.
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Application and Installation Guide
Fault tolerance
A fault-tolerant system can continue
to operate following a fault, but in a
down-graded mode.
Down-graded operation is generally
accompanied by an alarm to signal
the fault(s). It is generally possible to
repair the system rapidly and return to
normal operation, without shutting
down the system. UPS operation on
the static bypass is a type of faulttolerant operation.
Float current
DC current that maintains the battery
at nominal charge, corresponding to
the float voltage. This current
compensates for open-circuit losses.
Float voltage
DC voltage applied to the battery to
maintain its charge level. This voltage
depends on the type of battery, the
number of cells and the
manufacturer’s recommendations.
Fourier theorem
Theorem stating that any nonsinusoidal periodic function (of
frequency f) may be represented as a
sum of terms (series) made up of:
• A sinusoidal term with frequency
f, called the fundamental
frequency,
• Sinusoidal terms with
frequencies that are wholenumber multiples of the
fundamental frequency, i.e.
the harmonics,
• A DC component, where
applicable.
Page 177
Application and Installation Guide
The series may be expressed, where n
is a whole number, as:
∞
Y(t)=Y0 + Σ Yn √2 sin (nωt + φn)
Battery UPS
Harmonic distortion, individual
Ratio between the rms value of an nth
order harmonic and the rms value of
the fundamental.
n=1
n = 1 corresponds to the fundamental,
n > 1 corresponds to the nth harmonic.
Free-frequency chopping
Chopping technique where the
frequency increases or decreases
depending on the variation of a
reference value. Contrary to fixedfrequency chopping, this technique
increases regulation during major
variations and reduces it when
variation is low. This improves
regulation with respect to the
reference value.
Harmonic
Sinusoidal term of the Fourier series
expansion of a periodic function.
The harmonic (or harmonic
component) of the nth order is
characterised by:
Hn(t) = Hn√2 sin(nωt + φn)
Hn is the rms value of the given
harmonic component,
• ω is the angular frequency of the
fundamental, related to the
fundamental frequency by ω = 2
π f,
• φn is the phase displacement of
the given harmonic component
at t = 0.
Hn% = 100
Yn
Y1
Harmonic distortion, total (THD)
Ratio between the rms value of all
harmonics of a non-sinusoidal
alternating periodic value and that
of the fundamental.
∞
D%=100
√
∞
ΣY
n=2
2
n
Y1
This value may also be expressed as a
function of the individual distortion of
each harmonic Hn = Yn /Y1 by:
∞
D%=100
√
∞
ΣH
2
n
n=2
For current and voltage, these values
are called THDI and THDU respectively.
Harmonics, current and voltage
Any periodic current (frequency f) that
is not sinusoidal is made up of a set of
sinusoidal currents (see Fourier),
including a fundamental (frequency f)
and harmonics at various frequencies nf
(where n is a whole number). A voltage
harmonic corresponds to each current
harmonic. The instantaneous and rms
values are related by Ohm's law, where
the terms are both sinusoidal.
If Zsn is the voltage source output
impedance at frequency nf (angular
frequency nω), then Un = Zsn x In.
Consequently, for each current
harmonic, there is a voltage harmonic
that depends on the source output
impedance at the corresponding
frequency.
Page 178
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HF interference
High-frequency parasitic current that
is either conducted (electrostatic
origin) or radiated (electromagnetic
origin) by a device.
(IEEE) Institute of Electrical and
Electronic Engineers
Assists ANSI (American National
Standards Institute) in defining
standards for electric and electronic
equipment.
IIK
A protection index indicating the
degree of protection against
mechanical shocks as defined by
European standard EN 50102. The
IK code includes 11 values from IK01
to IK10, corresponding to different
energy levels expressed in Joules.
This code is complementary to the
IP code.
Inrush current
Transient currents observed in an
electrical installation when devices
are energised. These currents are
generally due to the magnetic circuits
of the devices. The effect is measured
by the current’s maximum peak value
and the rms current value it generates
during the time it lasts.
Inverter
UPS subassembly that recomposes
a sine-wave output (regulated and
without breaks) using the DC current
supplied by the rectifier/charger or the
battery. The main elements of the
inverter are the DC/AC converter, a
regulation system and an output filter.
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Application and Installation Guide
IP (International Protection)
A protection index defining the ability
of electrical equipment to withstand
certain environmental conditions. It is
composed of two digits (e.g. IP 20)
defined by standard IEC 529 and
included in standard EN60529. Each
digit corresponds to a certain degree
of protection with respect to a given
external influence.
• First digit (0 to 6): degree of
protection against penetration
of solid bodies,
• Second digit (0 to 7): degree of
protection against penetration of
liquids,
• Additional letter (A to D): safety
of persons.
The IP code may receive an additional
letter (A to D) when the protection
provided persons against dangerous
parts is better than that indicated by
the first digit. A - protection against
access by the back of the hand, B protection against access using a
finger, C - using a tool with a diameter
of 2.5 mm, D - using a tool with a
diameter of 1 mm. When the
protection of persons is the only
relevant factor, the two IP digits may
be replaced by “X” (e.g. IP XXB).
Example. IP 30D
3 = protection against solid bodies
larger than 2.5 mm.
0 = no protection against water.
D = protection against access using
a tool with a diameter of 1 mm.
Page 179
Application and Installation Guide
ISO 9000
Standard defining procedures
and systems used to attain an
internationally recognised level
of production quality. ISO 9000
certification is recognition that the
quality system effectively complies
with the standard. Certification is
carried out by an official organisation
(e.g. AFAQ), unaffiliated with either
clients or suppliers or the company
itself. The certificate is valid for a
three-year period with yearly audits
and checks.
IT system
System earthing arrangement in
which the neutral is isolated from the
earth or connected to the earth via a
high impedance and the various
exposed conductive parts are
connected to the earth via individual
earthing circuits. An alarm (generally
an insulation-monitoring device IMD)
must signal the appearance of a first
insulation fault.
The installation must be de-energized
immediately in the event of a second
insulation fault.
Load, linear
Load for which the input voltage and
current are both sinusoidal, with
possible phase displacement
(inductive and/or capacitive loads).
Linear loads include only resistances,
inductors or capacitors.
The Ohm law applies to both the
instantaneous and the rms values.
U = Z I, where Z is the equivalent
impedance of the load (constant
during each period).
Examples of linear loads: lighting
systems, motors, transformers.
Page 180
Battery UPS
Load, non-linear
Load drawing an input current that is
periodical, but not sinusoidal, with a
harmonic component. For this reason,
the input voltage is also distorted by
harmonics. Generally speaking, nonlinear loads comprise active electronic
components that vary the load
impedance over each period. The Ohm
law applies to the instantaneous
values, but the equivalent impedance
of the load is variable. As a result,
there is no simple law for the rms
values, as is the case for linear loads.
Examples of non-linear loads: switchmode power supplies for computers,
rectifier bridges using SCRs, variablespeed drives, fluorescent lighting.
Load power
Apparent power Su (kVA) that a UPS
inverter supplies under given load
conditions. It is less than or equal to
the rated output Sn (kVA).
The ratio Su/Sn defines the percent
load of the inverter.
Magnetic-susceptibility level
Level of electromagnetic emission
starting at which a nearby device or
system malfunctions.
Management-Pac™ (software)
Intended for network administrators,
this totally SNMP-compatible software
can manage and supervise an entire
park of UPS.
Micro-outage
Total absence of power for a duration
of less than one half cycle (< 10 ms at
50 Hz).
MLVS (Main low-voltage switchboard)
The low-voltage switchgear assembly
used to distribute power immediately
downstream of the HV/LV transformer.
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Battery UPS
MTBF (Mean Time Between Failures)
Expected value of the duration
(expressed in hours) of normal
operation of a repairable device
between failures. The MTBF is an
indication on the reliability of a device.
MTTF (Mean Time To Failure)
Expected value of the duration
(expressed in hours) of normal
operation of a non-repairable device
(i.e. one for which an MTBF cannot be
calculated). The MTTF is an indication
on the reliability of a device.
MTTR (Mean Time To Repair)
Expected value (or statistical average
if available) of the time required to
repair a device. This includes the time
required to detect the cause of the
failure, repair it and start the system
up again.
Noise level
Acoustic decibel level (dBA)
representing the sound power of a
source measured according to
standard ISO 3746.
Off-line
A UPS where the inverter is off during
normal mode.
On-line
A UPS where the invert is on in
normal mode.
Percent load
The ratio Su (kVA) / Sn (kVA) between
the load power Su and the rated
power Sn of a UPS.
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Application and Installation Guide
PFC (Power Factor Correction) (rectifier)
PFC is an electronic regulation device
for the UPS input rectifier that
maintains the input current sinusoidal
and in phase with the utility voltage.
It avoids drawing harmonic currents
upstream of the rectifier and thus the
need for a filter.
Power factor (λ)
Ratio between the active power P (kW)
supplied to a load and the apparent
power S (kVA) supplied to said load
by an AC power supply.
λ=
P
S
Power, primary
Power normally continuously
available which is usually supplied
by an electrical utility company, but
sometimes by the user's own
generation. Primary power is
connected to the normal AC input
of the UPS.
Power, rated
Apparent power Sn (kVA) that a UPS
can deliver under given load
conditions defined for cos φ = 0.8.
Power, standby
Power intended to replace the primary
power in the event of primary-power
failure. When standby power is
available, it is connected to the bypass
AC input of the UPS.
PWM (Pulse Width Modulation)
A high-frequency chopping technique
for UPS inverters using a means of
regulation enabling rapid modification
of pulse widths over a single period.
It is thus possible to maintain the
inverter output voltage within
tolerances, even for non-linear loads.
Page 181
Application and Installation Guide
Rectifier/charger
UPS component that draws utility
power to supply the inverter and to
float charge or recharge the battery.
The alternating input current is
rectified and then distributed to the
inverter and the battery.
Redundancy, active redundancy
N + 1, N + 2, etc.
Parallel UPS configuration in which
several UPS units (N + 1, N + 2, etc.)
with equal outputs are parallel
connected and share the load. In the
event one UPS unit (N + 1
redundancy) or more fail (N + 2, N + 3,
etc.), the other units pick up its share
without any interruption in the supply
of power to the load. The remaining
units are sufficient to continue
supplying the load as long as there
are at least N units.
Redundancy, isolated
UPS configuration in which one or
several UPS units operate on standby, with no load or only a partial load,
and can immediately back up a faulty
UPS unit by no-break transfer of the
load, carried out by a static switch.
Reliability
Probability that a device will
accomplish a required function under
given conditions over a given period
of time.
Page 182
Battery UPS
Short-circuit voltage of a transformer
(Uscx %)
Relative measurement (%) of the
internal impedance of a transformer.
This short-circuit impedance is
commonly called the short-circuit
voltage because it is measured during
a short-circuit test (shorted secondary
winding subjected to a current set to
In). For most common three-phase
transformers, the value ranges
between 3 and 6%.
Source impedance
It is possible to consider that a load
is supplied by a perfect voltage
generator Uo, in series with an
internal impedance Zs, where:
• Uo is the voltage measured
across the load terminals, if the
load is equal to zero (load
terminals in an open circuit),
• Zs is the source impedance, i.e.
the equivalent impedance as
seen from the load terminals
(open circuit), obtained by shortcircuiting the upstream voltage
generator(s).
Static switch
Power-electronics device that can be
used to switch from one source to
another without interruption in the
supply of power. In a UPS, transfer is
from normal AC power to bypass AC
power and back. Transfer without
interruption is possible due to the fact
that there are no mechanical parts and
the ultra-fast switching capabilities of
the electronic components.
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Battery UPS
Static Transfer Switch (STS)
An STS carries out transfer,
automatically or manually, of one
or more three-phase loads, from a
preferred source to an alternate or
reserve source without interruption.
If the preferred source fails, transfer
is automatic.
Subtransient reactance of a generator
set (Uscx %)
Relative measurement (%) of the
internal impedance of an AC generator
during harmonic phenomena. This
reactance, also called the longitudinal
subtransient reactance of the
generator, is sometimes identified as
X"d.
For most common generators, the
value ranges between 15 and 20%.
It can drop to 12% for optimised
systems and to 6% for special devices.
System earthing arrangements (SEA)
Standardised system for the
interconnection and earthing of
exposed conductive parts and the
neutral of a low-voltage electrical
installation. There are three
standardised arrangements:
• TN system, with the TN-C and TNS versions (exposed conductive
parts connected to the neutral),
• TT system (earthed neutral),
• IT system (isolated neutral).
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Application and Installation Guide
THDI
THD for Total Harmonic Distortion and
I for current. This is the ratio between
the rms value of current harmonics
and the rms value of the fundamental.
∞
THDI%=100
√
∞
ΣI
n=2
2
n
I1
This value may also be expressed in
terms of the individual harmonics, e.g.
Ihn = In / I1 using the equation:
∞
THDI%=100
√
∞
Σ Ih
n=2
2
n
THDU
THD for Total Harmonic Distortion and
U for voltage. This is the ratio between
the rms value of the voltage
harmonics and the rms value of the
fundamental.
∞
THDU%=100
√
∞
ΣU
n=2
2
U1
This value may also be expressed in
terms of the individual harmonics, e.g.
Uhn = Un / U1 using the equation:
∞
THDU%=100
√
∞
Σ Uh
n=2
2
n
Tolerances (%)
Permissible limits to the variation of a
quantity around its nominal or rated
value, expressed as a percentage.
Page 183
Application and Installation Guide
TN system
System earthing arrangement in
which the exposed conductive parts
are interconnected and connected to
the neutral, the latter being connected
to the earth. The installation must be
de-energized immediately in the event
of an insulation fault. There are two TN
systems, TN-S in which the neutral (N)
and the protective conductor (PE) are
separate, and TN-C in which the two
conductors are combined to form a
single conductor (PEN).
TT system
System earthing arrangement in
which the neutral and the exposed
conductive parts are directly earthed
via individual earthing circuits.
The installation must be de-energized
immediately in the event of an
insulation fault.
Ultracapacitors
An ultracapacitor (double-layer
electrochemical capacitor) is made
up of two porous, metal-carbon
electrodes placed in a non-aqueous
organic electrolyte.
This technology offers very high
capacitances (> 1 000 farads).
UPS (Uninterruptible Power System)
An electrical device providing an
interface between the normal source
of power, usually the utility, and an
elec trical installation generally
including sensitive loads (computers,
instrumentation, etc.).
The UPS supplies sinusoidal AC
power free of disturbances and within
strict amplitude and frequency
tolerances.
Page 184
Battery UPS
It is generally made up of a rectifier/
charger, an inverter, an energy storage
for backup power in the event of utility
outages, a static bypass and a
maintenance bypass. The bypasses
make it possible to supply the load
directly with standby power,
bypassing the rectifier/charger
and inverter line.
Transfer to the static bypass is
automatic and without a break in
power to the load if the inverter fails
or a downstream overload exceeds
UPS capacity. Transfer to the
maintenance bypass is carried out
using manual switches.
UPS operating in double-conversion
mode
A UPS in which the inverter is
connected in series between the
normal AC source and the load. All
power supplied to the load flows
through the inverter which completely
regenerates the voltage and isolates
the load from disturbances on the
utility. This type of UPS can also
supply the load with utility power
directly via a static bypass following
no-break transfer to a separate AC
input. This function ensures the
continuity of supply if an internal fault
occurs. What is more, this type of UPS
is systematically equipped with a
maintenance bypass.
UPS operating in line-interactive mode
A UPS in which the inverter is
connected in parallel to the AC input
and also charges the energy storage
(interactive operation in reversible
mode).
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Battery UPS
Application and Installation Guide
UPS operating in passive-standby mode
The UPS is connected in parallel to the
normal AC source to provide a
standby power source.
This configuration, a cost-saving
compromise, is used only for low
power ratings (≤ 3 kVA) because it
does not isolate the load from the
source and lets through inrush
currents. What is more, it requires a
relatively high transfer time (≈ 10 ms)
to inverter power in the event of a
power outage or a major disturbance
on the utility.
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Page 185
Application and Installation Guide
Battery UPS
Bibliography
Standards
• IEC 60529 / EN 60529: Degrees
of protection provided by
enclosures (IP index).
• IEC 60417: Graphical symbols for
diagrams.
• IEC 60742: Isolating transformers
and safety isolating
transformers.
• IEC 61000-3-4 / EN 61000-3-4:
Limits for harmonic current
emissions (equipment input
current > 16 A per phase).
• IEC 61000-3-5 / EN 61000-3-5:
Limitation of voltage fluctuations
and flicker.
• EN 50091-2: UPS Electromagnetic compatibility.
• IEC 60947: Low-voltage
switchgear and controlgear.
• EN 50160: Voltage characteristics
of public networks.
• IEC 60950-1 / EN 60950-1:
Information technology
equipment - Safety - Part 1:
General requirements.
• IEEE 519: Recommended
practices and requirements for
harmonic control in electrical
power systems.
• IEC 62040-1/ EN 62040-1:
Uninterruptible power systems
(UPS) - Part 1: General and safety
requirements for UPS.
• EMC Directive 2004/108/EC: For
equipment liable to cause or be
affected by electromagnetic
disturbances.
• IEC 62040-2/ EN 62040-2:
Uninterruptible power systems
(UPS) - Part 2: Electromagnetic
compatibility requirements.
• European LV directive:
2006/95/EC,
• IEC 62040-3 / EN 1000-3:
Uninterruptible power systems
(UPS) - Part 3: Method of
specifying the test and
performance requirements.
• ISO 3746: Determination of
sound power levels of noise
sources.
• ISO 7779 / EN 27779:
Measurement of airborne noise
emitted by computer and
business equipment.
• IEC 61000-2-2 / EN 610002-2:
Compatibility levels for lowfrequency conducted disturbances
and signalling in public lowvoltage power supply systems.
• IEC 61000-3-2 / EN 61000-3-2:
Limits for harmonic current
emissions (equipment input
current ≤ 16 A per phase).
Page 186
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