EN IEC 60034-27-2:2024

Rotating electrical machines - Part 27-2: On-line partial discharge measurements on the stator winding insulation

IEC 60034-27-2:2023 deals with on-line PD measurements and provides a common basis with standardized procedures if possible for: - measuring techniques and instruments; - the arrangement of the installation; - normalization and sensitivity assessment; - measuring procedures; - noise reduction; - the documentation of results; - the interpretation of results; with respect to partial discharge on-line measurements on the stator winding insulation of non‑converter driven rotating electrical machines with rated voltage of 3 kV and up. This document covers PD measuring systems and methods detecting electrical PD signals. The same measuring devices and procedures can also be used to detect electrical sparking and arcing phenomena.

Drehende elektrische Maschinen - Teil 27-2: Online-Teilentladungsmessungen an der Ständerwicklungsisolierung drehender elektrischer Maschinen

Machines électriques tournantes - Partie 27-2: Mesurages en fonctionnement des décharges partielles effectués sur le système d’isolation

IEC 60034-27-2:2023 traite des mesurages en fonctionnement des DP et fournit une base commune avec, lorsque c’est possible, des procédures normalisées pour: - les techniques et les appareils de mesure; - la mise en place de l’installation; - l'évaluation de la normalisation et de la sensibilité; - les procédures de mesure; - la réduction du bruit; - la documentation des résultats; - l'interprétation des résultats; pour les besoins des mesurages en fonctionnement des décharges partielles sur le système d'isolation des enroulements statoriques des machines électriques tournantes non entraînées par convertisseur, avec une tension assignée supérieure ou égale à 3 kV. Le présent document couvre les systèmes de mesure des DP et les méthodes de détection des signaux de DP électriques. Les mêmes appareils et procédures de mesure peuvent également être utilisés pour détecter les phénomènes d’étincelles et d’arc électriques.

Električni rotacijski stroji - 27-2 del: Sprotno merjenje delnih razelektritev na izolaciji statorskega navitja (IEC 60034-27-2:2023)

Ta del standarda IEC 60034-27 obravnava sprotno merjenje delnih razelektritev (PD) in zagotavlja skupno podlago s standardiziranimi postopki, če je to mogoče, za:
– merilne tehnike in instrumente;
– izvedbo napeljave;
– ocenjevanje normalizacije in občutljivosti;
– postopke merjenja;
– zmanjšanje hrupa;
– beleženje rezultatov;
– interpretacijo rezultatov;
v povezavi z merjenjem delnih razelektritev na izolaciji statorskega navitja odklopljenih električnih rotacijskih strojev, ki jih ne poganjajo pretvorniki, z nazivno napetostjo 3 kV in več. Ta dokument zajema sisteme in metode merjenja delnih razelektritev, ki zaznavajo električne signale delne razelektritve. Enake metode in postopke merjenja je mogoče uporabiti tudi za zaznavanje pojavov električnega iskrenja in obloka.

General Information

• Status: Published
• Publication Date: 18-Jan-2024
• ICS: 29.160.01 - Rotating machinery in general
• Technical Committee: CLC/TC 2 - Rotating machinery
• Drafting Committee: IEC/TC 2 - IEC_TC_2
• Current Stage: 6060 - Document made available - Publishing
• Start Date: 19-Jan-2024
• Due Date: 31-Aug-2021
• Completion Date: 19-Jan-2024
• Ref Project: SIST EN IEC 60034-27-2:2025 - Rotating electrical machines - Part 27-2: On-line partial discharge measurements on the stator winding insulation (IEC 60034-27-2:2023)

Overview

EN IEC 60034-27-2:2024 (published by CLC) is the international/european standard that defines requirements and standardized procedures for on-line partial discharge (PD) measurements on the stator winding insulation of rotating electrical machines. It applies to non‑converter driven machines with rated voltages of 3 kV and above and covers PD measuring systems and methods that detect electrical PD signals (the same devices/procedures can also detect electrical sparking and arcing).

Keywords: EN IEC 60034-27-2, on-line partial discharge measurements, stator winding insulation, rotating electrical machines, PD sensors, PD monitoring.

Key topics and technical requirements

• Measuring techniques and instruments: Principles for PD sensors, PD measuring devices, pulse propagation in windings, and signal transfer characteristics.
• Installation and cabling: Best practices for PD sensor placement, outside access points, cabling and integration with operational data acquisition systems.
• Normalization and sensitivity assessment: Procedures for normalizing measurements and verifying system sensitivity for both low-frequency and high/very-high-frequency PD systems.
• Measuring procedures: Baseline, periodic and continuous on-line measurement workflows, including machine operating parameter requirements.
• Noise reduction and disturbance rejection: Frequency and time-domain separation, synchronous multi-channel measurements, signal gating and pattern-recognition techniques to reject electrical and electromagnetic interference.
• Visualization and reporting: Guidance on trend visualization, Phase Resolved Partial Discharge (PRPD) patterns, interpretation rules and standardized test report contents.
• Interpretation and decision support: Evaluation of trending PD parameters, PRPD pattern analysis, and consideration of machine operating factors (steady-state and transient conditions).
• Informative annexes include PD types in rotating machines, disturbance rejection methods, typical PRPD examples, and PD coupling capacitor specifications.

Practical applications and users

This standard is intended for professionals involved in condition monitoring, testing and maintenance of medium‑ and high‑voltage rotating machines:

• Maintenance and reliability engineers in power plants and utilities
• Condition monitoring specialists and vibration/insulation testing teams
• OEMs and service providers for generators and large motors
• Test laboratories and certification bodies
• Asset managers implementing predictive maintenance and insulation health monitoring

Use cases include on-line PD monitoring for early detection of insulation degradation, trending to support maintenance decisions, commissioning checks, and detection of arcing/sparking events.

Related standards

• IEC/EN IEC 60034-27-1 (Off-line PD measurements)
• IEC 60270 (Partial discharge measurements)
• IEC TS 62478 (PD measurement by electromagnetic and acoustic methods)
• IEC 60034-27-3 (Dielectric dissipation factor on stator insulation)

Using EN IEC 60034-27-2 helps ensure consistent, repeatable on-line PD measurement practice and improves detection, analysis and documentation of stator insulation defects.

Standards Content (Sample)

SLOVENSKI STANDARD
01-marec-2025
Električni rotacijski stroji - 27-2 del: Sprotno merjenje delnih razelektritev na
izolaciji statorskega navitja (IEC 60034-27-2:2023)
Rotating electrical machines - Part 27-2: On-line partial discharge measurements on the
stator winding insulation (IEC 60034-27-2:2023)
Drehende elektrische Maschinen - Teil 27-2: OnlineTeilentladungsmessungen an der
Ständerwicklungsisolierung drehender elektrischer Maschinen (IEC 60034-27-2:2023)
Machines électriques tournantes - Partie 27-2: Mesurages en fonctionnement des
décharges partielles effectués sur le système d'isolation(IEC 60034-27-2:2023)
Ta slovenski standard je istoveten z: EN IEC 60034-27-2:2024
ICS:
29.160.01 Rotacijski stroji na splošno Rotating machinery in
general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 60034-27-2

NORME EUROPÉENNE
EUROPÄISCHE NORM January 2024
ICS 29.160.01
English Version
Rotating electrical machines - Part 27-2: On-line partial
discharge measurements on the stator winding insulation
(IEC 60034-27-2:2023)
Machines électriques tournantes - Partie 27-2: Mesurages Drehende elektrische Maschinen - Teil 27-2: Online
en fonctionnement des décharges partielles effectués sur le Teilentladungsmessungen an der
système d'isolation Ständerwicklungsisolierung drehender elektrischer
(IEC 60034-27-2:2023) Maschinen
(IEC 60034-27-2:2023)
This European Standard was approved by CENELEC on 2024-01-11. 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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2024 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 60034-27-2:2024 E

European foreword
The text of document 2/2153/FDIS, future edition 1 of IEC 60034-27-2, prepared by IEC/TC 2
"Rotating machinery" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC
as EN IEC 60034-27-2:2024.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2024-10-11
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2027-01-11
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 60034-27-2:2023 was approved by CENELEC as a
European Standard without any modification.
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1 Where an International Publication has been modified by common modifications, indicated by (mod), the
relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cencenelec.eu.
Publication Year Title EN/HD Year
IEC 60034-27-1 2017 Rotating electrical machines - Part 27-1: EN IEC 60034-27-1 2018
Off-line partial discharge measurements on
the winding insulation
IEC 60034-27-3 - Rotating electrical machines - Part 27-3: EN 60034-27-3 -
Dielectric dissipation factor measurement
on stator winding insulation of rotating
electrical machines
IEC 60060-1 - High-voltage test techniques - Part 1: EN 60060-1 -
General definitions and test requirements
IEC 60068-2-6 - Environmental testing - Part 2-6: Tests - EN 60068-2-6 -
Test Fc: Vibration (sinusoidal)
IEC 60068-2-27 - Environmental testing - Part 2-27: Tests - EN 60068-2-27 -
Test Ea and guidance: Shock
IEC 60112 - Method for the determination of the proof EN IEC 60112 -
and the comparative tracking indices of
solid insulating materials
IEC 60270 2000 High-voltage test techniques - Partial EN 60270 2001
discharge measurements
IEC 62271-1 - High-voltage switchgear and controlgear - EN 62271-1 -
Part 1: Common specifications for
alternating current switchgear and
controlgear
IEC TS 62478 - High voltage test techniques - - -
Measurement of partial discharges by
electromagnetic and acoustic methods
ISO 8528-9 - Reciprocating internal combustion engine - -
driven alternating current generating sets -
Part 9: Measurement and evaluation of
mechanical vibration
IEC 60034-27-2 ®
Edition 1.0 2023-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Rotating electrical machines –

Part 27-2: On-line partial discharge measurements on the stator winding

insulation
Machines électriques tournantes –

Partie 27-2: Mesurages en fonctionnement des décharges partielles effectués

sur le système d’isolation
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.160.01  ISBN 978-2-8322-7873-4

– 2 – IEC 60034-27-2:2023 © IEC 2023
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 11
4 Cause and effects of on-line PD . 13
5 Noise and disturbances . 14
5.1 General . 14
5.2 Noise and disturbance sources . 14
6 Measuring techniques and instruments . 15
6.1 General . 15
6.2 Pulse propagation in windings . 16
6.3 Signal transfer characteristics . 16
6.4 PD sensors . 19
6.4.1 General . 19
6.4.2 Design of PD sensors . 19
6.4.3 Reliability of PD sensors . 20
6.5 PD measuring device . 20
6.6 PD measuring parameters . 21
6.6.1 General . 21
6.6.2 PD magnitude . 21
6.6.3 Additional PD parameters . 21
7 Installation of measuring systems . 21
7.1 General . 21
7.2 Installation of PD sensors . 21
7.3 Outside access point and cabling . 22
7.4 Installation of the PD measuring device . 23
7.5 Installation of operational data acquisition systems . 23
8 Normalization of measurements . 24
8.1 General . 24
8.2 Normalization for low frequency systems . 24
8.2.1 General . 24
8.2.2 Normalization procedure . 24
8.3 Normalization / sensitivity check for high and very high frequency systems . 25
8.3.1 Specification for the electronic pulse generation . 25
8.3.2 Configuration of the machine . 27
8.3.3 Sensitivity check . 27
9 Measuring procedures . 27
9.1 General . 27
9.2 Machine operating parameters . 28
9.3 Baseline measurement . 28
9.3.1 General . 28
9.3.2 Comprehensive test procedure . 28
9.4 Periodic measurements . 29
9.5 Continuous measurements . 30
10 Visualization of measurements . 30

IEC 60034-27-2:2023 © IEC 2023 – 3 –
10.1 General . 30
10.2 Visualization of trending parameters . 31
10.3 Visualization of PD patterns . 31
11 Interpretation of on-line measurements . 34
11.1 General . 34
11.2 Evaluation of basic trend parameters . 34
11.3 Evaluation of PD patterns . 35
11.3.1 General . 35
11.3.2 PD pattern interpretation. 36
11.4 Effect of machine operating factors . 36
11.4.1 General . 36
11.4.2 Machine operating factors . 36
11.4.3 Steady state load conditions . 37
11.4.4 Transient load conditions . 37
12 Test report . 38
Annex A (informative) Nature of PD in rotating electrical machines . 41
A.1 Types of PD in rotating electrical machines . 41
A.1.1 General . 41
A.1.2 Internal discharges . 41
A.1.3 Slot discharges . 42
A.1.4 Discharges in the end-winding . 42
A.1.5 Conductive particles . 42
A.2 Arcing and sparking . 42
A.2.1 General . 42
A.2.2 Arcing at broken conductors . 43
A.2.3 Vibration sparking . 43
Annex B (informative) Disturbance rejection and signal separation . 44
B.1 General . 44
B.2 Frequency domain separation . 44
B.3 Time domain separation . 44
B.4 Combination of frequency and time domain separation . 45
B.5 Synchronous multi-channel measurement . 46
B.6 Signal gating . 47
B.7 Pattern recognition . 48
Annex C (informative) Examples of Phase Resolved Partial Discharge (PRPD) pattern . 50
C.1 General . 50
C.2 Principal appearance of phase resolved PD patterns . 50
C.3 Example of typical PRPD patterns recorded in laboratory . 53
C.3.1 General . 53
C.3.2 Internal discharges . 53
C.3.3 Slot partial discharges . 55
C.3.4 Discharges in the end-winding . 56
C.4 Example of typical PRPD patterns recorded on-line . 59
C.4.1 General . 59
C.4.2 Internal discharges . 59
C.4.3 Slot partial discharges . 61
C.4.4 Discharges in the end-winding . 62
C.5 Other complex examples . 65

– 4 – IEC 60034-27-2:2023 © IEC 2023
Annex D (normative) Specifications for conventional PD coupling capacitors . 67
D.1 General . 67
D.2 Datasheet information . 67
D.3 Type tests . 67
D.3.1 General . 67
D.3.2 Voltage endurance . 67
D.3.3 Tracking resistance . 68
D.3.4 Lightning impulse test . 68
D.3.5 Dissipation factor . 68
D.3.6 Capacitance stability in temperature . 68
D.3.7 Thermal cycling . 68
D.3.8 Frequency response . 68
D.4 Mechanical vibration and shock capabilities . 68
D.5 Routine tests. 69
D.5.1 General . 69
D.5.2 Dielectric withstand test at power frequency . 69
D.5.3 Partial discharge extinction voltage test . 69
D.5.4 Capacitance and dissipation factor . 69

Figure 1 – Generic overview of PD measuring system and its subsystems . 15
Figure 2 – Cascade of frequency response channels . 16
Figure 3 – Idealized frequency response of a PD pulse at the PD source and at the
machine terminals; frequency response of different PD measuring systems: a) low
frequency range, b) high frequency range, c) very high frequency range . 17
Figure 4 – Measuring object, during normalization, neutral point in same condition as
during operation . 25
Figure 5 – Arrangement for sensitivity check . 26
Figure 6 – Recommended test procedure with consecutive load and temperature
conditions . 29
Figure 7 – Example of the trend in peak PD activity in three phases over an 18-year
interval using periodic measurements . 31
Figure 8 – Examples of a PRPD pattern . 32
Figure 9 – Phase to phase PD PRPD plots where the PD is caused by insufficient
spacing between the endwindings of phases B and C . 33
Figure B.1 – Example for time domain separation by time of pulse arrival . 45
Figure B.2 – Combined time and frequency domain disturbance separation (time
frequency map) . 46
Figure B.3 – 3 phase star diagram of multi-channel measurement . 47
Figure C.1 – Phase-earth driven PD – PD predominantly centered on 45° and 225°
after zero crossing of phase-to-earth voltage . 51
Figure C.2 – PD events and other sources, e.g. non-PD sources, that are not centered
on 45° and 225° after zero crossing of phase-to-earth voltage . 52
Figure C.3 – Example of internal void discharges PRPD pattern, recorded during
laboratory simulation . 54
Figure C.4 – Example of internal delamination PRPD pattern, recorded during
laboratory simulation . 54
Figure C.5 – Example of delamination between conductor and insulation PRPD pattern,
recorded during laboratory simulation . 55

IEC 60034-27-2:2023 © IEC 2023 – 5 –
Figure C.6 – Slot partial discharges activity and corresponding PRPD pattern, recorded
during laboratory simulation . 56
Figure C.7 – Corona activity at the S/C and stress grading coating, and corresponding
PRPD pattern, recorded during laboratory simulation . 56
Figure C.8 – Surface tracking activity along the end arm and corresponding PRPD
pattern, recorded during laboratory simulation . 57
Figure C.9 – Surface discharges at the junction between stress control and conductive
slot coatings:a) Insulating tape simulating a bad electrical connection between
conductive slot coating and stress control coating and the corresponding PRPD;b) and
c) the connection is completely interrupted . 58
Figure C.10 – Gap type discharge activities and corresponding PRPD patterns,
recorded during laboratory simulations . 59
Figure C.11 – Example of internal void discharges PRPD pattern, recorded on-line . 60
Figure C.12 – Example of internal delamination PRPD pattern, recorded on-line . 60
Figure C.13 – Example of delamination between conductor and insulation PRPD
pattern, recorded on-line . 61
Figure C.14 – PD pattern of phase 2 recorded on-line in April 2012 without any filtering
indicating slot PD . 62
Figure C.15 – Picture of a bar removed for expertise chosen to be the one with the
highest level on phase 2 and close to line side when scanning slots using the TVA
probe in January 2014 . 62
Figure C.16 – PD pattern recorded on-line on phase 2 in September 2016
(maximum scale is 1 V) . 62
Figure C.17 – PRPD plot and photo of a stator bar in the same phase of a large
air-cooled turbine generator showing signs of deterioration of the slot conductive
coating, as well deterioration of the interface between the slot conductive coating and
the stress control coating . 63
Figure C.18 – Surface tracking activity along the end arm and corresponding PRPD
pattern, recorded on-line . 63
Figure C.19 – Degradation caused by gap type discharges and corresponding PRPD
patterns, recorded on-line . 64
Figure C.20 – PRPD pattern recorded on-line, illustrating multiple PD sources showing
the complexity . 65
Figure C.21 – Three phase PRPD showing phase to phase PD between A and B
phases as well as B and C phases; photo showing the as-found PD in the endwinding
area due to inadequate separation between the phases . 66

Table 1 – Operating condition stability to obtain valid trends in PD . 30

– 6 – IEC 60034-27-2:2023 © IEC 2023
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ROTATING ELECTRICAL MACHINES –

Part 27-2: On-line partial discharge measurements
on the stator winding insulation

FOREWORD
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9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
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the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC 60034-27-2 has been prepared by IEC technical committee 2: Rotating machinery. It is an
International Standard.
The text of this International Standard is based on the following documents:
Draft Report on voting
2/2153/FDIS 2/2166/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.

IEC 60034-27-2:2023 © IEC 2023 – 7 –
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 60034 series, published under the general title Rotating electrical
machines, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

– 8 – IEC 60034-27-2:2023 © IEC 2023
INTRODUCTION
Partial Discharge (PD) on-line measurement of rotating electrical machines has gained
widespread acceptance as it could reveal the presence of localized weak points of the stator
insulation system and also various arcing and sparking phenomena. Nevertheless, it has
emerged from several studies that not only are there many different methods of measurement
in existence, but also the criteria and methods of analysing and finally assessing the measured
data are often very different and not really comparable. Consequently, there is a need to have
an International Standard (IS) to give defined guidelines to the users of on-line PD
measurements to assess the condition of their insulation systems.
On-line PD measurements are recorded with the rotating electrical machine experiencing all of
the operating stresses; thermal, electrical, environmental and mechanical. Due to the realistic
stress impact on the winding during measurement and due to the fact that the measurement is
performed during all kinds of normal operation like base load and peak load, PD on-line testing
could identify changes of the winding insulation system at a premature stage and enables real-
time condition assessment as part of predictive maintenance strategies.
PD trend evaluation and comparisons with machines of similar design and similar insulation
system measured under similar conditions, using the same measuring equipment, are
recommended to ensure reliable assessment of the condition of the stator winding insulation.
The trending information provides a good measure for early indication of a change in insulation
condition. This gives time for planning further standstill examination in terms of visual inspection
and off-line testing during next inspection outage.
This document does not deal with on-line PD measurements on converter driven electrical
machines because different measuring techniques are needed to distinguish between noise
from the converter and PD from the winding.
Limitations:PD on-line tests on stator windings produce comparative, rather than absolute
measurements. This creates a fundamental limitation for the interpretation of PD data.
Therefore, acceptance criteria with simple limits for new or rewound stator windings cannot be
established as the following reasons demonstrate:
– There are many types of PD sensors as well as recording and analysing instruments.
Generally, they are incompatible and will produce different results for the same PD activity.
– Even with the same measuring system, the high frequency partial discharge pulses will
interact with the winding capacitance and inductance on their way from point of origin to the
measuring point, e.g. at the winding terminals. Thus, PD measurements taken at machines
with different winding design and rating produce different PD results, even though the actual
type of PD source is the same.
– Different types of winding defects produce different PD magnitudes and have different
impact on insulation destruction. There is no strong correlation between high PD and high
risk of insulation failure.
– PD activity may occur close or far from the PD sensor. In general, if the PD source is inside
the winding coils far away from the PD sensor, it will produce a smaller response at the PD
sensor at the terminals compared to a PD source at the phase connections nearby due to
pulse attenuation.
Users should also be aware that there is no evidence that the time to failure of the stator winding
insulation can be estimated using any PD quantity, alone or even in combination. In order to
more comprehensively describe the condition of the stator insulation, PD measurements are
required to be supplemented by other electrical tests. Also, determining the root cause of an
insulation deterioration process using PD pattern recognition, especially if more than one
process is occurring, is still somewhat subjective, although the digital analysing technology is
evolving rapidly.
IEC 60034-27-2:2023 © IEC 2023 – 9 –
Noise and disturbance from electrical environment have a great impact to on-line PD
measurement. Cross-coupling of PD and noise between different phases can make objective
interpretation of the test results difficult. Therefore, different analogue and digital noise
suppression techniques are used to improve PD measuring sensitivity and PD analysing tools.
Users of PD measurement should be aware that, due to the principles of the method, not all
insulation-related problems in stator windings can be detected by measuring on-line PD activity,
e.g. insulation failures involving continuous leakage currents due to conductive paths between
different electrical potential of the insulation system or fine main insulation cracks with too small
PD activity compared to normal delamination PD or pulse-less discharge phenomena.

– 10 – IEC 60034-27-2:2023 © IEC 2023
ROTATING ELECTRICAL MACHINES –

Part 27-2: On-line partial discharge measurements
on the stator winding insulation

1 Scope
This part of IEC 60034-27 deals with on-line PD measurements and provides a common basis
with standardized procedures if possible for:
– measuring techniques and instruments;
– the arrangement of the installation;
– normalization and sensitivity assessment;
– measuring procedures;
– noise reduction;
– the documentation of results;
– the interpretation of results;
with respect to partial discharge on-line measurements on the stator winding insulation of
non-converter driven rotating electrical machines with rated voltage of 3 kV and up. This
document covers PD measuring systems and methods detecting electrical PD signals. The
same measuring devices and procedures can also be used to detect electrical sparking and
arcing phenomena.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60034-27-1:2017, Rotating electrical machines – Part 27-1: Off-line partial discharge
measurements on the winding insulation
IEC 60034-27-3, Rotating electrical machines – Part 27-3: Dielectric dissipation factor
measurement on stator winding insulation of rotating electrical machines
IEC 60060-1, High-voltage test techniques – Part 1: General definitions and test requirements
IEC 60068-2-6, Environmental testing – Part 2-6: Tests – Test Fc: Vibration (sinusoidal)
IEC 60068-2-27, Environmental testing – Part 2-27: Tests – Test Ea and guidance: Shock
IEC 60112, Method for the determination of the proof and the comparative tracking indices of
solid insulating materials
IEC 60270:2000, High-voltage test techniques – Partial discharge measurements
IEC 62271-1, High-voltage switchgear and controlgear – Part 1: Common specifications for
alternating current switchgear and controlgear

IEC 60034-27-2:2023 © IEC 2023 – 11 –
IEC TS 62478, High voltage test techniques – Measurement of partial discharges by
electromagnetic and acoustic methods
ISO 8528-9: Reciprocating internal combustion engine driven alternating current generating
sets – Part 9: Measurement and evaluation of mechanical vibrations
3 Terms and definitions
For the purposes of this document the terms and definitions given in IEC 60270 apply, together
with the following.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
partial discharge
PD
localized electrical discharge that only partially bridges the insulation between conductors and
which can or cannot occur adjacent to a conductor
3.2
on-line measurement
measurement taken with the rotating electrical machine in operation
3.3
off-line measurement
measurement taken with the rotating electrical machine at standstill, the machine being
disconnected from the power system
Note 1 to entry: The necessary test voltage is applied to the winding from a separate voltage source.
3.4
conductive slot coating
conductive paint or tape layer in intimate contact with the groundwall insulation in the slot
portion of the coil side, often called ‘semiconductive’ coating
Note 1 to entry: This coating together with adequate slot design provides electrical contact to the stator core,
without shorting the core laminations.
3.5
stress control coating
paint or tape on the surface of the groundwall insulation that extends beyond the conductive
slot portion coating in high-voltage stator bars and coils
Note 1 to entry: The stress control coating reduces the electric field stress along the winding overhang to below a
critical value that would initiate PD on the surface. The stress control coating overlaps the conductive slot portion
coating to provide electrical contact between them.
3.6
corona discharge
visible partial discharge adjacent to the surface of a bare conductor or the surface of an
insulation of a conductor
– 12 – IEC 60034-27-2:2023 © IEC 2023
3.7
slot discharges
discharges that occur between the outer surface of the slot portion of a coil or bar and the
earthed core laminations due to high electrical field strength
3.8
vibration sparking
interrupted surface currents between the outer surface of the slot portion of a bar and the
earthed core laminations due to axially induced voltages on the conductive slot coating
combined with bar vibrations
3.9
internal discharges
discharges that occur within the mainwall insulation
3.10
surface discharges
discharges that occur on the surface of the insulation or on the surface of winding components
in the winding overhang or the active part of the machine winding
3.11
pulse magnitude distribution
number of pulses within a series of equally-spaced windows of pulse magnitude during a
predefined measuring time
3.12
pulse phase distribution
number of pulses within a series of equally-spaced windows of phase during a predefined
measuring time
3.13
phase resolved partial discharge pattern
PRPD
PD distribution map of PD magnitude and number of PD pulses versus AC cycle phase position,
for visualization of the PD behaviour during a
...