Designing Power Quality Systems for Mission Critical Applications

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Designing Power Quality Systems for

Mission Critical Applications

Michael Mallia,

General Manager, Power Quality

© 2014 Eaton Corporation. All rights reserved .

Agenda

• Understanding the key technology changes that are placing increasing demands on power infrastructure

• UPS Technology – Design and application techniques:

• 1: Designing for Performance

• 2: Designing for Efficiency

• 3: Designing for Capacity, Redundancy & Scalability

• 4: Designing for Reliability

• 5: Designing for Safety

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Section 1: Designing for Performance

Understanding the key technology changes that are placing increasing demands on power infrastructure

• Power quality application requirements and constraints

• Input distortion, power factor, crest factor

• What the customer wants

• Prioritising the top 5 typical customer requirements


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This image cannot currently be displayed.

Typical Power Quality Problems

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5

Events

Per

Year

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3

Understanding the type & frequency of power problems, plus the requirements of your loads may enable an increase in uptime and significant savings in energy costs

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Average of 50

Sags/Year

1

20-

50

10-

20

6-1

0 5

4

3

Duration ( cycles)

2

1

0 to1

0

30 to

40

60 to

70

Voltage (% of

Nominal)


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4

Harmonics of a Data Centre

Harmonic currents cause problems:

– Additional losses in supplying circuit

– Heat at transformer and generator windings

– Voltage distortion

– Neutral overload and N-PE voltage

– Malfunction of protective devices

Load current

– THD 70%

– p.f. 0.65 lag to 0.8 lead

?

N

– Errors in measurements

– Resonance in compensation capacitors

– Disturbances and malfunctions in IT & telecom equipment and networks


Load neutral current

(150Hz)

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The IT “Power Supply”

Common Theme:

Universal input

Power factor corrected (PFC)


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IT Equipment Power Requirements

• Modern IT Loads can handle:

• A Wide Range of Voltage

• Short Duration outages

• Common Mode Noise


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The UPS as an “interface”

Important Selection/Design Criteria:

• Rectifier design – choose most suitable rectifier technology to provide lowest impact on mains with highest reliability and efficiency

• Inverter design – Able to handle non-linear loads with leading power factor

• Cabling to suit worst case conditions – i.e. Double

Sized Neutrals if required

• Efficiency!

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Where does that bring us?

• Need to protect against the variety of power quality problems that are seen today……. although the key need may just be power availability

• How do you prepare for those challenges?

• Top 5 considerations that must be prioritised for any size critical power application:

1. Reliability

2. Efficiency

3. Flexibility/Scalability

4. Manageability

5. Serviceability

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Section 2: Designing for Efficiency

• UPS Technology – Design and application techniques

• UPS Topology (VFI, VI, VFD)

• Designing for Efficiency

• Transformer-Free, Variable Module Management, ECO/Energy

Saver Modes


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UPS topologies

IEC 62040-3 & ENV 500091-3

Passive standby

Load

Line interactive incl. “Delta conversion”

Load

Double conversion

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Load


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UPS topologies

Double Conversion with various modes:

Maximum Power Control (VFI)

Maximum Energy Saving (VFD)

High Efficiency & Power Conditioning (VI)


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Defining a “Green” UPS

Initial cost of ownership is not so relevant.

Customers must take into account…..

• Savings in delivery costs

• Savings in real estate requirements

• Savings in installation and cabling

• Savings in operating costs

• Savings in life-cycle costs

• Savings in maintenance costs

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Transformer-free technology

• Low frequency & analogue control designs require transformers

• Advanced high frequency digitally controlled IGBT designs don’t!


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Transformer-free: The result

250kW Transformerfree magnetics assembly

250kW Transformerbased magnetics assembly

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Transformer-free benefits

Higher

Efficiency at all loads

Better Input

Power

Performance

Better Output

Power

Performance

TRANSFORMER-FREE UPS

Smaller

Footprint &

Weight

Lower Total

Cost of

Ownership

The EATON

Advantages


Lowest TCO

Highest Efficiency

High Performance

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Challenge: Increasing efficiency in real life applications

F

• In double conversion mode, the efficiency of any UPS varies depending on the % of load

T

• Highest efficiency when close to full capacity

T

• UPS systems rarely loaded at full capacity

• This is fact in redundant systems

C

• How to maximise efficiency potential of

UPS systems with lighter loads

SOLUTIONS:

1.

Ensure higher “real life” base efficiency

2.

Module Management

3.

Energy Saver Modes


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Module Management Principles

• Example With Same Load Applied To Different Multi-UPS Configurations

* * * * * *

Thanks to power converter modularity, Module

Management Automatically optimises efficiency at UPM level Concentrate the load on certain UPM’s to maximise overall system efficiency!


* In “ready state,” the UPM rectifies DC-link, generates logic level PWM signals, and filters EMI and lightning spikes.

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VMMS Efficiency

VMMS allows to shift to higher efficiency curves (according to up to N+0 VMMS

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96

94

92

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9395 UPS Efficiency

Eaton 9395 825kVA UPS



Typical Operations Range

Load kVA

9395 275kVA

9395 550kVA Notes:

9395 825kVA

- Scaled drawing

9395 1100kVA

- VMMS and N+0 curves using VMMS default max UPM

9395 VMMS N+0

% load level @ 80% (*)

.

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Module Management Example:

825kVA Units in Dual Corded Load with A & B feeds

“A”

Example with 440kVA load

(A 220kVA + B 220kVA)

UPS Configuration

Efficiency

@ 440kVA load

Without VMMS

91.2%

Single / Dual Source

“B”

Data Center with Dual

Corded Servers

VMMS on N+1 Redundancy VMMS on N+0 Redundancy

92.8% 94.3%

UPS

Energy Savings

Additional Benefits

& Comments



Used as reference for savings calculation

Industry-leading

UPS efficiency in double conversion

56 MWh / year

($6160 @ 11¢ / kWhr)

108 MWh / year

($11,880 @ 11¢ / kWhr)

 Additional energy savings from reduced cooling in VMMS

(typically +30-40% to UPS energy savings)

 UPM’s in VMMS ready state available for redundancy

A Feed

220kVA

A Feed

220kVA

A Feed

220kVA

B Feed

220kVA


B Feed

220kVA

B Feed

220kVA

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Energy Saving / “ECO” Modes






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Is a double conversion UPS really needed?

• Line Interactive UPS ideal for SMB applications

• On Line UPS provide constant voltage regulation, but may unnecessarily waste energy

• On Line UPS with Energy Saver or “ECO” modes work in bypass mode when mains is suitable, and in Double Conversion mode when line voltage is close to the limits of ITIC Curve

• Eaton’s transition time between Normal and Double Conversion mode should be ~2-4 ms under all line/load conditions – up to 2x faster than any Mission Critical STS

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ECO/Energy Saver System saves even more at lower loadings

Maximum Efficiency Tracking

 ESS Efficiency - 99% across the complete operating range



85% reduction in losses compared to legacy transformer-based UPS

 Continuous power tracking and proprietary DSP algorithms combined with transformer free design topology ensures critical loads are always protected

Additional Benefits:



Increased component life: Fans, capacitors etc.

 Reduced audible & electrical noise


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ECO Mode – precautions:

• Standard ECO modes can be risky….

• Load mode may exposed to raw utility

• Detection and transfer times are long

• ….And most don’t work with parallel systems

• Critical loads require fast transfer times

• >10ms is a problem

• Storm Detection modes enhance security and reliability

• Advanced Fault Detection to prevent unnecessary transfers

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Utility Fault Transitions - Three Phase

Outage

Source Outage

ESS Output Response 1.2 ms


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Utility Fault Transitions - Single Phase

Outage

Source Outage

ESS Output Response 1 ms


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Energy Saver System

• ESS Response Example – 100% Outage


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Energy Saving / “ECO” Modes






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ECO with Harmonic Reduction System (VI)

Challenge: When operating in ESS or ECO modes, load harmonic currents are placed directly on mains supply

Solution:

U

L1

U

L1

I

I

L1

L1

• ESS + Harmonic Reduction System (HRS) utilises converters for active harmonic correction

• System provides 275kVAR of correction capacity

• Maintains up to 98.5% efficiency whilst providing power conditioning

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U

L1

I

L1

29 © 2014 Eaton Corporation. All rights reserved .

Section 3: Designing for Capacity,

Redundancy & Scalability


• Designing for Capacity & Redundancy

• Hot Standby, distributed parallel, centralised parallel, Hot Sync


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Increasing reliability

• Hardware additions to increase reliability

• Multi – corded (power supply) servers

• Redundant UPS Systems

• Dual power path power distribution (A & B design)

• Dual UPS systems (2N)

• Source Transfer Switches

• Surge Protection Devices

(SPD)

• Maintenance Bypass Switches


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Medium/Large Data centre UPS, single/dual supply loads

“Redundant Central UPS”

• Complete power redundancy – each module has integral static switch and separate battery

• Scalable by adding complete UPS/Battery modules to each System

• Static Transfer Switches provide redundancy for single source loads


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Back to Basics: UPS System Configurations

Basic On Line configurations:

• Reverse Transfer

• Isolated Redundant (Hot Standby)

• Parallel Redundant

• Parallel Capacity


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Reverse Transfer

One unit supplies reliable power to the critical load . . .

Utility

)

(


Battery

34

Critical

Load

34

Reverse Transfer

One unit supplies reliable power to the critical load . . .

)

(

Utility

Critical

Load

Battery

. . . and if the unit fails, the load is supported by the bypass.

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Isolated Redundant (Hot Standby)

Two units are used. The output of the Standby UPS feeds the bypass of the Primary UPS.

Utility

)

(

Standby

UPS

Battery

Utility

)

(

Battery


Critical

Primary

UPS

Load

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Isolated Redundant (Hot Standby)

Two units are used. The output of the Standby UPS feeds the bypass of the Primary UPS.

Utility

)

(

Standby

UPS

Battery

Utility

)

(

Primary

UPS

Critical

Load

Battery

If the Primary UPS is unable to support the critical load it transfers the load to the Standby UPS.

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Parallel Redundant System

Two or more units are paralleled together . . .

Utility Critical

Load

Battery

Note: Common Battery = false economy!

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Paralleling for capacity/redundancy

Complete System

MAINS

System Parallel Module

CRITICAL LOAD

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3+1 Redundancy or 4* Capacity

~

=

=

~

~

=

=

~

~

=

=

~

If total system is redundant (N+1), failure of any one system does not affect critical bus

If system is full capacity, failure of any one system forces all units to static bypass


~

=

=

~

I

I+II

II

LOAD

40

MAINS

40

Installation rule

Total length

1A + 1B = 2A + 2B =

3A + 3B = 4A + 4B

Maximum variance

10% combined input and output wire lengths

Requirement

... to ensure approximately equal current sharing when in static bypass mode.

Bypass inputs to UPMs

1A

2A

3A

4A

UPM 1

Battery

UPM 2

Battery

UPM 3

Battery

UPM 4

Battery

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3B

4B

1B

Outputs from UPMs

2B

41 © 2014 Eaton Corporation. All rights reserved .

Increasing capacity & reliability: N+1

Systems

30 kVA 30 kVA 30 kVA 30 kVA

Any single UPS can be taken off line for maintenance or repair

Systems that don’t rely on common control avoid single points of failure


Load

90 kVA total

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Reliability – Modularity Vs Centralisation

• What’s more reliable………………..

• Modular or Unitary UPS?

• Distributed or Common battery?

• Distributed or Centralised Parallel UPS?

• Is Scalability required?


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Unitary Vs Modular

• Single Static Bypass

• Higher MTBF

• Lower Cost

• Scalable & Redundant

• Distributed Logic

• Distributed Static Bypass

• Minimal Redundancy

• Fixed Rating

• Distributed Batteries

• Higher Cost

• Lower MTBF


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Unitary Vs Modular

Modular systems are an IT Manager’s dream, but an engineer’s problem!

Multiple systems in parallel become increasingly harder to manage with large kVA ratings and more than 6 modules in parallel

Issues: Common Controls, Common Batteries, Multiple Static Bypasses

Plug & Play??????


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Centralised Vs Distributed Large UPS

Distributed Parallel

Static Bypass Switch within each

UPS module

Centralised Parallel

Single Static Bypass Switch in a separate cabinet

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Distributed Parallel

 Redundancy & Capacity – Add as you grow



Lower Initial Cost

 Can provide more fault current – if all switches operate simultaneously



More components in Parallel (lower

MTBF)

 Impedance must be matched for current sharing

 Shorted SCR in one UPS affects whole system (unless back-feed protected)

 Difficult to manage with more than 4 large UPS



Initial fault clearing capacity may not be sufficient


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Centralised Parallel

 Single Static Bypass eliminates current sharing issues

 Full fault clearing capacity available from day 1

 Can enable paralleling of unlike ratings

 Easy to add UPS modules

 Simplifies upstream switchgear – up to 5000A rating

 No static switch redundancy

 Larger footprint

 Higher cost

 Higher initial capital investment


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Section 4:


• Designing for Reliability

• Supply redundancy & Maintenance Bypass

• Batteries, Controls design, Serviceability,

Maintenance, Cooling


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Dual feed input - Supply Redundancy

• Dual feed input means that UPS can be installed with separate input cables for rectifier and bypass

• Should the upstream fusing clear, for example in rectifier input short circuit, dual feed allows UPS to go to bypass, single feed will drop the load once batteries are drained

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External Bypass Switches

“Wraparound” Bypass

“Tail End” Bypass

Interlocking is essential to avoid disasters!

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Batteries need care!

…and no battery means NO UPS!

Battery has limited life span !

It’s a crucial component which maybe is seldom needed, but you just have to be able to count on it!

... cost a lot of money, disposed batteries are toxic waste !

is very sensitive to environmental factors, temperature is crucial


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Battery Selection – brief discussion

• Types:

• Valve Regulated Lead Acid

• Flooded Lead Acid

• Nickel Cadmium

• Life Expectancy:

• Design Life & end of life capacity

• Annual degradation

• Regular Maintenance:

- Post Commissioning checks

- Leaks

- Connection integrity

- Equalisation

• Degradation Factors:

• Ambient Temperature

• Ripple Current

• Multiple cycles

• Under charging

• Over charging

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Traditional battery charging

• Positive electrode corrosion with float charging

– + Float charging current

- is a chemical reaction between the electrodes and electrolyte

O

2 e -

-

-

-

-

Pb

-

-

-

O

2

H +

O

2

H

2

SO

4 e -

+

+

+

+

+

+

PbO

2

The main sealed battery aging factor is the positive electrode corrosion attack caused by the float charging current

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Control system design

Interface board

Logic board

Power Module

(Rectifier 1-2)

Power Module

(Inverter 1-2)

Power Supply #1

Power Supply #2


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Prioritised Redundant cooling

• Cool air is drawn in via the front door

• Warm air is exhausted out the top of the unit

• Fan tray assembly blows cool intake air up through the power modules

• Hot swappable fans with fan failure detection

• Fan redundancy


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Other reliability measures……

• “You can’t manage what you don’t measure”

• Monitoring UPS systems helps to avoid disasters

(overload, unbalancing, battery health etc.)

• Managing energy consumption helps to make and keep efficiency gains and also increase reliability

• Measure the whole powertrain – from incoming utility to sockets in the rack!

• Regular maintenance!!!!!!!


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Section 5: Designing for Safety


• Designing for Safety

• Back-feed protection


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Back-feeding – what is it?

• Back-feeding of power means that the power transfer within an electrical device is towards the input terminals

• This creates a safety hazard since, as a result, input terminals may be on power even if they have been disconnected from the mains supply.

• Back-feed protection is implemented to shield the bypass line from thyristor short circuit failure in the static switch.

• Back-feed protection is implemented to prevent leakage current via the static switch snubbers and SCRs from creating upstream voltages when mains is not present

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Backfeed protection requirements

• The international standard IEC 62040-1 and

AS62040.1.1:2003 require that the UPS device shall prevent all hazardous voltage and energy from being transferred to the UPS input terminals after the input power has been interrupted

• The standards allows for two alternative implementations of backfeed protection

• installing an internal backfeed isolation device within the UPS

• installing an external backfeed isolation device with only backfeed detection implemented within the UPS

• Note: (AS 62040.1.1-2003 Uninterruptible power systems (UPS) — General and safety requirements for UPS used in operator access areas, section 5.1.4 Back feed protection.)

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Backfeed protection requirements

The Australian Standard AS62040.1.1:2003 states the following:

“For permanently connected UPS without internal automatic backfeed isolation (see

5.1.4), the instructions shall require the fitting by the user of a warning label on all primary power isolators installed remote from the UPS area, to warn electrical maintenance personnel that the circuit feeds a UPS.

The warning label shall carry the following wording or equivalent.

ISOLATE UNINTERRUPTIBLE POWER SUPPLY (UPS)

BEFORE WORKING ON THIS CIRCUIT”

The practical implications are that all isolators in the chain feeding the UPS must be so identified if the UPS does not have back-feed protection.

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Backfeed protection in a single UPS system

• Back-feed contactor is situated in the bypass line


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Back-feed protection in a single UPS system

• The internal back-feed contactor is used to automatically protect against fault situations in the static switch

• If a thyristor suffers a short-circuit failure

• The inverter output to the bypass input terminal become shorted

• A back-feed contactor prevents the back-feeding of power

• The UPS can stay in double-conversion mode even in the case of a static switch failure

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Backfeed protection in a parallel UPS system

• If a fault in one of the static switches were to occur, inverters would start feeding current back to the input transformer

• Back-feed contactor opens

• The static bypass lines have redundancy

• Failure of one static bypass does not prevent the other bypass lines from operating

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Backfeed protection in a centralised bypass system

• In a centralised bypass topology the system bypass module (SBM) provides a common bypass line for the paralleled UPS modules


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Problems with external backfeed contactors

• External backfeed contactor means:

• Space needs to be reserved in the input switchgear for the

UPS backfeed isolation device

• Often only one backfeed contactor is installed per entire parallel UPS system

• Failure in one of the static switches results in the loss of all the static bypass lines connected to the common backfeed contactor

• If the UPS doesn’t have a circuit for controlling an external contactor, then the only functionality that you can have is to protect against feedback through SCRs and snubbers during mains failure

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Questions


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Designing Power Quality Systems for Mission Critical Applications

Basic On Line configurations:

• What’s more reliable………………..

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Designing Power Quality Systems for Mission Critical Applications

Basic On Line configurations:

• What’s more reliable………………..

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