EN 60034-18-41:2014

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Drehende elektrische Maschinen - Teil 18-41: Qualifizierung und Qualitätsprüfungen für teilentladungsfreie elektrische Isoliersysteme (Typ I) in drehenden elektrischen Maschinen, die von Spannungsumrichtern gespeist werden (IEC 60034-18-41:2014)Machines électriques tournantes - Partie 18-41: Qualification et essais de contrôle qualité pour des systèmes d'isolation électrique sans décharge partielle (Type I) utilisés dans des machines électriques tournantes alimentées par des convertisseurs de tension (CIE 60034-18-41:2014)Rotating electrical machines - Part 18-41: Qualification and quality control tests for partial discharge free (Type I) electrical insulation systems used in rotating electrical machines fed from voltage converters (IEC 60034-18-41:2014)29.160.01Rotacijski stroji na splošnoRotating machinery in general29.080.30Izolacijski sistemiInsulation systemsICS:Ta slovenski standard je istoveten z:EN 60034-18-41:2014SIST EN 60034-18-41:2014en01-oktober-2014SIST EN 60034-18-41:2014SLOVENSKI
STANDARD
EUROPEAN STANDARD NORME EUROPÉENNE EUROPÄISCHE NORM
EN 60034-18-41
June 2014 ICS 29.160
English Version
Rotating electrical machines - Part 18-41: Partial discharge free electrical insulation systems (Type I) used in rotating electrical machines fed from voltage converters - Qualification and quality control tests (IEC 60034-18-41:2014)
Machines électriques tournantes - Partie 18-41: Systèmes d'isolation électrique sans décharge partielle (Type I) utilisés dans des machines électriques tournantes alimentées par des convertisseurs de tension - Essais de qualification et de contrôle qualité (CEI 60034-18-41:2014)
Drehende elektrische Maschinen - Teil 18-41: Qualifizierung und Qualitätsprüfungen für teilentladungsfreie elektrische Isoliersysteme (Typ I) in drehenden elektrischen Maschinen, die von Spannungsumrichtern gespeist werden (IEC 60034-18-41:2014) This European Standard was approved by CENELEC on 2014-04-10. CENELEC members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the same status as the official versions. CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom. European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung CEN-CENELEC Management Centre: Avenue Marnix 17,
B-1000 Brussels © 2014 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 60034-18-41:2014 E SIST EN 60034-18-41:2014

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent rights. Endorsement notice The text of the International Standard IEC 60034-18-41:2014 was approved by CENELEC as a European Standard without any modification. SIST EN 60034-18-41:2014

- 3 - EN 60034-18-41:2014 Annex ZA (normative)
Normative references to international publications with their corresponding European publications The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
NOTE
When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD applies.
Publication Year Title EN/HD Year IEC 60034-18-1 2010
Rotating electrical machines Part 18-1: Functional evaluation of insulation systems - General guidelines EN 60034-18-1 2010
IEC 60034-18-21 -
Rotating electrical machines Part 18-21: Functional evaluation of insulation systems - Test procedures for wire-wound windings - Thermal evaluation and classification EN 60034-18-21 -
IEC 60034-18-31 -
Rotating electrical machines Part 18-31: Functional evaluation of insulation systems - Test procedures for form-wound windings - Thermal evaluation and classification of insulation systems used in rotating machines EN 60034-18-31 -
IEC 60172 -
Test procedure for the determination of the temperature index of enamelled winding wires EN 60172 -
IEC 60664-1 -
Insulation coordination for equipment within low-voltage systems Part 1: Principles, requirements and tests EN 60664-1 -
IEC/TS 60034-18-42 -
Rotating electrical machines Part 18-42: Qualification and acceptance tests for partial discharge resistant electrical insulation systems (Type II) used in rotating electrical machines fed from voltage converters CLC/TS 60034-18-42 -
IEC/TS 60034-25 2007
Rotating electrical machines Part 25: Guidance for the design and performance of a.c. motors specifically designed for converter supply CLC/TS 60034-25 2008
Rotating electrical machines Part 27: Off-line partial discharge measurements on the stator winding insulation of rotating electrical machines CLC/TS 60034-27 -
IEC/TS 61800-8 -
Adjustable speed electrical power drive systems Part 8: Specification of voltage on the power interface - -
IEC/TS 61934 -
Electrical insulating materials and systems - Electrical measurement of partial discharges (PD) under short rise time and repetitive voltage impulses - -
IEC 60034-18-41 Edition 1.0 2014-03 INTERNATIONAL STANDARD NORME INTERNATIONALE Rotating electrical machines –
Part 18-41: Partial discharge free electrical insulation systems (Type I) used in rotating electrical machines fed from voltage converters – Qualification and quality control tests
Machines électriques tournantes –
Partie 18-41: Systèmes d’isolation électrique sans décharge partielle (Type I) utilisés dans des machines électriques tournantes alimentées par des convertisseurs de tension – Essais de qualification et de contrôle qualité
INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNATIONALE X ICS 29.160 PRICE CODE CODE PRIX ISBN 978-2-8322-1416-9
– 2 – IEC 60034-18-41:2014 © IEC 2014 CONTENTS FOREWORD . 5 INTRODUCTION . 7 1 Scope . 9 2 Normative references . 9 3 Terms and definitions . 10 4 Machine terminal voltages arising from converter operation . 13 5 Electrical stresses in the insulation system of machine windings . 17 5.1 General . 17 5.2 Voltages stressing the phase/phase insulation . 18 5.3 Voltages stressing the phase/ground insulation . 18 5.4 Voltages stressing the turn and strand insulation . 18 5.5 Mechanisms of insulation degradation . 19 6 Types of machine insulation . 20 7 Stress categories for Type I insulation systems used in converter fed machines . 20 8 Design qualification and type tests for Type I insulation systems . 22 8.1 General . 22 8.2 Design qualification test . 22 8.3 Type test . 22 9 Test equipment . 22 9.1 PD measurement at power frequency . 22 9.2 PD measurement during voltage impulses. 22 9.3 Voltage impulse generators . 23 9.4 Sensitivity . 23 9.5 PD tests . 23 9.5.1 Power frequency voltage . 23 9.5.2 Impulse excitation . 23 10 Qualification of the design of Type I insulation systems . 23 10.1 General . 23 10.2 Approach . 24 10.2.1 General . 24 10.2.2 Twisted pair or equivalent arrangement . 24 10.2.3 Motorette (random wound) or formette (form-wound) . 24 10.2.4 Complete windings . 24 10.3 Preparation of test objects . 25 10.3.1 General . 25 10.3.2 Turn/turn insulation samples . 25 10.3.3 Motorette/formette test samples or complete windings . 25 10.4 Design qualification tests . 26 10.4.1 General . 26 10.4.2 Pre-diagnostic tests . 26 10.4.3 Diagnostic tests . 26 10.4.4 Ageing cycle . 26 10.4.5 PD tests . 26 10.5 Pass criterion for the design qualification test . 27 11 Type test procedure for Type I insulation systems . 27 11.1 General . 27 SIST EN 60034-18-41:2014

IEC 60034-18-41:2014 © IEC 2014 – 3 – 11.2 Power frequency PD tests . 27 11.3 Impulse PD tests . 28 12 Routine tests . 28 13 Analysis, reporting and classification . 28 Annex A (informative)
Derivation of possible terminal voltages in service for a converter-fed machine . 29 A.1 Calculation of d.c. bus voltage . 29 A.2 Calculation of maximum peak voltages for a 2-level converter . 30 Annex B (normative)
Derivation of test voltages for Type I insulation systems . 32 B.1 Stress categories . 32 B.2 Requirements for the applied impulse voltage . 32 B.3 Enhancement factors for PD tests . 33 B.4 Voltage for design qualification and type tests . 34 B.5 Examples of maximum peak/peak operating voltages . 37 B.6 Calculation of test voltages . 37 Annex C (normative)
Derivation of allowable voltages in service . 39 C.1 Impulse voltage insulation class (IVIC) of the machine . 39 C.2 Impulse voltage insulation class assigned in special designs . 39 Bibliography . 41
Figure 1 – Voltage impulse waveshape parameters . 13 Figure 2 – Five step phase to phase voltage at the terminals of a machine fed by a 3-level converter . 15 Figure 3 – Jump voltage (Uj) at the machine terminals associated with a converter drive . 15 Figure 4 – Voltage enhancement at the terminals of a motor due to reflection as a function of cable length for various impulse rise times . 17 Figure 5 – Example of a random wound design . 18 Figure 6 – Example of a form-wound design . 18 Figure 7 – Worst case voltage stressing the turn/turn insulation in a variety of random wound stators as a function of the rise time of the impulse . 19 Figure A.1 – Circuit diagram for a converter/machine system . 29 Figure B.1 – Forbidden zone (shaded) for impulse tests . 33 Figure B.2 – Examples of test waveforms . 33 Figure B.3 – Comparison of phase/phase, phase/ground, and turn/turn voltages for a 2-level converter . 35 Figure B.4 – Impulse test voltage waveforms and the levels for applying the same peak/peak voltage of 2aUj on the turn/turn insulation (schematic representation) . 36 Figure B.5 – Test voltages for phase/ground and turn/turn impulse tests using a unipolar impulse . 38
Table 1 – Common ranges of characteristics of the terminal voltages of converter fed machines . 14 Table 2 – Definition of symbols . 14 Table 3 – Influence of features of the machine terminal voltage on components of Type I insulation systems . 21 Table 4 – Stress categories for Type I insulation systems based on a 2-level converter . 21 Table 5 – Allowable voltage waveforms for testing system components . 25 SIST EN 60034-18-41:2014

– 4 – IEC 60034-18-41:2014 © IEC 2014 Table A.1 – Examples of maximum peak voltages . 31 Table B.1 – Summary of stress categories . 32 Table B.2 – Summary of enhancement factors to be applied to the operating voltages . 34 Table B.3 – Maximum peak/peak operating voltages related to Udc
for a 2-level converter according to the stress categories of Table 4 . 36 Table B.4 – Examples of maximum peak/peak operating voltage for a 500 V r.m.s. rated winding fed from a 2-level converter, according to the stress categories of Table 4. 37 Table B.5 – Examples of maximum peak/peak test voltage for a 500 V rated winding fed from a 2-level converter, according to the stress categories of Table 4 and with EF 1,25 . 37 Table B.6 – Turn/turn PD test levels for special windings and twisted pairs . 38 Table C.1 – Maximum allowable operating voltage at the machine terminals in units of UN . 39
IEC 60034-18-41:2014 © IEC 2014 – 5 – INTERNATIONAL ELECTROTECHNICAL COMMISSION ____________
ROTATING ELECTRICAL MACHINES –
Part 18-41: Partial discharge free electrical insulation systems (Type I)
used in rotating electrical machines fed from voltage converters –
Qualification and quality control tests
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 this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and non-governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any services carried out by independent certification bodies. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.
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. International Standard IEC 60034-18-41 has been prepared by IEC technical committee 2: Rotating machinery. IEC 60034-18-41 cancels and replaces IEC/TS 60034-18-41 (2006). The text of this standard is based on the following documents: FDIS Report on voting 2/1728/FDIS 2/1738/RVD
Full information on the voting for the approval of this standard 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. SIST EN 60034-18-41:2014

– 6 – IEC 60034-18-41:2014 © IEC 2014 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 • reconfirmed, • withdrawn, • replaced by a revised edition, or • amended.
IEC 60034-18-41:2014 © IEC 2014 – 7 – INTRODUCTION The approval of electrical insulation systems for use in rotating electrical machines driven from voltage converters is set out in two IEC documents. They divide the systems into those which are not expected to experience partial discharge activity within specified conditions in their service lives (Type I) and those which are expected to withstand partial discharge activity in any part of the insulation system throughout their service lives (Type II). For both Type I and Type II insulation systems, the drive system integrator (the person responsible for co-ordinating the electrical performance of the entire drive system) shall inform the machine manufacturer what voltage will appear at the machine terminals in service. The machine manufacturer will then decide upon the severity of the tests appropriate for qualifying the insulation system. The severity is based on the impulse rise time, the peak to peak voltage and, in the case of Type II systems, the impulse repetition rate. After installation of the converter/machine system, it is recommended that the drive system integrator measures the phase/phase and phase/ground voltages between the machine terminals and ground to check for compliance. IEC 60034-18-41 The Type I systems are dealt with in this standard. They are generally used in rotating machines rated at 700 V r.m.s. or less and tend to have random wound windings. The procedures described here are directed at: – Qualification of the insulation system. – Type and routine testing of the complete windings of service machines. Before undertaking any testing, the machine manufacturer shall decide upon the level of severity that the system will be required to withstand. The severity is based on how large the voltage overshoot and how short the impulse rise time will be at the machine terminals. The machine designer then makes a choice from a table in which the range of expected overshoot voltage is divided into bands. Testing is performed at the extreme value of each band. A default value of 0,3 µs is attributed to the impulse rise time. Other values of impulse rise time or voltage overshoot are dealt with as special cases.
In qualification testing, the insulation system is used to construct various representative test objects. These are subjected to the range of tests described in IEC 60034-18-21 or IEC 60034-18-31 with the addition of a high frequency voltage test and a partial discharge test. For the latter, it may be necessary to use impulse test equipment, as described in IEC/TS 61934. If the test object is partial discharge free under the specified test conditions at the end of the sequence of testing, the insulation system is qualified for the severity band that has been selected. Type and optional routine tests are performed on complete windings to demonstrate that they are partial discharge free under sinewave or impulse voltage conditions (as appropriate) for the band of severity that the manufacturer has chosen. An impulse voltage insulation class is then assigned to the machine. A mechanism is described for dealing with special cases. IEC/TS 60034-18-42
The tests for qualification and acceptance of electrical insulation systems chosen for Type II rotating electrical machines are described in this technical specification. These insulation systems are generally used in rotating machines and tend to have form-wound coils, mostly rated above 700 V r.m.s. The qualification procedure is completely different from that used for Type I insulation systems and involves destructive ageing of insulated test objects under accelerated conditions. The rotating machine manufacturer requires a life curve for the insulation system that can be interpreted to provide an estimate of life under the service conditions with converter drive. Great importance is attached to the qualification of any stress grading system that is used and testing here should be performed under repetitive impulse conditions. If the insulation system can be shown to provide an acceptable life under the SIST EN 60034-18-41:2014

– 8 – IEC 60034-18-41:2014 © IEC 2014 appropriate ageing conditions, it is qualified for use. Acceptance testing is performed on coils made using this insulation system when subjected to a voltage endurance test. SIST EN 60034-18-41:2014

IEC 60034-18-41:2014 © IEC 2014 – 9 – ROTATING ELECTRICAL MACHINES –
Part 18-41: Partial discharge free electrical insulation systems (Type I)
used in rotating electrical machines fed from voltage converters –
Qualification and quality control tests
1 Scope This part of IEC 60034 defines criteria for assessing the insulation system of stator/rotor windings which are subjected to voltage-source pulse-width-modulation (PWM) drives. It applies to stator/rotor windings of single or polyphase AC machines with insulation systems for converter operation. It describes qualification tests and quality control (type and routine) tests on representative samples or on completed machines which verify fitness for operation with voltage source converters. This standard does not apply to: – rotating machines which are only started by converters; – rotating electrical machines with rated voltage ≤ 300 V r.m.s.; – rotor windings of rotating electrical machines operating at ≤ 200 V (peak). 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC 60034-18-1:2010, Rotating electrical machines – Part 18-1: Functional evaluation of insulation systems – General guidelines IEC 60034-18-21, Rotating electrical machines – Part 18-21: Functional evaluation of insulation systems – Test procedures for wire-wound windings – Thermal evaluation and classification IEC 60034-18-31, Rotating electrical machines – Part 18-31: Functional evaluation of insulation systems – Test procedures for form-wound windings – Thermal evaluation and classification of insulation systems used in rotating machines IEC/TS 60034-18-42, Rotating electrical machines – Part 18-42: Qualification and acceptance tests for partial discharge resistant electrical insulation systems (Type II) used in rotating electrical machines fed from voltage converters1 IEC/TS 60034-25:2007, Rotating electrical machines – Part 25: Guidance for the design and performance of a.c. motors specifically designed for converter supply _______________ 1
This TS is in the process of being transformed into an IS. SIST EN 60034-18-41:2014

– 10 – IEC 60034-18-41:2014 © IEC 2014 IEC/TS 60034-27, Rotating electrical machines – Part 27: Off-line partial discharge measurements on the stator winding insulation of rotating electrical machines IEC 60172, Test procedure for the determination of the temperature index of enamelled winding wires IEC 60664-1, Insulation co-ordination for equipment within low voltage systems – Part 1: Principles, requirements and tests IEC/TS 61800-8, Adjustable speed electrical power drive systems – Part 8: Specification of voltage on the power interface IEC/TS 61934, Electrical insulating materials and systems – Electrical measurement of partial discharges (PD) under short rise time and repetitive voltage impulses
3 Terms and definitions For the purposes of this document, the following terms and definitions apply.
3.1
partial discharge
PD electric discharge that only partially bridges the insulation between electrical conductors Note 1 to entry: It may occur inside the insulation or adjacent to an electrical conductor. 3.2
partial discharge inception voltage
PDIV
lowest voltage at which partial discharges are initiated in the test arrangement when the voltage applied to the test object is gradually increased from a lower value at which no such discharges are observed Note 1 to entry: With sinusoidal applied voltage, the PDIV is defined as the r.m.s. value of the voltage. With impulse voltages, the PDIV is defined as the peak to peak voltage.
3.3
partial discharge extinction voltage
PDEV voltage at which partial discharges are extinguished in the test arrangement when the voltage applied to the test object is gradually decreased from a higher value at which such discharges are observed Note 1 to entry: With sinusoidal applied voltage, the PDEV is defined as the r.m.s. value of the voltage. With impulse voltages, the PDEV is defined as the peak to peak voltage. 3.4
peak (impulse) voltage Up maximum numerical value of voltage reached during a unipolar voltage impulse (e.g. Up in Figure 1) Note 1 to entry: For bi-polar voltage impulses, it is half the peak to peak voltage (see Figure 2). Note 2 to entry: The definition of peak to peak voltage is clarified in Clause 4. 3.5
steady state impulse voltage magnitude Ua final magnitude of the voltage impulse (see Figure 1) SIST EN 60034-18-41:2014

IEC 60034-18-41:2014 © IEC 2014 – 11 – 3.6
voltage overshoot Ub magnitude of the peak voltage in excess of the steady state impulse voltage (see Figure 1) 3.7
peak to peak impulse voltage U’pk/pk peak to peak voltage at the impulse repetition rate (see Figure 2) 3.8
peak to peak voltage Upk/pk peak to peak voltage at the fundamental frequency (see Figure 2) 3.9
repetitive partial discharge inception voltage RPDIV minimum peak-to-peak impulse voltage at which more than five PD pulses occur on ten voltage impulses of the same polarity
Note 1 to entry: This is a mean value for the specified test time and a test arrangement where the voltage applied to the test object is gradually increased from a value at which no partial discharges can be detected. 3.10
unipolar impulse voltage impulse, the polarity of which is either positive or negative Note 1 to entry: The term impulse is used to describe the transient stressing voltage applied to the test object and the term pulse is used to describe the partial discharge signal.
3.11
bipolar impulse voltage impulse, the polarity of which changes alternately from positive to negative or vice versa 3.12
impulse voltage repetition rate
f inverse of the average time between two successive impulses of the same polarity, whether unipolar or bipolar 3.13
impulse rise time tr time for the voltage to rise from 10 % to 90 % of its final value (see Figure 1) 3.14
electrical insulation system insulating structure containing one or more electrical insulating materials together with associated conducting parts employed in an electrotechnical device
3.15
formette special test model used for the evaluation of the electrical insulation systems for form-wound windings SIST EN 60034-18-41:2014

– 12 – IEC 60034-18-41:2014 © IEC 2014 3.16
motorette special test model used for the evaluation of the electrical insulation systems of random-wound windings 3.17
(electric) stress electric field in volts/mm 3.18
rated voltage UN voltage assigned by the manufacturer for a specified power frequency operating condition of a machine and indicated on its rating plate 3.19
impulse voltage insulation class IVIC safe peak to peak voltage assigned by the manufacturer in relation to the rated voltage for a specified converter-driven machine and indicated in its documentation and on its rating plate 3.20
fundamental frequency first frequency, in the spectrum obtained from a Fourier transform of a periodic time function, to which all the frequencies of the spectrum are referred.
Note 1 to entry: For the purposes of this standard, the fundamental frequency of the machine terminal voltage is the one defining the speed of the converter fed machine.
3.21
impulse duration impulse width interval of time between the first and last instants at which the instantaneous value of an impulse reaches a specified fraction of its impulse magnitude or a specified threshold. 3.22
jump voltage Uj change in voltage at the terminals of the machine occurring at the start of each impulse when fed from a converter (see Figure 3) 3.23
DC bus voltage Udc voltage of the intermediate circuit of the voltage converter (dc-link-circuit) Note 1 to entry: For a two level converter Udc is equal to Ua in Figure 1. Note 2 to entry: For a multilevel converter, Udc is equal to ½ Upk/pk minus the overshoot in Figure 2. 3.24
overshoot factor ratio of the voltage appearing at the machine terminals and the voltage at the converter for each converter level 3.25
power drive system complete drive module and rotating machine together with the connecting cable if necessary SIST EN 60034-18-41:2014

IEC 60034-18-41:2014 © IEC 2014 – 13 –
tr IEC
0561/14
Key U
voltage t
time Figure 1 – Voltage impulse waveshape parameters 4 Machine terminal voltages arising from converter operation Modern converter output voltage rise times may be in the 0,05 µs – 2,0 µs range due to power semiconductor switching characteristics. The voltage appearing at the terminals of a converter driven machine may be calculated using IEC/TS 61800-8 and depends upon several characteristics of the power drive system, such as,
a) operating line voltage of the converter;
b) architecture and control regime of the converter;
c) filters between the converter and machine;
d) length and type of cable between them;
e) design of the machine winding;
f) design and configuration of the installation.
In order to apply this Standard to the qualification and testing of the insulation system of a winding, it is necessary to specify the required parameters of the voltage appearing at the machine terminals (Clause 7). The amplitude and rise time of the voltage at the machine terminals depend upon the grounding system, various design aspects of the cable, the machine surge impedance and the presence of any filters that increase the impulse rise time. Common ranges of characteristics of converter impulses at the machine terminals are given in Table 1. SIST EN 60034-18-41:2014

– 14 – IEC 60034-18-41:2014 © IEC 2014 Table 1 – Common ranges of characteristics of the terminal voltages of converter fed machines Characteristics Range of values (depending on ratings, characteristics and service conditions of the drive system) Peak/peak voltage
0,5 kV – 7 kV Impulse rise time 0,05 µs
– 2,0 µs Impulse voltage repetition rate 100 Hz – 20 000 Hz Impulse duration 10 µs – 10 000 µs Shape Rectangular Polarity Unipolar or bipolar Fundamental frequency 5 Hz – 1 000 Hz Mean time between impulses ≥ 0,6 µs For the purpose of this standard, the symbols in Table 2 are used. Table 2 – Definition of symbols Symbol Parameter Units Type of feed Uline Phase to phase (rated) voltage V r.m.s. Line Uphase Phase to neutral voltage V r.m.s. Line Umax = 2Uphase Maximum phase/neutral voltage V Line Upk/pk Peak to peak voltage V Converter Udc DC bus voltage V Converter
In the case of 2-level or other U converters, depending on the rise time of the voltage impulse at the converter output and on the cable length and machine impedance, the impulses generate voltage overshoots at the machine terminals (typically Up up to 2Udc between phases). The voltage overshoot is created by reflected waves at the interface between cable and machine or converter terminals due to surge impedance mismatch. It is fully explained by transmission line and travelling wave theory.
Figure 2 shows the voltage that appears (during one period at the fundamental frequency) at the machine terminals when fed from a 3-level converter.
IEC 60034-18-41:2014 © IEC 2014 – 15 –
t U U' pk/pk U pk/pk
IEC
0562/14
Figure 2 – Five step phase to phase voltage at the terminals of a machine fed by a 3-level converter
t
U
U
j
IEC
0563/14
Figure 3 – Jump voltage (Uj) at the machine terminals associated with a converter drive The maximum change in voltage, Uj, at the impulse frequency is shown in Figure 3. This parameter is important in defining the voltage enhancement that can occur across the first or last coil in the winding. A double jump transition is possible but it is the duty of the drive system integrator to ensure that the software controlling the converter drive prevents this from happening. SIST EN 60034-18-41:2014

– 16 – IEC 60034-18-41:2014 © IEC 2014 For an “n” level converter, the phase/phase voltage can be estimated as follows: Peak/peak fundamental frequency voltage = 2(Udc + Ub)
(1) Peak/peak impulse frequency voltage = Udc/(n–1) + 2Ub
The phase/ground values are estimated as follows: Peak/peak fundamental frequency voltage = 0,7 × 2(Udc + Ub)
(2) Peak/peak impulse frequency voltage = 0,7(Udc/(n–1) + 2Ub) The jump voltage is given by 0,7(Udc/(n–1) + Ub)
(3) The proportion of jump voltage appearing across the first turn is obtained from Figure 7. The value of Ub in these formulae is the value shown in Figure 1 for the phase/phase voltage on the machine terminals. The values of the phase/ground voltages estimated from these formulae may be higher or lower in practice, depending upon the grounding system, converter control regime and other factors. It is known that a sudden rise can occur in the machine ground voltage level with respect to the d.c. zero point in the converter. The theoretical rise is determined capacitively to be 1/3 which gives a residual effect of about 0,7. This would apply to simple systems where only travelling wave theory determines the factor, i.e. stress categories A, B and C (see Clause 7). Examples of the enhancement that is produced for various rise times and cable lengths in the case of a motor driven from a converter are given in Figure 4. In this case, the enhancement to the voltage for an impulse rise time of 1,0 µs is insignificant below about 15 m and only exceeds 1,2 when the cable length is greater than about 50 m. Voltages above 2Udc can be produced at the terminals of the machine by drive double transition and by a converter fed drive algorithm that does not allow a minimum time between successive pulses. Double transition occurs, for example, when one phase switches from minus to plus d.c. bus voltage at the same instant that another phase switches from plus to minus. This generates a 2Udc voltage wave which travels to the machine and can then increase in magnitude when reflected at the machine terminals. If there is no minimum impulse time control in the drive and if the time between two impulses is matched with the time constant of the cable between the converter and the machine, an over voltage >2Udc can be generated at the machine terminals. The reflection can be reduced or prevented by using a filter in the converter, at the machine terminals or both. In the event of an earth fault on one of the phases of a system where the neutral star point is not grounded, the machine may be permitted by the manufacturer to run for a period of several hours until a suitable outage can be arranged for repairs. In this case, the voltage stress on the turn to ground insulation in the other phases will increase. SIST EN 60034-18-41:2014

IEC 60034-18-41:2014 © IEC 2014 – 17 –
Up/Ua IEC
0564/14
Key
”
tr = 0,05 µs
|
tr = 0,1 µs
z
tr = 0,2 µs
∇
tr = 1,0 µs l (m) cable length
Up/Ua ratio of peak voltages at the machine and at the converter terminals Figure 4 – Voltage enhancement at the terminals of a motor due to reflection as a function of cable length for various impulse rise times
5 Electrical stresses in the insulation system of machine windings 5.1 General If a winding experiences short rise time voltage impulses of significant magnitude, high voltage stresses will be created, for example, in the following locations (Figures 5 and 6): • between conductors in different phases, • between a conductor and ground,
• between adjacent turns in the line-end coil.
Due to space and surface charge creation within the insulation components, the electric stress is not only defined by the instantaneous voltage itself but also by the peak voltages that have been stressing the insulation previously. Generally, it has been shown by experience that, within certain limits valid for drive systems, the stressing parameter is the peak/peak voltage. This is also the reason why a unipolar voltage produces the same stress as a bi-polar voltage having a peak/peak voltage of the same value [1]2. _______________ 2
Numbers in square brackets refer to the Bibliography. SIST EN 60034-18-41:2014

– 18 – IEC 60034-18-41:2014 © IEC 2014
Key
a phase insulation / overhang insulation b mainwall insulation c turn insulation d slot corona protection e overhang corona protection (stress grading) 1 phase to phase 2 phase to ground 3 turn to turn
Figure 5 – Example of a random wound design Figure 6 – Example of a form-wound design 5.2 Voltages stressing the phase/phase insulation The maximum voltage stress on the phase/phase insulation is determined by the design of the winding and by the characteristics of the phase/phase voltage. 5.3 Volta
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