ANSI/IEEE Std 995-1987
IEEE Recommended Practice for Efficiency
Determination of Alternating-Current
Adjustable-Speed Drives
Part I-Load
Commutated Inverter Synchronous Motor Drives
Published by The Institute of Electrical and Electronics Engineers, Inc 345 East 47th Street, New York, N Y 10017, USA
March 21. 1988
SHIIBIO
ANSI / IEEE
Std 995-1987
An American National Standard
IEEE Recommended Practice for
Efficiency Determination of Alternating-Current
Adjustable-Speed Drives
Part I
Load Commutated Inverter Synchronous Motor Drives
Sponsor
Industrial Drives Committee of the
IEEE Industry Applications Society
Approved March 12, 1987
IEEE Standards Board
Approved September 11, 1987
American National Standards Institute
@
Copyright 1988 by
The Institute of Electrical and Electronics Engineers, Inc
345 East 47th Street, New York, NY 10017, USA
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Foreword
(This Foreword is not a part of ANSI/IEEE Std 995-1987, IEEE Recommended Practice for Efficiency Determination of
Alternating-Current Adjustable-Speed Drives)
This recommended practice was prepared by the Industrial Drives Committee of the IEEE Industry
Applications Society. Working Group P995 was established in 1983 to define a consistent method for
determining and specifying the efficiency of large adjustable-speed alternating-current motordrive
systems.
The working group was divided into two groups designated P995.1 and P995.2 with assigned
responsibilities for load commutated inverter synchronous motor drives and self-commutated inverter
induction motor drives, respectively. The membership of the working group that prepared this
recommended practice was as follows:
Herbert W. Weiss, Chairman
Nirmal K. Ghai
Leonard P. Gripp
Gunter Hausen
Thomas A. Higgins, J r
James L. Kirtley, J r
Charles P. Lemone
Edward F. Munk
Donald W. Novotny
James Oliver
Claude L. Philibert
Dana Ralston
Mohammad Safiuddin
John Yost
The following persons were on the balloting committee that approved this recommended practice
for submission to the IEEE Standards Board:
Albert0 Abbondanti
John P. C. Allen
Thomas H. Barton
Jesse A. Batten
Bimal K. Bose
William D. Brand
Dennis H. Braun
Frederick C. Brockhurst
Jimmie J . Cathey
Edward P. Cornel1
C. J . Cowie
A. Malcom Curry
Shashi B. Dewan
Paul C. Donatelli
Richard F. Dugan
Ben Esar
Donald Galler
David C. Hamilton
Gunter Hausen
Richard G. Hoft
S. S. Hubli
Peter Huetter
Linos J . Jacovides
Thomas M. Jahns
Atsuo Kawamura
Yuri Khersonsky
Daniel Kirschen
Frank N. Klein
Alexander Kusko
Thomas S. Latos
James F. Lindsay
Thomas A. Lip0
Robert D. Lorenz
James Lousier
Robert B. Maag
Walter A. Maslowski
George MacMunn
Ian M. MacDonald
Paul McNally
H. Paul Meisel
Richard W. Miller
T. J. E. Miller
Balarama V. Murty
Syed A. Nasar
Thomas W. Nehl
N. E. Nilsson
Donald W. Novotny
Guy Oliver
Steven Peak
Erland K. Persson
Allan B. Plunkett
Thomas H. Putman
M.A. Rahman
M. H. Rashid
Thomas Rehm
Harold Romanowitz
Mohammed Safiuddin
Lee A. Schlabach
Paresh C. Sen
Frank E. Simo
Jon W. Simons
Gordon R. Slemon
Victor R. Stefanovic
Loren F. Stringer
George H. Studtmann
K. Reed Thompson
Peter J. Tsivitse
Henry W. Wearsch
Herbert W. Weiss
Francis M. Wells
George Younkin
When the IEEE Standards Board approved this standard on March 12, 1987, it had the following
membership:
Donald C. Fleckenstein, Chairman
Marco W. Migliaro, Vice Chairman
Sava I. Sherr, Secretary
James H. Beall
Dennis Bodson
Marshall L. Cain
James M. Daly
Stephen R. Dillon
Eugene P. Fogarty
Jay Forster
Kenneth D. Hendrix
Irvin N. Howell
Member emeritus
Leslie R. Kerr
Jack Kinn
Irving Kolodny
Joseph L. Koepfinger'
Edward Lohse
John May
Lawrence V. McCall
L. Bruce McClung
Donald T. Michael*
L. John Rankine
John P. Riganati
Gary S. Robinson
Frank L. Rose
Robert E. Rountree
William R. Tackaberry
William B. Wilkens
Helen M. Wood
Contents
SECTION
PAGE
1.
Scope ..................................................................................................
5
2.
Reference .............................................................................................
5
3.
Definitions ............................................................................................
3.1 Basic Terms ...................................................................................
3.2
Performance Characteristics ................................................................
3.3
Letter Symbols................................................................................
6
6
8
9
4.
System Description ..................................................................................
4.1
Line-Side Interface ...........................................................................
4.2
Power Converter ..............................................................................
4.3
DC Link Inductor ............................................................................
4.4
Synchronous Machine .......................................................................
4.5
Service Conditions ............................................................................
9
9
10
10
10
11
5.
Efficiency Determination ...........................................................................
5.1 Methods for Determination of Losses ......................................................
5.2
System Operating Parameters ..............................................................
Determination of Losses .....................................................................
5.3
5.4
Recording of Losses ..........................................................................
Determination of Efficiency .................................................................
5.5
12
13
13
13
20
20
FIGURES
Drive System Configuration ..................................................................
Converter Circuit Elements ..................................................................
Waveform Definitions .........................................................................
Transformer Circuits ..........................................................................
Typical Power Converter ......................................................................
Efficiency Determination .....................................................................
Dual Winding Machine Test ..................................................................
Converter DC Circuit ..........................................................................
5
7
8
10
11
12
14
18
Table 1 Reference Temperature for Load Losses ....................................................
Table 2 Tabulation of Losses ............................................................................
12
19
Fig 1
Fig 2
Fig 3
Fig 4
Fig 5
Fig 6
Fig 7
Fig 8
TABLES
APPENDIXES
Appendix A
Appendix B
Explanation of Practices and Procedures ............................................
Example Efficiency Determination ...................................................
21
29
APPENDIX TABLES
Table B1
Table B2
Tabulation of Losses .......................................................................
Tabulation of Losses .......................................................................
29
30
An American National Standard
IEEE Recommended Practice for
Efficiency Determination of Alternating-Current
Adjustable-Speed Drives
Part I
Load Commutated Inverter Synchronous Motor Drives
1. Scope
included herein to account for operating characteristics of the adjustable-speed drive systems.
This recommended practice proposes a
method for determining the efficiency of large,
adjustable-speed ac motor-drive systems consisting of a load commutated inverter and a synchronous machine, in which a dc-linked
converter is connected between the line and the
load.
This recommended practice is directed primarily to high-capacity systems (exceeding
1000 hp) and drive systems, which normally
include equipments such as transformers,
reactors, thyristor power converters, and synchronous machines. The drive system configurations, which are covered specifically in this
recommended practice, are shown in Fig 1.
The method recommends that the existing test
standards for the system equipments be used as
reference, supplemented by test and calculations
2. References
The standards listed below cover the definition of losses and efficiency, and the test methods for the equipments that are part of the
adjustable-speed drive system. When approved
revisions of the reference standards are issued,
the revision should be used. This recommended
practice should be used in conjunction with the
following publications:
[l]ANSI C50.10-1977, American National Standard General Requirements for Synchronous
Machines.'
ANSI publications are available from the Sales Department, American National Standards Institute, 1430 Broadway, New York, NY 10018.
Fig 1
System Configurations (a) Single Channel System
(b)Dual Channel Parallel System ( c ) Dual Channel Series System
la)
(bl
1
I
I
I
POWER SOURCE
LINE SIDE
INTERFACE
LINE SIDE CONVERTER
DC LINK INDUCTOR
LOAD SIDE CONVERTER
SYNCHRONOUS MACHINE
FORM C
CONVERl
5
ANSI / IEEE
Std 995-1987
AC ADJUSTABLE-SPEED DRIVES
sion, comprising one or more electronic switching devices and any associated components, such
as transformers, filters, commutation aids, controls, and auxiliaries.
[2] ANSI (37.16-1958 (R1971), American National Standard Requirements, Terminology,
and Test Code for Current-Limiting Reactors.
[3] ANSI / IEEE C57.12.00-1987, IEEE Standard
General Requirements for Liquid-Immersed Distribution, Power and Regulating Transformew2
direct-current linked alternating-current converter. A converter comprising a
rectifier and an inverter, with a n intermediate dc link.
[4] ANSI / IEEE C57.12.01-1979, IEEE Standard
General Requirements for Dry-Type Distribution and Power Transformers.
NOTES: (1)This definition is intended to include only
those circuits in which the dc link is readily identified
or explicit, and not those circuits having an implicit
dc link but no single pair of conductors that can be
identified as the dc link.
(2) For the purpose of this recommended practice the rectifier and inverter are form C converter.
[5] ANSI / IEEE C57.12.90-1987, IEEE Standard
Test Code for Liquid-Immersed Distribution,
Power, and Regulating Transformers and Guide
for Short-circuit Testing of Distribution and
Power Transformers.
externally commutated converter.A converter in which the commutating voltages
are supplied by the ac supply lines, the ac
load, or some other ac source outside the
converter.
[6] ANSI / IEEE (37.12.91-1979, IEEE Standard
Test Code for Dry-Type Distribution and Power
Transformers.
[7] ANSI / IEEE C57.110-1986, IEEE Recommended Practice for Establishing Transformer
Capability when Supplying Nonsinusoidal Load
Currents.
NOTE: For the purpose of this recommended practice,
the term converter should be used.
form C converter. A single converter unit
in which the direct current can flow in one
direction only and which is capable of inverting energy from the load to the ac supPly.
[8] ANSI / IEEE Std 100-1984, IEEE Standard
Dictionary of Electrical and Electronic Terms.
[9] ANSIIIEEE Std 115-1983, IEEE Guide: Test
Procedures for Synchronous Machines.
inverter. A converter for conversion from
[lo] ANSI / IEEE Std 444-1973, IEEE Standard
Practices and Requirements for Thyristor Converters for Motor Drives Part I-Converters for
DC Motor Armature Supplies.
dc to ac.
NOTE: For the purpose of this recommended practice
the loud side converter normally operates as an inverter.
[ l l ] ANSI / NEMA MG1-1978, Standards Publication for Motors and Generators.
load commutatedinverter. A converter in
which the commutation voltages are supplied by the ac load.
[12] FISCHER, J.D., So You Don’t Think You
Have a Harmonic Problem. Conference Record,
1979, IEEE Industry and Applications Society
Annual Meeting (Power Systems Protection
Committee), Table IV, 41D.
NOTE: For the purpose of this recommended practice
the ac load is a synchronous machine operating as a
motor.
rectifier. A converter for conversion from
ac to dc.
NOTE: For the purpose of this recommended practice
the line-side converter normally operates as a rectifier.
3. Definitions
3.1 Basic Terms
3.1.1 converter or converter equipment.
3.1.2 convertor circuit elements (see Fig 2)
An operative unit for electronic power conver-
ac filter. Resistor-capacitor circuits connected in three-phase wye or delta on the
ac terminals of a converter.
ANSI / IEEE publications are available from IEEE service Center, 445 Hoes Lane, PO Box 1331,Piscataway, NJ
08855-1331,or from the Sales Department, American National Standards Institute, 1430 Broadway, New York, NY
10018.
converter switching element. A part of
6
ANSI / IEEE
Std 995-1987
LOAD COMMUTATED INVERTER
DC LINK
IN DUCT0 R
LINESIDE
LOADSIDE
LINE SIDE
TERMINALS
Fig 2
Converter Circuit Elements
the converter circuit, bounded by two principal terminals, containing one or more
semiconductor devices having the property
of controllable or noncontrollable conduction in a t least one direction.
principal terminal. A terminal (of a device
or circuit element) through which passes the
current transmitting the power that is controlled by the device or circuit element. The
term is used for distinction from control terminals, monitoring signal terminals, etc.
dc filter. A resistor-capacitor circuit connected between the positive and negative
terminals of the dc link.
NOTE: Examples of principal terminals are the anode
and cathode of thyristor or diode devices, the collector
and emitter of bipolar transistor devices, and the
source and drain of fieldeffect transistor devices.
equalizing resistor. The resistor connected
across the circuit element to equalize the off
state voltage across elements that are connected in series.
snubber. An auxiliary circuit element or
combination of elements employed to modify the transient voltage or current of a
semiconductor device during switching.
principal branch (main branch). A
branch involved in the major transfer of
energy from one side of the converter to the
other.
(1) shunt snubber. Circuit elements,
usually including a capacitor and a resistor connected in shunt with a switching
device to limit the rate of rise of voltage
7
ANSI / IEEE
Std 995-1987
AC ADJUSTABLE-SPEED DRIVES
3.1.3 Circuit Properties
or the peak voltage across the device (or
both) when switching from a conducting
to a blocking state or when subjected to
a n external voltage transient.
(2) series snubber. Circuit elements,
usually including an inductor, connected
in series with a switching device to limit
the rate of rise or fall of current through
the device when switching on or off, respectively.
commutation.The transfer of current from
one converter switching branch to another.
commutating voltage. The voltage that
causes the current to commutate from one
switching branch to another.
NOTE: In an externally commutated converter, the
commutating voltage is supplied by an ac source
outside the converter.
switching branch. A part of the circuit,
including at least one switching element,
Performance Characteristics
bounded by two principal terminals.
direct current. The time average value of
NOTE: A switching branch may include one or more
simultaneously conducting converter switching elements connected together, commutating reactor windings, and other devices intended to protect the
semiconductor devices or to ensure their proper function, such as voltage and current dividers, and snubbers. In the simplest case, a switching branch may
consist of only the switching element, which may be a
single semiconductor device. The adjective switching
may be omitted when the context of converter circuits
is clear.
the current in the dc link.
line-side converter alternating current.
The magnitude of the current expressed in
amperes of the rms value of current at the
output terminals of the line-side interface
and the input terminals of line-side converter.
Fig 3
Waveform Definitions
f-
PHASE VOLTAGE
+-%%
PHASE CURRENT
4 0 L P H A S O R ANGLE
LOAD-SIDE CONVERTER PHASE
VOLTAGE (COMMUTATING VOLTAGE)
FUNDAMENTAL
A T SYNCHRONOUS
MACHINE
/ /
FUNDAMENTAL
PHASE CURRENT
MACHINE
CURRENT
8
ANSI / IEEE
Std 995-1987
LOAD COMMUTATED INVERTER
line-side converter ac voltage. The rms
power-frequency voltage from line to line at
the ac terminals of the line-side converter.
NOTE: This voltage is the same as the rated system
voltage times the turns ratio of the input interface
equipment.
load-side converter ac voltage. The rms
value of the power-frequency sinusoidal envelope of voltage at the ac terminals of the
load-side converter (Fig 3). This is the commutating voltage of the load-side converter.
NOTE. This is the voltage that appears at the terminals
of the synchronous machine and is not the rms fundamental sine-wave voltage of the machine.
machine current. The rms magnitude of
the fundamental sinusoidal current at the
terminals of the machine.
machine voltage. The rms value of the fundamental sinusoidal voltage at the terminals of the machine.
phasor power factor. The power factor of
the synchronous machine defined by the
cosine of the phasor angle between the fundamental sinusoidal phase voltage and the
fundamental sinusoidal phase current.
NOTE: This is not the angle between the load converter
commutating voltage and the machine current (See
Fig 3).
rated system frequency. The frequency
expressed in hertz, of the power system alternating voltage.
rated system voltage. The rms power-frequency voltage from line to line that has
been designated as the basis for the system
rating. The line-side interface equipments
may or may not have the same rated voltage.
3.3 Letter Symbols
Ed = direct voltage, average
E = rms ac fundamental line-line
voltage at the synchronous machine
E , = rms ac fundamental phase voltage a t the synchronous machine
E L = rms ac system line-line voltage
I d = direct current, average
I,
rms fundamental line current a t
the synchronous machine armature
I L = rms ac line current at line-side
converter
P = active (real) power, average
FPP= phasor power factor
4 = phasor power-factor angle
p = commutation overlap angle expressed in degrees
a = delay angle, expressed in degrees
p = pulse number of a commutating
group
=
I ~ =
RI ~ R
= open circuit core loss
SL = stray loss
PRS = armature (stator) I ~ loss
R
12RR = field (rotor) 12R loss
P h = harmonic losses due to nonsinusoidal voltage and current
KWRL = test and drive motor running light
losses
I'RDMC = drive motor 12Rloss correction
KWDM = drive motor input power
KWEX = exciter input power
OCCL
4. System Description
The drive system consists of the equipments
that are utilized to convert electric energy from
the plant bus to mechanical energy in the form
of shaft speed and torque. The typical system
configurations are shown in Fig 1.
For the purpose of this recommended practice
the drive system efficiency is determined by the
losses associated with the equipments listed below and do not include the losses associated with
interconnecting cables or power switchgear
equipment.
NOTE: The interconnecting cable and power switchgear
equipment losses may be included in the efficiency determination if so specified.
4.1 Line-Side Interface. The line-side interface
is the equipment that is connected between the
power source and the power converter. This
equipment serves to insert impedance between
the converter and the power source, or to establish electrical isolation between the converter
system and the power source, or to transform
the voltage from the power source level to converter system level, or a combination of these
ANSI / IEEE
Std 995-1987
AC ADJUSTABLE-SPEED DRIVES
wye) for use with thyristor converter circuit
number 31 as shown in Fig 4 (see ANSI / IEEE
Std 444-1973 [lo], Fig 6)
(3) Line reactors iron or air core
The losses for the line-side interface equipment should include no-load and load losses. In
addition, the losses for auxiliary devices that are
required for the equipment to perform its function should be included in the equipment loss.
These auxiliary devices might be fans or pumps
for the equipment cooling system.
CIRCUIT
NUMBER 23
DELTA-WYE, THREE-PHASE
BRIDGE (DOUBLE-WAY). SIX-PULSE
4.2 Power Converter. The power converter
CIRCUIT
NUMBER 25
equipment includes the power and control electronics that convert and condition the power
from the line-side interface to the power that is
applied to the synchronous machine to achieve
adjustable speed at the machine shaft.
The power converter is a dc-linked ac converter consisting of a line-side converter to convert fixed frequency ac power to dc power and
a load-side converter to invert dc power to adjustable frequency ac power for an adjustable
speed synchronous machine. The control electronics include the gating circuits for the power
converters, the protective functions and the
drive system logic and regulating functions. The
excitation control for the synchronous machine
is also included in the control electronics,
whether ac or dc. Any auxiliary devices that may
be required by the power converter to perform
its function should be included within its scope.
These might be cooling fans, pumps, power supplies and UPS systems, etc. The typical power
converter configuration is shown in Fig 5.
DELTA-DELTA, THREE-PHASE
BRIDGE (DOUBLE-WAY),SIX-PULSE
CIRCUIT
NUMBER 31
DE LTA-DELTANvY E, THREE-PHASE
MULTIPLE-BRIDGE (DOUBLE-WAY),
TWELVE-PULSE
NOTE:Circuit numbers 23,25, and 31 aretakenfromANSI/
IEEE Std 444-1973 [lo].
Fig 4
Transformer Circuits
4.3 Direct-CurrentLink Inductor.This equip-
ment is connected between the line-side converter and the load-side converter and forms a
part of the dc link of the power converter.
The losses for this equipment are those that
are incident to the carrying of current. In addition, losses of auxiliary devices required by the
equipment to perform its function should be included. These auxiliary devices might be fans or
pumps for the cooling system.
functions. The line-side interface equipment
may be one or more of the following (l), (2), (3):
(1) Isolation transformer with one primary
winding and one secondary winding for use with
thyristor converter circuit numbers 23 and 25
as shown in Fig 4 (see ANSI / IEEE Std 444-1973
[lOI3,Fig 6)
(2) Isolation transformer with one primary
winding and two secondary windings (delta and
4.4 Synchronous Machine. The synchronous
machine converts the electric power from the
power converter to mechanical power to the
driven load. The power to the machine includes
that delivered to the armature winding (or windings in the case of dual-winding machines) and
the field winding or rotating exciter.
The numbers in brackets correspond to those of the references in Section 2.
10
ANSI / IEEE
Std 995-1987
LOAD COMMUTATED INVERTER
DC LINK
INDUCTOR
LINESIDE
LOADSIDE
LINE SIDE
INTERFACE
SYNCHRONOUS
MACHINE
I
I
I
I
I
I
I
I
r-
I
I
I
I
I
I
I
I
I
I
I
COOLING
SYSTEM
LOGIC
I T (
-
AND
CONTROL
AUXILIARY
CONTROL
POWER
I
I
b
EXCITATION
CONTROL
I
I
Fig 5
Typical Power Converter
4.5.2 Reference Altitude and Ambient
Temperature. Altitude at factory site:
The losses of auxiliary devices that are required for the equipment to perform its function
should be included. These might be auxiliary
blowers for ventilation or lube pump when the
machine has a dedicated system.
Ambient Temperature
(1) 20 "C for transformers, reactors and inductors
(2) 25 "C for synchronous machines
(3) 40 "C for power conversion /control
4.5.3 Temperature Reference for Load
4.5 Service Conditions. For the purpose of this
recommended practice the determination of
equipment losses should be based on the service
conditions listed below.
4.5.1 Input Voltage. The rms power-frequency voltage applied to the primary terminals
of the line-side interface equipment should be
taken as the rated system voltage and frequency
that has been designated for the system.
Loss
(1) When the equipment is tested for winding
temperature rise at a specific load, the reference
temperature should be taken as the measured
average temperature rise (by resistance) plus the
reference ambient temperature listed in 4.5.2.
(2) When the equipment is not tested for winding temperature rise at a specific load, the ref11
ANSI / IEEE
Std 995-1987
AC ADJUSTABLE-SPEED DRIVES
Table I
Reference Temperature for Load Loss
Class of
Insulation Svstem
A
B
5. Efficiency Determination
The efficiency of the adjustable-speed drive
system should be determined from the summation of the segregated losses of the drive system
equipments that are measured or calculated, or
both, as described in these recommendations at
a specific drive operating point or points.
The efficiency of the drive system is given by
the following equation:
Reference
Temperature "C
75
95
115
130
F
H
erence temperature should be taken from
Table 1. The reference temperature should be
used for determining load losses a t all loads. If
the rated temperature rise for the equipment is
specified as that of a lower class of insulation system, the temperature for resistance correction
should be that of the lower temperature rise.
4.5.4 Temperature Reference for Bus and
Cable. The reference temperature of the current
carrying conductors should be taken as 90 "Cfor
bare bus and 75 "C for insulated bus or cable.
Efficiency (%) =
output
* 100
losses
output
+
A drive operating point is defined in terms of
(1) Shaft speed
(2) Shaft torque (or horsepower)
The procedure for the determination of the
losses is illustrated in Fig 6.
Fig 6
Efficiency Determination
OPERATING POINTS
1
I
METHODS
(5.2)
SYSTEM
OPERATING PARAMETERS
I
I
(5.1)
METHODS FOR
DETERMINATION OF LOSSES
I
I
FUNDAMENTAL
SINE-WAVE
LOSSES
5.2.1
I
1
I
I
(2)ADJUSTMENT
LOSSES
5.2.2
5.3.1.3 SYNCHRONOUS MACHINE
5.3.2.2 ISOLATION TRANSFORMER
5.3.3.2 LINE REACTOR
5.3.4(3) DC LINK INDUCTOR
5.3.4(4) DC LINK INDUCTOR
5.3.5.3 POWER CONVERTER
5.3.5.4 POWER CONVERTER
LOSSES
I
5.3.1 SYNCHRONOUS MACHINE
5.3.2 ISOLATION TRANSFORMER
5.3.3 LINE REACTOR
5.3.4 ( 1 ) (2)DC LINK INDUCTOR
5.3.5.2 (1) POWER CONVERTER
AUXILIARY
LOSSES
12
5.3.1.4 SYNCHRONOUS MACHINE
5.3.3.3 LINE REACTOR
5.3.4(4) DC LINK INDUCTOR
5.3.5.5 POWER CONVERTER
5.3.5.6 POWER CONVERTER
ANSI / IEEE
Std 995-1987
LOAD COMMUTATED INVERTER
(2) DC link inductor
5.1 Methods for Determination of Losses.
The equipment losses should be determined by
one of the following methods, which are recommended by this recommended practice.
(1) Fundamental sine-wave losses that can be
determined by test
(2) Harmonic losses that are determined by a
standard adjustment factor applied to sine-wave
losses
(3) Losses that are determined by a standard
calculation procedure
(4) Auxiliary system losses that can be determined by test are to be included in the total
equipment loss.
The recommended practices herein include
practices and procedures that are simplified to
minimize the complexity when the accuracy of
the results is not significant. When a simplified
practice or procedure is used to reduce complexity it is identified by the symbol P followed
by a numeral in the right-hand margin of the
column. The explanation of the simplified practice or procedure is presented in Appendix A.
IT
Id
= Ia
3
P2
(3) Power converter
IT
Id
= Ia
3
P2
Line-side converter a
=
c0s-l
C92j
p3
Load-side converter a
=
-cos-'
(0.95F,,)
P4
~
and
Load-side converter E L = E
p = 0 for both converters
5.3 Determination of Losses
5.3.1 Synchronous Machine. The segregated losses of a synchronous machine should
be determined using the test procedure outline
in ANSI/IEEE Std 115-1983 [9] as amended by
the additional test procedures, harmonic losses,
and auxiliary losses presented in this section.
5.3.1.1 Additions to ANSI/IEEE Std 1151983 [9]
(1) Methods of Loss Measurements. For the
purpose of this recommended practice one of the
following test methods should be used:
ANSI / IEEE 115-1983 [9], 4.2, Separate-drive
method
ANSI / IEEE 115-1983 [9], 4.3, Electric-input
method
(2) Operating Parameters for Testing. For
the purpose of this recommended practice the
machine may be tested at operating points other
than at rated speed, rated voltage, and rated
current. Therefore, rated speed, voltage, and current should be that assigned only for the test,
as defined in 5.2.1 of this recommended practice.
(3) Test Speed and Torque. The machine
should be tested at the speed at which the losses
are to be determined. For each test speed, the
following operating parameters should be defined.
(a) Speed (and frequency)
(b) Shaft torque
(c) Fundamental sine-wave voltage, E
(d) Fundamental sine-wave current, I ,
(e) Fundamental phasor power factor, F,,
5.3.1.2 Additional Test Procedures
(1) Testing for dual winding machine
5.2 System Operating Parameters. The drive
system efficiency is a function of the equipment
losses at a given operating point. The operating
point as previously defined is in terms of shaft
speed and torque (or horsepower). For each of
the specified operating points the system operating parameters should be defined as the base
for determining the equipment losses.
5.2.1 SynchronousMachine Operating Parameters. The operating parameters for each
equipment should be derived from the operating
parameters of the synchronous machine a t a
given bperating point. The following machine
operating parameters should be specified by the
system supplier for each operating point that is
selected for efficiency determination:
(1) Shaft speed
(2) Shaft torque (or horsepower)
(3) Fundamental sine-wave voltage, E
(4) Fundamental sine-wave current, I ,
(5) Fundamental phasor power factor, F,,
5.2.2 System Equipment Operating Parameters. The operating parameters for the
other system equipments should be determined
by the following procedure.
(1) Line-side interface
P1
(Fig 7)
13
ANSI / IEEE
AC ADJUSTABLE-SPEED DRIVES
Std 995-1987
i
NORMAL
CONNECTION
TEST CONNECTION
METHOD 2
TEST CONNECTION
METHOD 1
Fig 7
Dual Winding Machine Test
(a) Separate Drive Method. Each of the
two stator windings should be tested independently and simultaneously.
For the open-circuit core loss test and saturation curve, measure and record the open-circuit voltage in all three phases of each winding
a t each data point during the test. The opencircuit core loss may be obtained by subtracting
the following losses from the drive motor plus
the exciter input power at each data point.
KWRL
I f V f (see 5.3.1.2(2)(a))
KW exc loss (see 5.3.1.2(2)(a))exciter electrical
loss
I~RDMC
12RS, stator 12R loss at the average winding
temperature at each test point.
Thus the short-circuit core loss at each point
is:
SCCL = KWDM
KWEXC - KWRL - 12RR
- KW exc loss - 12RS - 12RDMC.
+
(i) KWRL, the test and drive motor running light losses
(ii) I f V f ,the test motor rotor 12RR (see
5.3.1.2(2)(a))
(iii) KW exc loss, (see 5.3.1.2(2)(a)).Exciter
electrical loss.
(iv) I’RDMC, the drive motor 12R loss
correction from running light losses, if any
Thus the open-circuit core loss at each point
is:
OCCL = KWDM KWEXC - KWRL - 12RR
- KW exc loss - 12RDMC
For the short-circuit core loss test, and saturation curve, short circuit the three phases of
each winding together independently and measure and record the short-circuit current in all
three phases of each winding at each data point
during the test.
The short-circuit core loss may be obtained by
subtracting the following losses from the drive
motor plus exciter input power.
@) Electric-Input Method. These motors
present a special problem. To test them, two
three-phase power supplies with 30 electrical
phase difference are needed, which may not be
available to the manufacturer’s facility. These
motors can, however, be tested by interconnecting the windings.
Method 1-Delta Connection. The two threephase windings with 30°C phase belt have
phases A, B, C and A’, B’, C’, the test can be
made by connecting Phase A in series with
Phase A’; Phase B in series with Phase B’; and
Phase C in series with Phase C’;. The 3 phases
thus obtained are then connected in delta. The
motor should now be tested with a single
three-phase power supply at equivalent voltage and line currents given below:
+
I* =
14
0.746 - h p
77m . cos
. J3 . E ~ lop3
.
+
ANSI / IEEE
Std 995-1987
LOAD COMMUTATED INVERTER
Ert =
2Efm cos 15" (approximately)
Armature 12R loss = (armature 12R loss a t
IrJ (cos 15 1' '
a
where
Ert = rated line fundamental rms voltage
for test, V
Ef, = rated motor line fundamental rms
voltage, V
Irt= rated line rms current for test, A
I p h t = phase current measured for I r t line
current, A
hp = rated horsepower of the motor
qm = calculated motor efficiency at rated
load in per unit
cos 4 = motor rated phasor power factor
The open-circuit core loss, friction and windage loss, stray loss and field 12R loss and armature 12R loss are determined for Ert and Irt
at rated power factor.
The armature 12Rloss and stray load loss are
then corrected for efficiency determination as
follows:
Armature 12R loss = (armature loss at Irt)
. (cos 15°)2.K
Stray load loss = (stray load loss a t Irt)
. (cos 15 . K
P5
NOTE: The results should be corrected for 3rd harmonic
circulation current as follows:
Method 2-Wye Connection. The two threephase windings with 30 "Cphase belt and having phases A, B, C and A', B', C' are first
connected as follows: Phase A is connected in
series with Phase A'; Phase B in series with
Phase B' and Phase C in series with Phase C'.
Now we have winding with 60 phase belts.
This winding is connected as wye. The motor
can now be tested with single three-phase
power supply at equivalent line voltage and
line current given below:
E*
=
Irt =
2 Efm COS 15"
0.746 * hp
qm
. cos 4
.a.
E ~ 10-3
.
The armature 12Rloss and stray load loss are
then corrected for efficiency determination as
follows:
Stray load loss = (stray load loss a t I*)
. (cos 15")2
(2) Brushless Exciter Losses. The brushless exciter consists of the stator, rotor, rotor bearings
(when supplied as part of the exciter), power
rectifier elements (semiconductors, surge suppressors, heat sinks) and interconnecting cables.
The following test methods are recommended
to determine exciter losses:
(a) Separate-Drive Method. This test can be
executed during the regular segregated loss tests
at the designated test speed.
(i) Use a calibrated drive motor of reasonable size relative to the losses of the test
motor (see ANSI/IEEE Std 115-1983, [9], 4.2.1).
(ii) Mount a dc shunt on the exciter rotor
and attach a n instrument collector to read the
test motor field current and voltage Ifand Vf.
(iii) Measure the power (watts) input to
the exciter stator. The sinusoidal stator voltage
is adjusted to achieve the desired rotor field current.
Data can be taken during the OCCL test since
that loss also must be measured. The data should
be taken in steps from 20% to approximately
110% of rated full-load field current. The exciter
loss curve can be established by using the following example.
From the classic "M" induction motor equations:
Exciter KWtotal= KWEXC stator input . slip
Shaft power = (slip - 1.0) . KW stator input
where
+KW = power in the exciter shaft
-KW = power out the exciter shaft
I ~ motor
R
rotor = I ~ R R
Exciter electrical losses
= KWtotal
-
IfVf
= kw exc loss
+
Slip = rated speed
operating speed
rated speed for contra-rotation
Slip
=
rated speed - operating speed
rated speed for standard (forward
rotation)
rated speed
=
freq . 60
poled2
ANSI / IEEE
Std 995-1987
AC ADJUSTABLE-SPEED DRIVES
in the rotor winding caused by the rectifier connection, and the harmonic currents in the stator
that are induced from the rotor. These harmonic
losses are included in the test methods that are
recommended in sections 5.3.1.2(2)(a) and
5.3.1.2(2)@).When these recommended methods
are not used and the exciter stator and rotor are
tested on sinusoidal power without the rectifier,
the additional loss is given by
The exciter friction and windage loss is included with the motor friction and windage.
The diode drop losses are measured as a part
of the electrical losses by this method.
(b) Electrical-Input Method. Same as Separate-Drive Method.
(c) ANSUIEEE Std 115-1983 [9], 4.1.3 should
be deleted when the machine is equipped with
a brushless exciter.
5.3.1.3 Harmonic Losses. The test procedures outlined in ANSI/IEEE Std 115-1983 [9]
are based on sinusoidal voltage and current and
do not include a measurement of the losses that
are produced in the machine when it operates
with nonsinusoidal voltage and current. For the
purpose of this recommended practice, the harmonic losses are calculated as a fixed percentage
of the fundamental sine-wave losses at the specified operating point defined in 5.3.1.1(3).
The fixed percentage harmonic loss factor
should be used for the efficiency determination
unless a specific calculation procedure is established and agreed upon between the system supplier and the user.
Ph
0.2
5.3.1.4 Auxiliary Losses. The auxiliary
losses are classified as Ventilating and Cooling
Loss (see ANSI C50.10-1977 [l], 7.3.10). When
externally driven ventilation equipments are required, this power should be measured by conventional wattmeter methods and included in
the losses assigned to the machine.
5.3.2 Isolation Transformer. The losses of
the transformer should be determined using the
test procedures outlined in ANSI/IEEE
C57.12.90-1987 [5] and ANSI/IEEE C57.12.911979 [6] as amended by the harmonic loss, auxiliary loss, and additions presented in this section.
5.3.2.1 Additions
to
ANSI/IEEE
C57.12.90-1987 [5] and ANSI/IEEE C57.12.911979 [6]. For the purpose of this recommended
practice the rated current for the load-loss test
should be taken from the operating parameter
given in 5.2.2.
The rated current for the load loss is given by
IT
IL =
P6
+
= k2
. (sine-wave load losses)
I, 3
P1
5.3.2.2 Harmonic Losses. The harmonic
currents increase the stray losses as described
in ANSI/IEEE C57.110-1986 [7]. The increased
losses due to harmonic current should be taken
as a fixed multiplier of the stray load loss at the
specified operating point.
where
12RS
sine-wave load losses = SL
k1 = 0.3
(2)Dual Winding Machine Operating with SixPulse Converter Connected to each Three-phase
Winding. The two windings are phase displaced
30 electrical degrees. The additional loss due to
nonsinusoidal voltage and current is given by
Ph
P8
k3 =
(1) Three-phase Machine Operating with SixPulse Converter. The additional loss due to nonsinusoidal voltage and current is given by
. (sine-wave load losses)
. (exciter electrical sine-wave loss)
where
NOTE: The adjustment for harmonic losses is intended for
efficiency determination only and in no way should be used
as a design criteria for temperature rise of the machine. The
temperature rise of the machine is the responsibility of the
machine manufacturer.
The adjustment for harmonic losses listed below, K1 and
K z , assumes that the machine has a laminated salient pole
construction with amortisseur windings and closed end
rings. For other types of machine construction the adjustment for harmonic losses should be specified.
p h = k1
= k3
p h = k4
- (stray load loss)
P9
where
k4
P7
3
where
sine-wave load losses = SL
kz = 0.15
NOTE: The harmonic losses calculated by this method are
for the purpose of this recommended practice and should
not be used as a measure of winding temperature rise.
(3)Brushless Exciter. The additional losses in
the exciter are generated by harmonic currents
5.3.2.3 Auxiliary Losses. The power for
auxiliary devices, such as pumps or fans, which
+ 12RS
16
~
ANSI / IEEE
Std 995-1987
LOAD COMMUTATED INVERTER
be measured by conventional wattmeter methods and taken as a loss.
(5) When iron-core inductors are applied, core
losses should be taken as a fixed multiplier of
the 12R loss at the operating point.
Pc = k6 * 12R lOSS
P11
are required to operate for the transformer to
perform its function, should be measured by conventional wattmeter methods and stated as a
loss.
5.3.3 Line Reactor. The losses of the line reactors should be determined using the test procedures outlined in ANSI (357.16-1958 (R 1971)
[2] as amended by the harmonic loss, auxiliary
loss, and additions presented in this section.
5.3.3.1 Additions to ANSI C57.16-1958
(R 1971) [2]. For the purpose of this recommended practice the rated current for the load
loss test should be taken from the operating parameters given in 5.2.2.
The rated current for the load loss test is given
by
IL =
I,
7T
-
3
where
k6 =
P1
5.3.3.2 Harmonic Losses. The harmonic
currents increase the stray loss. The increased
loss due to harmonic current should be taken as
a fixed multiplier of the stray loss at the specified operating point.
P h = k5
. (stray loss)
P9
where
k5 =
3
NOTE: The harmonic losses calculated by this method are
for the purpose of this recommended practice and should
not be used as a measure of winding temperature.
5.3.3.3 Auxiliary Losses. The power for
auxiliary devices, such as pumps or fans, which
are required to operate for the reactor to perform its function, should be measured by conventional wattmeter methods and stated as a
loss.
5.3.4 Direct-Current Link Inductor
(1)The losses in an air-core inductor should
be the 12R losses. The current to be used to
determine the loss should be taken from the
operating parameters specified in 5.2.2.
I -I
7T
0.05
5.3.5 Power Converter. The losses of the
power converter should be determined using the
procedures outlined in this section. The losses
should be determined for the operating parameters specified in 5.2.2.
5.3.5.1 Classification of Losses. The following losses should be included:
(1)Losses in thyristors
(2) Power circuit connection losses should include power circuit fuses, bus and cable, branch
or line reactors, current balancing devices
(3) Losses in filters, thyristor snubbers, and
voltage equalizers
(4) Power for fans or pumps for moving the
cooling media through the cooling system of the
converter, whether or not these devices are integrally mounted in the converter
(5) Losses in control and signal electronics.
5.3.5.2 Thyristor Losses
(1) The forward power loss should be determined by passing direct current through the
thyristor and heat sink assembly and measuring
the voltage across the assembly.
The assembly should consist of the thyristor
or thyristors and the associated heat sinks and
connections.
The magnitude of direct current as defined in
5.2.2 is:
P2
A minimum of 10% of the thyristor and heat
sink assemblies for each converter should be
tested and the average value of power loss used
to determine the forward power loss.
P2
P (assembly)
d -
=
V . Id
The thyristor forward power loss for each sixpulse converter should be calculated.
(2) The resistance should be determined using
the procedure in ANSI C57.16-1958 (R 1971) [2],
16-91.
(3) Harmonic loss should not be assigned to
air-core inductors.
P10
(4) The power for auxiliary devices, such as
fans OT pumps, which are required to operate
for the inductor to perform its function, should
P6 =
P (assembly) . (assembly per converter
branch) . 2 (branches in conduction at any
given time)
The total thyristor forward power loss for the
line side and load side converter = Pfc= 2 Ps
-
17
~
ANSI / IEEE
Std 995-1987
AC ADJUSTABLE-SPEED DRIVES
Fig 8
Converter Direct-Current Circuit
culated using the procedure given in this section.
The operating parameters are given in 5.2.2 for
the specified operating point.
Filter losses are identified in two general categories; low frequency P l f and high frequency
P h f . Both categories are only slightly affected by
load but are significantly affected by voltage,
frequency, and gating angle. The total filter loss
is the summation of P l f and P h f .
It is recognized that filter losses for dual winding systems should be higher than a single winding system that is covered by the equations.
These additional filter losses are due to electromagnetic coupling between the two windings on
the synchronous machines. For the purpose of
this recommended practice the same calculation
procedure should be used for single and dual
winding systems.
P14
The equations presented in the following sections cover ac line filters that are connected in
ungrounded wye. When filters are connected in
delta, these same equations can be used by transposing the delta component values to wye equivalent values.
When the line filters are connected in
grounded wye, the filter loss calculations assume
that there is no other ground in the system.
Calculation of filter losses when neutral currents are present is beyond the scope of this
recommended practice.
(2) An alternate method to determine the forward power loss should use the published data
for the forward voltage drop of the semiconductor device at 125 "C.
(3) Thristor reverse power and turn-on/turnoff losses are acknowledged to be small and are
not included unless specifically requested. When
specified a mutually agreeable test or calculaP12
tion procedure should be established.
5.3.5.3 Power Circuit Conductor Losses.
The conduction losses should be calculated from
published or measured values for conductor resistance. The dc resistance should be corrected
to 90 "C for bare bus and 75 "C for insulated bus
or cable.
The conduction losses should be based on a dc
circuit path from the source ac terminals of the
converter to the load ac terminals of the converter. This circuit involves two branches of the
line side converter and two branches of the load
side converter. The conductor length, fuses, and
reactors in this loop should be included in the
loss. The circuit is shown in Fig 8.
The conduction loss should be 12R where the
magnitude of the direct current is given by 5.2.2
P2
NOTE: It is recognized that additional losses should result
from harmonic current and skin effects, but these should
not be included.
P13
(1)AC line-Neutral RC Filter Loss
5.3.5.4 Filter, Snubber, and VoltageEqualizer Losses. These losses should be cal18
ANSI / IEEE
Std 995-1987
LOAD COMMUTATED INVERTER
Cy = capacitor expressed in farads in one
phase of wye
Ry = resistor expressed in ohms in one phase
of wye
ELL= rms line-line voltage at ac terminals
of converter
a = thyristor gating retard angle
C, = capacitor expressed in farads for each
thyristor shunt snubber
n = number of thyristors in series string
R, = resistor expressed in ohms for each
thyristor shunt snubber
Re = resistor expressed in ohms for each
thyristor voltage equalizer
cd = capacitor expressed in farads in dc filter
R d = resistor expressed in ohms in dc filter
p = commutation overlap angle = 0 (for
this recommended practice)
P3
(2) Thyristor Shunt Snubber Loss
P1f = l 2 0 f
2
(CSl2 ELL^ R, n (1
(n)
+ 0.5 Sin2 a )
(3) Thyristor Voltage Equalizer Loss
(4) DC Filter Loss
+
+
f 2 cd2 ELL^ Rd [1
11.5 Sin2 a]
1.5 f Cd ELL^ [Sin2 a
Sin2 (a p)]
(5) Letter Symbols for Quantities Used for Filter-Loss Calculations
Pif = 5.2
Phf =
+
P l f = low-frequency filter loss
Phf = high-frequency filter loss
f = frequency
Operating Parameters (Section 5.2)
Shaft Speed
Shaft Torque
Synchronous machine
5.3.2
Isolation transformer
(b) Open Circuit Core
(c) Stray Load
(d) Arm 12R
(e) Field 12R
(0 Exciter
(g) Harmonic
(h) Auxiliary
(a) No Load
(b)
Fundamental Sine-Wave Volts (E)
Fundamental Sine-Wave Ampers ( I a )
Fundamental Phasor Power Factor (F’,,)
I
5.3.1
5.3.1
5.3.1
5.3.1
5.3.1.2(2)
I
5.3.1.3
5.3.1.4
5.3.2
5.3.2
5.3.2
I ~ R
(c) Stray
(d) Harmonic
(e) Auxiliary
5.3.3
Line reactor
5.3.4
DC link inductor
5.3.5
Power converter
5.3.2.2
5.3.2.3
(a) 12R
(b) Stray
(c) Harmonic
(d) Auxiliary
5.3.3
5.3.3
(a) 12R
(b) Core Losses
(c) Harmonic
(d) Auxiliary
(a) Thyristor
03) Poker Circuit Connectors
(c) RC Filters and Snubbers
(d) Cooling System
(e) Control
Total Losses
5.3.4
5.3.3.2
5.3.3.3
I
5.3.4(5)
5.3.4(3)
5.3.4(4)
5.3.5.2
5.3.5.3
5.3.5.4
5.3.5.5
5.3.5.6
0
19
+(
)
+(
)
ANSI / IEEE
Std 995-1987
AC ADJUSTABLE-SPEED DRIVES
electric power under specified conditions. On
larger equipment where the system staging is
not readily available and mechanical power cannot be measured accurately, a conventional efficiency is used, based on segregated losses.
(2) The conventional efficiency is related to
the sum of the segregated losses as follows:
5.3.5.5 Power for Cooling System. The
power input to pump or fan motors should be
measured directly by conventional wattmeter
methods.
5.3.5.6 Control Losses. The power input to
the logic and gating circuits should be measured
directly by conventional wattmeter methods
with the control system fully activated and the
gating circuits producing pulses to the thyristors
on the line-side and load-side converters.
Efficiency (%) =
output
* 100
output
losses
+
In the above equation, power output and losses
are expressed in watts (or kilowatts). When the
drive output is expressed in horsepower the conversion to kilowatts is:
5.4 Recording of Losses. The segregated losses
that have been determined for each operating
point should be tabulated according to the classifications listed in 5.1.
Table 2 includes a listing of the segregated
losses and the classification of the losses.
Kilowatts
=
horsepower
. 0.746
(3) The calculated value for efficiency should
be rounded off to two decimal places (hundredths). For example, the efficiency value that
is calculated at 93.4524% should be expressed
as 93.45%.
5.5 Determination of Efficiency
(1)The true efficiency of the drive system is
the ratio of output mechanical power to input
20
ANSI / IEEE
Std 995-1987
LOAD COMMUTATED INVERTER
Appendixes
(These Appendixes are not a part of ANSI / IEEE Std 995 1987, IEEE Recommended Practice for Efficiency Determination
of Alternating-Current Adjustable-Speed Drives, but are included for information only.)
Appendix A
Explanation of Practices and Procedures
A2. P3-Derivation of a for Line-Side
Converter Filter Loss Calculations
The practices and procedures that are presented in this recommended practice are based
on a goal to determine the losses within 5% of
actual on a total drive system basis. This level
of accuracy should result in the determination
of the drive system efficiency within one percentage point down to 80% efficiency. This is
well within the accuracy that can be achieved
by measurement of input and output power.
The practices and procedures that are identified by a P number on the right-hand side of
a column have been selected to eliminate rigorous calculations and procedures when the accuracy of the recommended approaches was
deemed to be adequate to meet the accuracy
goal. The goal of the accuracy of loss calculation
on equipment is f.10% or better. It is expected
that the deviations from the exact loss will be
both plus and minus, and in most cases will be
less than lo%, therefore the 5% accuracy goal
on a drive system basis is realistic.
The recommended practices and procedures
are presented in A1 through A14.
Neglecting losses, the power at the synchronous machine must equal the power at the dc link
of the load-side converter.
-
I, F,,
E
*
8 = Ed
- Id
IT
Id = I,
then
3
Ed (load side)
=
E
- I, - F,, - 8
IT
and
Ed (load side)
=
E
3Jz
Fp, IT
If we assume that p = 0 then the dc voltage
from the line-side converter becomes
Ed (line side)
Al. P1 and P2-Conversion Factors
for Current
=
3Jz
E L -cos a
IT
Ed (line) must be higher than Ed (load) by the
IR drops in the loop. Typical values for loop IR
drop will range from 0.5% at light load to 3%
at rated load. For simplicity a one percent adjustment is recommended.
The recommended method for the conversion
of dc to rms ac (Pl) and the conversion of fundamental ac to dc (P2) are presented in [A5].4
P1 is covered in [A5], Appendix A-Effective
Value of Alternating Current of a Six-pulse Converter.
P2 is covered in [A5], Ch 3-Analysis of a
Bridge Converter, Eq 39
The conversion errors are less than 5% in the
normal operating range for the simplified procedure of setting p = 0.
Then
Ed ( h e side)
=
1.01 Ed (load side)
Ed (line side)
=
1.01 E
3Jz
. Fpp-
1.01 E
-
l7
EL
and
The numbers in brackets preceded by A correspond to
the references in Appendix A.
21
3 4
~
IT
COS
a
=
3'8
FppIT
ANSI / IEEE
Std 995-1987
AC ADJUSTABLE-SPEED DRIVES
Ratio of filter loss calculation for p # 0 versus p
1
1
=
0
+ cos 6 = cos a 0 (for the case with p = 0)
2
1 I 1 1 I 1 1 1 1 1 1 1 I 1
+ 0.2 cos' 2a
+ 0.2 cos2 2a
1.01
1.01
1.02
1.01
1.01
=
-
1.01
1.02
1.02
1.01
1.01
1.02
1.01
related to the phasor power factor Fppof the
machine at the specified operating point.
As stated in P3
3Jz c o s a + ~
EL 77
1.01
1.02
With commutation overlap ( p # 0)
Ed ( h e side)
cos a
2
E
where
*
1, *
Fpp
8 = Ed I d
From Fig 3 of this recommended practice it is
evident that the commutating voltage is not the
same magnitude or phase angle as the synchronous machine phase voltage E,. Since it is the
commutating voltage and the gating angle of the
load-side converter that determine the filter loss,
a n expression will be derived to account for the
differences in voltage and angle. The envelope
of the commutating voltage is greater than the
envelope of the fundamental by a function that
includes the volt-seconds of the commutation
notches. At zero current the two are the same.
To avoid the complexity of including commutation voltages and commutation reactances
(thus p = 0) and to maintain reasonable accuracy, the following expressions are recommended for the derivation of the gating angle
for the load-side converter.
6 = a + p
Since a and p are used to determine filter
losses only, the above tabulation shows the magnitude of the difference in filter loss calculation
for the recommended method with p = 0.
The difference between the two cases is not
significant for three of the four functions and in
all cases becomes small at the greater values of
phase retard where the filter losses become significant. The function (1 11.5 sin2a) for the
low-frequency dc filt.er loss shows the greatest
departure from 1.0 but this is used in only one
calculation and normally represents a small
part of the total.
+
Let the commutation voltage
loads.
A3. P4-Derivation of a for Load-Side
Converter Filter Loss Calculations
=
1.05 E for all
Then
E
3 4 - 1.05 E
Fpp* 7r
The calculation of filter losses on the load-side
converter require a value for a and p at each
operating point. As in the line side filter loss
calculation the accuracy of the results is not
significant if p = 0.
The gating angle of the load-side converter is
COS
*
3 3
ll
and
a = cos-' (0.95 Fpp)
and
ELLin the filter calculation = E
22
ANSI / IEEE
Std 995-1987
LOAD COMMUTATED INVERTER
The fixed multiplier kl = 0.3 establishes a
reasonable value for the additional losses in the
machine with a six-pulse power converter. There
is minimal information available on the subject
but a 10% to 15% machine derating for operation with a six-pulse static inverter is a reasonable and accepted practice. The 0.3 multiplier
on machine SL and 12RS losses represents approximately 15% additional electric losses over
the sinusoidal losses at rated power.
P15
P h = K1
(sine-wave load losses)
A4. P5-Definition of E,t
The motor has two three-phase windings
phase-shifted by 30". For testing, they are connected in series as indicated in Fig 7 of this
recommended practice.
For the wye connection
Ert =
2 EfmCOS 15"
Efm* 0.966
= 2
-
where
K1 =
0.3
is recommended to determine the machine harmonic losses with a six-pulse converter.
NOTE: This assumes that machines with laminated field
poles will have amortisseur windings and closed end-ring
connection.
trt
There is a 3.4% difference in voltage and magnetic saturation.
The test voltage is cos 15" times actual and
the test current is l / c o s 15" times actual. The
tested stator 1 2 R and stray load loss is approximately ( l / c o s 15")' . actual. The correction,
then, is a (cos 15"12 multiplier.
A6. P7-Synchronous Machine
Harmonic Loss
With reference to P5, the fixed multiplier for
harmonic loss is reduced from 0.3 to 0.15. A
reduction is necessary to account for the cancellation of rotor harmonic currents by the 30
degree phase displacement in the stator windings of a dual winding machine. The 5thand 7th,
17th and lgth, etc are cancelled by the stator
phase displacement and the 6th, 18th,etc harmonics do not appear in the rotor.
Thus, the harmonic losses in the rotor, which
represented the major part of the harmonic
losses in the machine, are significantly reduced.
The stator windings are still exposed to the sixpulse current wave forms, but the losses are reduced slightly due to some cancellation of harmonic fluxes.
P h = K 2 (sine-wave load losses)
P15
A5. P6-Synchronous Machine
Harmonic Loss
The additional loss due to nonsinusoidal voltage and current is taken as a fixed multiplier
of the machine losses due to stator current
( S L 12RS).The harmonic losses in the stator
and rotor are a function of the current in the
stator winding, not the rotor field winding and
the excitation losses.
The load commutated inverter is a current
source, which means that the harmonic currents
are a function of the current applied to the stator
winding. The ijth and 7th stator harmonics both
produce a 6th harmonic rotor current. The llth
and 13th stator harmonics both produce a 12th
harmonic rotor current, etc. The harmonic currents in the rotor produce losses in the amortisseur winding and the pole face. Thus, the
harmonic currents in the rotor are a direct function of the stator winding harmonic currents and
the additional losses due to harmonics should be
based on the machine load losses, SL and 12RS.
+
where
Kz
=
0.15
is recommended to determine the machine harmonic losses with dual six-pulse converters.
NOTE: This assumes that machines with laminated field
poles will have amortisseur windings and closed end-ring
connection.
23
ANSI / IEEE
Std 995-1987
AC ADJUSTABLE-SPEED DRIVES
A7. P8-Brushless
Exciter
Harmonic Loss
square of the load current and the square of
frequency.
The other stray losses (POSL) will also increase as a result of nonsinusoidal load current
and are generally considered to be proportional
to the square of the load current and to frequency to the first power. To accurately determine the harmonic losses the subdivision of the
stray losses into PEC and POSL must be known.
This subdivision of stray loss is not part of the
transformer test procedure and can only be determined from the design data (if available).
Therefore, it is recommended that the harmonic
loss be taken as a fixed multiplier to the measured stray load loss.
The additional losses due to nonsinusoidal
voltage and current is taken as fixed multiplier
of the exciter electrical sine-wave loss. The voltage applied to the exciter stator is considered to
be sinusoidal. The brushless exciter rotor is connected to a static converter, which is normally
a three-phase, six-pulse rectifier. The exciter rotor current contains harmonics of the order 6 n
'. 1 where n is any integer of the rotor frequency.
The rotor fundamental frequency is a function
of the exciter slip and may become quite high
for contra-rotation exciters. The rotor winding
harmonic currents are coupled into the stator
winding at frequencies that are also a function
of rotor slip, therefore are not a constant harmonic order on the supply frequency.
The fixed multiplier k 3 = 0.2 establishes a
reasonable level for the additional losses due to
the high frequencies and beat frequencies, which
might be present at various operating conditions.
P h = k 3 . (exciter electrical sine-wave loss)
P h = K4
P15
where
k4 =
3
The accuracy of this recommendation is discussed below.
A8.1 Alternate 1
For the worst-case harmonic current distribution
P15
where
k3 =
. (stray load loss)
0.2
Ih =
is recommended to determine the exciter harmonic loss.
1
For this case the winding eddy-current losses
due to harmonic currents are
A8. P9-Transformer Harmonic Loss
(See ANSIIIEEE C57.110-1987[All
The nonwinding stray losses due to harmonic
currents are
25
The transformer load losses are divided into
12RS loss and stray loss. Stray loss can be defined as those losses due to stray electromagnetic
flux in the windings, core, core clamps, magnetic
shields, enclosure or tank walls, etc. Thus the
stray losses are subdivided into the winding
stray losses and stray losses in components other
than windings.
The winding stray load loss includes winding
conductor strand eddy-current losses and losses
due to circulating currents between strands or
parallel winding circuits. All of this loss may be
considered to be winding eddy-current (PEC)
losses. Winding eddy-current losses in the power
frequency spectrum are proportional to the
Ph
= POSL
& (A)h
=5
2
h = 0.7 POSL
It is reasonable to assume that the winding
eddy-current losses PEC are not more than half
of the total stray load loss. In the maximum case
the total harmonic loss is
Ph = 0.5
*
Ph = 4.35
8
*
PEC 4- 0.5
- 0.7
POSL
. (stray load loss)
This represents a worst-case example and the
actual harmonic loss is less than this value.
Therefore, the recommended procedure, which
uses the fixed multiplier of k4 = 3, should provide reasonably accurate results.
24
ANSI / IEEE
Std 995-1987
LOAD COMMUTATED INVERTER
that the ac currents are rectangular in shape;
therefore, the current in the dc link inductor is
purely dc with no harmonic content and the
eddy current loss, circulating current loss and
stray loss will be zero.
A8.2 Alternate 2
(1) The transformer stray losses are assumed
to be winding eddy-current losses PEC.
(2) The winding eddy-current losses due to
any defined nonsinusoidal load current can be
expressed as
h
=
A10. P11-Core Losses in Iron-Core DC
Link Inductors
25
The additional losses in the dc link inductor
due to a n iron core are taken as a constant multiplier on the 12Rloss. The multiplier k6 = 0.05
is based on limited test data but does recognize
the additional core loss as compared to air-core
inductors.
P15
where
PEC = fundamental eddy-current loss
(3) A reasonable harmonic distribution for the
nonsinusoidal load current in pu of the fundamental is
h
Ih
Ih2 h2
5
7
11
13
17
19
23
25
0.19
0.13
0.07
0.90
0.83
0.59
0.42
0.26
0.14
0.05
0.03
0.02
0.01
0.005
A l l . P12-Thyristor Reverse Power
and Turn-ON / Turn-OFF Losses
These losses are a small part of the total converter loss and are difficult to determine accurately.
The thyristor reverse power loss is heavily
dependent on device operating temperature and
applied voltage. The turn-off loss is dependent
on circuit d i l d t and snubber design. The turnon loss can be determined from device test data
(if supplied) but is heavily dependent on snubber
design and commutation overlap angle p, which
has been set to zero for this recommended practice.
The losses covered by this recommendation
should be less than 5% of the thyristor forward
power loss in a power converter designed for
large ac motor drives. The recommendation to
not include these losses is supported by the recommended practice documents listed below.
(1) ANSI/IEEE Std 444-1973 [A2], 6.3.4.
When the total reverse current loss in the
semiconductors, voltage divider resistors, and
surge suppressor circuits is reasonably estimated to be less than 5% of the converter forward power loss, these losses need not be
measured and may be disregarded in determination of efficiency.
(2) IEC Publication 146-1973 [A3], Semiconductor Converters
Section 472.1, Power loss determination for
diode assemblies and rectifier equipment.
(a) The losses in the cells in service, due to
reverse current and voltage, are normally negligible.
0.05
0.02
3.21
Therefore, the fixed multiplier of k4 = 3 for
harmonic losses represents a reasonable accuracy for the recommended procedure.
For the case of line reactors the harmonic
losses should be similar to those of a transformer. Therefore, the fixed multiplier k5 = 3
is recommended for reasonable accuracy. P15
A9. P10-Harmonic Losses in Air-Core
DC Link Inductors
The IEC Publication 146-1973 [A31 has established the precedent for this recommendation
for the determination of harmonic losses in a
series-smoothing reactor-by stating
(1) Iron losses are, by convention, to be ignored
(2) The losses in the winding are calculated
as the product of the dc resistance and the
square of the direct current in the winding.
This is consistent with other recommendations presented in Appendix A which assume
25
ANSI / IEEE
Std 995-1987
AC ADJUSTABLE-SPEED DRIVES
A12. P13-Power Circuit Conduction
Harmonic Losses
chines due to the electromagnetic coupling between the two windings.
The line-line commutating voltage waveforms
are shown below for single- and dual-winding
machines with a 30 degree electrical phase displacement between windings. The waveforms
show the commutation notches from the A-B
winding being coupled into the A'-B' voltage and
vice-versa. The magnitude of the coupling is dependent on the self and mutual leakage inductance of the two windings. Mutual coupling of
50% is reasonable and this results in the coupled
voltage notch being 50% of the depth of the
notch in the commutating winding.
The increased filter loss occurs mainly in the
high-frequency loss component of the ac lineneutral filters and the thyristor shunt snubbers.
The high-frequency loss is a function of the voltage step squared, that is,
The Wave Shape Working Group of the IEEE
Power Systems Protection Committee recognized the additional losses in current carrying
conductors due to skin effects at higher frequencies. The ac to dc resistance ratio for copper
bus is presented in [A4], Table IV.
Table IV
ac to dc Resistance Ratio for 0.25 x 4 in Cu Bus
f
Rac / Rdc
1
60
1.158
5
300
1.64
7
420
1.79
11
660
2.05
13
780
2.15
H
[sin2 a
ELL'
The 50% coupling will increase the high-frequency losses of the ac line-neutral and shunt
snubber loss by approximately 25%, but this will
generally not result in a total increase in filter
loss (line and load side) by more than 5%.
Using the resistance data presented in
Table IV (Taken from Reference [A411 for
harmonics to the thirteenth and assuming the
harmonic current magnitude of 1 / H, the conduction losses calculate to be 1.037 times the
method recommended in this recommended
practice. This difference represents a very minimal effect on the total power converter equipment losses and therefore the harmonic losses
are not included.
A13. P14-Filter
+ sin2 (a + p)]
A14. P15-Constant Multiplier for
Harmonic Losses
The application of a constant multiplier to
determine harmonic losses is a n estimate that
is based on engineering judgment of the information available to date. When more exact data
becomes available from test data or published
papers, or both, the recommendations herein
should be changed to include more accurate
methods. Prior to any improved method the recommended constant multipliers do provide a n
Losses for Dual-
Winding Machines
The filter losses on the load-side converters of
systems with dual winding machines will be
slightly higher than those for single-winding ma-
I
A-B
A-B
B'
SINGLE WINDING MACHINE VOLTAGE
D U A L WINDING MACHINE VOLTAGE
26
ANSI / IEEE
Std 995-1987
LOAD COMMUTATED INVERTER
[A31 IEC Publication 146-1973, Semiconductors
~onverters.~
acceptable means to account for harmonic losses
within the accuracy goals for this recommended
practice.
[A41 IEEE Conference Record. So You Don’t
Think You Have a Harmonic Problem. Industry
Applications Society, Annual Meeting, 1979.
IAS79: 41D.
A15. References
[A51 KIMBARK, EDWARD WILSON. Direct
Current Transmission vol I. New York: WileyInterscience, 1971.
[All ANSI / IEEE C57.110-1987, IEEE Recommended Practice for Establishing Transformer
Capability when Supplying Nonsinusoidal Load
Currents.
IEC publications are available in the United States from
the Sales Department, American National Standards Institute, 1430 Broadway, New York, NY 10018, USA, and also
from International Electrotechnical Commission, 3, rue de
Varembe, Case postale 131,1211-Geneve 20, Switzerland /
Suisse.
[A21 ANSI/ IEEE Std 444-1973, IEEE Standard
Practices and Requirements for Thyristor Converters for Motor Drives, Part I-Converters for
DC Motor Armature Supplies.
27
ANSI / IEEE
Std 995-1987
LOAD COMMUTATED INVERTER
Appendix B
Example Efficiency Determination
An example is presented to illustrate the recommended practice for the efficiency determination of a ac adjustable speed drive.
The drive system is a dual channel parallel
system (see Fig 16) rated to produce 4200 hp a t
720 r l m i n . The system efficiency was determined for two specified operating points.
Point
Shaft
Speed
Shaft
Torque
Shaft
Horsepower
1
2
720 r / m i n
562 r / m i n
30 637 lbf . ft
18 625 lbf ft
4200
1933
.
eters a t these operating points were specified by
the system supplier.
Point
E (Volt)
I, (Ampere)
1
2
1885/1885
2000/ 2000
516/516
233 / 233
Fpp(%I
95/ 95
95/ 95
The system equipment operating parameters
were determined using the procedures of 5.2.2
and the equipment losses were then determined
by the recommended procedures. The losses are
tabulated in Tables B1 and B2.
The synchronous machine operating param-
Table B1
Tabulation of Losses
Operating parameters (Section 5.2)
Shaft Speed 720 r / m i n
Shaft Torque 30 637 lbf. ft
5.3.2
Isolation transformer
5.3.3
Line reactor
5.3.4
Direct-Current link inductor
5.3.5
Power converter
Loss Determination Class (Section Reference)
Fundamental
Losses by
Sine-Wave Losses
Losses by
Input Power
by Test
Calculation
Measurement
Segregated
Loss Component
Equipment
5.3.1
Synchronous machine
Fundamental Sine-Wave Volts ( E ) 1885/ 1885
Fundamental Sine-Wave Amperes (I, 5161516
Fundamental Phasor-Power Factor (FDp)
0.95/ 0.95
(a) Windage and friction
Open-circuit core
(c) Stray Load
(d) Arm 12R
(e) Field 12R
(f) Exciter
(g) Harmonic
(h) Auxiliary
(a) No Load
15.0
11.7
6.6
23.5
9.8
3.6
(b)
4.5
I ~ R
(c) Stray
(d) Harmonic
(e) Auxiliary
(a) I ~ R
(b) Stray
(c) Harmonic
(d) Auxiliary
(a) PR
(b) Core Losses
(c) Harmonic
(d) Auxiliary
(a) Thyristor
(b) Power-Circuit connectors
(c) RC filters and snubbers
(d) Cooling system
(e) Signal electric
(b)
Total Losses
4.4
28.2
3.2
9.6
20.0
22.2
1.1
9.2
5.0
5.0
126.0
NOTE: All losses, kW
29
+46.6
+ 10.0
ANSI / IEEE
Std 995-1987
Table B2
Tabulation of Losses
Operating Parameters (Section 5.2)
Shaft Speed 562 r / m i n
Shaft Torque 18625 lbf ft
Fundamental Sine-Wave Volts
( E ) 2000/2000
Fundamental SineWave Ampers
(I,) 233 /233
Fundamental Phasor Power Factor ( F A0.95/ 0.95
Loss Determination Class (Section Reference)
Fundamental
Losses by
Sine Wave Losses
Losses by
Input Power
by Test
Calculation
Measurement
8.7
19.1
1.3
4.8
10.1
3.6
0.9
Segregated
Loss Component
(a) Windage and friction
(b) Open-circuit core
(c) Stray Load
(d) Arm Z2R
(e) Field 12R
(f) Exciter
(g) Harmonic
(h) Auxiliary
(a) No Load
(b) I ~ R
(c) Stray
(d) Harmonic
(e) Auxiliary
(a) I'R
(b) Stray
(c) Harmonic
(d) Auxiliary
(a) Z2R
(b) Core Losses
(c) Harmonic
(d) Auxiliary
(a) Thyristor
(b) Power-circuit connectors
(c) RC filters and snubbers
(d) Cooling system
(e) Signal electric
Total Losses
Equipment
5.3.1
Synchronous machine
5.3.2
Isolation transformer
5.3.3
Line reactor
5.3.4
DC link inductor
5.3.5
Power converter
4.4
5.7
0.6
1.8
4.1
8.4
0.2
7.1
5.0
5.0
+ 18.4
62.4
+ 10.0
NOTE: All losses, kW
The drive system efficiency at the specified
operating points is then calculated.
Point 1
Output kW
Point 2
Output kW = 1993 * 0.746 = 1486.8
1486.8
Efficiency (%) =
100
1486.8(62.4 18.4 10)
+
-
4200 0.746 = 3133.2
3133.2
Efficiency (%) =
100
3133.2 (126 46.6 10)
-~
- 3133-2
100 = 94.493
3315.8
= 94.49%
=
+
+
+
+
--.1486*8 100 = 94.244
-
1577.6
= 94.24%
30