IEC TS 60034-25:2007

TECHNICAL IEC
SPECIFICATION TS 60034-25
Second edition
2007-03
Rotating electrical machines –
Part 25:
Guidance for the design and performance of a.c.
motors specifically designed for converter supply
Reference number
IEC/TS 60034-25:2007(E)
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TECHNICAL IEC
SPECIFICATION TS 60034-25
Second edition
2007-03
Rotating electrical machines –
Part 25:
Guidance for the design and performance of a.c.
motors specifically designed for converter supply
© IEC 2007 ⎯ Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
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Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
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– 2 – TS 60034-25 © IEC:2007(E)
CONTENTS
FOREWORD.6
INTRODUCTION.8
1 Scope.9
2 Normative references .9
3 Terms and definitions .10
4 System characteristics.11
4.1 General .11
4.2 System information.11
4.3 Torque/speed considerations.12
4.4 Motor requirements .16
5 Losses and their effects (for induction motors fed from U-converters).18
5.1 General .18
5.2 Location of the additional losses due to converter supply and ways to
reduce them .18
5.3 Converter features to reduce the motor losses .18
5.4 Use of filters to reduce additional motor losses due to converter supply .20
5.5 Temperature and life expectancy.20
5.6 Determination of motor efficiency .21
6 Noise, vibration and torsional oscillation.21
6.1 Noise .21
6.2 Vibration (excluding torsional oscillation).24
6.3 Torsional oscillation .25
7 Motor insulation electrical stresses.25
7.1 General .25
7.2 Causes.25
7.3 Winding electrical stress.27
7.4 Insulation stress limitation .29
7.5 Responsibilities .29
7.6 Converter characteristics.30
7.7 Methods of reduction of voltage stress .31
7.8 Motor choice .31
8 Bearing currents .32
8.1 Sources of bearing currents in converter-fed motors.32
8.2 Generation of high-frequency bearing currents .32
8.3 Common mode circuit.34
8.4 Stray capacitances .34
8.5 Consequences of excessive bearing currents .36
8.6 Preventing high-frequency bearing current damage.36
8.7 Additional considerations for motors fed by high voltage U-converters .38
8.8 Bearing current protection for motors fed by high-voltage current-source
converters (I-converters) .39
9 Installation.39
9.1 Earthing, bonding and cabling .39
9.2 Reactors and filters .45
9.3 Integral motors (integrated motor and drive modules).46

TS 60034-25 © IEC:2007(E) – 3 –
10 Additional considerations for permanent magnet (PM) synchronous motors fed by
U-converters.47
10.1 System characteristics .47
10.2 Losses and their effects .47
10.3 Noise, vibration and torsional oscillation.47
10.4 Motor insulation electrical stresses.47
10.5 Bearing currents.48
10.6 Particular aspects of permanent magnets .48
11 Additional considerations for cage induction motors fed by high voltage U-
converters .48
11.1 General .48
11.2 System characteristics .48
11.3 Losses and their effects .50
11.4 Noise, vibration and torsional oscillation.50
11.5 Motor insulation electrical stresses.51
11.6 Bearing currents.53
12 Additional considerations for synchronous motors fed U-converters.53
12.1 System characteristics .53
12.2 Losses and their effects .53
12.3 Noise, vibration and torsional oscillation.53
12.4 Motor insulation electrical stresses.53
12.5 Bearing currents.53
13 Additional considerations for cage induction motors fed by block-type I-converters .54
13.1 System characteristics .54
13.2 Losses and their effects .55
13.3 Noise, vibration and torsional oscillation.55
13.4 Motor insulation electrical stresses.56
13.5 Bearing currents.56
13.6 Additional considerations for six-phase cage induction motors .56
14 Additional considerations for synchronous motors fed by LCI .56
14.1 System characteristics .56
14.2 Losses and their effects .58
14.3 Noise, vibration and torsional oscillation.58
14.4 Motor insulation electrical stresses.58
14.5 Bearing currents.58
15 Additional considerations for pulsed I-converters (PWM CSI) feeding induction
motors .58
15.1 System characteristics .58
15.2 Losses and their effects .59
15.3 Noise, vibration and torsional oscillation.59
15.4 Motor insulation electrical stresses.59
15.5 Bearing currents.59
16 Other motor/converter systems.60
16.1 Drives supplied by cyclo-converters .60
16.2 Wound rotor induction (asynchronous) machines supplied by I-converters in
the rotor circuit .61
16.3 Wound rotor induction (asynchronous) machines supplied by U-converters in
the rotor circuit .61

– 4 – TS 60034-25 © IEC:2007(E)
Annex A (normative) Converter characteristics .63
Annex B (informative) Converter output spectra.67
Annex C (informative) Noise increments due to converter supply .70
Bibliography.71
Figure 1 – Torque/speed capability .13
Figure 2 – Converter output current .13
Figure 3 – Converter output voltage/frequency characteristics .15
Figure 4 – Example of measured losses P as a function of frequency f and supply type.19
L
Figure 5 – Additional losses ΔP of a motor (same motor as Figure 4) due to converter
L
supply, as a function of pulse frequency f , at 50 Hz rotational frequency .20
p
Figure 6 – Fan noise as a function of fan speed.22
Figure 7 – Vibration modes .23
Figure 8 – Typical surges at the terminals of a motor fed from a PWM converter .26
Figure 9 – Typical voltage surges on one phase at the converter and at the motor
terminals (2 ms/division) .26
Figure 10 – Individual short rise time surge from Figure 9 (1 μs/division) .27
Figure 11 – Definition of the peak rise time t of the voltage at the motor terminals .28
r
Figure 12 – First turn voltage as a function of the peak rise time.28
Figure 13 – Discharge pulse occurring as a result of converter generated voltage surge
at motor terminals (100 ns/division) .29
Figure 14 – Limiting curves of impulse voltage U , measured between two motor
pk
phase terminals, as a function of the peak rise time t .30
r
Figure 15 – Possible bearing currents.33
Figure 16 – Motor capacitances .35
Figure 17 – Bearing pitting due to electrical discharge (pit diameter 30 μm to 50 μm) .36
Figure 18 – Fluting due to excessive bearing current .36
Figure 19 – Bonding strap from motor terminal box to motor frame .41
Figure 20 – Examples of shielded motor cables and connections .42
Figure 21 – Parallel symmetrical cabling of high-power converter and motor.43
Figure 22 – Converter connections with 360º HF cable glands showing the Faraday
cage .43
Figure 23 – Motor end termination with 360º connection .44
Figure 24 – Cable shield connection .44
Figure 25 – Characteristics of preventative measures .46
Figure 26 – Schematic of typical three-level converter .49
Figure 27 – Output voltage and current from typical three-level converter .49
Figure 28 – Typical first turn voltage ΔU (as a percentage of the line-to-ground voltage)
as a function of du/dt .51
Figure 29 – Medium-voltage and high-voltage form-wound coil insulating and voltage
stress control materials.52
Figure 30 – Schematic of block-type I-converter .54
Figure 31 – Current and voltage waveforms of block-type I-converter .54

TS 60034-25 © IEC:2007(E) – 5 –
Figure 32 – Schematic and voltage and current waveforms for a synchronous motor
supplied from an I-converter .57
Figure 33 – Schematic of pulsed I-converter .58
Figure 34 – Voltages and currents of pulsed I-converter .59
Figure 35 – Schematic of cyclo-converter .60
Figure 36 – Voltage and current waveforms of a cyclo-converter.60
Figure A.1 – Effects of switching frequency on motor and converter losses.65
Figure A.2 – Effects of switching frequency on acoustic noise.66
Figure A.3 – Effects of switching frequency on torque ripple .66
Figure B.1 – Typical frequency spectra of converter output voltage.67
Figure B.2 – Typical frequency spectra of converter output voltage.67
Figure B.3 – Typical spectra of converter output voltage.68
Figure B.4 – Typical time characteristics of motor current .68
Figure B.5 – Typical time characteristics of motor current .69
Table 1 – Alphabetical list of terms .10
Table 2 – Significant factors affecting torque/speed capability .14
Table 3 – Motor design considerations.16
Table 4 – Motor parameters .17
Table 5 – Effectiveness of bearing current countermeasures .37
Table C.1 – Noise increments .70

– 6 – TS 60034-25 © IEC:2007(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ROTATING ELECTRICAL MACHINES –
Part 25: Guidance for the design and performance of a.c. motors
specifically designed for converter supply
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
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5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
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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) 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 60034-25, which is a technical specification, has been prepared by IEC technical
committee 2: Rotating machinery.
This second edition cancels and replaces the first edition published in 2004.

TS 60034-25 © IEC:2007(E) – 7 –
This second edition contains the following significant technical changes with respect to the
previous edition:
a) replacement of the original introduction by a shorter introduction;
b) extension of the scope to include all converter-fed motors, not just LV-induction
motors;
c) minor changes throughout Clauses 4 to 9;
d) addition of subclauses 4.3.4, 4.3.5, 5.4, 6.2.1, 8.6.3, 8.7 and 8.8, and Figure 7;
e) inclusion of subclauses 4.4 and 4.5 in Annex A;
f) expansion of original Annex A which becomes Annex B;
g) re-drafting of Clause 5;
h) upgrading of 6.1.4 to 6.3;
i) removal of noise limits from normative text;
j) addition of reference to IEC 60034-9;
k) addition of Annex C.
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
2/1406/DTS 2/1420A/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.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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
• transformed into an International standard,
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this technical specification may be issued at a later date.

– 8 – TS 60034-25 © IEC:2007(E)
INTRODUCTION
The performance characteristics and operating data for converter-fed motors are influenced
by the complete drive system, comprising supply system, converter, cabling, motor,
mechanical shafting and control equipment. Each of these components exists in numerous
technical variants. Any values quoted in this technical specification are thus indicative only.
In view of the complex technical interrelations within the system and the variety of operating
conditions, it is beyond the scope and object of this technical specification to specify
numerical or limiting values for all the quantities which are of importance for the design of the
drive system.
To an increasing extent, it is practice that drive systems consist of components produced by
different manufacturers. The object of this technical specification is to explain, as far as
possible, the influence of these components on the design of the motor and its performance
characteristics.
This technical specification deals with a.c. motors which are specifically designed for
converter supply. Converter-fed motors within the scope of IEC 60034-12, which are designed
originally for mains supply, are covered by IEC 60034-17.
Clauses 5 to 9 of this technical specification consider mainly the requirements for low voltage
induction motors fed from voltage-source converters (U-converters). Clauses 10 to 16 provide
additional information for other configurations.

TS 60034-25 © IEC:2007(E) – 9 –
ROTATING ELECTRICAL MACHINES –
Part 25: Guidance for the design and performance of a.c. motors
specifically designed for converter supply
1 Scope
This part of IEC 60034 describes the design features and performance characteristics of a.c.
motors specifically designed for use on converter supplies. It also specifies the interface
parameters and interactions between the motor and the converter including installation
guidance as part of a power drive system.
The general requirements of relevant parts of the IEC 60034 series of standards also apply to
motors within the scope of this technical specification.
NOTE 1 For motors operating in potentially explosive atmospheres, additional requirements as described in the
IEC 60079 series apply.
NOTE 2 This technical specification is not primarily concerned with safety. However, some of its
recommendations may have implications for safety, which should be considered as necessary.
NOTE 3 Where a converter manufacturer provides specific installation recommendations, they should take
precedence over the recommendations of this technical specification.
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 60034-2, Rotating electrical machines – Part 2: Methods for determining losses and
efficiency of rotating electrical machinery from tests (excluding machines for traction vehicles)
IEC 60034-6, Rotating electrical machines – Part 6: Methods of cooling (IC Code)
IEC 60034-9, Rotating electrical machines – Part 9: Noise limits
IEC 60034-14, Rotating electrical machines – Part 14: Mechanical vibration of certain
machines with shaft heights 56 mm and higher – Measurement, evaluation and limits of
vibration severity
IEC 60034-17:2006, Rotating electrical machines – Part 17: Cage induction motors when fed
from converters – Application guide
IEC 61000-5-1, Electromagnetic compatibility (EMC) – Part 5: Installation and mitigation
guidelines – Section 1: General considerations – Basic EMC publication
IEC 61000-5-2, Electromagnetic compatibility (EMC) – Part 5: Installation and mitigation
guidelines – Section 2: Earthing and cabling
IEC 61800-2, Adjustable speed electrical power drive systems – Part 2: General requirements
– Rating specifications for low voltage adjustable frequency a.c. power drive systems

– 10 – TS 60034-25 © IEC:2007(E)
IEC 61800-3, Adjustable speed electrical power drive systems – Part 3: EMC product
standard including specific test methods
IEC 61800-5-1, Adjustable speed electrical power drive systems – Part 5-1: Safety
requirements – Electrical, thermal and energy
IEC 61800-5-2, Adjustable speed electrical power drive systems – Part 5-2: Safety
requirements – Functional
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
Table 1 provides an alphabetical cross-reference of terms.
Table 1 – Alphabetical list of terms
Term Term Term
Term Term Term
number number number
bearing voltage ratio 3.1 electromagnetic 3.5 protective earthing 3.9
(BVR) compatibility (EMC)
bonding 3.2 field weakening 3.6 skip band 3.10
common mode voltage 3.3 peak rise time 3.7 surface transfer 3.11
(current) impedance
converter 3.4 power drive system 3.8
(PDS)
NOTE Throughout this technical specification, references to the following definitions are identified by italic script.
3.1
bearing voltage ratio
BVR
ratio of the capacitively coupled bearing voltage to the common mode voltage
3.2
bonding
electrical connection of metallic parts of an installation together and to ground (earth)
NOTE For the purposes of this part of IEC 60034, this definition combines elements of IEV 195-01-10
(equipotential bonding) and IEV 195-01-16 (functional equipotential bonding).
3.3
common mode voltage (current)
arithmetic mean of the phase voltages (currents) to earth
3.4
converter
unit for electronic power conversion, changing one or more electrical characteristics and
comprising one or more electronic switching devices and associated components, such as
transformers, filters, commutation aids, controls, protections and auxiliaries, if any
[IEC 61800-2, 2.2.1, modified]
NOTE This definition is taken from IEC 61800-2 and, for the purposes of this technical specification, embraces
the terms complete drive module (CDM) and basic drive module (BDM) as used in the IEC 61800 series.
___________
To be published.
TS 60034-25 © IEC:2007(E) – 11 –
3.5
electromagnetic compatibility
EMC
ability of an equipment or system to function satisfactorily in its electromagnetic environment
without introducing intolerable electromagnetic disturbances to anything in that environment
[IEV 161-01-07]
3.6
field weakening
motor operating mode where motor flux is less than the flux corresponding to the motor rating
3.7
peak rise time
time interval between the 10 % and 90 % points of the zero-to-peak voltage (see Figure 11)
3.8
power drive system
PDS
system consisting of power equipment (composed of converter section, a.c. motor and other
equipment such as, but not limited to, the feeding section), and control equipment (composed
of switching control – on/off for example – voltage, frequency, or current control, firing
system, protection, status monitoring, communication, tests, diagnostics, process interface/
port, etc.)
3.9
protective earthing
PE
earthing a point or points in a system or in an installation or in equipment for the purposes of
electrical safety
[IEV 195-01-11, modified]
3.10
skip band
small band of operating frequencies where steady-state operation of the PDS is inhibited
3.11
surface transfer impedance
quotient of the voltage induced in the centre conductor of a coaxial line per unit length by the
current on the external surface of the coaxial line
[IEV 161-04-15]
4 System characteristics
4.1 General
Although the steps in specifying motor and converter features are similar for any application,
the final selections are greatly influenced by the type of application. In this clause, these
steps are described and the effects of various application load types are discussed.
4.2 System information
Complete application information that considers the driven load, motor, converter, and utility
power supply, is the best way to achieve the required performance of the entire system. In
general, this information should include
• the power or torque requirements at various speeds;
• the desired speed range of the load and motor;
• the acceleration and deceleration rate requirements of the process being controlled;

– 12 – TS 60034-25 © IEC:2007(E)
• starting requirements including the frequency of starts and a description of the load (the
inertia reflected at the motor, load torque during starting);
• the duty cycle of the application (a continuous process or a combination of starts, stops,
and speed changes; see 3.1 of IEC 60034-1);
• a general description of the type of application including the environment in which the PDS
components will operate;
• a description of additional functionality that may not be met with the motor and converter
only (for example: motor temperature monitoring, ability to bypass the converter if
necessary, special sequencing circuits or speed reference signals to control the PDS);
• a description of the available electrical supply power and wiring. The final configuration
may be affected by the requirements of the system selected.
4.3 Torque/speed considerations
4.3.1 General
The typical torque/speed characteristics of converter-fed motors, the significant influencing
factors and their consequences are shown in Figure 1, Figure 2 and Figure 3. Depending on
the performance requirements of the PDS, different motor designs are possible for an
adaptation of the individual limiting values.
NOTE Figure 1 to Figure 3 do not show the possible skip bands (see 4.3.7).
4.3.2 Torque/speed capability
Figure 1 shows the torque/speed capability of converter-fed motors. The maximum available
torque is limited by the rating of the motor and by the current limitation of the converter.
Above the field weakening frequency f and speed n the motor can operate with constant
0 0
power with a torque proportional to 1/n. For induction motors, if the minimum breakdown
torque (which is proportional to 1/n ) is reached, the power has to be further reduced
proportional to 1/n, resulting in torque proportional to 1/n (extended range). For synchronous
motors, the extended range does not apply. The maximum usable speed n is limited not
max
only by the reduction of torque due to field weakening at speeds above n , but also by the
mechanical strength and stability of the rotor, by the speed capability of the bearing system,
and by other mechanical parameters.
At low frequency, the available torque may be reduced in self-cooled motors to avoid the
possibility of overheating.
In some applications, it may be possible to apply a short-time torque boost for starting.

TS 60034-25 © IEC:2007(E) – 13 –
C
X
T
C
S
~ 1/n
~ 1/n
T P E
C C X
n n n
0 max
IEC  359/07
Key
——— Continuous operation T Constant torque range C Separate cooling
C X
-------- Short-time operation PC Constant power range CS Self-cooling
—--—-- Starting torque boost E Extended range (for induction motors)
X
Figure 1 – Torque/speed capability
Figure 2 shows the corresponding converter output current (I) capability.
I
T P E
C C X
f f f
0 max
IEC  360/07
Figure 2 – Converter output current
4.3.3 Limiting factors on torque/speed capability
The significant factors which influence the torque/speed capability are shown in Table 2.

– 14 – TS 60034-25 © IEC:2007(E)
Table 2 – Significant factors affecting torque/speed capability
Condition Motor Converter
Breakaway Maximum flux capability Maximum current
Constant flux Cooling (I R losses) Maximum current
Field weakening Maximum speed (mechanical strength and stability) Maximum voltage
(reduced flux)
Maximum torque (breakdown torque)
Dynamic response Equivalent circuit parameters (determined by modelling) Control capability
4.3.4 Overspeed capability
As specified in IEC 60034-1, the overspeed of a.c. machines is fixed to 1,2 times the
maximum rated speed, but an overspeed test is not normally considered necessary. The
intention of a test, if specified and agreed, is to check the integrity of the rotor design with
respect to centrifugal forces. Although for a fixed speed motor it is practically impossible to
reach an operating speed above its synchronous speed, electrical generators can be
accelerated above their synchronous speed by the turbine, for example in case of a sudden
load rejection.
For converter-fed electrical motors, an acceleration to a speed higher than the maximum
operational speed determined in the control of the converter is impossible. Especially for large
‘super synchronous’ motors, it is often beneficial for the overall design to limit the test
overspeed to 1,05 times the maximum operation speed. There is no technically justified
argument against such agreement.
NOTE It should be appreciated that with high speed running fine balancing of the rotor may be required. If the high
speed is required for more than short periods the bearing life may be reduced. Also, for high-speed applications,
special attention should be paid to both the grease service life and the re-greasing interval.
4.3.5 Cooling arrangement
As Figure 1 indicates, the type of cooling influences the maximum torque/speed capability of
PDS. Electrical machines with power ratings in the megawatt range have often a cooling
arrangement consisting of a primary cooling circuit (usually with air as primary coolant) and a
secondary cooling circuit (with air or water as secondary coolant). The losses are transferred
via a heat exchanger from the primary into the secondary circuit.
• Where both primary and secondary coolants are moved by a separate device, and their
flow is thus independent of the machine’s rotor speed (for example, IC656 according to
IEC 60034-6), the curve in Figure 1 for separate cooling applies.
• Where the secondary coolant is moved by a separate device and the primary coolant by a
shaft-driven device (for example, IC81W or IC616), the curve in Figure 1 for self-cooling
applies.
• Where both primary and secondary coolants are moved by a shaft driven device, the
output torque should not exceed the curve T/T = n²/n ² and the minimum operational
N 0
speed is recommended to be • 70 % of rated speed.
4.3.6 Voltage/frequency characteristics
The relationship between the converter output voltage (U) and frequency can have several
characteristics, as shown in Figure 3.

TS 60034-25 © IEC:2007(E) – 15 –
U
max
C
A
U
D
B
f f f
f 01 max
IEC  361/07
Key
The voltage increases with frequency, and the maximum converter output voltage U is achieved at the
A
max
field weakening frequency f .
B The voltage increases with frequency, and the maximum converter output voltage U is achieved above f
max 0
at a new field weakening frequency f . This provides an extended speed range at constant flux (constant
torque), but the available torque in this speed range is less than that of case A.
C The voltage increases with frequency up to f , and then increases at a lower rate, the maximum converter
output voltage U being achieved at f . This avoids excessive torque reduction in the constant flux
max max
range.
D A voltage boost is applied at very low frequencies to improve starting performance, and to prevent an
unwanted increase in current.
In all of these cases, the voltage/frequency dependence may be linear or non-linear, according to the torque-
speed requirements of the load.
Figure 3 – Converter output voltage/frequency characteristics
4.3.7 Resonant speed bands
The speed range of a converter-fed motor may include speeds that can excite resonances in
parts of the motor stator, in the motor/load shaft system or in the driven equipment.
Depending on the converter, it may be possible to skip the resonant frequencies. However,
even when resonant frequencies are skipped, the load will be accelerated through that speed
if the motor is set to run at any speed above this resonant speed. Decreasing the acceleration
time can help minimize the time spent in resonance.
4.3.8 Duty cycles
4.3.8.1 General
Cyclic duty applications are those in which transitions between speeds or loads are common
(see IEC 60034-1). Several aspects of this type of application affect the motor and the
converter.
• Motor heat dissipation is variable, depending on rotation speed and cooling method.
• Torque demands above motor full-load torque may be required. Operation above motor full
load may be required to accelerate, handle peak loads, and even decelerate the load.
Operation above motor rated current will increase motor heating. This may require a
higher thermal class of insulation, a motor rated for the overload, or evaluation of the duty
cycle to determine if the motor has enough cooling for the application (see IEC 60034-1,
duty type S10).
• DC injection, dynamic, or regenerative braking may be required to reduce the motor
speed. Regardless of whether the motor is generating torque to drive the application,

– 16 – TS 60034-25 © IEC:2007(E)
generating power back to the converter due to the motor being driven by the load, or
supplying braking torque during deceleration by applying d.c. current to the windings,
motor heating takes place approximat
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