Bsi bs en 60034 2 1999 (2000)

If, however, these are given separately, they should be regarded I1 = load current at rated voltage I1r = main primary current at reduced voltage Io = no-load current at rated voltage Io

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Rotating electrical

machines —

Part 2: Methods for determining losses

and efficiency of rotating electrical

machinery from tests (excluding

machines for traction vehicles)

The European Standard EN 60034-2:1996 together with amendments A1:1996

and A2:1996 has the status of a British Standard

ICS 29.160.01

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This British Standard, having

been prepared under the

direction of the

Electrotechnical Sector

Board, was published

under the authority of the

Standards Board and

comes into effect on

Text introduced by amendments A1 and A2 is indicated by a sideline

The UK participation in its preparation was entrusted to Technical Committee PEL/2, Rotating electrical machinery, which has the responsibility to:

— aid enquirers to understand the text;

— present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed;

— monitor related international and European developments and promulgate them in the UK

A list of organizations represented on this committee can be obtained on request to its secretary

From 1 January 1997, all IEC publications have the number 60000 added to the old number For instance, IEC 27-1 has been renumbered as IEC 60027-1 For a period of time during the change over from one numbering system to the other, publications may contain identifiers from both systems

Cross-references

The British Standards which implement these international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic

Catalogue

A British Standard does not purport to include all the necessary provisions of

a contract Users of British Standards are responsible for their correct application

Compliance with a British Standard does not of itself confer immunity from legal obligations.

Amendments issued since publication

Amd No Date Comments

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Page

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November 1996

UDC 621.313.017.2/.6.017.8.083.001.4

ICS 29.160.00

Supersedes HD 53.2 S1:1974 Descriptors: Rotating electrical machines, power losses, efficiency, determination, tests, power measurements

Machines électriques tournantes

Partie 2: Méthodes pour la détermination des

pertes et du rendement des machines

électriques tournantes à partir d’essais

(à l’exclusion des machines pour véhicules de

traction)

(inclut les amendements A1:1996 et A2:1996)

(CEI 34-2:1972 + IEC 34-2A:1974 +

A1:1995 + A2:1996)

Drehende elektrische Maschinen Teil 2: Verfahren zur Bestimmung der Verluste und des Wirkungsgrades von drehenden elektrischen Maschinen aus Prüfungen (ausgenommen Maschinen für Schienen- und Straßenfahrzeuge) (enthält Änderungen A1:1996 und A2:1996) (IEC 34-2:1972 + IEC 34-2A:1974 + A1:1995 + A2:1996)

This European Standard was approved by CENELEC on 1996-07-02

CENELEC members are bound to comply with the CEN/CENELEC Internal

Regulations which stipulate the conditions for giving this European Standard

the status of a national standard without any alteration

Up-to-date lists and bibliographical references concerning such national

standards may be obtained on application to the Central Secretariat or to any

CENELEC member

This European Standard exists in three official versions (English, French,

German) A version in any other language made by translation under the

responsibility of a CENELEC member into its own language and notified to the

Central Secretariat has the same status as the official versions

CENELEC members are the national electrotechnical committees of Austria,

Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy,

Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and

United Kingdom

CENELEC

European Committee for Electrotechnical StandardizationComité Européen de Normalisation ElectrotechniqueEuropäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B-1050 Brussels

Ref No EN 60034-2:1996 + A1:1996 + A2:1996 E

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The text of the International Standard

IEC 34-2:1972 + IEC 34-2A:1974, prepared by

SC 2G, Test methods and procedures, of IEC TC 2,

Rotating machinery, was approved by CENELEC as

HD 53.2 S1 on 1974-12-11

This Harmonization Document was submitted to

the formal vote for conversion into a European

Standard and was approved by CENELEC as

EN 60034-2 on 1996-07-02

The following date was fixed:

Foreword to amendment A1

The text of amendment 1:1995 to the

International Standard IEC 34-2:1972, prepared by

Rotating machinery, was submitted to the formal

vote and was approved by CENELEC as

amendment A1 to EN 60034-2 on 1996-07-02

without any modification

The following dates were fixed:

For products which have complied with

HD 53.2 S1:1974 (converted into EN 60034-2)

before 1997-06-01, as shown by the manufacturer or

by a certification body, this previous standard may

continue to apply for production until 2002-06-01

Foreword to amendment A2

The text of document 2/939/FDIS, prepared by

IEC TC 2, Rotating machinery, was submitted to

the formal vote and was approved by CENELEC as

The text of document 2G/73/FDIS, prepared by

was submitted to the IEC-CENELEC parallel vote

and was approved by CENELEC for inclusion into

NOTE Amendment 2 to IEC 34-2, published in November 1996, contains both documents 2/939/FDIS and 2G/73/FDIS.

The following dates were fixed:

For products which have complied with

HD 53.2 S1:1974 (converted into EN 60034-2) before 1997-06-01, as shown by the manufacturer or

by a certification body, this previous standard may continue to apply for production until 2002-06-01

— latest date by which the EN

has to be implemented at

national level by publication

of an identical national

standard or by endorsement (dop) 1997-06-01

— latest date by which the

or by endorsement (dop) 1997-06-01

— latest date by which the national standards conflicting with the amendment have to be withdrawn (dow) 1997-06-01

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4.4 Calibrated driving machine test 6

4.5 Mechanical back-to-back test 6

4.6 Electrical back-to-back test 6

4.10 Open-circuit test 6

4.11 Sustained short-circuit test 7

4.12 Zero power factor-test 7

7.2 Total loss measurement 10

7.3 Direct measurement of efficiency 10

Section 3 Polyphase induction machines

9.2 Total loss measurement 12

9.3 Direct measurement of efficiency 12

Section 4 Synchronous machines

11 Determination of efficiency 1311.1 Summation of losses 1311.2 Total loss measurement 1511.3 Direct measurement of efficiency 15Section 5 Methods of test

13 Calibrated machine test 16

14 Zero power factor test 16

vector of load current I1 at rated voltage 23Figure 4 — Method of the chord 23Figure 5 — Method of the limiting secant 24Figure A.1 — Maximum permissible

relative error (%P/Pin)max of input as well

as output measurement 25Figure A.2 — Schematic diagram of a

test set-up for the calorimetric calibration

by the calorimetric method 31

Section 1 General

2 Determination of losses P1 by measurement of the volume rate

of flow and rise in temperature of the cooling medium 32

3 Losses Pi measured electrically using the calorimetric calibration method 32

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6 Losses external to the reference surface Pe 33

Section 2 Water as the cooling medium

7 Application and basic relationship 34

8 Measurement of water flow 34

9 Measurement of the temperature rise

10 Measuring accuracy 35

Section 3 Air as the cooling medium

11 Application and basic relationship 36

12 Determination of the mass rate of flow 36

13 Measurement of the temperature rise

14 Determination of the specific heat

capacity of the air 38

15 Measuring accuracy 38

Section 4 Practical considerations

16 Preparations for calorimetric

measurements with liquid coolants 39

17 Connections and equipment for

calorimetric measurements with

Figure 1 — Reference surface 41

Figure 2 — Parallel coolers 42

Figure 3 — Series coolers 42

Figure 4 — Characteristic values of pure

water as a function of temperature 43

Figure 5 — Position of thermometer

pockets in the water conduit 44

Figure 6 — Measuring throttles placed in

the cooling circuit on site 44

Figure 7 — Air density depending on

temperature and humidity 45

Figure 8 — Specific heat capacity cp of air for

different values of humidity and temperature 46

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Section 1 General

1 Scope

This Recommendation applies to d.c machines and

to a.c synchronous and induction machines of all

sizes within the scope of IEC Publication 34-1 The

principles can, however, be applied to other types of

machines such as rotary convertors, a.c

commutator motors and single- phase induction

motors for which other methods of determining

losses are generally use

2 Object

This Recommendation is intended to establish

methods of determining efficiencies from tests, and

also to specify methods of obtaining particular

losses when these are required for other purposes

3 General

Tests shall be conducted on a completely sound

machine with all covers fitted in the manner

required for normal service, with any devices for

automatic voltage regulation not a composite part of

the machine itself being made inoperative, unless

otherwise agreed

Unless otherwise agreed, measuring instruments

and their accessories, such as measuring

transformers, 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 an accuracy class

shall be 1,0 or better

Instruments shall be selected to give readings over

the effective range such that a fraction of a division

is a small percentage of the actual reading and can

be easily estimated

On machines with adjustable brushes, the brushes

shall be placed in the position corresponding to the

specified rating For measurements on no-load, the

brushes may be placed on the neutral 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 frequency during the

test

When the over-all efficiency or the absorbed power

is measured for a group of machines comprising two

electrical machines, or a machine and a

transformer, or a generator and its driving machine,

or a motor and its driven machine, there is no need

to indicate the individual efficiencies If, however,

these are given separately, they should be regarded

I1 = load current at rated voltage

I1r = main primary current at reduced voltage

Io = no-load current at rated voltage

Ior = no-load current at reduced voltage

J = moment of inertia

n = speed of rotation in revolutions per minute

nN = rated speed

N = number of full revolutions of the shaft

P = losses which can be directly measured

P1 = power absorbed at rated voltage

P1r = power absorbed by main primary winding

at reduced voltage

PFe = iron losses defined in accordance

with 6.2 a), 8.1 a) and 10.1 a)

Pf = 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)

Pk = short-circuit losses representing the sum

of the I2R losses in operating windings on

load in accordance with 10.2 and

additional load losses in accordance

Ur = reduced voltage for load test

$ = per unit deviation of rotational speed from

rated speed: = load phase angle at rated voltage:r = load phase angle at reduced voltage:o = no-load phase angle at rated voltage:or = no-load phase angle at reduced voltage

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4 Definitions

For definitions of general terms used in this

Recommendation, reference should be made to the

International Electrotechnical Vocabulary [IEC

Publication 50]

For the purpose of this Recommendation, the

following definitions apply:

4.1

efficiency

the ratio of output to input expressed in the same

units and usually given as a percentage

4.2

total loss

the difference between the input and the output

4.3 braking test

a test in which the mechanical power output of a machine acting as a motor is determined by the measurement of the shaft torque, by means of a brake or dynamometer, together with the rotational speed Alternatively, a test performed on a machine acting as a generator, by means of a dynamometer

to determine the mechanical power input

4.4 calibrated driving machine test

a test in which the mechanical input or output of an electrical machine is calculated from the electrical output or input of a calibrated machine

mechanically coupled to the machine on test

4.5 mechanical back-to-back test

a test in which two identical machines are mechanically coupled together, and the total losses

of both machines are calculated from the difference between the electrical input to one machine and the electrical output of the other machine

(see Figure 1, page 22)

4.6 electrical back-to-back test

a test in which two identical machines are mechanically coupled together, and they are both connected electrically to a power system The total losses of both machines are taken as the power input drawn from the system (see Figure 2, page 22)

4.7 retardation test

a test in which the losses in a machine are deduced from the rate of deceleration of the machine when only these losses are present

4.8 calorimetric test

a test in which the losses in a machine are deduced from the heat produced by them The losses are calculated from the product of the amount of coolant and its temperature rise, and the heat dissipated in the surrounding media

4.9 no-load test

a test in which the machine is run as a motor providing no useful mechanical output from the shaft

4.10 open-circuit test

a test in which a machine is run as a generator with its terminals open-circuited

Pi = losses inside reference surface

Pe = losses outside reference surface

P1 = losses which are dissipated by the cooling

circuits in the form of heat and which can be

measured calorimetrically

P2 = losses not transmitted to the cooling medium

but which are dissipated through the

reference surface by conduction, convection,

radiation, leakage, etc

cp = specific heat capacity of the cooling medium

Q = volume rate of flow of the cooling medium

Õ = density of the cooling medium

%t = rise in temperature of the cooling medium or

temperature difference between the machine

reference surface and the external ambient

temperature

É = exit velocity of cooling medium

! = discharge coefficient

e = error in measurement of losses, P1 and P2

h = coefficient of heat transfer

%p = difference between the static pressure in the

intake nozzle and ambient pressure

A = cross-sectional area of the intake nozzle

t = temperature

t1 = inlet temperature of the cooling medium

t2 = outlet temperature of the cooling medium

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4.11

sustained short-circuit test

a test in which a machine is run as a generator with

its terminals short-circuited

4.12

zero power factor test

a no-load test on a synchronous machine which is

over-excited and operates at a power factor very

close to zero

5 Reference temperature

Unless otherwise specified, all I2R losses shall be

corrected to the temperatures given below:

If the rated temperature rise or the rated

temperature is specified as that of a lower thermal

class than that used in the construction, the

reference temperature shall be that of the lower

thermal class

Section 2 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) I2R losses in shunt or separately excited

windings and in the excitation rheostats

b) Exciter losses

All the losses in an exciter mechanically driven from

the main shaft, which forms part of the complete

unit and is used solely for exciting the machine,

together with losses in the rheostat in the excitation

circuit of such an exciter, but with the exception of

friction and windage losses

In the case of a separate excitation supply such as

battery, rectifier or motor generator set, no

allowance is made for the losses in the excitation

source or in the connections between the source and

the brushes

NOTE When the losses in a separate excitation system are

require, these should be listed separately and can be taken as the

difference between the excitation power divided by the efficiency

of the excitation system and the excitation power.

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

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 The losses in auxiliary machines such as external fans, water and oil pumps not forming an integral part of the machine, but provided exclusively for the machine in question, shall be included only by agreement

NOTE When the losses in a separate ventilating system are required, they should be listed separately as they are not part of the machine losses.

6.3 Load losses

a) I2R losses in armature, and windings carrying

armature current (e.g commutating, compensating, excitation and series connected windings)

b) Electrical losses in brushes

6.4 Additional load losses

a) Losses introduced by load in active iron, and other metal parts other than the conductors.b) Eddy current losses in armature conductors caused by current dependent flux pulsation and commutation

c) Losses in the brushes caused by commutation

NOTE These losses are sometimes called additional losses, but they do not include the additional no-load losses in

Sub-clause 6.2 a).

Thermal class of the

insulation system Reference temperature°C

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7 Determination of efficiency

7.1 Summation of losses

The efficiency can be calculated from the total losses

which are assumed to be the summation of the

losses obtained in the following manner:

7.1.1 Excitation losses

These are:

7.1.1.1 Excitation winding I 2 R losses

These losses are calculated from the formula I2R,

where R is the resistance of the shunt excitation

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

excitation current 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 commutation

poles; 110 % of the excitation current,

corresponding to no-load at a voltage equal to the

rated voltage plus ohmic drop in the armature

circuit (armature, brushes and commutating

windings if any, see also Sub-clause 7.1.3.2) at

rated load current

b) For compensated shunt or separately excited

generators: the excitation current corresponding

to no-load at a voltage equal to the rated voltage

plus the ohmic drop in the armature circuit

(armature, brushes, commutating windings and

compensating windings, see also

Sub-clause 7.1.3.2) at rated load current.

c) For level-compounded generators: the

excitation current for the rated no-load voltage

d) For over-compounded and under-compounded

generators, and special types of generator not

covered by items a) to c): as agreed between

manufacturer and purchaser

e) For shunt wound motors: equal to no-load

excitation current corresponding to the rated

voltage

7.1.1.2 Main rheostat losses

where R is the resistance of the part of the rheostat

in circuit for the rating considered, and I is the value

of the excitation current defined as in

Sub-clause 7.1.1.1 above They are also equal to the

product, IU, of the excitation current multiplied by

U, the excitation voltage which must be absorbed in

the rheostat

The sum of the losses, Sub-clauses 7.1.1.1

and 7.1.1.2, is also equal to the product IUe of the

excitation current I and the total excitation voltage Ue

NOTE Where a resistance is permanently connected in series in the excitation circuit it should be dealt with in the 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 used solely for exciting the main machine.

These losses include the difference between the power absorbed at the shaft by the exciter and the useful power which it provides at its terminals,1) as well as the excitation losses in the exciter if this is excited from a separate source

If the exciter can be uncoupled from the main machine and tested separately, the power which it absorbs may be measured by using the

calibrated-machine method

If the exciter cannot be uncoupled from the main machine, the power which it absorbs may be measured either by the method of working the main machine as a motor on no-load, or by the calibrated

machine method (Clause 13), or by the retardation method (Clause 15), applied to the whole unit In

these three methods, the power absorbed by the exciter is obtained as the difference between the total losses of the unit measured under identical conditions, first with the exciter on-load and secondly with the exciter non-excited, the excitation being supplied by an independent source

If none of these methods is applicable, the power absorbed by the exciter is obtained by adding to the power, measured at the terminals, the different

separate losses determined as under Clause 6

However, mechanical friction and windage losses which are measured at the same time as those of the main machine need not be taken into account

7.1.2 Constant losses 7.1.2.1 No-load test at rated voltage

The constant losses shall be determined by running the machine under no-load conditions as a motor with rated voltage applied and with rated speed achieved by adjustment of the excitation, which shall preferably be derived from a separate source

The total electric power absorbed, less the I2R losses

in the armature and in the excitation winding or, if necessary, less the power absorbed by the exciter, gives the sum of the constant losses

1) The useful power at the terminals of the exciter is equal to the sum of the losses, Sub-clauses 7.1.1.1 and 7.1.1.2, of the main

machine.

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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 by means of a

calibrated machine The machine on test is excited

(preferably from an independent 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

power absorbed by the calibrated machine, giving

the sum of the constant losses By removing the

excitation, the sum of the friction and windage

losses is obtained in the same way The core losses

may be determined separately by subtracting the

losses during this test from those measured during

the previous no-load test By lifting the brushes the

brush friction loss may be determined separately by

subtracting the losses during this test from those

measured during the previous, unexcited test

7.1.2.3 Retardation test

In machines with large inertia, the total constant

losses, as well as the separate constant losses, can

be determined by the retardation method

7.1.3 Load losses

These are:

7.1.3.1 Armature circuit I 2 R losses

These losses are calculated from the current and the

measured resistance, corrected to the reference

temperature, except that where resistance

measurement is impracticable due to very low

resistances, calculation is permissible

NOTE Under this heading are included compensating

windings, commutating pole windings and diverters In the case

of diverters in parallel with a series winding, the I2R losses

should be determined using the total current and the resulting

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 fixed voltage

drop

The voltage drop allowed for all brushes of each

polarity shall be 1.0 V for carbon or graphite

brushes and 0.3 V for metal-carbon brushes, i.e a

total drop of 2.0 V for carbon or graphite brushes,

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

For constant speed machines, the rated output or input as appropriate is taken as the output or input 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 rated input is defined at each speed as being the input when the maximum rated current at any speed is associated with the applied voltage of the particular speed considered

For variable speed motors where the increase in speed is obtained by weakening the field, the rated input is defined as being the input when the rated voltage is associated with the maximum rated current For variable speed generators where the voltage is maintained constant by varying the field, the rated output is defined as being the output which is available at the terminals at rated voltage and maximum rated current The allowances for additional losses at the speed corresponding to the full field shall be as specified above The allowances for additional losses at other speeds shall be calculated using the appropriate multiplying factors given in Table I, 36

The speed ratio in the first column of Table I shall

be taken as the ratio of actual speed under consideration to the minimum rated speed for continuous running

For speed ratios other than those given in Table I the appropriate multiplying factors can be ascertained by interpolation

NOTE The additional load loss may be obtained from an input-output test or from a back-to-back test by subtracting 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 voltage machines,

the sum, Sub-clause 6.2 a) and 6.4 a), may be

measured as described for the constant losses in

active iron, Sub-clause 6.2 a) by one or other of the

two methods, by operating as a motor on no-load or

as 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 the current

considered, depending on whether the machine is a generator or a motor

Multiplying factors for different speed ratios

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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 current

exceeds 0,1, the additional losses caused by the a.c

component of the armature current shall be

considered in addition to the losses specified

in 7.1.4.

They shall be calculated as the eddy current losses

caused by the fundamental component of the

above-mentioned a.c component

The method of calculation used shall be the subject

of agreement between manufacturer and purchaser

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 supplied from the

electrical system are assumed to be equally

distributed and the efficiency is calculated as 7.3.3.

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 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 is then

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 winding temperature 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 is taken as

the ratio of output to input

7.3.3 Mechanical back-to-back test

same rated conditions, the losses are assumed to be

equally distributed, and the efficiency is calculated

from half the total losses and the electrical input (in

the case of a motor) or electrical output (in the case

of a generator)

Section 3 Polyphase induction machines

NOTE When the losses in a separate lubricating system are required these should be listed separately.

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 The losses in auxiliary machines such as external fans, water and oil pumps not forming an integral part of the machine, but provided exclusively for the machine in question, shall be included only by agreement

NOTE When the losses in a separate lubricating system are required they should be listed separately.

8.2 Load losses

a) I2R losses in primary windings.

b) I2R 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 the conductors.b) Eddy current losses in primary or secondary winding conductors caused by current dependent flux pulsation

NOTE 1 Losses, Sub-clause 8.3 a) and b), are sometimes called

additional losses, but they do not include the additional no-load

losses in Sub-clause 8.1 a).

NOTE 2 In the case of auxiliary machines such as phase advancers driven mechanically from the 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 rated operating conditions of the main machine These losses should be determined by the standard method for the types of apparatus involved.

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The efficiency can be calculated from the total losses

which are assumed to be the summation of the

losses obtained in the following manner:

9.1.1 Constant losses

9.1.1.1 No-load test at rated voltage

The sum of the constant losses, Sub-clause 8.1 a), b)

and c), is determined by running the machine as a

motor on no-load The machine is fed at its rated

voltage and frequency The power absorbed,

decreased by the I2R losses in the primary winding,

gives the total of the constant losses The I2R losses

in 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 from the

network, at its rated speed by means of a calibrated

motor (see Sub-clause 9.2.2) With the brushes, if

any, in place, the power absorbed at the shaft of the

machine, which may be deduced from the electrical

power absorbed by the calibrated motor, gives the

sum of the losses in Sub-clause 8.1 b) and 8.1 c)

With the brushes, if any, lifted the sum of the

bearing friction losses and the total windage losses

is obtained in the same manner The losses

described in Sub-clause 8.1 a) may be obtained from

the test described in Sub-clause 9.1.1.1 by

subtraction

9.1.1.3 No-load test at variable voltage

The losses described in Sub-clause 8.1 a) and the

sum of the losses described in Sub-clause 8.1 b)

and c) may alternatively be separated by running

the machine as a motor at rated frequency but at

different voltages The power absorbed, less the I2R

losses in the primary winding, is plotted against the

square of the voltage This, at low values of

saturation, will give a straight line which can be

extrapolated to zero voltage to give the sum of the

losses, Sub-clause 8.1 b) and c).

It should be borne in mind that at very low voltages,

losses plotted on the diagram may be high because

of the increased secondary winding losses with

increased slip When plotting the straight 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 if the supply generator is started at the

same time as the motor) the bearing friction 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 machines with 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 Sub-clause 8.2 a) are

calculated from the resistance of the primary windings measured using direct current and corrected to the reference temperature, and from the current corresponding to the load at which the losses are being calculated

To determine the losses in Sub-clause 8.2 b) when

an on-load test is made the secondary winding losses are taken to be equal to the product of the slip and the total power transmitted to the secondary winding, i.e the power absorbed, decreased by the

core losses in Sub-clause 8.1 a) and the I2R losses in

the primary winding in Sub-clause 8.2 a) This

method gives directly the sum of the losses in

Sub-clauses 8.2 b) and 8.2 c) for wound rotor machines, and the losses in Sub-clause 8.2 b) for

cage machines For this latter type of machine, this

is the only applicable method as it is not possible to measure the resistance and current of the secondary winding directly When use is 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 secondary windings) or the terminals of an auxiliary coil (for motors with short-circuited secondary windings) or between the ends of the shaft

9.1.2.2 Calculated values

For wound rotor motors, the losses in

Sub-clause 8.2 b) may be calculated from the

resistance measured by direct current and corrected

to the reference temperature, and from the secondary current calculated 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 agreed between manufacturer and purchaser

To make an on-load test, the losses in

Sub-clause 8.2 c) in the brushes cannot be measured

directly and these losses shall be taken as the product of the current flowing in the brushes and a fixed voltage drop The voltage drop in all brushes of the same phase shall be taken as 1.0 V for carbon 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

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When the voltage is reduced, while keeping the

rotational speed of the machine constant, the

currents diminish approximately in proportion to

the voltage, and the power approximately in

proportion to the square of the voltage When the

voltage is down to half its rated value, the currents

will then be reduced to about one half, and the

power to about one quarter, of their values at the

rated voltage

When a load is applied to an induction motor at a

reduced voltage Ur, the power absorbed P1r, the

main primary current I1r and the slip s are

measured, as well as the no-load current Ior at the

same reduced voltage Ur, and the no-load current Io

at the rated voltage Un

The current vector It of the load at rated voltage is

obtained by constructing a vector diagram

(Figure 3, page 23) in the following manner:

To the current vector I1r, multiplied by the ratio

add the vector:

The resultant vector represents the current which

would flow at the rated voltage Un for the following

absorbed power:

By means of the values I1, P1, thus determined, and

with the slip s measured at reduced voltage, it is

then possible to calculate the on-load losses, as

indicated in Sub-clause 9.1.2.1.

Unless otherwise specified, it is assumed that the

losses specified in Sub-clauses 8.3 a) and 8.3 b) vary

as the square of the primary current and that their

total value at full load is equal to 0.5 % of the rated

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 a particular case,

the value is of importance, the loss should be determined by the

direct method of efficiency 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 supplied from the electrical system are assumed to be equally

distributed and the efficiency is calculated from half the total losses and the electrical input to one machine

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 winding

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

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

When the machine is running in accordance with

clause 13 at rated conditions of speed, voltage and

current, the efficiency is then taken as the ratio of output to input

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

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Section 4 Synchronous machines

10 Losses to be included

The total losses may be taken as the sum of the

following component losses:

10.1 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 a separate lubricating

system Losses in common bearings shall be

stated separately whether or not such bearings

are supplied with the machine For water-driven

generators and synchronous motors for pump

storage schemes, the losses in thrust bearings,

and if the thrust bearings are associated with

guide bearings the total losses in those bearings

shall be stated separately The thrust-load,

temperature of the bearings, and type of oil and

oil temperature at which the loss values are valid

shall also be given

NOTE When the losses in a separate lubricating system are

required these should be listed separately.

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 The losses in auxiliary

machines such as external fans, water and oil

pumps not forming an integral part of the

machine, but provided exclusively for the

machine in question, shall be included only by

agreement

NOTE 1 When the losses in a separate ventilating system are

required they should be listed separately.

NOTE 2 For machines indirectly cooled or directly cooled by

hydrogen, see 11.5 of IEC 34-1.

10.2 Load losses

a) I2R losses in primary windings.

b) I2R losses in starting or damping windings.

NOTE These are significant only for single-phase machines.

10.3 Excitation circuit losses

a) I2R losses in the excitation windings and in the

excitation rheostats

b) All the losses in an exciter mechanically driven

from the main shaft which forms part of the

complete unit, and is used solely for exciting the

machine, together with losses in the rheostat in

the excitation circuit of such an exciter, but with

the exception of friction and windage losses

Losses in rotary rectifiers and in a gear, rope or

belt, or similar drive between shaft 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

In the case of a separate excitation supply such

as a battery, rectifier or motor generator set, no allowance is made for the losses in the excitation source or in the 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 the conductors.b) Eddy current losses in primary winding conductors

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

11.1.1 Excitation circuit losses 11.1.1.1 Excitation winding I 2 R losses

taking for R the resistance of the excitation winding corrected to the reference temperature, and for I the

value of the exciting current for the particular rating of the machine, measured directly during the on-load test or calculated when 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

where R is the resistance of the part of the rheostat

in circuit for the rating considered, and I is the value

of the exciting current for the rating considered

defined as in Sub-clause 11.1.1.1 They are also

equal to the product IU of the excitation current 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 in the 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 rating considered and a fixed voltage drop The voltage drop allowed for all brushes of each polarity shall

be 1.0 V for carbon, or graphite brushes, and 0.3 V for metal-carbon brushes, i.e a total drop of 2.0 V for carbon or graphite brushes, and 0.6 V for metal-carbon brushes

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The sum of the losses according to

Sub-clauses 11.1.1.1, 11.1.1.2 and 11.1.1.3, is also

equal to the product IUe of the exciting current I and

the total excitation voltage Ue

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 used solely for

exciting the synchronous machine.

These losses include the difference between the

power absorbed at the shaft of the exciter and the

useful power which it provides at the terminals of

the exciter2), and the excitation losses of the 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 power which it

absorbs may be measured by the calibrated machine

method

If the exciter cannot be uncoupled from the main

machine, the power which it absorbs may be

measured either by the calibrated machine method

or by the retardation method applied to the whole

unit In these two methods, the power absorbed by

the exciter is obtained as the difference between the

total losses of the unit measured under identical

conditions, first with the exciter on-load and

secondly with the exciter not excited, the excitation

being furnished by an independent source

If none of these methods is applicable, the separate

losses should be determined as described under

Clause 6 for d.c machines (see Sub-clause 7.1.1.3,

last paragraph)

NOTE The manufacturer and purchaser should agree on the

method of determining the losses in apparatus for self-excitation

and regulation receiving their input from the a.c lines connected

to the terminals of the machine.

11.1.2 Constant losses

11.1.2.1 Unity power factor test at rated voltage and

frequency

The sum of the constant losses is generally

determined by the method of running the machine

as a motor on no-load The synchronous machine is

fed at its rated voltage and rated frequency, so as to

work as a motor on no-load The excitation is

adjusted so that the machine absorbs the minimum

a.c current The electrical power absorbed,

decreased by the I2R loss in the primary windings,

and, if appropriate, by the power absorbed by the

exciter, gives the sum of 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,

Sub-clauses 10.1 a), 10.1 b) and 10.1 c), the losses Sub-clause 10.1 a), and the sum of the losses, Sub-clauses 10.1 b) and 10.1 c), may also be

determined by driving the machine at its rated speed 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 power which it absorbs at its shaft, and which may be calculated from the power absorbed from the calibrated motor, gives the sum of the constant losses

Sub-clauses 10.1 a), 10.1 b) and 10.1 c) By

removing the excitation, the sum of the losses,

Sub-clauses 10.1 b) and 10.1 c) is obtained in the same manner The core losses Sub-clause 10.1 a)

are obtained by subtraction Given the small number of brushes used on synchronous machines,

it is generally not possible to separate the brush friction losses from the sum of the other constant losses by means of a test with the brushes lifted

11.1.2.3 Retardation test (see Clause 15)

The sum of the constant losses

Sub-clauses 10.1 a), 10.1 b) and 10.1 c), the losses Sub-clause 10.1 a) and the sum of the losses, Sub-clauses 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 Sub-clause 10.1 a), 10.1 b) and 10.1 c)

may be separated by running the machine as a motor at rated frequency, but at different voltages

as described in Sub-clause 9.1.1.3 of Section 3.

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

11.1.2.5 Variable cooling gas density test

For machines cooled by a gas at variable pressure, the total windage loss may be separated from 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 calorimetric method

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

2) The useful power at the terminals of the exciter is equal to the sum of the losses according to Sub-clauses 11.1.1.1, 11.1.1.2 and 11.1.1.3, of the main machine.

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11.1.3 Load losses

These consist of I2R losses in primary windings The

I2R losses in the primary winding are normally

measured during the short-circuit test described

in 11.1.4.

When they are to be given separately, the losses are

calculated from the rated current and the resistance

of the windings corrected to the reference

temperature

Unless otherwise specified, the sum of the losses,

Sub-clauses 10.4 a) and 10.4 b) is measured by

means of the short-circuit test method

The machine to be tested, with its primary winding

short-circuited, is driven at its rated speed and so

excited that the current in the short-circuited

primary winding is equal to the rated current The

power absorbed at the shaft, decreased by the

mechanical losses, Sub-clauses 10.1 b) and 10.1 c),

and the power absorbed by the exciter, if

appropriate, presents the sum of the load losses and

the additional losses, Sub-clauses 10.2 and 10.4 If

the leakage reactance is abnormally high, as for a

machine for high frequency, a correction shall also

be made for core losses The load losses vary in

different senses as a function of the temperature

The sum of the load losses and additional losses is

assumed to be independent of the temperature and

no correction is made to a reference temperature

Unless otherwise specified, it is assumed that the

additional load losses vary as the square of the

armature current

NOTE It is recognized that the sum of the additional losses,

Sub-clauses 10.4 a) and 10.4 b), thus determined, is generally a

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 measured by

the calibrated machine method (Clause 13), or by

the retardation method (Clause 15).

11.2.1 Electrical back-to-back test

(see clause 16)

same rated conditions, the losses are assumed to be

equally distributed and the efficiency shall be

calculated as in 11.3.3.

11.2.2 Zero power factor test (see clause 14)

When the machine is run at rated conditions of speed, voltage and current, the total losses are equivalent to the absorbed power during the test, corrected for the difference between actual and the full-load exciting current losses

When identical machines are run at essentially the same rated conditions, the losses are assumed to be equally distributed, and the efficiency shall be calculated from half the total losses and the electrical input

Section 5 Methods of test

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

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This is not usually the total loss, but comprises

certain component losses The method may,

however, be used to calculate the total loss or to

calculate a component loss

The choice of test to be made depends on the

information required, the accuracy required, and

the type and size of the machine involved Where

alternative methods are available for a particular

type of machine, the preferred method is indicated

(see Clause 18).

A distinction is made between direct and indirect

efficiency determination

The direct determination of efficiency is made by

measuring directly the power supplied by the

machine 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 absorbed power

The indirect determination may be carried out by

the 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 is therefore not possible

to make a comparison between the losses obtained by the direct

method of measurement and those obtained by the measurement

of the separate losses.

Unless otherwise specified, the guaranteed

efficiency of a machine is that which is based on the

determination of separate losses, but when there is

a choice of method, the evaluation of efficiency

should be base on the accuracy obtainable from the

method, the efficiency and the type of machine

involved.3)

When the efficiency or total loss is derived from the

measured input and output power, any inaccuracy

in these measurements appears as a direct error in

the efficiency (e.g with an accuracy of power

measurement not better than 1 %, the efficiency can

be 2 % in error or the total losses can be in error

by 2 % of the total input power) On small machines

or machines with relatively low efficiencies (say

below 90 %),3) this method may be quite acceptable

and gives a convenient form of test for such

machines On these and other machines efficiency

can be obtained with high accuracy by the

calculation of losses from direct measurements

13 Calibrated machine test

The machine of which the losses are to be measurement is separated from the network, uncoupled from its driving motor if necessary, and driven at its rated speed by a calibrated motor, that

is by an electric motor of which the losses have been previously determined with great accuracy, such that it is possible to determine the mechanical power which it furnishes at its shaft, knowing the electric power which it absorbs and its speed of rotation The mechanical power transmitted by the calibrated motor to the shaft of the machine under test is a measure of the losses of this latter machine for the working conditions under which the test is made In this method, the machine tested may be on no-load, excited or not excited, with or without brushes or short-circuit which enables categories of losses to be separated

As an alternative, the calibrated motor may be replaced by a dynamometer or by any other motor driving the machine under test through an appropriate torsionmeter, which enables the torque transmitted to the machine under test to be known, and hence the mechanical power absorbed by this latter machine

When use is made of this alternative, the speed of rotation, which comes directly into the calculation of the power, must be measured with extreme care

14 Zero power factor test

The machine operates as a motor at no-load and at rated speed, with a power factor in the

neighbourhood of zero, while the excitation current

is adjusted so that the machine carries its rated primary current

The supply voltage is such that the magnetic losses have the same value as in no-load operation at rated voltage The supply voltage is usually equal to the rated voltage unless this would give an active iron loss appreciably greater than that at full load In principle, the reactive power should be positive, i.e over-excited, but when this is impossible because the exciter voltage is not sufficient, the test can be made with absorption of the reactive power (i.e under-excited)

NOTE The accuracy of this method is dependent upon the accuracy at low power factor of the wattmeters used.

3) NOTE In some countries 90 % efficiency is accepted as a basis for using the indirect method whereas some other countries prefer a lower value, e.g 70 %.

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15 Retardation method

A retardation method can be used for determining

the separate losses of rotating electrical machines

The methods of determination of losses covered by

this clause are basically intended for large

synchronous machines, but the principles used can

also be applied to other machines (a.c induction and

d.c machines, exhibiting mainly an appreciable

rotational inertia) using the appropriate 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 all types;

— sum of losses in active iron and additional

open-circuit losses in d.c and synchronous

machines;

— sum of I2R losses in an operating winding and

additional load losses (“short-circuit losses”) in

synchronous machines

15.1.1 Fundamentals

The total of the loss Pt which retard the machine is

proportional to the product of the speed to which

these losses correspond and the deceleration at this

speed:

When n is expressed in rev/min and Pt is given in

kW, then the retardation constant C is:

where J is given in kg/m2

The deceleration dn/dt can be obtained either

directly, using an accelerometer, or indirectly, by

one 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

t2 – t1 during which the speed of the tested machine

changes from nN (1 + $) to nN (1 – $), see Figure 4

The ratio of speed interval 2 $ nN to time interval

t2– t1 is approximately the deceleration at rated

speed:

The value of deviation $ shall not be greater than 0,1 and may have to be less than this depending on the characteristics of the machine

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 the speed of rotation cannot be increased above the rated value The instant of time when the speed of rotation is of

the rated value nN is marked as t1, and the time instants at which the speed of rotation acquires the

values of (1 – $) nN are marked as t2 The deviation $ is successively decreased, and the time derivative of the speed of rotation is the limit of the tangent of the angle made by the line passing

through the points t1 and t2 with the time axis, as $ approaches zero, see Figure 5

15.1.4 Method of the average speed of rotation

If t1, t2 and t3 represent the successively recorded

time readings, the shaft making N complete

revolutions within the time interval between any two subsequent readings, then the average values of speed during the time intervals shall be:

and the deceleration of the shaft at an intermediate

moment of time t2

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 tests 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 For a synchronous machine

a third retardation test should be made with the armature winding being short-circuited and the excitation set to give the rated armature current

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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:

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 and first tests

The sum of the I2R losses and the additional losses

in the armature circuit are determined as the

difference of losses measured in the third and first

tests Separation of this sum into components If

required, is done by subtracting from it the I2R

losses in the armature circuit calculated from the

armature circuit resistance corresponding to the

test temperature For this purpose the winding

temperature shall be deduced by the appropriate

method of temperature measurement directly after

each retardation test with the armature circuit

being short-circuited

15.2.2 Composition of test with unknown

moment of inertia

When the moment of inertia of a machine rotating

part is not known, or the machine is coupled

mechanically to other rotating parts, e.g a turbine,

whose inertia is not known, some additional 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 motor from a power supply of the proper voltage, number of phases and frequency (in the case of a.c machines), and the power supplied to the tested machine can be measured, (equal to the sum of the mechanical

losses and iron losses as the armature circuit I2R are

usually ignored), then the retardation constant C is

determined from the formula:

If the measurement of power is difficult because of frequency oscillations of the power supply, then as

an alternative the energy supplied to the tested machine may be measured with an integrating meter For this purpose it is necessary to run the machine as a motor for some time at constant supply conditions

In the instance where there is no possibility of running the tested machine as an unloaded motor, then, in addition to the three retardation test

considered in 15.2.1, one more retardation test shall

be conducted The tested machine in this case is

slowed down by any losses P which can be measured and are of the same order as the expected losses PFeand Pk For this purpose the open-circuit or short-circuit losses of a connected transformer can

be used, which are separately measured

Alternatively, if an exciter or auxiliary generator mounted on the tested machine shaft is available, its load with a ballast resistance may be used

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

hence

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When the tested machine is slowed down by the

transformer short-circuit losses, usually the iron

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 a ballast

resistance, the retardation losses consist only of the

tested machine mechanical losses Pf and the

measured load P (with allowance for efficiency of the

load machine that can be determined 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 shall be “run in”

prior to the test The air temperature shall be

adjusted wherever possible to the normal

temperature at which the windage loss

measurement is required by throttling the air

coolant flow The bearing temperatures shall be

adjusted to the normal temperature at which the

bearings operate with rated load, by adjusting the

of the runner in the air produces windage losses which can be stated experimentally or from calculation 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 Pelton turbine where the water supply to the runner can be cut off instantly However, the tested machine is usually running as a motor on no-load, fed from a separate source with a wide range of variable speed In all cases the excitation shall be obtained from a separate source with 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 when the value of the deviation of speed $ is relatively small, e.g it does not exceed 0,05 In all these cases the 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 + $) nN so 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 losses, the machine field is suppressed;

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

— in the case of retardation by the transformer losses after field suppression, the tested machine

is connected to the transformer previously set to

a certain state (at no-load or short-circuit) and excited to the preset values of current or open-circuit voltage;

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— in the case of retardation by the exciter load

losses or auxiliary generator mounted on the

machine shaft, the tested machine field is

suppressed and the specified load is set

simultaneously

In all cases described above a sufficient time delay

shall separate the switching off of the supply and

starting the measurements to allow electromagnetic

transients to decay

In the case of retardation by the sum of mechanical

and iron losses or by the open-circuit losses of a

supply transformer, no procedures are required

after the machine is disconnected from 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

15.3.5 Procedures during retardation

The readings of all instruments used for each test

(field current ammeter, open-circuit voltage

voltmeter, short-circuit current ammeter) and of all

instruments required to measure the power in

additional retardation tests when the moment of

inertia J is not known shall be taken at the instant

when the tested machine passes through rated

speed; no readings at this instant are required in the

case of an unexcited retardation test

The measured values of open-circuit voltage or

short-circuit current shall not differ from the preset

values by more than ± 2 % The calculated final

value of the speed derivative in time for each of the

tests shall be adjusted proportionally by the ratio of

the square of the preset value to the measured

value

15.3.6 Programme of retardation tests

The retardation tests shall be conducted as a series

without interruption, whenever possible It is

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 is recommended that

each subsequent series of tests start and finish with

some unexcited retardation tests

Tests may be either repeated several times at the

same preset values of open-circuit voltage or

short-circuit current, e.g at rated values, or at

various values within limits of the order

of 95 %–105 % of the rated values In the first case

the arithmetic mean values obtained from all

measurements are assumed to be the real measured

value of each type of loss In the second case the

values are plotted on a curve as a function of voltage

or current Real measured values are assumed to be

those occurring at the points of intersection of the

preset values of voltage 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 the same values of voltage or current

as those obtained with the winding open or short-circuited If this is not possible the respective values shall be determined from curves 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 of the 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:

n = f (t);

c) chronographic — by determining the dependence of angular displacement of the tested machine shaft with time:

S = f (t).

For all cases recording measuring instruments may

be used both with continuous and with discrete recording of measured values and time

15.4.2 Accelerometric method

The dependence of speed on time for large machines having a complex ventilation route may not be regular As a consequence of this the instantaneous values of deceleration during retardation at the moment of passing through rated speed may be random Therefore, true values of the speed derivative may be determined by plotting measured decelerations versus time or speed and using a suitable curve fitting or correlation technique

15.4.3 Tachometric method

A plot of speed versus time is obtained from the results of measurements On this plot the time instants are defined at which the speed acquired the values indicated for the chord or limiting secant method The differences between the times at the lower and upper limits of speed are used to calculate the decelerations

If there is in exciter or any other electrical machine

on the tested machine shaft, it can be used as a tachogenerator, provided that the voltage signal does not pulsate with the speed of rotation of the tested machine The excitation shall be supplied from a stable d.c source, such as a separate storage battery

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If the voltage signal does pulsate with the speed of

rotation or when there is no such tachogenerator on

the tested machine, a coupled d.c machine may be

used It can be driven from the shaft of the tested

machine by a seamless belt or by other means to

provide smooth rotation

Readings of the speed may be made either in the

exact time intervals, specified by the respective

method, in which case there is no need for special

recording of time or of signals from the tested

machine shaft; in this case, the readings of time

shall be taken concurrently with readings of speed

There is no need to take readings with each turn of

the shaft; usually 30 to 40 readings during the

whole test are quite sufficient

With the availability of high-accuracy measuring

instruments, the measurement of speed of rotation

may be substituted by measurement of the

instantaneous values of speed or of the period of the

voltage of the tested machine or of any other a.c

machine situated on its shaft; it is not necessary

that the number of pole pairs of both machines is

equal

15.4.4 Chronographic method

The time-counters used may be either visual

indicators with continuous (non-stepwise) motion of

the pointer, or digital indicators with printers

(electrical or mechanical)

Time readings shall be taken according to the

signals obtained from the tested machine shaft,

either with each complete revolution of the shaft or

for a known number of revolution

NOTE If when using the tachometric method the speed of

rotation is determined by signals from the tested machine shaft,

then the time readings may be used both for tachometric and

chronographic methods, thus providing a mutual check.

In some cases, when the unit has smooth

deceleration characteristics, sufficient accuracy can

be obtained by measuring the time for retardation

between two speeds with the same difference to the

rated speed

The stator voltage frequency provides the best

means of determining the speed of a synchronous

machine

15.4.5 Measurement of losses in bearings

The losses in bearings and thrust bearings can be subtracted from the total sum of the mechanical losses, if required These may be determined by the calorimetric method in with IEC 34-2A If the tested machine uses direct-flow cooling of the bearings, these losses are distributed between the tested machine and any other coupled to it mechanically, such as turbine, in proportion to the masses of their rotating parts If there is no direct-flow cooling, the distribution of bearing losses shall be determined from empirical formulae by agreement between manufacturer and purchaser

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 the other as a generator The actual temperature at which the measurements are carried out should be as close as possible to the working temperature and no further correction should be made The losses of the assembled machines are supplied either by a network to which they are connected, or by a calibrated driving motor, or by a booster, or else by

a combination of these various means

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

Where two induction machines are electrically connected, they should be mechanically coupled with a speed adjusting device, such as a gear box, to ensure the correct circulation of power The

magnitude of power circulated depends upon the difference in speed The electrical system supplying the losses to the two machines will be required to provide magnetizing kvar to both machines

When two synchronous machines are electrically connected, they should be mechanically coupled with a correct angular phase relationship The magnitude of the power circulated depends upon the difference in phase angle between them

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17 Calorimetric test

Measurement of losses by calorimetric methods

shall be performed in accordance with IEC 34-2A

(given in Annex B)

18 Schedule of preferred tests

18.1 D.C machines

The preferred test for d.c machines is in accordance

with Sub-clause 7.1 and the preferred method of

calculating the efficiency is in accordance with

Sub-clause 7.1.2.

18.2 Polyphase induction machines

The preferred test for polyphase induction machines

is in accordance with Sub-clause 9.1 and the

preferred method of determining the constant losses

is in accordance with Sub-clause 9.1.1.1.

18.3 Synchronous machines

The preferred test for synchronous machines is in

accordance with Sub-clause 11.1 and the preferred

method of determining the constant losses is in

accordance with Sub-clause 11.1.2.1.

Figure 1 — Mechanical back-to-back test

Figure 2 — Electrical back-to-back test

Tiêu đề	Rotating Electrical Machines — Part 2: Methods For Determining Losses And Efficiency Of Rotating Electrical Machinery From Tests
Trường học	British Standards Institution
Chuyên ngành	Electrical Engineering
Thể loại	British Standard
Năm xuất bản	1999
Thành phố	London

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Số trang	52
Dung lượng	1,75 MB