IEC 60034-12:2024
(Main)Rotating electrical machines - Part 12: Starting performance of single-speed three-phase cage induction motors
Rotating electrical machines - Part 12: Starting performance of single-speed three-phase cage induction motors
IEC 60034-12:2024 specifies the parameters for eight designs of starting performance of single-speed three-phase 50 Hz or 60 Hz cage induction motors in accordance with IEC 60034‑1 that:
- have a rated voltage up to 1 000 V;
- are intended for direct-on-line or star-delta starting;
- are rated on the basis of duty type S1;
- are constructed to any degree of protection as defined in IEC 60034-5 and explosion protection.
This document also applies to dual voltage motors provided that the flux saturation level is the same for both voltages. This fourth edition cancels and replaces the third edition published in 2016. Aligned with the requirements for explosion protected motors from TC31 WG27
- new clause on methods for measuring locked-rotor current and torque;
- new informative annex on the general current and torque characteristics with locked rotor;
- new informative annex on correction of voltage and frequency;
- aligned with the requirements for explosion protected motors from TC31 WG27.
Machines électriques tournantes - Partie 12: Caractéristiques de démarrage des moteurs triphasés à induction à cage à une seule vitesse
L'IEC 60034-12:2024 spécifie les paramètres de huit conceptions de caractéristiques de démarrage de moteurs triphasés à induction à cage à une seule vitesse fonctionnant à 50 Hz ou 60 Hz conformes à l'IEC 60034-1, qui:
- ont des tensions assignées jusqu'à 1 000 V;
- sont prévus pour démarrage direct ou étoile-triangle;
- sont dimensionnés pour le service type S1;
- peuvent avoir n'importe quel degré de protection tel qu'il est défini dans l'IEC 60034-5 et incluant les protections contre les explosions.
Ce document s'applique également aux moteurs bitension à condition que le niveau de saturation du flux soit le même aux deux tensions. Cette quatrième édition annule et remplace la troisième édition parue en 2016. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- aligné sur les exigences du CE 31, GT 27, concernant les moteurs antidéflagrants;
- nouvel article relatif aux méthodes de mesure du courant et du couple à rotor bloqué;
- nouvelle annexe informative relative aux caractéristiques générales de courant et de couple à rotor bloqué;
- nouvelle annexe informative relative à la correction de la tension et de la fréquence.
General Information
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Standards Content (Sample)
IEC 60034-12 ®
Edition 4.0 2024-05
REDLINE VERSION
INTERNATIONAL
STANDARD
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inside
Rotating electrical machines –
Part 12: Starting performance of single-speed three-phase cage induction
motors
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IEC 60034-12 ®
Edition 4.0 2024-05
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Rotating electrical machines –
Part 12: Starting performance of single-speed three-phase cage induction
motors
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.160.01 ISBN 978-2-8322-8990-7
– 2 – IEC 60034-12:2024 RLV © IEC 2024
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Symbols . 8
5 Designation . 9
5.1 General . 9
5.2 Design N . 9
5.3 Design NE . 9
5.4 Designs NY and NEY . 9
5.5 Design H . 9
5.6 Design HE . 9
5.7 Designs HY and HEY . 10
6 Design N requirements . 10
6.1 Torque characteristics . 10
6.2 Locked rotor current and apparent power . 10
6.3 Starting requirements . 10
7 Design NE starting requirements . 11
8 Designs NY and NEY starting requirements . 11
9 Design H requirements . 11
9.1 Starting torque . 11
9.2 Locked rotor current and apparent power . 11
9.3 Starting requirements . 11
10 Design HE starting requirements . 12
11 Designs HY and HEY starting requirements . 12
12 Determination of current and torque from measurement. 12
12.1 Locked-rotor current and locked-rotor torque . 12
12.2 Breakdown torque . 12
12.3 Torque-speed curve and current-speed curve . 13
12.3.1 General . 13
12.3.2 Torque-speed and current-speed curves from direct measurement
(method a) . 13
12.3.3 Torque-speed and current-speed curves from acceleration (method b) . 13
12.3.4 Torque-speed and current-speed curves from measured input power
(method c) . 14
12.4 Correction of data for tests performed at reduced voltage and/or other than
rated frequency . 14
Annex A (informative) Current and torque characteristics with locked rotor . 20
Annex B (informative) Correction method for test done on reduced voltage . 24
Bibliography . 25
Figure A.1 – Locked-rotor current in multiples of rated current versus time . 20
Figure A.2 – Locked-rotor torque in multiples of rated torque versus time . 21
Figure A.3 – Locked-rotor torque in cNm versus rotor position in °; left: preferable
number of rotor slots, right: less preferable number of rotor slots . 21
Figure A.4 – Locked-rotor torque in cNm versus rotor position in ° . 22
Figure A.5 – Time -courses (in s) of rotational speed (upper left), torque (lower left),
phase voltage (upper right) and phase current (lower right) during a star-delta start-up . 23
Table 1 – Minimum values of torques for design N . 15
Table 2 – Maximum values of locked rotor apparent power for designs N and H . 16
Table 3 – Maximum values of locked rotor apparent power for designs NE and HE . 16
Table 4 – External moment of inertia (J) . 17
Table 5 – Minimum values of torques for design H . 18
Table 6 – Minimum values of torques for design N motors with type of protection 'Ex
eb – increased safety' . 18
Table 7 – External moment of inertia (J) for motors with type of protection 'Ex eb –
increased safety' . 19
– 4 – IEC 60034-12:2024 RLV © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ROTATING ELECTRICAL MACHINES –
Part 12: Starting performance of single-speed
three-phase cage induction motors
FOREWORD
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
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shall not be held responsible for identifying any or all such patent rights.
This redline version of the official IEC Standard allows the user to identify the changes
made to the previous edition IEC 60034-12:2016. A vertical bar appears in the margin
wherever a change has been made. Additions are in green text, deletions are in
strikethrough red text.
IEC 60034-12 has been prepared by IEC technical committee 2: Rotating machinery. It is an
International Standard.
This fourth edition cancels and replaces the third edition published in 2016. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
Clause or
Change
subclause
Table 6 Aligned with the requirements for explosion protected motors from TC31 WG27
12 New clause on methods for measuring locked-rotor current and torque
Annex A New informative annex on the general current and torque characteristics with locked
rotor
Annex B New informative annex on correction of voltage and frequency
The text of this International Standard is based on the following documents:
Draft Report on voting
2/2132/CDV 2/2150A/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts of the IEC 60034 series, published under the general title Rotating electrical
machines, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.
– 6 – IEC 60034-12:2024 RLV © IEC 2024
ROTATING ELECTRICAL MACHINES –
Part 12: Starting performance of single-speed
three-phase cage induction motors
1 Scope
This part of IEC 60034 specifies the parameters for eight designs of starting performance of
single-speed three-phase 50 Hz or 60 Hz cage induction motors in accordance with
IEC 60034-1 that:
– have a rated voltage up to 1 000 V;
– are intended for direct-on-line or star-delta starting;
– are rated on the basis of duty type S1;
– are constructed to any degree of protection as defined in IEC 60034-5 and explosion
protection.
This document also applies to dual voltage motors provided that the flux saturation level is the
same for both voltages.
The values of torque, apparent power and current given in this document are limiting values
(that is, minimum or maximum without tolerance).
NOTE 1 It is not expected that all manufacturers will produce machines for all eight designs. The selection of any
specific design in accordance with this document will be a matter of agreement between the manufacturer and the
purchaser.
NOTE 2 Designs other than the eight specified may can be necessary for particular applications.
NOTE 3 It should be noted that Values given in manufacturers' catalogues may can include tolerances in
accordance with IEC 60034-1.
NOTE 4 The values tabled for locked rotor apparent power are based on RMS symmetrical steady state locked rotor
currents.; at motor switch on there will be a one-half cycle asymmetrical instantaneous The start of the motor leads
to transient asymmetrical currents in the whole supply, so called inrush currents, the peak current value of which
may can range from 1,8 to 2,8 times the steady state locked rotor value. The current peak and decay time are a
function of the motor design and switching angle. Similar effects can occur during the switchover from star to delta
operation. A more detailed description is provided in Annex A.
The application of the test methods described in Clause 12 can be applied to cage induction
motors outside the scope of this document. However, special care shall be taken in such cases
to prevent overheating of the stator or the rotor winding depending on the concrete method and
parameters chosen.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60034-1:2022, Rotating electrical machines – Part 1: Rating and performance
IEC 60034-5:2020, Rotating electrical machines – Part 5: Degrees of protection provided by the
integral design of rotating electrical machines (IP code) – Classification
IEC 60034-30-1:2014, Rotating electrical machines – Part 30-1: Efficiency classes of line-
operated AC motors (IE-code)
IEC 60079-7:2015, Explosive atmospheres – Part 7: Equipment protection by increased
safety "e"
IEC 60079-7:2015/AMD1:2017
ISO 80000-4:2019, Quantities and units – Part 4: Mechanics
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
rated torque
T
N
torque the motor develops at its shaft end at rated output and speed
[SOURCE: IEC 60050-411:1996, 411-48-05]
3.2
locked-rotor torque
T
l
smallest measured torque the motor develops at its shaft end with the rotor locked, over all its
angular positions, at rated voltage and frequency
[SOURCE: IEC 60050-411:1996, 411-48-06]
3.3
pull-up torque
T
u
smallest steady-state asynchronous torque which the motor develops between zero speed and
the speed which corresponds to the breakdown torque, when the motor is supplied at the rated
voltage and frequency
[SOURCE: IEC 60050-411:1996, 411-48-42, modified – The notes 1 and 2 to entry have been
modified.]
Note 1 to entry: This definition does not apply to those motors whose torque continually decreases with increase in
speed.
Note 2 to entry: In addition to the steady-state asynchronous torques, harmonic synchronous torques, which are a
function of rotor load angle, will be present at specific speeds. At such speeds, the accelerating torque may can be
negative for some rotor load angles. Experience and calculation show this to be an unstable operating condition and
therefore harmonic synchronous torques do not prevent motor acceleration and are excluded from this definition.
– 8 – IEC 60034-12:2024 RLV © IEC 2024
3.4
breakdown torque
T
b
maximum steady-state asynchronous torque which the motor develops without an abrupt drop
in speed, when the motor is supplied at the rated voltage and frequency
[SOURCE: IEC 60050-411:1996, 411-48-43, modified – The notes 1 and 2 to entry have been
modified.]
Note 1 to entry: This definition does not apply to those motors whose torque continually decreases with increase in
speed.
3.5
rated output
P
N
value of the output power included in the rating
Note 1 to entry: The terms rated value and rating are defined in IEC 60034-1:2022, 3.1 and 3.2 (see also IEC 60050-
411:1996, 411-51-23 and 411-51-24).
3.6
rated voltage
U
N
value of the voltage included in the rating
Note 1 to entry: The terms rated value and rating are defined in IEC 60034-1:2022, 3.1 and 3.2 (see also IEC 60050-
411:1996, 411-51-23 and 411-51-24).
3.7
locked rotor apparent power
S
l
apparent power input with the motor held at rest at rated voltage and frequency after the inrush
currents have decayed to a symmetrical system of current
[SOURCE: IEC 60050-411:1996, 411-48-49, modified – "after the inrush currents have decayed
to a symmetrical system of current" has been added.]
3.8
locked rotor current
I
l
steady state current with the motor held at rest at rated voltage and frequency after the inrush
currents have decayed to a symmetrical system of current
4 Symbols
I Locked rotor current
l
J External moment of inertia
J Moment of inertia of motor under test
M
n Rotational speed
p Number of pole pairs
P Power at the motor terminals during test method c) in 12.3.4
P Power at the generator terminals during test method a) in 12.3.2
1,g
P Motor iron losses during test method c) in 12.3.4
fe
P Motor I R losses during test method c) in 12.3.4
L
P Total losses of the generator during test method a) in 12.3.2
T,g
P Rated output
N
S Locked rotor apparent power
l
T Rated torque
N
T Locked rotor torque
l
T Pull-up torque
u
Breakdown torque
T
b
T Motor friction and windage torque during test method c) in 12.3.4
fw
U Rated voltage
N
5 Designation
5.1 General
Motors designed according to this document are classified according to 5.2 to 5.7. The letters
used to specify the different designs stand for:
N: normal starting torque.
H: high starting torque.
Y: star-delta starting.
E: motors utilizing extended / higher locked rotor apparent power and current to achieve
a higher efficiency classes of IE3 or higher according to IEC 60034-30-1.
5.2 Design N
Normal starting torque three-phase cage induction motors, intended for direct-on-line starting,
having 2, 4, 6 or 8 poles, rated from 0,12 kW to 1 600 kW.
5.3 Design NE
Normal starting torque three-phase cage induction motors having higher locked rotor apparent
power than design N, intended for direct-on-line starting, having 2, 4, 6 or 8 poles, rated from
0,12 kW to 1 600 kW.
5.4 Designs NY and NEY
Motors similar to designs N or NE, respectively, but intended for star-delta starting. For these
motors in star-connection, minimum values for T and T are 25 % of the values of design N or
l u
NE, respectively, see Table 1.
5.5 Design H
High starting torque three-phase cage induction motors with 4, 6 or 8 poles, intended for direct-
online starting, rated from 0,12 kW to 160 kW at a frequency of 60 Hz.
5.6 Design HE
High starting torque three-phase cage induction motors having higher locked rotor apparent
power than design H, with 4, 6 or 8 poles, intended for direct-online starting, rated from 0,12 kW
to 160 kW at a frequency of 60 Hz.
– 10 – IEC 60034-12:2024 RLV © IEC 2024
5.7 Designs HY and HEY
Motors similar to designs H or HE, respectively, but intended for star-delta starting. For these
motors in star-connection, minimum values for T and T are 25 % of the values of design H or
l u
HE, respectively, see Table 5.
6 Design N requirements
6.1 Torque characteristics
The starting torque is represented by three characteristic features. These features shall be in
accordance with the appropriate values given in Table 1 or Table 6. The values in Table 1 and
Table 6 are minimum values at rated voltage. Higher values are allowed.
The motor torque at any speed between zero and that at which breakdown torque occurs shall
be not less than 1,3 times the torque obtained from a curve varying as the square of the speed
and being equal to rated torque at rated speed. However, for 2-pole motors with type of
protection 'Ex eb – increased safety' having a rated output greater than 100 kW, the motor
torque at any speed between zero and that at which breakdown torque occurs shall not be less
than 1,3 times the torque obtained from a curve varying as the square of the speed and being
equal to 70 % rated torque at rated speed. For motors with type of protection 'Ex eb', the three
characteristic torques shall be in accordance with the appropriate values given in Table 6.
NOTE The factor 1,3 has been chosen with regard to an undervoltage of 10 % in relation to the rated voltage at the
motor terminals during the acceleration period.
6.2 Locked rotor current and apparent power
The locked rotor apparent power shall be not greater than the appropriate value given in
Table 2. The values given in Table 2 are independent of the number of poles and are maximum
values at rated voltage. For motors with type of protection 'e', locked rotor apparent power shall
be in accordance with the appropriate values specified in IEC 60079-7.
The locked rotor current is calculated from the locked rotor apparent power according to:
SP
lN
I ×
(1)
l
P
3U
N
N
NOTE The advantage of specifying S /P instead of I /I is that the locked rotor current can be
l N l N
calculated from rated power and rated voltage only, not requiring to know the rated current
which depends on quantities such as power factor and efficiency that are usually not known in
early stages of a project.
6.3 Starting requirements
Motors shall be capable of withstanding two starts in succession (coasting to rest between
starts) from cold conditions and one start from hot after running at rated conditions. The
retarding torque due to the driven load will be in each case proportional to the square of the
speed and equal to the rated torque at rated speed with the external moment of inertia given in
Table 4 or Table 7.
=
In each case, a further start is permissible only if the motor temperature before starting does
not exceed the steady temperature at rated load. However, for 2-pole motors with type of
protection 'Ex eb – increased safety' having a rated output greater than 100 kW, the retarding
torque due to the driven load is proportional to the square of the speed and equal to 70 % rated
torque at rated speed, with the external moment of inertia given in Table 7. After this starting,
load with rated torque is possible.
NOTE It should be recognized that the number of starts should be minimized since these affect
the life of the motor.
7 Design NE starting requirements
The starting requirements are as for design N, except that the limits for locked rotor apparent
power in Table 3 apply, as increasing efficiency values require physically increasing values for
locked rotor apparent power.
8 Designs NY and NEY starting requirements
The starting requirements are as for designs N or NE, respectively. In addition, however, a
reduced retarding torque is necessary as the starting torque in 'star connection' may be
insufficient to accelerate some loads to an acceptable speed.
NOTE It should be recognized that the number of starts should be minimized since these affect
the life of the motor.
9 Design H requirements
9.1 Starting torque
The starting torque is represented by three characteristic features. These features shall be in
accordance with the appropriate values given in Table 5. These values are minimum values at
rated voltage. Higher values are allowed.
9.2 Locked rotor current and apparent power
The locked rotor apparent power shall be not greater than the appropriate value given in
Table 2. The values in Table 2 are independent of the number of poles and are maximum values
at rated voltage.
The locked rotor current is calculated from the locked rotor apparent power according to the
formula given in 6.2.
9.3 Starting requirements
Motors shall be capable of withstanding two starts in succession (coasting to rest between
starts) from cold conditions, and one start from hot after running at rated conditions. The
retarding torque due to the driven load is assumed to be constant and equal to rated torque,
independent of speed, with an external moment of inertia of 50 % of the values given in Table 4.
In each case, a further start is permissible only if the motor temperature before starting does
not exceed the steady temperature at rated load.
NOTE It should be recognized that the number of starts should be minimized since these affect
the life of the motor.
– 12 – IEC 60034-12:2024 RLV © IEC 2024
10 Design HE starting requirements
The starting requirements are as for design H, except that the limits for locked rotor apparent
power in Table 3 apply, as increasing efficiency values require physically increasing values for
locked rotor apparent power.
11 Designs HY and HEY starting requirements
The starting requirements are as for design H or HE, respectively. In addition, however, a
reduced retarding torque is necessary as the starting torque in 'star connection' may be
insufficient to accelerate some loads to an acceptable speed.
NOTE It should be recognized that the number of starts should be minimized since these affect
the life of the motor.
12 Determination of current and torque from measurement
12.1 Locked-rotor current and locked-rotor torque
When possible, the locked-rotor current shall be measured at rated voltage and frequency as
the current is not directly proportional to the voltage because of changes in reactance caused
by saturation of the leakage paths. In case this isn't possible, see 12.4.
The locked-rotor torque may be measured with, e.g. a scale or force transducer with a brake or
beam, or it may be measured directly using an in-line torque transducer, or it may be determined
from the electrical input power using Formula (5). Depending on the chosen number of rotor
slots, the locked-rotor torque of cage induction motors is subject to variations depending on the
angular position of the rotor with respect to the stator. In case a preferable number of rotor slots
is chosen according to the manufacturer's experience, it is usual practice to lock the rotor of a
cage induction motor in any convenient position or to measure current and torque values with
the rotor being stalled at very low speed, i.e. with a speed below 2 % of the rated speed.
12.2 Breakdown torque
The breakdown torque can be measured by loading the motor, starting at no-load condition,
with an increasing load torque. The load torque that is reached when the motor starts quickly
loosing speed, is the breakdown torque.
Alternatively, the values of pull-up and breakdown torque can be measured during acceleration
from reverse speed to no-load speed (see method c) below), provided the load machine inertia
or load torque is sufficiently large. Sufficiently large means in case of power ratings up to
100 kW that the change of rotational speed during test satisfies, depending on the motor's
moment of inertia J and the motor's locked-rotor torque T , the relation
M l
dn 0,05
≤ T .
(2)
l
dtJ2 π
M
Otherwise, the breakdown torque will be underestimated. For power ratings above 100 kW,
different relations of the moment of inertia and the locked-rotor torque may be suitable
according to the experience to the manufacturer.
In case the complete torque-speed curve is measured using one of the methods below, no
separate measurement of the breakdown torque is required.
12.3 Torque-speed curve and current-speed curve
12.3.1 General
Any one of the methods listed below may be used to obtain data for a speed-torque curve. The
selection of the method will depend upon the size and the speed-torque characteristics of the
machine and the testing facilities. In all three methods, sufficient test points should be recorded
to ensure that reliable curves, including irregularities, can be drawn in the regions of interest
from the test data. It is important that the frequency of the power supply be maintained constant
throughout the test.
Method a) requires the maintenance of constant speed for each reading. Therefore, it cannot
be used in regions where the torque of the machine increases with speed more rapidly than
that of the loading device. From the results of the following tests, adjusted to the rated voltage
and frequency, curves of torque and current should be plotted vs. speed.
It is understood that the temperature of the stator and the rotor winding will influence the
measured torque-speed and current-speed curves (see Annex A).
12.3.2 Torque-speed and current-speed curves from direct measurement (method a)
In this method, a calibrated generator with known losses versus speed or a transducer or
mechanical brake is coupled to the motor being tested. The motor is supplied preferably with
rated frequency and rated voltage. The speed of the motor for each test point is controlled by
varying the load on the generator or the brake.
In this test, readings of voltage, current, and speed of the motor as well as readings of
– either the torque directly measured by, e.g. a torque transducer, a dynamometer or a
mechanical brake,
– or the power at the generator are taken at speeds between approximately 30 % of
synchronous speed and the maximum speed obtainable. The total power output of the motor
is the sum of the power at the generator terminals P and the total losses of the generator
1,g
P . The torque T at each speed n is calculated from
T,g
TP+ P / 2 π n
( ) (3)
( )
1,g T,g
NOTE For determining losses and loss portions by measurement, see IEC 60034-2-1.
The speed should be constant or sufficiently low satisfying Formula (2) when the readings are
taken, so that acceleration or deceleration power does not affect the results. Care should be
taken not to overheat the motor. The accuracy of speed measurement is particularly important
at low slip.
In case the voltage and/or the frequency differ from the rated values, the values of torque and
current are corrected as described in 12.4.
12.3.3 Torque-speed and current-speed curves from acceleration (method b)
In this method, the motor is started with no load, and the values of voltage, current, and speed
are recorded versus time. The torque is determined from the acceleration of the inertia J of the
rotating parts. An accurate measurement of speed versus time is an essential requirement of
this method. In addition, the accelerating time should be long enough so that electrical transient
effects do not distort the readings of voltage, current, and speed. In order to achieve this, the
accelerating time may be increased by using a lower applied voltage or by coupling a suitable
inertia to the motor shaft. In case the accelerating time is too short, the measured torque will
underestimate the motor's steady state torque-speed curve.
=
– 14 – IEC 60034-12:2024 RLV © IEC 2024
If the motor's starting friction is high, or if more accurate data in the zero speed range are
desired, the motor can be started rotating in the reverse direction prior to application of power
for the acceleration.
The torque T at each speed is calculated from the time-derivative of speed according to
dn
TJ= 2 π
(4)
dt
This requires a sufficiently exact knowledge of the moment of inertia. In case the voltage and/or
the frequency differ from the rated values, the values of torque and current are corrected as
described in 12.4.
12.3.4 Torque-speed and current-speed curves from measured input power (method c)
In this method, the torque is determined by subtracting the iron losses P and the I R losses
Fe
of the stator winding P in the machine from the motor's terminal power P . The difference
L 1
divided by the synchronous angular velocity 2πf/p of the motor is the sum of friction and
windage torque T and motor torque, leading to
fw
p
T PP−−P−T
( )
(5)
1 Fe L fw
2πf
NOTE For determining losses and loss portions by measurement, see IEC 60034-2-1.
The motor does not have to be unloaded. The values of voltage, current, power, and speed are
recorded versus time.
In case the voltage and/or the frequency differ from the rated values, the values of torque and
current are corrected as described in 12.4.
12.4 Correction of data for tests performed at reduced voltage and/or other than rated
frequency
In case tests of a motor with a rated frequency of 60 Hz are done at a 50 Hz supply, the voltage
shall be reduced to 50/60 times (i.e. 83,3 %) of the rated voltage in order to maintain the rated
flux. If this is done, no further correction of the measured current and torque values is required.
In case tests of a motor with a rated frequency of 50 Hz are done at a 60 Hz supply, the supply
voltage shall not be increased as this would exceed the rated voltage. Instead, this shall be
considered as an (additional) reduction of the test voltage in the ratio of 50 Hz/60 Hz.
In addition, the change of frequency will lead to a different current displacement in the rotor
cage and thus to a different locked-rotor impedance and a different rotor resistance, which will
influence the locked-rotor current and torque. For larger power ratings, a method for correcting
the measured current and torque values to rated frequency according to the experience of the
manufacturer can be used.
Ignoring saturation, the current varies linearly with voltage and the torque varies with the square
of voltage. However, saturation of leakage flux paths will lead, depending on the motor design,
to voltage dependencies that are somewhat higher than this.
=
In case tests are done at reduced voltage, a method for correcting the measured current and
torque values to rated voltage according to the experience of the manufacturer shall be used.
In case no such method is available, Annex B offers a possible and suitable method for a
manufacturer to develop his own saturation factors correcting the measured values considering
saturation.
Table 1 – Minimum values of torques for design N
Range of rated output Number of poles
kW 2 4 6 8
T T T T T T T T T T T T
l u b l u b l u b l u b
0,12 ≤ P ≤ 0,63 1,9 1,3 2,0 2,0 1,4 2,0 1,7 1,2 1,7 1,5 1,1 1,6
N
0,63 < P ≤ 1,0 1,8 1,2 2,0 1,9 1,3 2,0 1,7 1,2 1,8 1,5 1,1 1,7
N
1,0 < P ≤ 1,6 1,8 1,2 2,0 1,9 1,3 2,0 1,6 1,1 1,9 1,4 1,0 1,8
N
1,6 < P ≤ 2,5 1,7 1,1 2,0 1,8 1,2 2,0 1,6 1,1 1,9 1,4 1,0 1,8
N
2,5 < P ≤ 4,0 1,6 1,1 2,0 1,7 1,2 2,0 1,5 1,1 1,9 1,3 1,0 1,8
N
4,0 < P ≤ 6,3 1,5 1,0 2,0 1,6 1,1 2,0 1,5 1,1 1,9 1,3 1,0 1,8
N
6,3 < P ≤ 10 1,5 1,0 2,0 1,6 1,1 2,0 1,5 1,1 1,8 1,3 1,0 1,7
N
10 < P ≤ 16 1,4 1,0 2,0 1,5 1,1 2,0 1,4 1,0 1,8 1,2 0,9 1,7
N
16 < P ≤ 25 1,3 0,9 1,9 1,4 1,0 1,9 1,4 1,0 1,8 1,2 0,9 1,7
N
25 < P ≤ 40 1,2 0,9 1,9 1,3 1,0 1,9 1,3 1,0 1,8 1,2 0,9 1,7
N
40 < P ≤ 63 1,1 0,8 1,8 1,2 0,9 1,8 1,2 0,9 1,7 1,1 0,8 1,7
N
63 < P ≤ 100 1,0 0,7 1,8 1,1 0,8 1,8 1,1 0,8 1,7 1,0 0,7 1,6
N
100 < P ≤ 160 0,9 0,7 1,7 1,0 0,8 1,7 1,0 0,8 1,7 0,9 0,7 1,6
N
160 < P ≤ 250 0,8 0,6 1,7 0,9 0,7 1,7 0,9 0,7 1,6 0,9 0,7 1,6
N
250 < P ≤ 400 0,75 0,6 1,6 0,75 0,6 1,6 0,75 0,6 1,6 0,75 0,6 1,6
N
400 < P ≤ 630 0,65 0,5 1,6 0,65 0,5 1,6 0,65 0,5 1,6 0,65 0,5 1,6
N
630 < P ≤ 1 600 0,5 0,3 1,6 0,5 0,3 1,6 0,5 0,3 1,6 0,5 0,3 1,6
N
NOTE The values given are per unit T .
N
– 16 – IEC 60034-12:2024 RLV © IEC 2024
Table 2 – Maximum values of locked rotor apparent power
for designs N and H
Range of rated output S /P
l N
kW
P ≤ 0,4
N
0,4 < P ≤ 0,63
N
0,63 < P ≤ 1,0
N
1,0 < P ≤ 1,8
N
1,8 < P ≤ 4,0
N
4,0 < P ≤ 6,3
N
6,3 < P ≤ 25 12
N
25 < P ≤ 63 11
N
63 < P ≤ 630 10
N
630 < P ≤ 1 600 9
N
Table 3 – Maximum values of locked rotor apparent power for designs NE and HE
Range of rated output S /P
l N
kW
P ≤ 0,4
N
0,4 < P ≤ 0,63
N
0,63 < P ≤ 1,0
N
1,0 < P ≤ 6,3
N
6,3 < P ≤ 25 14
N
25 < P ≤ 63 13
N
63 < P ≤ 630 12
N
630 < P ≤ 1 600 11
N
Table 4 – External moment of inertia (J)
Number of poles 2 4 6 8
Frequency 50 60 50 60 50 60 50 60
Hz
a
Rated output
Moment of inertia
kW
kg m
0,12 0,006 0,004 0,034 0,025 0,092 0,069 0,190 0,142
0,25 0,011 0,009 0,065 0,049 0,179 0,134 0,368 0,276
0,4 0,018 0,014 0,099 0,074 0,273 0,205 0,561 0,421
0,63 0,026 0,020 0,149 0,112 0,411 0,308 0,845 0,634
1,0 0,040 0,030 0,226 0,170 0,624 0,468 1,28 0,960
1,6 0,061 0,046 0,345 0,259 0,952 0,714 1,95 1,46
2,5 0,091 0,068 0,516 0,387 1,42 1,07 2,92 2,19
4,0 0,139 0,104 0,788 0,591 2,17 1,63 4,46 3,34
6,3 0,210 0,158 1,19 0,889 3,27 2,45 6,71 5,03
10 0,318 0,239 1,80 1,35 4,95 3,71 10,2 7,63
16 0,485 0,364 2,74 2,06 7,56 5,67 15,5 11,6
25 0,725 0,544 4,10 3,07 11,3 8,47 23,2 17,4
40 1,11 0,830 6,26 4,69 17,2 12,9 35,4 26,6
63 1,67 1,25 9,42 7,06 26,0 19,5 53,3 40,0
100 2,52 1,89 14,3 10,7 39,3 29,5 80,8 60,6
160 3,85 2,89 21,8 16,3 60,1 45,1 123 92,5
250 5,76 4,32 32,6 24,4 89,7 67,3 184 138
400 8,79 6,59 49,7 37,3 137 103 281 211
630 13,2 9,90 74,8 56,1 206 155 423 317
1 600 30,6 23 173 130 477 358 979 734
NOTE 1 The values of the moment of inertia given are in terms of mr where m is the mass and r is the mean
radius of gyration.
NOTE 2 Moment of inertia is defined in ISO 80000-4:20062019, 4.7.
a
NOTE 3 For intermediate and higher values, external moments of inertia shall be calculated according to
the following formula from which the values in the table have been calculated:
0,9 2,5
– for 50 Hz motors J = 0,04P p
0,9 2,5
– for 60 Hz motors J = 0,03P p
where:
J is the external moment of inertia in kg m2;
P is the output in kW;
p is the number of pairs of poles.
– 18 – IEC 60034-12:2024 RLV © IEC 2024
Table 5 – Minimum values of torques for design H
Range of rated output Number of poles
kW 4 6 8
T T T T T T T T T
l u b l u b l u b
0,12 ≤ P ≤ 0,63 3,0 2,1 2,1 2,55 1,8 1,9 2,25 1,65 1,9
N
0,63 < P ≤ 1,0 2,85 1,95 2,0 2,55 1,8 1,9 2,25 1,65 1,9
N
1,0 < P ≤ 1,6 2,85 1,95 2,0 2,4 1,65 1,9 2,1 1,5 1,9
N
1,6 < P ≤ 2,5 2,7 1,8 2,0 2,4 1,65 1,9 2,1 1,5 1,9
N
2,5 < P ≤ 4,0 2,55 1,8 2,0 2,25 1,65 1,9 2,0 1,5 1,9
N
4,0 < P ≤ 6,3 2,4 1,65 2,0 2,25 1,65 1,9 2,0 1,5 1,9
N
6,3 < P ≤ 10
2,4 1,65 2,0 2,25 1,65 1,9 2,0 1,5 1,9
N
10 < P ≤ 16 2,25 1,65 2,0 2,1 1,5 1,9 2,0 1,4 1,9
N
16 < P ≤ 25 2,1 1,5 1,9 2,1 1,5 1,9 2,0 1,4 1,9
N
25 < P ≤ 40 2,0 1,5 1,9 2,0 1,5 1,9 2,0 1,4 1,9
N
40 < P ≤ 160
2,0 1,4 1.
...
IEC 60034-12 ®
Edition 4.0 2024-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Rotating electrical machines –
Part 12: Starting performance of single-speed three-phase cage induction
motors
Machines électriques tournantes –
Partie 12: Caractéristiques de démarrage des moteurs triphasés à induction à
cage à une seule vitesse
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IEC 60034-12 ®
Edition 4.0 2024-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Rotating electrical machines –
Part 12: Starting performance of single-speed three-phase cage induction
motors
Machines électriques tournantes –
Partie 12: Caractéristiques de démarrage des moteurs triphasés à induction à
cage à une seule vitesse
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.160.01 ISBN 978-2-8322-8544-2
– 2 – IEC 60034-12:2024 © IEC 2024
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Symbols . 8
5 Designation . 9
5.1 General . 9
5.2 Design N . 9
5.3 Design NE . 9
5.4 Designs NY and NEY . 9
5.5 Design H . 9
5.6 Design HE . 9
5.7 Designs HY and HEY . 10
6 Design N requirements . 10
6.1 Torque characteristics . 10
6.2 Locked rotor current and apparent power . 10
6.3 Starting requirements . 10
7 Design NE starting requirements . 11
8 Designs NY and NEY starting requirements . 11
9 Design H requirements . 11
9.1 Starting torque . 11
9.2 Locked rotor current and apparent power . 11
9.3 Starting requirements . 11
10 Design HE starting requirements . 12
11 Designs HY and HEY starting requirements . 12
12 Determination of current and torque from measurement. 12
12.1 Locked-rotor current and locked-rotor torque . 12
12.2 Breakdown torque . 12
12.3 Torque-speed curve and current-speed curve . 13
12.3.1 General . 13
12.3.2 Torque-speed and current-speed curves from direct measurement
(method a) . 13
12.3.3 Torque-speed and current-speed curves from acceleration (method b) . 13
12.3.4 Torque-speed and current-speed curves from measured input power
(method c) . 14
12.4 Correction of data for tests performed at reduced voltage and/or other than
rated frequency . 14
Annex A (informative) Current and torque characteristics with locked rotor . 20
Annex B (informative) Correction method for test done on reduced voltage . 24
Bibliography . 25
Figure A.1 – Locked-rotor current in multiples of rated current versus time . 20
Figure A.2 – Locked-rotor torque in multiples of rated torque versus time . 21
Figure A.3 – Locked-rotor torque in cNm versus rotor position in °; left: preferable
number of rotor slots, right: less preferable number of rotor slots . 21
Figure A.4 – Locked-rotor torque in cNm versus rotor position in ° . 22
Figure A.5 – Time -courses (in s) of rotational speed (upper left), torque (lower left),
phase voltage (upper right) and phase current (lower right) during a star-delta start-up . 23
Table 1 – Minimum values of torques for design N . 15
Table 2 – Maximum values of locked rotor apparent power for designs N and H . 16
Table 3 – Maximum values of locked rotor apparent power for designs NE and HE . 16
Table 4 – External moment of inertia (J) . 17
Table 5 – Minimum values of torques for design H . 18
Table 6 – Minimum values of torques for design N motors with type of protection 'Ex
eb – increased safety' . 18
Table 7 – External moment of inertia (J) for motors with type of protection 'Ex eb –
increased safety' . 19
– 4 – IEC 60034-12:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ROTATING ELECTRICAL MACHINES –
Part 12: Starting performance of single-speed
three-phase cage induction motors
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
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the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 60034-12 has been prepared by IEC technical committee 2: Rotating machinery. It is an
International Standard.
This fourth edition cancels and replaces the third edition published in 2016. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
Clause or
Change
subclause
Table 6 Aligned with the requirements for explosion protected motors from TC31 WG27
12 New clause on methods for measuring locked-rotor current and torque
Annex A New informative annex on the general current and torque characteristics with locked
rotor
Annex B New informative annex on correction of voltage and frequency
The text of this International Standard is based on the following documents:
Draft Report on voting
2/2132/CDV 2/2150A/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts of the IEC 60034 series, published under the general title Rotating electrical
machines, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.
– 6 – IEC 60034-12:2024 © IEC 2024
ROTATING ELECTRICAL MACHINES –
Part 12: Starting performance of single-speed
three-phase cage induction motors
1 Scope
This part of IEC 60034 specifies the parameters for eight designs of starting performance of
single-speed three-phase 50 Hz or 60 Hz cage induction motors in accordance with
IEC 60034-1 that:
– have a rated voltage up to 1 000 V;
– are intended for direct-on-line or star-delta starting;
– are rated on the basis of duty type S1;
– are constructed to any degree of protection as defined in IEC 60034-5 and explosion
protection.
This document also applies to dual voltage motors provided that the flux saturation level is the
same for both voltages.
The values of torque, apparent power and current given in this document are limiting values
(that is, minimum or maximum without tolerance).
NOTE 1 It is not expected that all manufacturers will produce machines for all eight designs. The selection of any
specific design in accordance with this document will be a matter of agreement between the manufacturer and the
purchaser.
NOTE 2 Designs other than the eight specified can be necessary for particular applications.
NOTE 3 Values given in manufacturers' catalogues can include tolerances in accordance with IEC 60034-1.
NOTE 4 The values tabled for locked rotor apparent power are based on RMS symmetrical steady state locked rotor
currents. The start of the motor leads to transient asymmetrical currents in the whole supply, so called inrush
currents, the peak value of which can range from 1,8 to 2,8 times the steady state locked rotor value. The current
peak and decay time are a function of the motor design and switching angle. Similar effects can occur during the
switchover from star to delta operation. A more detailed description is provided in Annex A.
The application of the test methods described in Clause 12 can be applied to cage induction
motors outside the scope of this document. However, special care shall be taken in such cases
to prevent overheating of the stator or the rotor winding depending on the concrete method and
parameters chosen.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60034-1:2022, Rotating electrical machines – Part 1: Rating and performance
IEC 60034-5:2020, Rotating electrical machines – Part 5: Degrees of protection provided by the
integral design of rotating electrical machines (IP code) – Classification
IEC 60034-30-1:2014, Rotating electrical machines – Part 30-1: Efficiency classes of line-
operated AC motors (IE-code)
IEC 60079-7:2015, Explosive atmospheres – Part 7: Equipment protection by increased
safety "e"
IEC 60079-7:2015/AMD1:2017
ISO 80000-4:2019, Quantities and units – Part 4: Mechanics
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
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3.1
rated torque
T
N
torque the motor develops at its shaft end at rated output and speed
[SOURCE: IEC 60050-411:1996, 411-48-05]
3.2
locked-rotor torque
T
l
smallest measured torque the motor develops at its shaft end with the rotor locked, over all its
angular positions, at rated voltage and frequency
[SOURCE: IEC 60050-411:1996, 411-48-06]
3.3
pull-up torque
T
u
smallest steady-state asynchronous torque which the motor develops between zero speed and
the speed which corresponds to the breakdown torque, when the motor is supplied at the rated
voltage and frequency
[SOURCE: IEC 60050-411:1996, 411-48-42, modified – The notes 1 and 2 to entry have been
modified.]
Note 1 to entry: This definition does not apply to those motors whose torque continually decreases with increase in
speed.
Note 2 to entry: In addition to the steady-state asynchronous torques, harmonic synchronous torques, which are a
function of rotor load angle, will be present at specific speeds. At such speeds, the accelerating torque can be
negative for some rotor load angles. Experience and calculation show this to be an unstable operating condition and
therefore harmonic synchronous torques do not prevent motor acceleration and are excluded from this definition.
– 8 – IEC 60034-12:2024 © IEC 2024
3.4
breakdown torque
T
b
maximum steady-state asynchronous torque which the motor develops without an abrupt drop
in speed, when the motor is supplied at the rated voltage and frequency
[SOURCE: IEC 60050-411:1996, 411-48-43, modified – The notes 1 and 2 to entry have been
modified.]
Note 1 to entry: This definition does not apply to those motors whose torque continually decreases with increase in
speed.
3.5
rated output
P
N
value of the output power included in the rating
Note 1 to entry: The terms rated value and rating are defined in IEC 60034-1:2022, 3.1 and 3.2 (see also IEC 60050-
411:1996, 411-51-23 and 411-51-24).
3.6
rated voltage
U
N
value of the voltage included in the rating
Note 1 to entry: The terms rated value and rating are defined in IEC 60034-1:2022, 3.1 and 3.2 (see also IEC 60050-
411:1996, 411-51-23 and 411-51-24).
3.7
locked rotor apparent power
S
l
apparent power input with the motor held at rest at rated voltage and frequency after the inrush
currents have decayed to a symmetrical system of current
[SOURCE: IEC 60050-411:1996, 411-48-49, modified – "after the inrush currents have decayed
to a symmetrical system of current" has been added.]
3.8
locked rotor current
I
l
current with the motor held at rest at rated voltage and frequency after the inrush currents have
decayed to a symmetrical system of current
4 Symbols
I Locked rotor current
l
J External moment of inertia
J Moment of inertia of motor under test
M
n Rotational speed
p Number of pole pairs
P Power at the motor terminals during test method c) in 12.3.4
P Power at the generator terminals during test method a) in 12.3.2
1,g
P Motor iron losses during test method c) in 12.3.4
fe
P Motor I R losses during test method c) in 12.3.4
L
P Total losses of the generator during test method a) in 12.3.2
T,g
P Rated output
N
S Locked rotor apparent power
l
T Rated torque
N
T Locked rotor torque
l
T Pull-up torque
u
Breakdown torque
T
b
T Motor friction and windage torque during test method c) in 12.3.4
fw
U Rated voltage
N
5 Designation
5.1 General
Motors designed according to this document are classified according to 5.2 to 5.7. The letters
used to specify the different designs stand for:
N: normal starting torque.
H: high starting torque.
Y: star-delta starting.
E: motors utilizing extended / higher locked rotor apparent power and current to achieve
efficiency classes of IE3 or higher according to IEC 60034-30-1.
5.2 Design N
Normal starting torque three-phase cage induction motors, intended for direct-on-line starting,
having 2, 4, 6 or 8 poles, rated from 0,12 kW to 1 600 kW.
5.3 Design NE
Normal starting torque three-phase cage induction motors having higher locked rotor apparent
power than design N, intended for direct-on-line starting, having 2, 4, 6 or 8 poles, rated from
0,12 kW to 1 600 kW.
5.4 Designs NY and NEY
Motors similar to designs N or NE, respectively, but intended for star-delta starting. For these
motors in star-connection, minimum values for T and T are 25 % of the values of design N or
l u
NE, respectively, see Table 1.
5.5 Design H
High starting torque three-phase cage induction motors with 4, 6 or 8 poles, intended for direct-
online starting, rated from 0,12 kW to 160 kW at a frequency of 60 Hz.
5.6 Design HE
High starting torque three-phase cage induction motors having higher locked rotor apparent
power than design H, with 4, 6 or 8 poles, intended for direct-online starting, rated from 0,12 kW
to 160 kW at a frequency of 60 Hz.
– 10 – IEC 60034-12:2024 © IEC 2024
5.7 Designs HY and HEY
Motors similar to designs H or HE, respectively, but intended for star-delta starting. For these
motors in star-connection, minimum values for T and T are 25 % of the values of design H or
l u
HE, respectively, see Table 5.
6 Design N requirements
6.1 Torque characteristics
The starting torque is represented by three characteristic features. These features shall be in
accordance with the appropriate values given in Table 1 or Table 6. The values in Table 1 and
Table 6 are minimum values at rated voltage. Higher values are allowed.
The motor torque at any speed between zero and that at which breakdown torque occurs shall
be not less than 1,3 times the torque obtained from a curve varying as the square of the speed
and being equal to rated torque at rated speed. However, for 2-pole motors with type of
protection 'Ex eb – increased safety' having a rated output greater than 100 kW, the motor
torque at any speed between zero and that at which breakdown torque occurs shall not be less
than 1,3 times the torque obtained from a curve varying as the square of the speed and being
equal to 70 % rated torque at rated speed. For motors with type of protection 'Ex eb', the three
characteristic torques shall be in accordance with the appropriate values given in Table 6.
NOTE The factor 1,3 has been chosen with regard to an undervoltage of 10 % in relation to the rated voltage at the
motor terminals during the acceleration period.
6.2 Locked rotor current and apparent power
The locked rotor apparent power shall be not greater than the appropriate value given in
Table 2. The values given in Table 2 are independent of the number of poles and are maximum
values at rated voltage. For motors with type of protection 'e', locked rotor apparent power shall
be in accordance with the appropriate values specified in IEC 60079-7.
The locked rotor current is calculated from the locked rotor apparent power according to:
SP
lN
I ×
l (1)
P
3U
N
N
The advantage of specifying S /P instead of I /I is that the locked rotor current can be
l N l N
calculated from rated power and rated voltage only, not requiring to know the rated current
which depends on quantities such as power factor and efficiency that are usually not known in
early stages of a project.
6.3 Starting requirements
Motors shall be capable of withstanding two starts in succession (coasting to rest between
starts) from cold conditions and one start from hot after running at rated conditions. The
retarding torque due to the driven load will be in each case proportional to the square of the
speed and equal to the rated torque at rated speed with the external moment of inertia given in
Table 4 or Table 7.
=
In each case, a further start is permissible only if the motor temperature before starting does
not exceed the steady temperature at rated load. However, for 2-pole motors with type of
protection 'Ex eb – increased safety' having a rated output greater than 100 kW, the retarding
torque due to the driven load is proportional to the square of the speed and equal to 70 % rated
torque at rated speed, with the external moment of inertia given in Table 7. After this starting,
load with rated torque is possible.
It should be recognized that the number of starts should be minimized since these affect the
life of the motor.
7 Design NE starting requirements
The starting requirements are as for design N, except that the limits for locked rotor apparent
power in Table 3 apply, as increasing efficiency values require physically increasing values for
locked rotor apparent power.
8 Designs NY and NEY starting requirements
The starting requirements are as for designs N or NE, respectively. In addition, however, a
reduced retarding torque is necessary as the starting torque in 'star connection' may be
insufficient to accelerate some loads to an acceptable speed.
It should be recognized that the number of starts should be minimized since these affect the
life of the motor.
9 Design H requirements
9.1 Starting torque
The starting torque is represented by three characteristic features. These features shall be in
accordance with the appropriate values given in Table 5. These values are minimum values at
rated voltage. Higher values are allowed.
9.2 Locked rotor current and apparent power
The locked rotor apparent power shall be not greater than the appropriate value given in
Table 2. The values in Table 2 are independent of the number of poles and are maximum values
at rated voltage.
The locked rotor current is calculated from the locked rotor apparent power according to the
formula given in 6.2.
9.3 Starting requirements
Motors shall be capable of withstanding two starts in succession (coasting to rest between
starts) from cold conditions, and one start from hot after running at rated conditions. The
retarding torque due to the driven load is assumed to be constant and equal to rated torque,
independent of speed, with an external moment of inertia of 50 % of the values given in Table 4.
In each case, a further start is permissible only if the motor temperature before starting does
not exceed the steady temperature at rated load.
It should be recognized that the number of starts should be minimized since these affect the
life of the motor.
– 12 – IEC 60034-12:2024 © IEC 2024
10 Design HE starting requirements
The starting requirements are as for design H, except that the limits for locked rotor apparent
power in Table 3 apply, as increasing efficiency values require physically increasing values for
locked rotor apparent power.
11 Designs HY and HEY starting requirements
The starting requirements are as for design H or HE, respectively. In addition, however, a
reduced retarding torque is necessary as the starting torque in 'star connection' may be
insufficient to accelerate some loads to an acceptable speed.
It should be recognized that the number of starts should be minimized since these affect the
life of the motor.
12 Determination of current and torque from measurement
12.1 Locked-rotor current and locked-rotor torque
When possible, the locked-rotor current shall be measured at rated voltage and frequency as
the current is not directly proportional to the voltage because of changes in reactance caused
by saturation of the leakage paths. In case this isn't possible, see 12.4.
The locked-rotor torque may be measured with, e.g. a scale or force transducer with a brake or
beam, or it may be measured directly using an in-line torque transducer, or it may be determined
from the electrical input power using Formula (5). Depending on the chosen number of rotor
slots, the locked-rotor torque of cage induction motors is subject to variations depending on the
angular position of the rotor with respect to the stator. In case a preferable number of rotor slots
is chosen according to the manufacturer's experience, it is usual practice to lock the rotor of a
cage induction motor in any convenient position or to measure current and torque values with
the rotor being stalled at very low speed, i.e. with a speed below 2 % of the rated speed.
12.2 Breakdown torque
The breakdown torque can be measured by loading the motor, starting at no-load condition,
with an increasing load torque. The load torque that is reached when the motor starts quickly
loosing speed, is the breakdown torque.
Alternatively, the values of pull-up and breakdown torque can be measured during acceleration
from reverse speed to no-load speed (see method c) below), provided the load machine inertia
or load torque is sufficiently large. Sufficiently large means in case of power ratings up to
100 kW that the change of rotational speed during test satisfies, depending on the motor's
moment of inertia J and the motor's locked-rotor torque T , the relation
M l
dn 0,05
≤ T .
(2)
l
dtJ2 π
M
Otherwise, the breakdown torque will be underestimated. For power ratings above 100 kW,
different relations of the moment of inertia and the locked-rotor torque may be suitable
according to the experience to the manufacturer.
In case the complete torque-speed curve is measured using one of the methods below, no
separate measurement of the breakdown torque is required.
12.3 Torque-speed curve and current-speed curve
12.3.1 General
Any one of the methods listed below may be used to obtain data for a speed-torque curve. The
selection of the method will depend upon the size and the speed-torque characteristics of the
machine and the testing facilities. In all three methods, sufficient test points should be recorded
to ensure that reliable curves, including irregularities, can be drawn in the regions of interest
from the test data. It is important that the frequency of the power supply be maintained constant
throughout the test.
Method a) requires the maintenance of constant speed for each reading. Therefore, it cannot
be used in regions where the torque of the machine increases with speed more rapidly than
that of the loading device. From the results of the following tests, adjusted to the rated voltage
and frequency, curves of torque and current should be plotted vs. speed.
It is understood that the temperature of the stator and the rotor winding will influence the
measured torque-speed and current-speed curves (see Annex A).
12.3.2 Torque-speed and current-speed curves from direct measurement (method a)
In this method, a calibrated generator with known losses versus speed or a transducer or
mechanical brake is coupled to the motor being tested. The motor is supplied preferably with
rated frequency and rated voltage. The speed of the motor for each test point is controlled by
varying the load on the generator or the brake.
In this test, readings of voltage, current, and speed of the motor as well as readings of
– either the torque directly measured by, e.g. a torque transducer, a dynamometer or a
mechanical brake,
– or the power at the generator are taken at speeds between approximately 30 % of
synchronous speed and the maximum speed obtainable. The total power output of the motor
is the sum of the power at the generator terminals P and the total losses of the generator
1,g
P . The torque T at each speed n is calculated from
T,g
TP+ P / 2 π n
( ) (3)
( )
1,g T,g
NOTE For determining losses and loss portions by measurement, see IEC 60034-2-1.
The speed should be constant or sufficiently low satisfying Formula (2) when the readings are
taken, so that acceleration or deceleration power does not affect the results. Care should be
taken not to overheat the motor. The accuracy of speed measurement is particularly important
at low slip.
In case the voltage and/or the frequency differ from the rated values, the values of torque and
current are corrected as described in 12.4.
12.3.3 Torque-speed and current-speed curves from acceleration (method b)
In this method, the motor is started with no load, and the values of voltage, current, and speed
are recorded versus time. The torque is determined from the acceleration of the inertia J of the
rotating parts. An accurate measurement of speed versus time is an essential requirement of
this method. In addition, the accelerating time should be long enough so that electrical transient
effects do not distort the readings of voltage, current, and speed. In order to achieve this, the
accelerating time may be increased by using a lower applied voltage or by coupling a suitable
inertia to the motor shaft. In case the accelerating time is too short, the measured torque will
underestimate the motor's steady state torque-speed curve.
=
– 14 – IEC 60034-12:2024 © IEC 2024
If the motor's starting friction is high, or if more accurate data in the zero speed range are
desired, the motor can be started rotating in the reverse direction prior to application of power
for the acceleration.
The torque T at each speed is calculated from the time-derivative of speed according to
dn
TJ= 2 π (4)
dt
This requires a sufficiently exact knowledge of the moment of inertia. In case the voltage and/or
the frequency differ from the rated values, the values of torque and current are corrected as
described in 12.4.
12.3.4 Torque-speed and current-speed curves from measured input power (method c)
In this method, the torque is determined by subtracting the iron losses P and the I R losses
Fe
of the stator winding P in the machine from the motor's terminal power P . The difference
L 1
divided by the synchronous angular velocity 2 f/p of the motor is the sum of friction and
π
windage torque T and motor torque, leading to
fw
p
T PP−−P−T
( ) (5)
1 Fe L fw
2πf
NOTE For determining losses and loss portions by measurement, see IEC 60034-2-1.
The motor does not have to be unloaded. The values of voltage, current, power, and speed are
recorded versus time.
In case the voltage and/or the frequency differ from the rated values, the values of torque and
current are corrected as described in 12.4.
12.4 Correction of data for tests performed at reduced voltage and/or other than rated
frequency
In case tests of a motor with a rated frequency of 60 Hz are done at a 50 Hz supply, the voltage
shall be reduced to 50/60 times (i.e. 83,3 %) of the rated voltage in order to maintain the rated
flux. If this is done, no further correction of the measured current and torque values is required.
In case tests of a motor with a rated frequency of 50 Hz are done at a 60 Hz supply, the supply
voltage shall not be increased as this would exceed the rated voltage. Instead, this shall be
considered as an (additional) reduction of the test voltage in the ratio of 50 Hz/60 Hz.
In addition, the change of frequency will lead to a different current displacement in the rotor
cage and thus to a different locked-rotor impedance and a different rotor resistance, which will
influence the locked-rotor current and torque. For larger power ratings, a method for correcting
the measured current and torque values to rated frequency according to the experience of the
manufacturer can be used.
Ignoring saturation, the current varies linearly with voltage and the torque varies with the square
of voltage. However, saturation of leakage flux paths will lead, depending on the motor design,
to voltage dependencies that are somewhat higher than this.
=
In case tests are done at reduced voltage, a method for correcting the measured current and
torque values to rated voltage according to the experience of the manufacturer shall be used.
In case no such method is available, Annex B offers a possible and suitable method for a
manufacturer to develop his own saturation factors correcting the measured values considering
saturation.
Table 1 – Minimum values of torques for design N
Range of rated output Number of poles
kW 2 4 6 8
T T T T T T T T T T T T
l u b l u b l u b l u b
0,12 ≤ P ≤ 0,63 1,9 1,3 2,0 2,0 1,4 2,0 1,7 1,2 1,7 1,5 1,1 1,6
N
0,63 < P ≤ 1,0 1,8 1,2 2,0 1,9 1,3 2,0 1,7 1,2 1,8 1,5 1,1 1,7
N
1,0 < P ≤ 1,6 1,8 1,2 2,0 1,9 1,3 2,0 1,6 1,1 1,9 1,4 1,0 1,8
N
1,6 < P ≤ 2,5 1,7 1,1 2,0 1,8 1,2 2,0 1,6 1,1 1,9 1,4 1,0 1,8
N
2,5 < P ≤ 4,0 1,6 1,1 2,0 1,7 1,2 2,0 1,5 1,1 1,9 1,3 1,0 1,8
N
4,0 < P ≤ 6,3 1,5 1,0 2,0 1,6 1,1 2,0 1,5 1,1 1,9 1,3 1,0 1,8
N
6,3 < P ≤ 10 1,5 1,0 2,0 1,6 1,1 2,0 1,5 1,1 1,8 1,3 1,0 1,7
N
10 < P ≤ 16 1,4 1,0 2,0 1,5 1,1 2,0 1,4 1,0 1,8 1,2 0,9 1,7
N
16 < P ≤ 25 1,3 0,9 1,9 1,4 1,0 1,9 1,4 1,0 1,8 1,2 0,9 1,7
N
25 < P ≤ 40 1,2 0,9 1,9 1,3 1,0 1,9 1,3 1,0 1,8 1,2 0,9 1,7
N
40 < P ≤ 63 1,1 0,8 1,8 1,2 0,9 1,8 1,2 0,9 1,7 1,1 0,8 1,7
N
63 < P ≤ 100 1,0 0,7 1,8 1,1 0,8 1,8 1,1 0,8 1,7 1,0 0,7 1,6
N
100 < P ≤ 160 0,9 0,7 1,7 1,0 0,8 1,7 1,0 0,8 1,7 0,9 0,7 1,6
N
160 < P ≤ 250 0,8 0,6 1,7 0,9 0,7 1,7 0,9 0,7 1,6 0,9 0,7 1,6
N
250 < P ≤ 400 0,75 0,6 1,6 0,75 0,6 1,6 0,75 0,6 1,6 0,75 0,6 1,6
N
400 < P ≤ 630 0,65 0,5 1,6 0,65 0,5 1,6 0,65 0,5 1,6 0,65 0,5 1,6
N
630 < P ≤ 1 600 0,5 0,3 1,6 0,5 0,3 1,6 0,5 0,3 1,6 0,5 0,3 1,6
N
NOTE The values given are per unit T .
N
– 16 – IEC 60034-12:2024 © IEC 2024
Table 2 – Maximum values of locked rotor apparent power
for designs N and H
Range of rated output S /P
l N
kW
P ≤ 0,4
N
0,4 < P ≤ 0,63
N
0,63 < P ≤ 1,0
N
1,0 < P ≤ 1,8
N
1,8 < P ≤ 4,0
N
4,0 < P ≤ 6,3
N
6,3 < P ≤ 25 12
N
25 < P ≤ 63 11
N
63 < P ≤ 630 10
N
630 < P ≤ 1 600 9
N
Table 3 – Maximum values of locked rotor apparent power for designs NE and HE
Range of rated output S /P
l N
kW
P ≤ 0,4
N
0,4 < P ≤ 0,63
N
0,63 < P ≤ 1,0
N
1,0 < P ≤ 6,3
N
6,3 < P ≤ 25 14
N
25 < P ≤ 63 13
N
63 < P ≤ 630 12
N
630 < P ≤ 1 600 11
N
Table 4 – External moment of inertia (J)
Number of poles
...
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