AS 1359.102.1꞉1997 (EN) IEC 34-2+A2꞉1996 ᴾᴼᴼᴮᴸᴵᶜᴽ

8/13/2019 AS 1359.102.1꞉1997 (EN) IEC 34-2+A2꞉1996 ᴾᴼᴼ ᴸBᴵc ᴽ

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AS 1359.102.1—1997IEC 34-2:1972IEC 34-2:1972/Amd.1:1995IEC 34-2:1972/Amd.2:1996

Australian Standard ®

Rotating electrical machines—General requirements

Part 102.1: Methods for determininglosses and efficiency—General

[ IEC title: Rotating electrical machines, Part 2: Methods fordetermining losses and efficiency of rotating electrical machineryfrom tests (excluding machines for traction vehicles)]



This Australian Standard was prepared by Committee EL/9, Rotating ElectricalMachinery. It was approved on behalf of the Council of Standards Australia on10 March 1997 and published on 5 July 1997.

The following interests are represented on Committee EL/9:

Australian British Chamber of Commerce

Australian Chamber of Commerce and Industry

Australian Electrical and Electronic Manufacturers Association

Bureau of Steel Manufacturers of Australia

Department of Defence

Electricity Supply Association of Australia

Institution of Engineers Australia

Review of Australia n Standards. To keep abreast of progress in industry, Australian Standards are subject to periodic review and are kept up to date by t he issue of amendments or new editions as necessary. It isimportant t herefore that Standards users ensure that they are in possession of the l atest edition, and anyamendments thereto.Full details of all Australian Standards and related publications will be found in the Standards AustraliaCatalogue of Publications; this information is supplemented each month by the magazine ‘The AustralianStandard’, which subscribing members receive, and which gives details of new publications, new editi onsand amendments, and of wit hdrawn Standards.Suggestions f or improvements to Australian Standards, addressed to the head office of S tandards Australia,are welcomed. Notification of any inaccuracy or ambiguity found in an Australian Standard should be madewithout delay in order that t he matter may be i nvestigated and appropriate action taken.

This Standard was issued in draft form for comment as DR 96091 and 96206.



AS 1359.102.1—1997

Australian Standard ®

Rotating electrical machines—General requirements

Part 102.1: Methods for determininglosses and efficiency—General

Originated as part of AS 1359.33—1983.Revised and redesignated in part as AS 1359.102.1— 1997.

PUBLISHED BY STANDARDS AUSTRALIA(STANDARDS ASSOCIATION OF AUSTRALIA)1 THE CRESCENT, HOMEBUSH, NSW 2140

ISBN 0 7337 1178 2



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PREFACE

This Standard was prepared by the Standards Australia Committee EL/9, Rotating ElectricalMachinery to supersede, in part, AS 1359.33— 1983, G eneral requirements for rotating electricalmachines , Part 33: Methods for determining losses and efficiency .

It is identical to and has been reproduced from IEC 34-2:1972, Rotating electrical machines ,Part 2: Methods for determining losses and efficiency of rotating electrical machinery from tests(excluding machines for traction vehicles ), including Amd.1:1995 and Amd.2:1996 as indicated bymarginal bars near the affected text. Reproduction was done by scanning the IEC text and adjustingthe style of the original publication to conform with later IEC style.

This Standard is a Part of the AS 1359 series listed in AS 1359.0, Part titled: Introduction and list of Parts .

The objective of this Standard is to provide the rotating electrical machine industry with standard

methods for determining losses and efficiency.The objective of this Revision is to clarify certain methods and to provide more details of theretardation method (from IEC 34-2 Amd.1); to amend the reference temperature used for correcting I 2 R losses (from IEC 34-2 Amd.2); and to transfer the calorimetric method to a new AS 1359.102.2.

As this Standard is reproduced from an International Standard, the following applies:

(a) Its number does not appear on each page of text and its identity is shown only on the coverand title page.

(b) In the source text ‘this Recommendation’ should read ‘this Australian Standard’.

(c) A full point substitutes for a comma when referring to a decimal marker.

(d) References to International Standards should be replaced by references to AustralianStandards, as follows:

Reference to International Standard Australian Standard

34 Rotating electr ical machines 1359 Rotating electr ical machines—Generalrequirements

34-1 Part 1: Rating and performance 1359.101 Part 101: Rating and performance34-2A First supplement: Measurement of

losses by the calorimetric method1359.102.2 Part 102.2: Methods for

determining losses andefficiency— Calorimetric method

50 International ElectrotechnicalVocabulary (IEV)

1852 International ElectrotechnicalVocabulary

51 Direct acting indicating analogue —electrical measuring instruments andtheir accessories

The references in Paragraph A.1.4 to clauses 11 and 13 and to table II of IEC 34-2A applyrespectively to Clauses 4.4, 3.7 and Table 2 of AS 1359.102.2.



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CONTENTS

Page

ClauseSECTION ONE - GENERAL

1 Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Object . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

3.1 List of symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

4.1 Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24.2 Total loss . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24.3 Braking test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34.4 Calibrated driving machine test . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34.5 Mechanical back-to-back test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34.6 Electrical back-to-back test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34.7 Retardat ion test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34.8 Calorimetric test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34.9 No-load test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34.10 Open-circuit test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34.11 Sustained short-circuit test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34.12 Zero power factor test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 5 Reference temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

SECTION TWO - D.C. MACHINES

6 Losses to be included . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56.1 Excitation circuit losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56.2 Constant losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56.3 Load losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56.4 Additional load losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

7 Determination of efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67.1 Summation of losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67.2 Total loss measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

7.3 Direct measurement of efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

SECTION THREE - POLYPHASE INDUCTION MACHINES

8 Losses to be included . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118.1 Constant losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118.2 Load losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 118.3 Additional load losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

9 Determination of efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129.1 Summation of losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129.2 Total loss measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 149.3 Direct measurement of efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . 14



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Page

ClauseSECTION FOUR - SYNCHRONOUS MACHINES

10 Losses to be included . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1510 1 Constant losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1510.2 Load losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1510.3 Excitation circuit losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1510.4 Additional load losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

11 Determination of efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1611.1 Summation of losses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1611.2 Total loss measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

1 11.3 Direct measurement of efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

SECTION FIVE - METHODS OF TEST

12 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2013 Calibrated machine test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2114 Zero power factor test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2115 Retardation method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

15.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2215.2 Composition of retardation tests . . . . . . . . . . . . . . . . . . . . . . . . . . . 2315.3 Retardation test procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2515.4 Taking of measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

16 Electrical back-to-back test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2917 Calorimetric test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2918 Schedule of preferred tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

18.1 D.C. machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2918.2 Polyphase induction machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3018.3 Synchronous machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

FIGURES (1 to 5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

ANNEX A2 Provisional methods for determining losses and efficiency of converter-fed

cage induction machines . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

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AUSTRALIAN STANDARD

Rotating electrical machines— General requirements

Part 102.1:Methods for determining losses and efficiency—General

SECTION ONE - GENERAL

1 Scope

This Recommendation applies to d.c. machines and to a.c. synchronous and inductionmachines of all sizes within the scope of IEC Publication 34-1. The principles can, however, beapplied to other types of machines such as rotary converters, a.c. commutator motors andsingle-phase induction motors for which other methods o f determining losses are g enerallyused.

2 Object

This Recommendation is intended to establish methods o f determining efficiencies from tests,and also to specify methods of obtaining particular losses when these are required for otherpurposes.

3 General

Tests shall be conducted on a completely sound machine with all covers fitted in the mannerrequired for normal service, with any devices for automatic voltage regulation not a compositepart of the machine itself being made inoperative, unless otherwise agreed.

1 Unless otherwise agreed, measuring in struments and th eir accessories, such as measuringtransformers, shunts and bridges used during the test shall have an accuracy of 0,5 or better(IEC 51), excluding three-phase wattmeters and wattmeters for low power factor, for which anaccuracy class shall be 1,0 or better.

Instruments shall be selected to give readings over the effective range such th at a fraction of adivision is a small percentage of the actual reading and can be easily estimated.

On machines with adjustable brushes, the b rushes shall be placed in the position correspond-ing to the specified rating. For measurements on no-load, the brushes may be placed on theneutral axis.

Speed of rotation may be measured by a stroboscopic method, digital counter or tachometer.When measuring slip, the synchronous speed should be determined from the supply frequencyduring the test.

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When the over-all efficiency or the absorbed power is measured for a group of machinescomprising two electrical machines, or a machine and a transformer, or a generator and itsdriving machine, or a motor and its driven machine, there is no need to indicate the individualefficiencies. If, however, these are given separate ly, they should be regarded as approximate.

3.1 List of symbols

A list of symbols used in the draft, with the general meanings attributed to each one, is givenbelow:

1 C = retardat ion constantI = currentI 1 = load current at rated voltageI 1r = main primary current at reduced voltageI o = no-load current at rated voltageI or = no-load current at reduced voltageJ = moment of iner tia

n = speed of rotation in revolutions per minuten N = ra ted spe ed,N = number of full revolutions of the shaftP = losses which can be directly measuredP 1 = power absorbed at rated voltageP 1r = power absorbed by main primary winding at reduced voltageP Fe = iron losses definedin accordance with 6.2 a), 8.1 a) and 10.1 a)P f = friction and windage losses (”mechanical losses” defined in

accordance with 6.2 b), 6.2 c), 8.1 b), 8.1 c), 10.1 b) and 10.1 c))P k = short-circuit losses representing the sum of the I 2R losses in operating

windings on lo ad in accordance with 10 .2 and additional load losses inaccordance with 10.4

P t

= total of the losses during the retardationtestS = angular displacement of the machine shafts = slipU = excitation voltage across terminals of main rheostatU e = total excitationvoltageU n = ra ted vol tag eU r = reduced voltage for load testδ = per unit deviation of rotational speed from rated speedϕ = load phase angle at rated voltageϕr = load phase angle at reduced voltageϕo = no-load phase angle at rated voltageϕor = no-load phase angle at reduced voltage

4 Definitions

For definitions of general terms used in this Recommendation, reference should be made tothe Internationa lE lectrotechnical Vocabulary [IEC Publication 50].

For the purpose of this Recommendation, the following definitions apply:

4.1EfficiencyThe ratio of output to input expressed in the same units and usually given as a percentage.

4.2Total l ossThe difference between the input and the output.

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4.3Braking testA test in which the mechanical power output of a machine acting as a motor is determined bythe measurement of the shaft torque, by means of a brake or dynamometer, together with therotational speed. Alternatively,a test performed on a machine acting as a generator, by meansof a dynamometer to determine the mechanical power input.

4.4Calibrated driving machine testA test in which the mechanical input or output of an electrical machine is calculated from theelectrical output or input of a calibrated machine mechanically coupled to the machine on test.

4.5Mechanical back-to-back testA test in which two id entical machines are mechanically coupled together, and the total lossesof both machines are calculated from the difference between the electrical input to onemachine and t he electrical outpu t of the other machine (see figure 1).

4.6Electrical back-to-back testA test in which two identical machines are mechanically coupled together, and they are bothconnected electrically to a power system. The total losses of both machines are taken as thepower input drawn from the system (see figure 2).

4.7Retardation testA test in which the losses in a machine are deduced from the rate of deceleration of themachine when only these losses are present.

4.8Calorimetric testA test in which the losses in a machine are deduced from the heat produced by them. Thelosses are calculated from the product of the amount of coolant and its temperature rise, andthe heat dissipated in the surrounding media.

4.9No-load testA test in which the machine is run as a motor providing no useful mechanical output from theshaft.

4.10Open-circuit testA test i n which a machine is run as a generator with its terminals open-circuited.

4.11Sustained short-circuit testA test in which a machine is ru n as a generator with its terminals short-circuited.

4.12Zero power factor testA no-load test on a synchronous machine which is o ver-excited and operates at a p ower factorvery close to zero.

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5 Reference temperature

2 Unless otherwise specified, all I 2R losses shall be corrected to the temperatures given below:

Thermal class ofthe insulation system

Reference temperature°C

A, EBFH

7595

115130

If the rated temperature rise or the rated temperature is specified as that of a lower thermalclass than that used in the construction, the reference temperature shall be that of the lowerthermal class.

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SECTION TWO - D.C. MACHINES

6 Losses to be included

The total losses may be taken as the sum of the following component losses:

6.1 Excitation circuit losses

a) I 2R losses in shunt or separately excited windings and i n the excitation rheostats.

b) Excite r losses.

All the losses in an exciter mechanically driven from the main shaft, which forms part ofthe complete unit and is used solely for exciting the machine, t ogether with losses in therheostat in the excitation circuit of such an exciter, but with the exception of friction andwindage losses.

In the case of a separate excitation supply such as battery, rectifier or motor generatorset, no allowance is made for the losses in the excitation source or in the connectionsbetween the source and the brushes.

NOTE - When the losses in a separate excitation system are required, these should be listed separately andcan be taken as the difference between the excitation power divided by the efficiency of the excitation system,and the excitation power.

6.2 Constant losses

a) Losses in active iron, and additional no-load losses in other metal parts.

b) Losses due to friction (bearings and brushes) not including any losses in aseparate lubricating system. Losses in common bearings shall be statedseparately, whether or not such bearings are supplied with the machine.

NOTE - When the losses in a separate lubricating system are required, these should be listedseparately.

c) The total windage loss in the machine including power absorbed in integral fansand in auxiliary machines, if any, forming an integral part of the machine. Thelosses in auxiliary machines such as external fans, water and oil pumps n otforming an integral part of the machine, but provided exclusively for the machinein question, shall be included only by agreement.

NOTE - When the losses in a separate ventilating system are r equired, they should be listedseparately as they are not part of the machine losses.

6.3 Load losses

a) I 2R losses in armature, and winding s carrying armature current (e.g. commutating,compensating, excitatio n and series connected windings).

b) Electrical losses in brushes.

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6.4 Additional load losses

a) Losses introduced by load in active iron, and other metal parts other than theconductors.

b) Eddy current losses in armature conductors caused by current dependent fluxpulsation and commutation.

c) Losses in the brushes caused by commutation.

NOTE - These l osses are sometimes called additional losses, but they do not include the additional no-loadlosses in 6.2 a).

7 Determination of efficiency

7.1 Summation of losses

The efficiency can be calculated from the total losses which are assumed to be the summationof the losses obtained in the following manner:

7.1.1 Excitation losses

These are:

7.1.1.1 Excitation winding I 2R losses

These losses are calculated from the formula I 2R, where R is the resistance of the shuntexcitation winding (or separately excited winding), corrected to the reference temperature,and I is the excitation current. Except for case c) below, the excitation current shall be that

corresponding to rated speed under rated load conditions. For case c) below, the excitationcurrent shall be that corresponding to rated speed at no-load.

If the excitation current cannot be measured during a test on load, it should be taken as:

a) For shunt connected or separately excited generators with or without commutationpoles; 110% of the excitation current, corresponding to no-load at a voltage equalto the rated voltage plus ohmic drop in the armature circuit (armature, brushesand commutating windings if any, see also 7.1.3.2) at rated load current.

b) For compensated shunt or separately excited generators: the excitation currentcorresponding to no-load at a voltage equal to the rated voltage plus the o hmicdrop in the armature circuit (armature, brushes, commutating windings andcompensating windings, see also 7.1.3.2) at rated load current.

c) For level-compounded generators: the excitation current for the rated no-loadvoltage.

d) For over-compounded and under-compounded generators, and special types ofgenerator not covered by items a) to c): as agreed between manufacturer andpurchaser.

e) For shunt wound motors: equal to no-load excitation current corresponding to therated voltage.

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7.1.1.2 Main rheostat losses

These losses are calculated from the formula I 2R , where R is the resistance of the part of therheostat in circuit for the rating considered, and I is the value of the excitation current definedas in 7.1.1.1 above. They are also equal to the product, IU, of the excitation current multipliedby U , the excitation voltage which must be absorbed in the rheostat.

The sum of the losses, 7.1.1.1 and 7.1.1.2, is also equal to the product IU e of the excitationcurrent I and the total excitation voltage U e .

NOTE - Where a resistance is permanently connected in series in the excitation circuit it should be dealt with inthe same way as the main rheostat.

7.1.1.3 Exciter losses

NOTE - This applies only to the case where the exciter is mechanically driven from the main shaft and is usedsolely for exciting the main machine.

These losses include the difference between the power absorbed at the shaft by the exciterand the useful power which it provides at its terminals,* as well as the excitation losses in theexciter if this is excited from a separate source.

If the e xciter can be uncoupled from the main machine and tested separately, the power whichit absorbs may be measured by using the calibrated-machine method.

If th e exciter cannot be uncoupled from the main machine, the power which it absorbs may bemeasured either by the method of working the main machine as a motor on no-load, or by thecalibrated machine method (clause 13), or by the retardation method (clause 15), applied tothe whole unit. In these three methods, the power absorbed by the exciter is obtained as thedifference between the total losses of the unit measured under identical conditions, first withthe e xciter on -load and secondly with th e exciter non-excited, the excitation being supplied byan independentsource.

If none of these methods is applicable, the power absorbed by the exciter is obtained byadding to the power, measured at the terminals, the different separate losses determined asunder clause 6. However, mechanical friction and windage losses which are measured at thesame ti me as those of the main machine need not be ta ken into account.

7.1.2 Constant losses

7.1.2.1 No-load test at rated voltage

The constant losses shall be de termined by running the machine under n o-load conditions as a

motor with rated voltage applied and with rated speed achieved by adjustment of the exci-tation, which shall preferablybe derived from a separate source.

The total electric power absorbed, less the I 2R losses in the armature and in the excitationwinding or, if necessary, less the power absorbed by the exciter, gives the sum of the constantlosses.

* The useful power at the terminals of the exciter is equal to the sum of the losses, 7.1.1.1 and 7.1.1.2, of the mainmachine.

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7.1.2.2 Open circuit test

The constant losses can be determined separately by driving the machine at its rated speed bymeans of a calibrated machine. The machine on test is excited (preferably from an indepen-dent source), so as to work as a generator on no-load at a voltage equal to its rated voltage,the power which it absorbs at its shaft, and which can be obtained from the electric powerabsorbed by the calibrated machine, g iving the sum of the constant losses. By removing theexcitation, the sum of the friction and windage losses is obtained in the same way. The corelosses may be determined separately by subtracting the losses during this test from thosemeasured during the previous no-load test. By lifting the brushes the brush friction loss may bedetermined separately by subtracting the losses during this test from those measured duringthe previous, unexcited test.

7.1.2.3 Retardation test

In machines with large inertia, the total constant losses, as well as the separate constantlosses, can be determined by the retardation method.

7.1.3 Load losses

These are:

7.1.3.1 Armature circuit I 2R losses

These losses are calculated from the current and the measured resistance, corrected to thereference temperature, except that where resistance measurement is impracticable due to verylow resistances, calculation is permissible.

NOTE - U nder this heading are included compensating windings, commutating pole windings and diverters. Inthe case of diverters in parallel with a series winding, the I 2 R losses should be determined using the t otal

current and t he r esulting resistance.

7.1.3.2 Electrical losses in brushes

The sum of these losses shall be taken as the product of the armature current and a fixedvoltage drop.

The voltage drop allowed for all brushes of each polarity shall be 1.0 V for carbon or graphitebrushes and 0.3 V for metal-carbon brushes, i.e. a total drop of 2.0 V for carbon or graphitebrushes, and 0.6 V for metal-carbon brushes.

7.1.4 Additional load losses

Unless otherwise specified, it is assumed that these losses vary as the square of the current,and that their total value at maximum rated current is, for:

Uncompensated machines

1% of the rated input for motors;1% of the rated output for generators.

Compensated machines

0.5% of the rated input for motors;0.5% of the rated output for generators.

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For constant speed machines, the rated output or input as appropriate is taken as the output orinput which would be obtained at maximum rated current and maximum rated voltage.

For variable speed motors where the speed change is obtained by applied voltage, the ratedinput is defined at each speed as being the input when the maximum rated current at anyspeed is associated with the applied voltage o f the particular speed considered.

For variable speed motors where th e increase in speed is obtained by weakening the field, therated input is defined as being the input when the rated voltage is associated with the maxi-mum rated current. For variable speed generators where the voltage is maintained constant byvarying the field, the rated o utput is d efined as being the output which is available at the te rmi-nals at rated voltage and maximum rated current. The allowances for additional losses at thespeed corresponding to the full field shall be as specified above. The allowances for additionallosses at other speeds shall be calculated using the appropriate multiplying factors given intable 1.

Table 1

Multiplying factors for different speed ratios

Speed rati o Mult iplying fact or

1.5:12 :13 :14 :1

1.41.72.53.2

The speed ratio in the first column of table 1 shall be taken as the ratio of actual speed underconsideration to the minimum rated speed for continuous running.

For speed ratios other than those given in table 1 the appropriate multiplying factors can beascertained by interpolation.

NOTE - The additional load loss may be obtained from an input-output test or from a back-to-back test by sub-tracting from the total measured losses all other known losses.

7.1.4.1 Change in core loss due to load

In general, this variation is usually negligible. By special agreement, for very low voltagemachines, the sum, 6.2 a) and 6.4 a), may be measured as described for the constant lossesin active iron, 6.2 a) by one or other of the two methods, by operating as a motor on no-load oras a generator on no-load, but instead of making the test at the rated voltage, the test is made

at the rated voltage increased or decreased by the voltage drop in the armature circuit for thecurrent considered, depending on whether the machine is a generator or a motor.

1 7.1.4.2 Additional load losses in d.c. motors supplied by static power converters

Whenever the current ripple factor (see 2.29, IEC 34-1: 1994) of the armature currentexceeds 0,1, the additional losses caused b y the a.c. component of the a rmature current shallbe considered in a ddition to the losses specified in 7.1.4.

They shall be calculated as the eddy current losses caused by the fundamental component ofthe above-mentioned a.c. component.

The method of calculation used shall be the subject of agreement between manufacturer andpurchaser.

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1 7.2 Total loss measurement

7.2.1 Electrical back-to-back tests (see clause 16)

When identical machines are run at essentially the same rated conditions, the losses suppliedfrom the electrical system are assumed to be equally distributed and the efficiency iscalculated as 7.3.3.

The test shall be made as nearly as possible at the temperature attained in operation at theend of the time specifiedin the rating. No winding temperature correction shall be made.

7.3 Direct measurement of efficiency

7.3.1 Braking test

When the machine is run at rated conditions of speed, voltage and current, the efficiency isthen taken as the ratio of output to input. The test shall be made as nearly as possible at the

temperature attained in operation at the end of the time specified in the rating. No windingtemperature correction shall be made.

7.3.2 Calibrated machine test (see clause 13)

When the machine is run at rated conditions of speed, voltage and current, the efficiency istaken as the ratio of output to input.


7.3.3 Mechanical back-to-back test

When identical machines are run at essentially the same rated conditions, the losses areassumed to be equally distributed, and the efficiency is calculated from half the total lossesand the electrical input (in the case o f a motor) or electrical output (in the case of a g enerator).


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SECTION THREE - POLYPHASE INDUCTION MACHINES



8.1 Constant losses


b) Losses due to friction (bearings and brushes, if not lifted during operation) notincluding any losses in a separate lubricating system. Losses in common be aringsshall be stated separately whether or not such bearings are supplied with themachine.

NOTE - When the losses in a separate lubricating system are r equired these should be listedseparately.

c) The total windage loss in the machine, including power absorbed in integral fans,and in auxiliary machines, if any, forming an integral part of the machine. Thelosses in auxiliary machines such as external fans, water and oil pumps notforming an integral part of the machine, but provided exclusively for the machinein question, shall be included only by agreement.

NOTE - When the losses in a separate ventilating system are required they should be listedseparately.

8.2 Load losses

a) I 2R losses in primary windings.

b) I 2R losses in secondary windings.

c) Electrical losses in brushes (if any).


a) Losses introduced by load in active iron and other metal parts other than theconductors.

b) Eddy current losses in primary or secondary winding conductors caused by

current dependent flux pulsation.NOTE 1 - Losses, 8.3 a) and b), are sometimes called additional losses, but they do not include the additionalno-load losses in 8.1 a).

NOTE 2 - In t he case of auxiliary machines such as phase advancers driven mechanically from t he main shaft,the losses should be included in the same way as the exciter losses are included for synchronous machines.Losses in separately driven phase advancers or regulating equipment should be given separately for ratedoperating conditions of the main machine. These losses should be determined by the standard method for thetypes of apparatus involved.

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The efficiency can be calculated from th e total losses which are assumed to be the summationof the losses obtained in the following manner:


9.1.1.1 No-load test at rated voltage

The sum of the constant losses, 8.1 a), b) and c), is determined by running the machine as amotor on no-load. The machine is fed at its rated voltage and frequency. The po wer absorbed,decreased by the I 2R losses in th e primary winding, gives the total of the constant losses. TheI 2R lo sses i n the secondary winding may be neglected.

9.1.1.2 Calibrated machine test (see clause 13)

The constant losses may be determined separately by driving the machine, disconnected fromthe network, at its rated speed b y means of a calibrated motor (see 9.2.2). With the brushes, ifany, in place, the power absorbed a t the shaft o f the machine, which may be deduced from theelectrical power absorbed by the calibrated motor, gives the sum of the losses in 8.1 b)and 8.1 c). With the brushes, if any, lifted the sum of the bearing friction losses and the totalwindage losses is obtained in the same manner. The losses described in 8.1 a) may beobtained from th e test described in 9.1.1.1 by subtraction.

9.1.1.3 No-load test at variable voltage

The losses described in 8.1 a) and the sum of the losses described in 8.1 b) and c) may

alternatively be separated by running the machine as a motor at rated frequency but atdifferent voltages. The power absorbed, less the I 2R losses in the primary winding, is plottedagainst the square of the voltage. This, at low values of saturation, will give a straight linewhich can be extrapolated to zero voltage to give the sum of the losses, 8.1 b) and c).

It should be borne in mind that at very l ow voltages, losses plotted on th e diagram may be highbecause of the increased secondary winding losses with increased slip. When plotting thestraight line, those values should not be taken into account.

If the motor is started with a short-circuited secondary winding and the brushes are lifted(which is possible i f the supply generator is started at t he same time as the motor) the bearingfriction and total windage losses are obtained at zero voltage by extrapolation as above.

NOTE - For wound rotor motors a synchronous no-load test can be carried out as for synchronous machineswith d.c. excitation in two rotor phases (or three if desired).

9.1.2 Load losses

9.1.2.1 Load test

The losses described in 8.2 a) are calculated from the resistance of the primary windingsmeasured using direct current and corrected to the reference temperature, and from thecurrent corresponding to the load at which the losses are being calculated.

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To determine the l osses i n 8.2 b) when an on-load test is made, the secondary winding lossesare taken to be equal to the product of the sl ip and the total power transmitted to thesecondary winding, i.e. the power absorbed, decreased by the core losses in 8.1 a) and theI 2R losses in the primary winding in 8.2 a). This method gives directly the sum of the lossesin 8.2 b) and 8.2 c) for wound rotor machines, and the losses in 8.2 b) for cage machines. Forthis latter type of machine, this is the only applicable method as it is not possible to measurethe resistance and current of the secondary winding directly. When use i s made of this method,the slip may be measured by a stroboscopic method or by counting the beats of a permanent-magnet millivoltmeter connected between two rings (for motors with wound secondarywindings) or the terminals of an auxiliary coil (for motors with short-circuited secondarywindings) or between the ends of the shaft.

9.1.2.2 Calculated values

For wound rotor motors, the losses in 8.2 b) may be calculated from the resistance measuredby direct current and corrected to the reference temperature, and from the secondary currentcalculated from a circle diagram or equivalent circuit, account being taken of the true

transformation ratio of the machine. The type of circle diagram to be used should be agreedbetween manufacturer and purchaser.

To make an on-load test, the losses in 8.2 c) in the brushes cannot be measured directly andthese losses shall be taken as the product of the current flowing in the brushes and a fixedvoltage drop. The voltage drop in all brushes of the same phase shall be taken as 1.0 V forcarbon or graphite brushes, and 0.3 V for metal-carbon brushes.

9.1.2.3 Load test at reduced voltage

This method is also applicable to cage rotor machines.

When the voltage is reduced, while keeping the rotational speed of the machine constant, thecurrents diminish approximately in proportion to the voltage, and the power approximately inproportion to the square of the voltage. When the voltage is down to h alf its rated value, thecurrents will then be reduced to about one half, and the power to about one quarter, of theirvalues at the rated voltage.

When a load is applied to an induction motor at a reduced voltage U r, the power absorbed P 1r ,the main primary current I 1r and the slip s are measured, as well as the no-load current I or , atthe same reduced voltage U r, an d the n o-load current I o at the rated voltage U n.

The current vector I 1 of the load at rated voltage is obtained by constructing a vector diagram(figure 3) i n the fo llowing manner:

To the current vector I 1r multiplied by the ratio

add the vector:

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The resultant vector represents the current which would flow at the rated voltage U n for thefollowing absorbed power:

By means of the values I 1 , P 1 , thus determined, and with the slip s measured at reducedvoltage, it is then p ossible to calculate t he on-load losses, as indicated in 9.1.2.1.


Unless otherwise specified, it is assumed that the losses specified in 8.3 a) and 8.3 b) vary asthe square of the primary current and that their total value at full load is equal to 0.5% of therated input for motors and 0.5% of the rated output for generators.

NOTE - For some designs of small machines these losses might be higher than 0.5% of the rated input. If, for aparticular case, the value is of importance, the loss should be determined by the direct method of efficiencymeasurement.

1 9.2 Total loss measurement

9.2.1 Electrical back-to-back test (see clause 16)

When identical machines are run at essentially the same rated conditions, the losses suppliedfrom the electrical system are assumed to be equally distributed and the efficiency iscalculated from half the total losses and the electrical input to one machine.


NOTE - Where a gear box is required, as in the case of induction motors, it is necessary for the loss in this tobe deducted from the electrical input before determining the losses in the electrical machine.

9.3 Direct measurement of efficiency

9.3.1 Braking test

When the machine is run at rated conditions of speed, voltage and current, the efficiency istaken as the ratio of output to input.


9.3.2 Calibrated machine test (see clause 13)

When the machine is running in accordance with clause 13 at rated conditions of speed,voltage and current, the e fficiency is then taken as the ratio of output to input.

The test shall b e made as nearly as possible at the temperature attained in operation at theend of the time specifiedin the rating. No winding temperature correction shall be made.

9.3.3 Mechanical back-to-back test

When identical machines are run at essentially the same rated conditions, the losses areassumed to be equally distributed, and the efficiency shall be calculated from half the total lossand the electrical input. The driven machine operates as an induction generator if a source ofreactive power is provided, and a suitable load is connected to its terminals.


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SECTION FOUR - SYNCHRONOUS MACHINES



10.1 Constant losses


b) Losses due to fr iction (bearings and brushes), not including any losses in aseparate lubricating system. Losses in common bearings shall be statedseparately whether or not such bearings are supplied with the machine. Forwater-driven generators and synchronous motors for pump storage schemes, thelosses in thrust bearings, and if the thrust bearings are associated with guidebearings the total losses in those bearings, shall b e stated separately. The thrust-load, temperature of the bearings, and type of oil and oil temperature at which theloss values are valid shall also be given.

NOTE - When the losses in a separate lubricating system are r equired these should be listedseparately.

c) The total windage loss in the machine including power absorbed in integral fans,and in auxiliary machines, if any, forming an integral part of the machine. Thelosses in auxiliary machines such as external fans, water and oil pumps n otforming an integral part of the machine, but provided exclusively for the machinein question, shall be included only by agreement.

1 NOTE 1 - When the losses in a separate ventilating system are required they should be listedseparately.

NOTE 2 - For machines indirectly cooled or directly cooled by hydrogen, see 11.5 of IEC 34-1.

10.2 Load losses

a) I 2R losses in primary windings.

b) I 2R losses in starting or damping windings.

NOTE - These are significant only for single-phase machines.

10.3 Excitation circuit losses

a) I 2R losses in the excitation windings and in the excitation rheostats.

b) All the losses in an exciter mechanically driven from the main shaft which formspart of the complete unit, and is used solely for exciting the machine, togetherwith losses in the rheostat in the excitation circuit of such an exciter, but with theexception of friction and windage losses.

Losses in rotary rectifiers and in a gear, rope or belt, or similar drive betweenshaft and exciter should be included.

All the losses in any apparatus for self-excitation and regulation receiving its input

from the a.c. supply connected to the terminals of the synchronous machine.

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In the case of a separate excitation supply such a s a battery, rectifier or motorgenerator set, no allowance is made for the losses in the excitation source or inthe connections between the source and the brushes.

c) The electrical losses in brushes.


a) Losses introduced by load in active iron and other metal parts other than theconductors.

b) Eddy current losses in primary winding conductors.



The efficiency can be calculated from the total losses which are assumed to be t he summationof the losses obtained in the following manner:

11.1.1 Excitation circuit losses

11.1.1.1 Excitation winding I 2R losses

These losses are calculated from the formula I 2R , taking for R the resistance of the excitationwinding corrected to the reference temperature, and for I the value of the exciting current forthe particular rating of the machine, measured directly during the on-load test or calculatedwhen this test is not possible. Where such a calculation is made, the method to be used is for

agreement between manufacturer and purchaser.11.1.1.2 Main rheostat losses

These losses are calculated from the formula I 2R , where R is the resistance of the part of therheostat in circuit for the rating considered, and I is the value of the exciting current for therating considered defined as in 11.1.1.1. They are a lso equal to the product IU of the excitationcurrent at the particular rating, and the voltage U at the terminals of the rheostat.

NOTE - Where a resistance is permanently connected in series in the excitation circuit it should be dealt with inthe same way as the main rheostat.

11.1.1.3 Electrical losses in brushes

The sum of these losses shall be taken as the product of the excitation current at the ratingconsidered and a fixed voltage drop. The voltage drop allowed for all brushes of each polarityshall be 1.0 V for carbon or graphite brushes, and 0.3 V for metal-carbon brushes, i.e. a totaldrop of 2.0 V for carbon or graphite brushes, and 0.6 V for metal-carbon brushes.

The sum of the losses according to 11.1.1.1, 11.1.1.2 and 11.1.1.3, is also equal to the productIU e , of the exciting current I and the total excitation voltage U e .

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11.1.1.4 Exciter losses

NOTE - This applies only to the case where the exciter is mechanically driven from the main shaft and is usedsolely for exciting the synchronous machine.

These losses include the difference between the power absorbed at the shaft of the exciter andthe useful power which it provides at the terminals of the exciter*, and the excitation losses ofthe exciter if this machine itself is excited by a separate source.

If the exciter can be uncoupled from the main machine and tested separately, the p ower whichit absorbs may be measured by the calibrated machine method.

If th e exciter cannot be uncoupled from the main machine, the power which it absorbs may bemeasured either by the calibrated machine method or by the retardation method a pplied to thewhole unit. In these two methods, the power absorbed by the exciter is obtained as the dif-ference b etween the total losses of the unit measured under i dentical conditions, first with theexciter on-load and secondly with the exciter not excited, the excitation being furnished by anindependent source.

If none of these methods is a pplicable, the separate losses should be determined as describedunder clause 6 for d.c. machines (see 7.1.1.3, last paragraph).

NOTE - The manufacturer and purchaser should agree on the method of determining the losses in apparatus forself-excitation and r egulation receiving their input from the a.c. lines connected to the terminals of the machine.


11.1.2.1 Unity p ower factor test at rated voltage and frequency

The sum of the constant losses is generally determined by the method of running the machineas a motor on no-load. The synchronous machine is fed at its rated voltage and ratedfrequency, so as to work as a motor on no-load. The excitation is ad justed so that the machineabsorbs the minimum a.c. current. The electrical power absorbed, decreased by the I 2R loss inthe primary windings, and, if appropriate, by the power absorbed by the exciter, gives the sumof the constant losses.

NOTE - This latter correction may be avoided by the use of a separate source of excitation power.

11.1.2.2 Open circuit test

The sum of the constant losses, 10.1 a), 10.1 b) and 10.1 c), the losses 10.1 a), and the sumof the losses, 10.1 b) and 10.1 c), may also be determined by driving the machine at its ratedspeed by means of a calibrated machine. The machine is excited by an independent source so

as to work as a generator with open circuit at a voltage equal to its rated voltage. The powerwhich it absorbs at its shaft, and which may be calculated from the power absorbed from thecalibrated motor, gives the sum of the constant losses 10.1 a), 10.1 b) and 10.1 c). Byremoving the excitation, the sum of the losses, 10.1 b) and 10.1 c) is obtained in the samemanner. The core losses 10.1 a) are obtained by subtraction. Given the small number ofbrushes used on synchronous machines, it is generally not possible to separate the brushfriction losses from the sum of the other constant losses by means of a test with the brusheslifted.

* The useful power at the terminals of the exciter is equal to the sum of the l osses according to 11.1.1.1,11.1.1.2 and 11.1.1.3, of the main machine.

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11.1.2.3 Retardation test (see clause 15)

The sum of the constant losses 10.1 a), 10.1 b) and 10.1 c), the losses 10.1 a) and the sum ofthe losses, 10.1 b) and 10.1 c) may be determined by using the retardation method.

11.1.2.4 Unity power factor test at variable voltage

The losses 10.1 a), 10.1 b) and 10.1 c) may be separated by running the machine as a motorat rated frequency, but at different voltages as described in 9.1.1.3 of Section Three.

The power factor shall be maintained at unity by adjusting the excitation current during thetest.

11.1.2.5 Variable cooling gas density test

For machines cooled by a gas at variable pressure, the total windage loss may be separatedfrom the friction losses by tests at different densities of cooling gas.

NOTE - Tests at different speeds are under consideration.

11.1.2.6 Calorimetric test (see clause 17)

The bearing losses may be separately determined when possible by using the calorimetricmethod.

NOTE - The determination of losses in thrust bearings, possibly combined with guide bearings, in vertical shaftmachines, should only be made by agreement.

1 11.1.3 Load losses

These consist of I 2

R losses in primary windings. The I 2

R losses in the primary winding arenormally measured during the short-circuit test described in 11.1.4.

When they are t o be given separately,the losses are calculated from the rated current a nd theresistance of the windings corrected to the reference temperature.


Unless otherwise specified, the sum of the losses, 10.4 a) and 10.4 b) is measured by meansof the short-circuit test method.

The machine to be tested, with its primary winding short-circuited, is driven at its rated speedand so excited that the current in the short-circuited primary winding is equal to the ratedcurrent. The power absorbed at the shaft, decreased by the mechanical losses, 10.1 b)and 10.1 c), and the power absorbed by the exciter, if appropriate, presents the sum of theload losses and the additional losses, 10.2 and 10.4. If the leakage reactance is abnormallyhigh, as for a machine for high frequency, a correction shall a lso be made for core losses. Theload losses vary in different senses as a function of the temperature. The sum of the loadlosses and additional losses is assumed to be independent of the temperature and nocorrection is made to a reference temperature. Unless otherwise specified, it is assumed thatthe additional load losses vary as the square of the armature current.

1

NOTE - It is recognized that the sum of the additional losses, 10.4 a) and 10.4 b), thus determined, is generallya little higher than the losses which actually exist at rated load.

The power absorbed at the shaft of the machine during the short-circuit test may be measuredby the calibrated machine method (clause 13), or by the retardation method (clause 15).

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SECTION FIVE - METHODS OF TEST

12 General

Tests can be grouped in one of the three following categories:

a) Input-output measurement on a s ingle machine. This usually involves themeasurement o f mechanical power into, or out of a machine.

b) Input and output measurement on two machines connected back-to-back, e.g. twoidentical machines or a test machine coupled to a calibrated machine. This isdone to eliminate the measurement of mechanical power into or out of themachine.

c) Measurement of the actual loss in a machine under a particular condition.

This is not usually the total loss, but comprises certain component losses. Themethod may, however, be used to calculate the total loss or to calculate acomponent loss.

The choice of test to be made depends on the information required, the accuracy required, andthe type and size of the machine involved. Where alternative methods are available for aparticular type of machine, the preferred method is indicated (see clause 18).

1 A distinction is made between direct and indirect efficiency determination.

The direct determination of efficiency is made by measuring directly the power supplied by th emachine and the power absorbed by it.

The indirect determination of efficiency is made by measuring the losses of the machine.Those losses are added to the power supplied by the machine, thus giving the absorbedpower.

The indirect determination may be carried out by th e following methods:

(i) determination of separate losses for summation;

(ii) determination of total losses.

NOTE - The methods for determining the efficiency of machines are based on a number of assumptions; it i stherefore not possible to make a comparison between the losses obtained by the direct method of measurementand those obtained by the measurement of the separate losses.

Unless otherwise specified, the guaranteed efficiency of a machine is that which is based onthe determination of separate losses, but when there is a choice of method, the evaluation ofefficiency should be based on the a ccuracy obtainable from the method, the efficiency and thetype of machine involved.*

* In some countries 90% efficiency is accepted as a basis f or using the indirect method whereas some other countriesprefer a lower value, e.g. 70%.

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1 The methods of determination of losses covered b y this clause are basically intended for largesynchronous machines, b ut the principles used can also be applied to other machines (a.c.induction and d.c. machines, exhibiting mainly an appreciable rotational inertia) using theappropriate losses for such machines.

15.1 General

The retardation method is used to determine:

- sum of the friction loss and windage loss (”mechanical losses”) in machines of a lltypes;

- sum of losses in active iron and additional open-circuit losses in d.c. and syn-chronous machines;

- sum of I 2R losses in an operating winding and additional load losses (”short-circuitlosses”) in synchronous machines.

15.1.1 Fundamentals

The total of the loss P t which retard the machine is proportional to the product of the speed towhich these losses correspond and the deceleration at this speed:

When n is expressed in rev/min and P t is given in kW, then the retardation constant C i s:

where J is given in kg/m 2.

The deceleration d n /d t can be obtained either directly, using an accelerometer, or indirectly, byone of the methods given in 15.1.2, 15.1.3 and 15.1.4 below.

15.1.2 Method of the chord

This requires the measurement of the time interval t 2 − t 1 during which the speed of the testedmachine changes from n N (1 + δ) to n N (1 − δ), see figure 4. The ratio of speed interval 2 δ n Nto time interval t 2 − t 1 is approximately the deceleration at rated speed:

The value of deviation δ shall not be greater than 0,1 and may have to be less than thisdepending on the characteristics of the machine.

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1 15.1.3 Method of the limiting secant

This is a variant of the method of the chord and is intended to be applied in cases when thespeed of rotation cannot be increased above the rated value. The instant of time when thespeed of rotation is of the rated value n N is marked as t 1, and the time instants at which thespeed of rotation acquires the values of (1 − δ)n N are marked as t 2. The deviation δ issuccessively decreased, and the time derivative of the speed of rotation is the limit of thetangent of the angle made by the line passing through the points t 1 a nd t 2 with the t ime axis, asδ approaches zero, see figure 5.

15.1.4 Method of the average speed of rotation

If t 1, t 2 and t 3 represent the successively recorded time read ings, the shaft making N completerevolutions within the time interval between any two subsequent readings, then the averagevalues of speed d uring the time intervals shall be:

and the deceleration of the shaft at an intermediate moment of time t 2

Calculated values of deceleration are plotted against the average values of speed of rotation.The value of deceleration at the rated speed of rotation is determined from the curve.

15.2 Composition of retardation tests

15.2.1 Composition of te sts with known moment of inertia

When the moment of inertia of a machine rotating part is known by measurement or by design,then for a d.c. machine two basic retardation tests are sufficient: the machine running

unexcited and the machine running open-circuited, excited at rated voltage at rated speed. Fora synchronous machine a third retardation test should be made with the armature windingbeing short-circuited and the excitation set to give the rated armature current.

The first test gives the mechanical losses of the tested machine from the formula:

The second test gives the total of mechanical losses and iron losses from the formula:

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1 The third test gives the sum of mechanical losses and short-circuit losses from the formula:

In the above equations

are the values of speed derivative in time in the first, second and third tests respectively.

The iron losses are determined as the difference of the losses measured in the second a ndfirst t ests.

The sum of the I 2R losses an d the a dditional losses in the armature circuit are determined as

the difference of losses measured in the third and first tests. Separation of this sum intocomponents, if required, is done by subtracting from it the I 2R losses in the armature circuitcalculated from the armature circuit resistance corresponding to the test temperature. For thispurpose the winding temperature shall be deduced by the appropriate method of temperaturemeasurement directly after each retardation test with the armature circuit being short-circuited.

15.2.2 Composition of te st with unknown moment of inertia

When the moment of inertia of a machine rotating part is n ot known, or the machine is coupledmechanically to other rotating parts, e.g. a turbine, whose inertia is not known, then someadditional tests shall be carried out to determine the retardation constant C .

In the instance where there is a possibility to run the tested machine as an unloaded motorfrom a power supply of the proper voltage, number of phases and frequency (in the case ofa.c. machines), and the power supplied to the tested machine can be measured, (equal to thesum of the mechanical losses and iron losses as the armature circuit I 2R losses are usuallyignored), then the retardation constant C is determined from the formula:

If the measurement of power is d ifficult because of frequency oscillations of the power supply,then as an alternative the energy supplied to the tested machine may be measured with anintegrating meter. For this p urpose it is necessary t o run the machine as a motor for some timeat constant supply conditions.

In the instance where there is no possibility of running the tested machine as an unloadedmotor, then, i n addition to the three retardation test considered in 15.2.1, one more retardationtest shall be conducted. The tested machine in this case is slowed down by any losses P whichcan be measured and a re of the same order as the expected losses P Fe , and P k. For thispurpose the open-circuit or short-circuit losses of a connected transformer can be used, whichare separately measured. Alternatively, if an exciter or auxiliary generator mounted on thetested machine shaft is available, its load with a ballast resistance may be used.

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1 If the tested machine is slowed d own by the transformer open-circuit losses, and the short-circuit losses according to the transformer open-circuit current are ignored, then

hence

When the tested machine is slowed down by the transformer short-circuit losses, usually theiron losses corresponding to magnetic flux in the short-circuited transformer are ignored.

Hence

and

When the tested machine is slowed down by an exciter or auxiliary generator loaded with aballast resistance, the retardation losses consist only of the tested machine mechanical lossesP f and the measured load P (with allowance for efficiency of the load machine that can bedetermined by calculations). Hence:

so that

15.3 Retardation test procedure

15.3.1 State of a tested machine during retardation tests

A tested machine shall be completely assembled as for normal operation. The bearings shallbe ”run in” prior to the test. The air temperature shall be adjusted wherever possible to thenormal temperature at which the windage loss measurement is required by throttling the aircoolant flow. The bearing temperatures shall be adjusted to the normal temperature at whichthe b earings operate with rated load, by adjusting the coolant flow.

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1 15.3.2 Tested machine coupled with other mechanisms

When possible, the tested machine shall be uncoupled from ot her rotating parts. If the machinecannot be uncoupled, all possible steps shall be taken to reduce the mechanical losses inother rotating parts, e.g. by partial dismantling or in the case of a water turbine, by removingwater from the runner chamber. Means shall also be ta ken to eliminate the possibility of waterflowing from the upstream side and from drawing water by the rotating runner from thedownstream side. Rotation of the runner in the air produces windage losses which can bestated experimentally or from calculations by agreement between manufacturer and purchaser.

15.3.3 Rotation of a tested machine

In some cases the tested machine can be driven by its normal prime mover, e.g. by Peltonturbine where the water supply to the runner can be cut off instantly. However, the testedmachine is usually running as a motor on no-load, fed from a separate source with a widerange of variable speed in all cases the excitation shall be obtained from a separate sourcewith a rapid and precise voltage control. The excitation from the inherent mechanically-coupled

exciter is not recommended in principle, but may be permitted in those cases when the valueof the deviation of speed δ is relatively small, e.g. it does not exceed 0,05. In all these casesthe losses in exciters coupled to the shaft of the tested machine shall be taken into account.

15.3.4 Procedure performed prior to starting the tests

Each test begins with the tested machine being rapidly accelerated to a speed above (1 + δ) n Nso that during deceleration to this speed the machine can be placed in the required condition,namely:

- the machine is disconnected from a supply source;

- in the case of retardation by only mechanical loss, the machine field is suppressed;

- in the case of retardation by the sum of the mechanical loss and short-circuit losses,the machine field is suppressed, the armature terminals are short-circuited and themachine is reexcited to the preset short-circuit current;

- in the case of retardation by the transformer losses after field suppression, the testedmachine is connected to the transformer previously set to a certain state (at no loador short-circuit) and excited to the preset values o f current or open-circuit voltage;

- in the case of retardation by the exciter load losses or auxiliary generator mountedon the machine shaft, the tested machine field is suppressed and the specified loadis set simultaneously.

In all cases described above a sufficient time delay shall separate the switching off of thesupply and starting the measurements to al low electromagne tic transients to decay.

In the case of retardation by the sum of mechanical and iron losses or by the open-circuitlosses of a supply transformer, no procedures are required after the machine is disconnectedfrom the supply if the tested machine excitation corresponds to the preset open-circuit voltage,in the case of a synchronous machine, at rated speed and unity power factor.

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1 15.3.5 Procedures during retardation

The readings of all instruments used for each te st (field current ammeter, open-circuit voltagevoltmeter, short-circuit current ammeter) and o f all instruments required to measure the powerin ad ditional retardation tests when the moment of inertia J is not known shall be taken at theinstant when the tested machine passes through rated speed; no readings at this instant arerequired in the case o f an unexcited retardation test.

The measured values of open-circuit voltage or short-circuit current shall not differ from thepreset values by more than ±2%. T he calculated final value o f the speed derivative in time foreach of the tests shall be adjusted proportionallyby the ratio of the square of the preset valueto the measured value.

15.3.6 Program of retardation tests

The retardation tests shall be conducted as a series without interruption, whenever possible. Itis recommended that the series start and finish with some retardation tests of an unexcited

machine. If for any reason the test series is not conducted in a continuous manner then it isrecommended that each subsequent series of tests start and finish with some unexcitedretardation tests.

Tests may be either repeated several times at the same preset values of open-circuit voltageor short-circuit current, e.g. at ra ted values, or at various values within limits of the order of95% - 105% of the rated values. In the first case the arithmetic mean values obtained from allmeasurements are assumed to be the real measured value of each type of loss. In the secondcase the values are plotted on a curve as a function of voltage or current. Real measuredvalues are assumed to be those occurring at the points of intersection of the preset values ofvoltage or current as read from the curves.

Additional retardation tests, when the moment of inertia of the tested machine is not known,shall be conducted at th e same values of voltage or current a s those obtained with the windingopen or short-circuited. If this is not possible the respective values shall be determined fromcurves as indicated above.

15.4 Taking of measurements

15.4.1 Methods of measurements

The measurements taken during retardation tests are aimed at obtaining the required value ofthe speed derivative in time and may be performed by one of the three methods:

a) accelerometric - direct measurement of deceleration with time:

b) tachometric - by determining the dependence of speed with time:

c) chronographic - by determining the dependence of angular displacement of thetested machine shaft with time:

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1 The stator voltage frequency provides the best means of determining the speed of asynchronous machine.

15.4.5 Measurement of losses in bearings

The losses in bearings and thrust bearings can be subtracted from the total sum of themechanical losses, if required. These may be determined by the calorimetric method inaccordance with IEC 34-2A. If the tested machine u ses direct-flow cooling of the bearings,these losses are distributed between the tested machine and any other coupled to itmechanically, such as tu rbine, in p roportion to the masses of their rotating parts. If there is nodirect-flow cooling, the distribution of bearing losses shall be determined from empiricalformulae by agreement between manufacturer and p urchaser.

16 Electrical back-to-back test

This method is applicable when two identical machines are available. The machines are

coupled mechanically and electrically so as to operate at rated speed, one as a motor and theother as a generator. The actual temperature at which the measurements are carried outshould be a s close as possible to the working temperature and n o further correction should bemade. The losses of the assembled machines are supplied either by a network to which theyare connected, or by a calibrated driving motor, or by a booster, or else by a combination ofthese various means.

The average value of the armature currents is adjusted to the rated value, the average of thevoltage of the two armatures is above or below the rated voltage by an amount equal to thevoltage drop, d epending on whether the d.c. machines are intended to be used respectively asgenerators or as motors.

Where two induction machines are electrically connected, they should be mechanically coupledwith a speed adjusting device, such as a gear box, to ensure the correct circulation of power.The magnitude of power circulated d epends upon the difference in speed. The electricalsystem supplying the losses to the two machines will be required to provide magnetizing kvarto both machines.

When two synchronous machines are electrically connected, they should be mechanicallycoupled with a correct angular ph ase relationship. The magnitude of the power circulateddepends upon the d ifference in phase angle between them.

1 17 Calorimetric test

Measurement of losses by calorimetric methods shall be performed in accordance withIEC 34-2A.

18 Schedule of preferred tests

18.1 D.C. machines

The preferred test for d.c. machines is in accordance with 7.1 and the preferred method ofcalculating the efficiency is in accordance with 7.1.2.

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18.2 Polyphase induction machines

The preferred test for polyphase induction machines is in accordance with 9.1 and thepreferred method of determining the constant losses is in accordance with 9.1.1.1.

18.3 Synchronous machines

The preferred test for synchronous machines is in accordance with 11.1 and the preferredmethod of determining the constant losses is in accordance with 11.1.2.1.

Figure 1 - Mechanical back-to-back test.

Figure 2 - E lectrical back-to-back test.

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Figure 3 - Vector diagram for obtaining vector of load current I 1 at rated voltage.

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1

Figure 4 - Method of the chord

Figure 5 - Method of the limiting secant

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2 Annex A

(Informative)Provisional methods for determining losses and efficiency

of converter-fed cage induction machines

INTRODUCTION

This annex applies to cage induction machines with rated frequencies up to 120 Hz supplied byconverters which have an intermediate circuit and are of the following types: I-converters andU-converters, typically Pulse Width Modulated (PWM).

The methods to determine losses and efficiency given in section 3 are partly no longerapplicable and this annex indicates the test modificationsthat are necessary.

NOTE - The six-step converter is a special case of the pulsed converter.

In general, when fed from a converter, the motor losses are higher than during operation on asinusoidal system. These additional losses depend on the harmonic spectrum of the impressedsupply quantity (either current or voltage). Their magnitude is influenced by circuitry andcontrol method of the converter. Consequently a simple factor to cover these additional lossescannot be found.

The determination of l osses and e fficiency will therefore preferably use procedures where themotor is operated together with the same converter with which it is g oing into service. It is alsounderstood that suitable methods shall not re quire the knowledge of d esign data of the motor,such as the rotor bar geometry.

A.1 Determination of losses and efficiency of converter-fed motors

A.1.1 Components of the additional losses

In cage induction motors additional losses 1) are produced due to the harmonics in eithercurrent or voltage; they are made up of the following components:

a) additional I 2R losses in primary windings;

b) additional I 2R losses in secondary windings;

c) additional losses in active iron.

NOTE - The physical effects giving rise to the additional losses are treated in Chapter 5 of IEC 34-17,1992: ”Guide for the application of cage i nduction motors when fed from converters”.

1) These additional losses are due to harmonics of the supply and do not contain the additional losses describedin 8.1 a) and 8.3 which refer to sinusoidal supply of fundamental frequency only.

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2 A.1.2 Efficiency determination by input-output measurement

The motor input-output measurement as indicated in clause 12 is a preferred method since alladditional losses are incorporated in the result (see clause A.3); however, the measuringequipment must have sufficient accuracy for measuring power, torque and speed as well as anappropriate frequency range. Therefore, additional requirements for measuring instruments andaccessories beyond the content s of clause 3 have to be specified (see clause A.2).

To keep within a required relative tolerance of the resulting motor efficiency, the maximumrelative e rror ( ∆P / P in) max of the power measurement has to be decreased with increasingefficiency, as shown in figure A.1.

Figure A.1 - Maximum permissible relative error ( ∆P /P in) max

of input as well as output measurement 2)

There is also the possibility to determine the overall efficiency of the complete systemconsisting of converter and motor by input-output measurement, applicable on agreementbetween manufacturer and purchaser. In this case the motor efficiency cannot be determinedseparately.

A.1.3 Efficiency determination by summation of losses

A number of presumptions made in 9.1 are no longer valid for motors fed from converters. Inthe no-load test, the I 2R losses in the secondary winding (9.1.1.1) may not be neglected.Therefore the iron losses cannot be separated. The no-load test at variable voltage (i.e. atvariable flux) according to 9.1.1.3 cannot be carried through with many commercial converters,due to the limited range of adjustment; consequently there will be no possibility to separate thefriction and windage losses (8.1 b) and c)) from the other losses by a no-load test.

Concerning the load test, the statement in 9.1.2.1 that ”the secondary winding losses are takento be equal to the p roduct of the slip and the t otal power transmitted to the secondary winding”is only valid for a machine operated with a sinusoidal current of fundamental frequency.Moreover, to calculate the I 2R losses of the primary winding by means of the resistancemeasured using direct current (9.1.2.1) will produce an error due to eddy currents.

2) δ = tolerance as described in IEC 34-1, table VIII, items 1 and 2. The curves are based on a simplified errorconsideration, assuming errors ∆P of equal magnitude in P in and P out . Figure A.1 is a graph of the equation(∆P / P in) max = δ . (1 − η) / (1 + η).

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2Hence when using the method of summation of losses certain assumptions have to be made(see clause A.4).

A.1.4 Efficiency determination by the ca lorimetric method

The calorimetric method is especially useful for application to converter-fed motors since thelosses are measured independently of the waveforms of volt ages and current s.

The calorimetric calibration method according to clause 3 of IEC 34-2A has been found ofadvantage since it does not require measurement of the mass rate of flow; hence the densityof the cooling medium, being functions of humidity and temperature, need not be known.Moreover, the variation of specific heat capacity can usually be disregarded.

In a set-up according to Figure A.2 the power absorbed in the dissipation resistor can bemeasured without difficulty, so that the motor losses may be calculated from the proportion:

where

P v represents the motor losses;P d represents the power absorbed in the dissipation resistor;T 1, T 2, T 3 represents the measured temperatures at the points indicated in Figure A.2.

The measuring accuracy depends mainly on the magnitude of temperature rise values ( T 2 − T 1)and ( T 3 − T 2). The measurement has to be made in accordance with clause 13 of IEC 34-2A, toenable an accuracy of measurement as indicated in clause 15 and table II.

Figure A.2 - Schematic diagram of a test set-up for thecalorimetric calibration method

A.1.5 Efficiency determination by summation of losses from tests on a sinusoidalsystem with lumped increments to take care of the additional losses

Often standard design motors and converters are coupled together only on the site of service.Especially in these cases a method to determine efficiency by adding a lumped increment tothe known losses on sinusoidal supply would be welcome, but, as mentioned before, there is

no chance to define suitable values covering the wide variety of converter circuits and controlmethods. At the present state, experimental data collected for a certain range of output andcircuitry allow only a limited statement on lumped increments (see clause A.5).

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2 A.1.6 Recommended methods

Depending on the rating of the motors, application of the following methods is recommendedfor machines of rated frequency 50 Hz or 60 Hz:

a) Input-output measurement (clause A.3) when fed from I- or U-converter for motors≤50 kW.

The method may also be applied to motors of higher rated output by agreementbetween the purchaser and the manufacturer. 3)

b) Summation of losses when fed from I-converter (A.4.1) or U-converter (A.4.2) formotors >50 kW.

c) Summation of losses with sinusoidal supply (9.1) and no-load test when fed fromU-converter (clause A.4.3) for motors tested in a test-shop (irrespective of rating).

d) The calorimetric method (A.1.4) applicable to all ratings with I- and U-converter.

A.2 Requirements for the measuring instruments

Instruments for r.m.s. current and voltage and for active power are necessary. In theinput-output measurement method, the latter determines, together with the equipment tomeasure torque and speed, the accuracy of the results.

Regarding the contribution of the harmonics to the losses, care has to be taken to selectmeasuring equipment capable of operating in the range of relevant frequencies with sufficientaccuracy. The following is required of the frequency range 4) f r of the measuring equipment with

inclusion of instrument transformers, transducers and shunt resistors:f r = 10 f 1 for six-step converters;

f r = 6 f p for PWM converters, with a maximum of 100 kHz;

where

f 1 is the maximum rated frequen cy;

f p is the maximum pulse frequency (carrier frequency).

For six-step converters, these requirements can be met by conventional electrodynamicinstruments. For PWM converters it is necessary to employ equipment with a broaderfrequency range. These will preferably be electronic instruments with AD-converters and digitaldata p rocessing.

3)If by agreement the method is applied to motors of higher rating, i t has to be accepted that the error of thedetermined efficiency can exceed the tolerance values given in IEC 34-1, Table VIll.

4) For conventional indicating measuring instruments (see IEC 51) the accuracy is specified for the nominal

frequency (e.g. 0,2 % for 40 ... 60 Hz), while an additional error of the class accuracy is tolerated at an upperspecified frequency (e.g. 0,4% at 1000 Hz). For electronic measuring instruments, usually a frequency range isindicated which means the upper specified frequency. The accuracy is given both for 50 Hz or 60 Hz and for theupper specified frequency. In the following this will be called the frequency range of an instrument.

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2 NOTES

1 With high values of pulse frequency the two-wattmeter (Aron) method should not be used since, due tocapacitive currents, the sum of input currents may differ from zero. Hence, one power measuring instrument perphase shall be applied.

2 It is considered that t he following accuracies are within reach with appropriate measuring equipment: powerwith 0,5%, torque with 0,4% and speed with 0,1%.

3 The converter output harmonics and their dominant order numbers depend on the modulation method. Basicconsiderations are given in clause A.6.

A.3 Total loss measurement

To determine the efficiency of motors when fed from converters, the braking test ((9.3.1) seeamendment 1) or the calibrated machine test ((9.3.2) see amendment 1) may be applied.These methods are also applicable to operating conditions with other t han rated frequency,including field-weakening.

This direct method is restricted to machines not exceeding the limit of rated power referred toin A.1.6.

A.4 Summation of losses

The summation of losses can be applied by means of a modified no-load test (9.1.1.1) and amodified load test (9.1.2.1). Both are carried through at rated frequency and voltage, thevoltage being adjusted according to the features of the converter, e.g. by means of an inherentcharacteristic curve or by field-orientedcontrol.

Different modifications have to be observed for I-converters and U-converters.

A.4.1 Motor supplied by I-converter with block-wave output. 5)

It is assumed th at the waveform of the current does not change between no-load and full load,so that the relative harmonic content is independent of the load. It is also a ssumed that theadditional iron losses are predominantly losses due t o magnetic reversal of leakage fluxes.Under these assumptions the additional losses due to harmonics depend mainly on t he currentand vary with the square of the primary r.m.s. current.

In theory this allows determination of the additional losses under load from the difference of”constant losses” measured in no-load tests on both sinusoidal and converter supply. Inpractice, however, considerable errors would have to be expected from such a method.

A.4.1.1 No-load test when fed by converter

The difference between the measured in put and the primary winding losses as calculated fromthe d .c. resistance contains the constant losses (according to 8.1, taking only the fundamentalinto account) and the following components:

- additional primary winding losses due to increased resistance because of eddycurrents,

- additional iron losses,

- secondary winding losses due to harmonics.

5) Specifications for supply by I-converters with pulse-width-modulation are not contained in this document.

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2 All these components will appear within the sum of the constant losses when applying the no-load tests (9.1.1.1).

A.4.1.2 Load test when fed by converter

When applying the method of 9.1.2.1 with readings from the load test with converter, thecalculated secondary winding losses will be too small. In order to compensate for thedifference of harmonic secondary winding losses u nder load a nd no-load, and for eddy currentlosses of the harmonics in the primary winding, 0,5% of the input power shall be added to thelosses at full load (i.e. additionally to the lumped additional losses of 0,5% prescribedby 9.1.3), unless otherwise agreed, and assuming that the losses vary as the square of theprimary current.

A.4.2 Motor supplied by U-converter

NOTE - The following applies both to six-step and PWM converters.

It may be assumed that the absolute values of the harmonic currents are independent of theload. The efficiency will be obtained by applying a no-load test and a load test both withconverter.

The additional losses are contained in the ”sum of the constant losses” as determined from theno-load test according to 9.1.1.1. Consequently the I 2R losses in the secondary winding to betaken into account in the summation of losses are those due to the fundamental slip frequencycurrents only. They are determined from the load test in a way different from 9.1.2.1; they aretaken to be equal to the product of the slip and the fundamental power transmitted to the rotor,i.e. the power absorbed, decreased by the I 2R losses in the primary winding and the ”sum ofthe constant losses” except the friction and windage losses. Th e latter can be determined froma retardation test. The lumped value of the additional load losses due to the fundamentalaccording to 9 .1.3 has to be applied.

Figure A.3 gives a diagram of the harmonic power and corresponding additional losses.Separation of the additional losses is only possible when the constant losses with sinusoidalsupply are known.

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2

Figure A .3 - Power and losses diagram 6) :a) with a sinusoidal supply, andb) harmonic power and corresponding

additional losses due to non-sinusoidal supply

A.4.3 Summation of losses by a load test with sinusoidal supply and a no-load test with

converter s upply

When a sinusoidal supply is available, the load losses shall be determined from the load testas specified in 9.1.2.1. The n o-load test is performed according to 4.9.

The additional load losses as specified in 9.1.3 have to be applied.

A.5 Method with assumed increments to the losses determined on sinusoidalsupply

Experience available from three-phase cage induction motors tested both with sinusoidal

waveform and with converter supply has been e valuated to obtain the additional losses,expressed as percentage of the input, whilst the output was the same in both cases.

- For machines between 30 kW and 1015 kW rated output, operated with six-stepI-converter and 50 Hz or 60 Hz rated frequency, the additional losses due toconverter supply are between 0,6% and 1,25% of the input. A suitable assumedincrement for motors above 30 kW rated output is 1%.

6) Symbols in figure A.3:P in, f = fundamental input power;

P δ = power transmitted to the secondary winding;P out = output ;P in, h = harmonic input power;P out ,h = harmonic output power.

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2 - For machines with U-converters the results depend on pulse-frequency, pulse-generating scheme and modulation index. The experimental results from PWMconverters with sinusoidal reference wave showed additional losses from almostnegligible values up to 3% of the input. With six-step U-converters a suitableassumed increment is 1,5%.

A.6 Basic considerations concerning converters

A.6.1 Typical converter output waveforms

Figure A.4 - Typical voltage and current waveform:a) six-step I-converter drive;b) six-step U-converter drive;c) PWM U-converter drive

A.6.2 PWM-converter harmonics

The harmonic spectrum of the converter output voltages and currents depends on themodulation method.

Analytical expressions can be found for synchronous pulse generation by interaction of acarrier-wave an d a reference-wave, with a constant ratio of their frequencies. Examples areU-converters with pulse-width modulation. The spectrum o f voltage harmonics can then bedescribed in terms of fundamental frequency f 1, pulse frequency f p and modulation index M.

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2 Let f 1 be the converter fundamental frequency, then the harmonics will be of f n = n . f 1;n being an integer for synchronous modulation methods. With three-phase bridgesix-step converters the harmonics are of the order n = 5, 7, 11, 13..., the harmoniccontent decreasing with increasing n .

The pulse frequency f p is equal to the number o f turns-on per second of the valves in onemain branch of the converter; for PWM modulation it is identical with the samplingfrequency. The quantity p = f p / f 1, called the carrier ratio, is selected to be a multiple of 3to give a balanced three-phase output. Sine- and square-wave modulation produce aharmonic spectrum at the output with harmonics of the order numbers n = p ± m g(m g = 2, 4, ...) and n = 2p ± m u (m u = 1, 3, ...).

The modulation index M is defined as the ratio of the reference wave amplitude and thecarrier wave amplitude. Over a wide range of M a harmonic near 2 f p is dominant in themotor terminal voltage spectrum.

Given the voltage harmonics at the motor input, the current ha rmonics will depend on the

motor impedance.

Asynchronous pulse-pattern generation schemes can result in fractional harmonic ordernumbers.

Motor current harmonics can further be decreased by inserting filters between converter outputand motor input. In the case of I-converters operated with pulse-width modulation, a filter (withcapacitors) is essential for its performance.

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AS 1359.102.1꞉1997 (EN) IEC 34-2+A2꞉1996 ᴾᴼᴼᴮᴸᴵᶜᴽ

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Transcript of AS 1359.102.1꞉1997 (EN) IEC 34-2+A2꞉1996 ᴾᴼᴼᴮᴸᴵᶜᴽ