IEC TS 60034-31:2010

IEC/TS 60034-31 ®
Edition 1.0 2010-04
TECHNICAL
SPECIFICATION
SPÉCIFICATION
TECHNIQUE
colour
inside
Rotating electrical machines –
Part 31: Selection of energy-efficient motors including variable speed
applications – Application guide

Machines électriques tournantes –
Partie 31: Choix des moteurs éconergétiques incluant les applications à vitesse
variable – Guide d’application

IEC/TS 60034-31:2010
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IEC/TS 60034-31 ®
Edition 1.0 2010-04
TECHNICAL
SPECIFICATION
SPÉCIFICATION
TECHNIQUE
colour
inside
Rotating electrical machines –
Part 31: Selection of energy-efficient motors including variable speed
applications – Application guide

Machines électriques tournantes –
Partie 31: Choix des moteurs éconergétiques incluant les applications à vitesse
variable – Guide d’application

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
X
CODE PRIX
ICS 29.160 ISBN 978-2-88910-023-1
– 2 – TS 60034-31 © IEC:2010
CONTENTS
FOREWORD.5
INTRODUCTION.7
1 Scope.8
2 Normative references .8
3 Terms, definitions and symbols .8
3.1 Terms and definitions .8
3.2 Symbols .8
4 General .9
5 Efficiency .10
5.1 General .10
5.2 Motor losses.11
5.3 Additional motor-losses when operated on a frequency converter.12
5.4 Motors for higher efficiency classes.12
5.5 Variations in motor losses .13
5.6 Part load efficiency.14
5.7 Efficiency testing methods.15
5.8 Power factor (see Figure 4) .16
5.9 Matching motors and variable frequency converters .17
5.10 Motors rated for 50 Hz and 60 Hz.18
5.11 Motors rated for different voltages or a voltage range.20
5.12 Motors rated for operation at frequencies other than 50/60 Hz.20
5.13 Variable frequency converter efficiency .20
5.14 Frequency converter power factor .22
6 Environment .22
6.1 Starting performance.22
6.2 Operating speed and slip.23
6.3 Effects of power quality and variation in voltage and frequency .23
6.4 Effects of voltage unbalance .23
6.5 Effects of ambient temperature.24
7 Applications.24
7.1 General .24
7.2 Energy savings by speed control (variable speed drives, VSD).24
7.3 Correct sizing of the motor .24
7.4 Continuous duty application .25
7.5 Applications involving extended periods of light load operations.25
7.6 Applications involving overhauling loads.26
7.7 Applications where load-torque is increasing with speed (pumps, fans,
compressors, etc.).26
7.8 Applications involving frequent starts and stops and/or mechanical braking.27
7.9 Applications involving explosive gas or dust atmospheres .27
8 Economy .28
8.1 Relevance to users.28
8.2 Initial purchase cost .28
8.3 Operating cost.29
8.4 Rewinding cost.30
8.5 Payback time.31

TS 60034-31 © IEC:2010 – 3 –
8.6 Life cycle cost .31
9 Maintenance.32
Annex A (informative) Super-premium efficiency (IE4) .34
Bibliography.40

Figure 1 – Overview of different areas for savings of electrical energy with drive
systems .9
Figure 2 – Typical losses of energy-efficient motors, converters and electro-
mechanical brakes.10
Figure 3 – Typical efficiency versus load curve bands for three-phase, cage-induction
motors of different output power ranges (approximately 1,1 kW, 15 kW and 150 kW).14
Figure 4 – Typical power factor versus load curve bands for three-phase, cage-
induction motors of different output power ranges (approximately 1,1 kW, 15 kW and
150 kW) .16
Figure 5 – Typical reduction of energy efficiency in %-points for 4-pole, low-voltage
motors between 50 Hz and 60 Hz when compared at the same torque (60 Hz power 20
% increased).19
Figure 6 – Typical reduction of energy efficiency in %-points for 4-pole, low-voltage
motors between 50 Hz and 60 Hz when compared at the same output power (60 Hz
torque 20 % reduced) .19
Figure 7 – Typical efficiency of indirect three-phase voltage source type converters
with a passive front-end for typical load points of pumps, fans and compressors .20
Figure 8 – Typical efficiency of indirect three-phase voltage source type converters
with a passive front-end for typical load points of constant torque.21
Figure 9 – Typical variations of current, speed, power factor and efficiency with
voltage for constant output power .23
Figure 10 – Potential energy savings by improvement of efficiency classes for motors
running at rated load.25
Figure 11 – Typical torque versus speed curves for 11 kW, 4-pole, three-phase, cage-
induction motors and load versus speed curves for speed-square-loads .26
Figure 12 – 11 kW IE3 motor operated at full load, 4 000 operating hours per year, 15
years life cycle.28
Figure 13 – Example of a load factor graph: fraction of annual operating hours .29
Figure 14 – Life cycle cost analysis of an 11 kW motor operating at full load .32
Figure A.1 – IE4 efficiency limits.39

Table 1 – Loss distribution in three-phase, 4-pole, cage-induction electric motors .12
Table 2 – Exemplary efficiency calculation of a motor when operated at 50 Hz and
60 Hz with the same torque, using a 50 Hz motor rating as the basis.18
Table 3 – Loss distribution for low-voltage U-converters .21
Table 4 – Example of changing of efficiency, speed and torque demand with energy
efficiency class of three 11 kW, 50 Hz motors in the same application .27
Table 5 – Average lifecycles for electric motors .30
Table A.1 – Interpolation coefficients .35
Table A.2 – Nominal limits (%) for super-premium efficiency (IE4) .35
Table A.3 – Standard power in kW associated with torque and speed for line-operated
motors .36
Table A.4 – Nominal limits for super-premium efficiency (IE4) for 50 Hz line operated
motors .37

– 4 – TS 60034-31 © IEC:2010
Table A.5 – Nominal limits for super-premium efficiency (IE4) for 60 Hz line operated
motors .38

TS 60034-31 © IEC:2010 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ROTATING ELECTRICAL MACHINES –

Part 31: Selection of energy-efficient motors including
variable speed applications – Application guide

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 co-operation on all questions concerning standardization in the electrical and electronic fields. To
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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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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) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 60034-31, which is a technical specification, has been prepared by IEC technical
committee 2: Rotating machinery.

– 6 – TS 60034-31 © IEC:2010
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
2/1575/DTS 2/1594/RVC
Full information on the voting for the approval of this technical specification can be found in
the report on voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
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.
NOTE A table of cross-references of all IEC TC 2 publications can be found in the IEC TC 2 dashboard on the
IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be be
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication 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.
TS 60034-31 © IEC:2010 – 7 –
INTRODUCTION
The present technical specification gives technical guidelines for the application of energy-
efficient motors in constant-speed and variable speed applications. It does not cover aspects
of a purely commercial nature.
Standards developed by IEC technical committee 2 do not deal with methods of how to obtain
a high efficiency but with tests to verify the guaranteed value. IEC 60034-2-1 is the most
important standard for this purpose.
For approximately 15 years regional agreements were negotiated in many areas of the world
regarding efficiency classes of three-phase, cage-induction motors with outputs up to about
200 kW maximum, as motors of this size are installed in high quantities and are for the most
part produced in series production. The design of these motors is often driven by the market
demand for low investment cost, hence energy efficiency was not a top priority.
In IEC 60034-30, IE efficiency classes for single-speed cage-induction motors have been
defined and test procedures specified:
IE1 Standard efficiency
IE2 High efficiency
IE3 Premium efficiency
IE4 Super-premium efficiency
Determination of efficiency for motors powered by a frequency converter will be included in
IEC standard 60034-2-3.
However, for motors rated 1 MW and above, which are usually custom made, a high efficiency
has always been one of the most important design goals. The full-load efficiency of these
machines typically ranges between 95 % and 98 %. Efficiency is usually part of the purchase
contract and is penalized if the guaranteed values are not met. Therefore, these higher
ratings are of secondary importance when assigning efficiency classes.
With permission from the National Electrical Manufacturers Association (NEMA), some parts
of this TS are based on NEMA MG 10, Energy Management Guide For Selection and Use of
Fixed Frequency Medium AC Squirrel-Cage Polyphase Induction Motors.

– 8 – TS 60034-31 © IEC:2010
ROTATING ELECTRICAL MACHINES –

Part 31: Selection of energy-efficient motors including
variable speed applications – Application guide

1 Scope
This part of IEC 60034 provides a guideline of technical aspects for the application of energy-
efficient, three-phase, electric motors. It not only applies to motor manufacturers, OEMs
(original equipment manufacturers), end users, regulators and legislators but to all other
interested parties.
This technical specification is applicable to all electrical machines covered by IEC 60034-30.
Most of the information however is also relevant for cage-induction machines with output
powers exceeding 375 kW.
2 Normative references
The following referenced documents are indispensable for the application 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, Rotating electrical machines – Part 1: Rating and performance
IEC 60034-30, Rotating electrical machines – Part 30: Efficiency classes of single-speed
three-phase, cage induction motors (IE-code)
3 Terms, definitions and symbols
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60034-1 and in
IEC 60034-30 apply.
3.2 Symbols
η is the nominal efficiency, %
n
η is the rated efficiency, %
N
f is the rated frequency, Hz
N
–1
n is the rated speed, min
N
P is the rated output power, kW
N
T is the rated output torque, Nm
N
U is the rated voltage, V
N
TS 60034-31 © IEC:2010 – 9 –
4 General
Mechanical Energy
Electrical
Factory
Application
components
components recovery
automation
Proper and regular maintenance
Energy efficiency
Energy efficient, Variable speed
Most efficient
motors
gearboxes, bolts, … drive systems
power supply
Energy efficient Reducing elect. Low-energy
Power factor
pumps, fans, transmission mode during
correction devices
compressors, … losses standstill
Use most economical
components
Regenerative
Variable speed
Most efficient
braking
drive systems
power supply
Soft-start Minimize
with frequency rotating
DC-link coupling
control inertia
Low-energy
Optimized mass
Batteries
mode during
and flow
ultra-cap,
standstill
fly-wheels etc…
IEC  700/10
Figure 1 – Overview of different areas for savings of electrical energy
with drive systems
Energy can be saved in different areas of electrical drive systems depending on the duty type
(continuous or intermittent).
In continuous duty applications, improved efficiency of the electrical motor is beneficial. An
improved power factor (frequency converter, synchronous motor) can help reduce I²R losses
in cables. Mechanical optimizations (gearbox, belts, pumps, fans, etc.) may lead to much
greater savings than improvements of the electrical motor.
The application should also be regarded as well because, in many cases, the main part of the
energy saving can be obtained by managing the application load from the system point of
view. For that purpose, a demand-oriented speed control is often helpful.
Proper maintenance is usually beneficial. Many industrial plants have a high energy
consumption within the low voltage control circuits (typically 24 V power supply). Therefore,
high-efficiency low-voltage power supplies should be used. If possible, the factory should also
be shut down during long standstill periods (weekends, holidays).
S3…S10
S2 S1
Intermittent duty
Short-time Continuous duty
– 10 – TS 60034-31 © IEC:2010
10 000
IE2-Motor
IE3-Motor
IE2-Motor+converter
IE3-Motor+converter
IE2-Motor+converter+brake coil
1 000
1,1 11 110
Rated output power (kW)
IEC  701/10
Figure 2 – Typical losses of energy-efficient motors, converters
and electro-mechanical brakes
Figure 2 gives an overview of typical losses of energy-efficient motors and typical losses for
the power drive system including motors with voltage-source frequency converters with and
without brake coils of electro-mechanical motor brakes.
In intermittent duty applications, energy efficient motors are not very effective and may even
use more energy due to their increased inertia and start-up currents. For these applications,
the energy consumption during the starting phase can be reduced by ramping with a
frequency converter. Intermediate energy storage may be beneficial when the operating cycle
includes frequent regenerative braking phases (for example hoist drives, lifts, cranes etc.).
5 Efficiency
5.1 General
Motor efficiency is a measure of the effectiveness with which electrical energy is converted to
mechanical energy, and is expressed as the ratio of power output to power input:
OutputPower OutputPower
Efficiency = =
InputPower OutputPower + losses
Motor efficiencies are usually given for rated load, although approximations for 3/4 load and
1/2 load may also be provided.
The efficiency of a motor is primarily a function of load, rated power, and speed, as indicated
below.
Losses (W)
TS 60034-31 © IEC:2010 – 11 –
a) A change in efficiency as a function of load is an inherent characteristic of motors.
Operation of the motor at loads substantially different from rated load may result in a
change in motor efficiency (see Figure 3).
b) Generally, the full-load efficiency of motors increases with physical size and rated output
of motors.
c) For the same power rating, motors with higher speeds generally, but not always, have a
higher efficiency at rated load than motors with lower rated speeds. This does not imply,
however, that all apparatus should be driven by high-speed motors. Where speed-
changing mechanisms, such as pulleys or gears, are required to obtain the necessary
lower speed, the additional power losses could reduce the efficiency of the system to a
value lower than that provided by a direct drive lower speed motor.
–1
A definite relationship exists between the rated speed (min ) and the efficiency of a cage-
induction motor. That is, the lower the rated speed, the lower is the efficiency, for slip is a
measure of the losses in the rotor winding (slip of an induction motor is the difference
between synchronous speed and operating speed). Slip, expressed in %, is the difference in
speeds divided by the synchronous speed and multiplied by 100. Therefore, Design N cage-
induction motors having a slip at full-load of less than 5 % are more efficient than motors
having a higher slip and should be used when permitted by the application.
For loads such as pumps, fans and air compressors, it may be possible to make a significant
saving in energy by utilizing a multispeed motor or by using a variable speed drive (VSD).
However, it should be noted that the efficiency of a multispeed motor at each operating speed
is somewhat lower than that of a single-speed motor having a comparable rating. Single-
winding (for example Dahlander winding), multispeed motors are generally more efficient than
two-winding, multispeed motors.
Motors which operate continuously or for long periods of time provide a significant opportunity
for reducing energy consumption. Examples of such applications are processing machinery,
air moving equipment, pumps, and many types of industrial equipment.
While many motors are operated continuously, some motors are used for very short periods of
time and for a very low total number of hours per year. Examples of such applications are
valve motors, dam gate operators, industrial door openers, fire pumps and sewage pumps. In
these instances, a change in motor efficiency would not substantially change the total energy
cost since very little total energy is involved and may decrease the required performance.
A modest increase of a few percentage points in motor efficiency can represent a rather
significant decrease in percentage of motor losses. For example, for the same output, an
increase in efficiency from 75 % to 78,9 %, from 85 % to 87,6 %, or from 90 % to 91,8 %
represents a 20 % decrease in losses in each case.
As efficiency typically increases with the size of the motor, high-voltage machines with output
powers exceeding 1 MW usually have an efficiency above 95 %.
NOTE While an electric motor’s output power increases with the square of its diameter the permissible heat
dissipation increases almost linearly. Therefore, a higher efficiency is an inevitable precondition for the design of
larger motors.
5.2 Motor losses
An electric motor converts electrical energy into mechanical energy and in so doing incurs
losses which are generally described as follows:
a) Electrical (stator and rotor) losses (vary with load) – Current flowing through stator and
rotor windings produces losses which are proportional to the current squared times the
winding resistance (I R). Rotor loss increases with slip.
b) Iron (core) loss (essentially independent of load) – This loss is produced mainly in the
laminated core of the stator and, to a lesser degree, in the rotor. The magnetic field,

– 12 – TS 60034-31 © IEC:2010
essential to the production of torque in the motor, causes hysteresis and eddy current
losses.
c) Mechanical (friction and windage) losses (essentially independent of load) – Mechanical
losses occur in the bearings, fans, and seals of the motor. These losses are generally
small in IP2X, IP4X and IP5X slow-speed motors, but may be appreciable in large, high-
speed or totally-enclosed IP6X motors.
d) Additional load losses (stray load losses) – The additional fundamental and high
frequency losses in the iron; conductor and circulating current losses in the stator winding;
and harmonic losses in the rotor conductors under load. These losses are assumed to be
proportional to the torque squared.
Listed below (Table 1) are the motor loss components, with the typical % of the total motor
losses they represent, and the design and construction factors which influence their
magnitude.
Table 1 – Loss distribution in three-phase, 4-pole, cage-induction electric motors
Typical % of losses Factors affecting these losses
4-pole motors
Stator loss 30 to 50 Stator conductor size and material.
Rotor loss 20 to 25 Rotor conductor size and material.
Core loss 20 to 25 Type and quantity of magnetic material.
Additional-load loss 5 to 15 Primarily manufacturing and design methods.
Friction and windage 5 to 10 Selection/design of fan and bearings.

In general, by increasing the active material in the motor, i.e., the type and volume of
conductors and magnetic materials, losses can be reduced.
5.3 Additional motor-losses when operated on a frequency converter
Harmonics of voltage and current in a cage-induction motor supplied from a frequency-
converter cause additional iron and I²R winding losses in the stator and the rotor. The total
value of these additional losses is essentially independent of load. These additional losses
decrease with increasing switching frequency in the converter.
In adverse circumstances the additional losses in the motor caused by the frequency
converter can increase the total motor losses up to 15 % to 20 % more than when operating
on a sinusoidal power supply.
For details see IEC 60034-17 and IEC 60034-25.
5.4 Motors for higher efficiency classes
It is expected that advanced technologies will enable manufacturers to design motors for
higher efficiencies than IE3 with mechanical dimensions (flanges, shaft heights etc.)
compatible to existing motors of lower efficiency classes (for example EN 50347, NEMA MG1
and other local standards). These motors usually require power electronics (frequency
converters) to operate.
Losses in the rotor are almost eliminated when using synchronous motors without a field
winding.
In Annex A, this technical specification proposes a super-premium efficiency-class IE4 which
is specifically targeted at such motors (although the efficiency class IE4 as such is not limited
to specific motors).
TS 60034-31 © IEC:2010 – 13 –
Permanent magnet (PMSM) and reluctance (RSM) synchronous motors are already developed
and to some extent commercially available. PMSM usually have some inherent reluctance
torque and RSM can be PM enforced, thus hybrids are possible.
Depending on the amount of magnet material used, a PMSM can have a higher power factor
than an induction motor thus improving efficiency in the distribution network and in the
frequency converter. These motors however require a frequency converter and a rotor
position sensor (encoder) (unless an encoder-less control algorithm is used in the converter)
for proper operation.
A simpler motor control with block commutated voltage of low switching frequency is also
commonly used in small size and/or high speed motors (“brushless-DC” or “electronically
commutated (EC) motors”). The main disadvantage is the additional losses due to parasitic
harmonic voltages and currents. The improvement in efficiency over asynchronous motors is
less when compared to the improvement of PWM (pulse-width modulation) controlled
permanent magnet or reluctance synchronous motors.
Another synchronous motor design features both permanent magnets and a cage. It can
therefore be used for on-line starting (line-start, permanent magnet, synchronous motors
“LSPM”). These motors do not necessarily need a frequency converter for operation. However
their starting performance is rather poor with torque ripple and noise and considerable
restrictions on the permissible load torque and load inertia. They need to be closely matched
to the application and cannot be used as general-purpose machines.
NOTE It is envisaged to expand the scope of IEC 60034-30 and amend it with this Annex A (as normative) when
more experience with synchronous motors in standard applications becomes available.
5.5 Variations in motor losses
All manufactured products are subject to tolerances associated with materials and
manufacturing methods. No two products will perform exactly the same, even though they are
of the same design and produced on the same assembly line at the same time.
This is also true for electric motors. Product tolerances in materials, such as steel used for
laminations in the stator and rotor cores, will lead to variations in magnetic properties and
ultimately affect iron losses and therefore motor efficiency. Using a tested 7,5 kW motor as an
example, a 10 % increase in iron loss (300 W to 330 W), which is within the tolerance offered
by steel suppliers, would increase total motor losses from 946 W to 976 W and reduce
efficiency from 88,8 % (IE2) to 88,5 % (IE1).
Variations also occur as the result of manufacturing process limitations. There is an economic
limit to the practical dimensional tolerances on motor parts. Combinations of mating parts
contribute to dimensional variations, such as the size of the air gap, which cause variations in
additional-load loss and hence motor efficiency.
In addition, uncertainties can be caused by manufacturing processes and testing procedures.
Thus in forecasting the efficiency of a given motor, one can speak of the rated efficiency as
defined by the manufacturer (which should be equivalent to the average efficiency of a large
population of motors). The rated efficiency should also be above or equal to the required
nominal efficiency of the rated efficiency class (in accordance to IEC 60034-30).
The actual efficiency at rated load of any individual motor, when operating at rated voltage
and frequency, can be lower than the rated efficiency but not less than rated efficiency minus
the tolerance of the efficiency according to IEC 60034-1. This is the level reached when both
raw materials and manufacturing processes are at the least favourable end of their specified
tolerances.
– 14 – TS 60034-31 © IEC:2010
The rated efficiency should be used in estimating the power required to supply a number of
motors. The minimum efficiency (rated minus tolerance) permits the motor user the assurance
of having received the specified level of performance.
5.6 Part load efficiency
Three-phase cage-induction motors offer fairly constant efficiencies over a wide range of
partial loads as indicated by Figure 3.

150 kW
15 kW
1,1 kW
0 0,25 0,5 0,75 1,0 1,25
P/P
N
IEC  702/10
Figure 3 – Typical efficiency versus load curve bands for three-phase,
cage-induction motors of different output power ranges
(approximately 1,1 kW, 15 kW and 150 kW)
The efficiency bands given in this figure are typical for 2- and 4-pole motors alike. Motors with
a higher number of poles will have a different characteristic.
Efficiency  (%)
TS 60034-31 © IEC:2010 – 15 –
When the efficiency for rated load and 3/4 load is given, the following formula may be used to
compute a good approximation of the efficiency at any other partial load:
⎛ ⎞ ⎛ ⎞
100 100
⎜ − 1⎟ − 0,75 ⋅⎜ − 1⎟
⎜ ⎟ ⎜ ⎟
η η
⎝ 100 ⎠ ⎝ 75 ⎠
ν =
L
0,4375
⎛ ⎞
⎜ ⎟
ν = − 1 −ν
0 L
⎜ ⎟
η
⎝ 100 ⎠
η =
p
ν
1+ +ν ⋅ p
L
p
where:
η is the efficiency at rated load, in %;
η is the efficiency at 3/4 load, in %;
, ν are the intermediate results;
ν
L 0
p is the desired power (relative to rated load, i.e. from 0.1.overload);
η is the resulting efficiency, in %.
p
NOTE The application of this algorithm is not recommended for loads less than 50 % or greater than 125 % of
rated load.
5.7 Efficiency testing methods
There are a number of test methods for determining motor efficiency. Standard methods for
testing induction machines are internationally defined in IEC 60034-2-1, which recognizes
several methods for determining motor efficiency, each of which has certain advantages as to
accuracy, cost, and ease of testing, depending primarily on motor rating. Some of the
methods in IEC 60034-2-1 are harmonized with national standards such as CSA C390 and
IEEE 112 Part B.
The residual-loss method in IEC 60034-2-1 is a defined calculation procedure for segregating
the various types of losses from the raw data and smoothing the additional (stray-) load loss
by linear regression analysis. This can reduce the effect of errors introduced from making
measurements over the range of loads from 25 % to approximately 150 % of rated- load. It
also adjusts the tested ambient temperature to 25 °C to reduce variation due to different
testing environments.
The common practice for obtaining the raw data for 0,75 kW to 370 kW is to test the motor
with a load machine and a torque meter and to carefully measure the power input and output
for several load points to determine loss components and thus efficiency.
Even with the use of a consistent and accurate efficiency test method, variations in results for
the same motor do occur, primarily due to test equipment and instrument characteristics, and
in the case of non-automated testing, personnel factors.

– 16 – TS 60034-31 © IEC:2010
5.8 Power factor (see Figure 4)

150 kW
15 kW
1,1 kW
0,9
0,8
0,7
0,6
0,5
0,4
0,3
0 0,25 0,5 0,75 1,0 1,25
P/P
N
IEC  703/10
Figure 4 – Typical power factor versus load curve bands for three-phase,
cage-induction motors of different output power ranges
(approximately 1,1 kW, 15 kW and 150 kW)
The power factor bands given in this figure are typical for 2- and 4-pole motors alike. Motors
with a higher number of poles will have a different characteristic.
The total motor load in a facility is usually a major factor in determining the system power
factor. Low system power factor results in increased losses in the distribution system.
Induction motors inherently cause a lagging system power factor.
The power factor of an induction motor decreases as the load decreases.
Rated-load power factor increases with an increase in the power rating of the motor. A
number of induction motors, all operating at light load, can cause the electrical system to
have a low power factor. The power factor of induction motors at rated loa
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