SIST-TS CLC/TS 60034-24:2011

Rotating electrical machines - Part 24: Online detection and diagnosis of potential failures at the active parts of rotating electrical machines and of bearing currents - Application guide (IEC/TS 60034-24:2009)

This part of IEC 60034 is applicable to the on-line detection and diagnosis of failures at the active parts of multi-phase rotating electrical machines (induction and synchronous machines) and of bearing currents.

Drehende elektrische Maschinen - Teil 24: Erkennung und Diagnose von möglichen Schäden an den Aktivteilen drehender elektrischer Maschinen und von Lagerströmen - Anwendungsleitfaden (IEC/TS 60034-24:2009)

Machines électriques tournantes - Partie 24: Détection et diagnostic en ligne de défaillances potentielles des parties actives de machines électriques tournantes et de courants de palier - Guide d'application (CEI/TS 60034-24:2009)

La CEI/TS 60034-24:2009 est applicable à la détection et au diagnostic en ligne de défaillances des parties actives de machines électriques tournantes polyphasées (machines à induction et machines synchrones) et des courants de palier. L'analyse des défaillances comprend
- les défauts entre spires;
- les courts-circuits entre phases;
- les défauts de terre doubles et les défauts de terre simples des moteurs avec connexion à la terre du point étoile;
- les excentricités statiques et dynamiques;
- les imperfections ou les défauts des cages (par exemple, barres ou bagues d'extrémité brisées);
- les courants de  palier.

Električni rotacijski stroji - 24. del: Sprotno odkrivanje in diagnostika mogočih odpovedi na aktivnih delih električnih rotacijskih strojev in ležajnih tokov - Navodilo za uporabo (IEC/TS 60034-24:2009)

Ta del IEC 60034 velja za sprotno odkrivanje in diagnostiko odpovedi na aktivnih delih večfaznih električnih rotacijskih strojev (indukcijski in sinhroni stroji) in ležajnih tokov.

General Information

• Status: Published
• Publication Date: 03-Mar-2011
• ICS: 29.160.01 - Rotating machinery in general
• Technical Committee: ERS - Rotating machinery
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 01-Mar-2011
• Due Date: 06-May-2011
• Completion Date: 04-Mar-2011
• Ref Project: CLC/TS 60034-24:2011 - Rotating electrical machines - Part 24: Online detection and diagnosis of potential failures at the active parts of rotating electrical machines and of bearing currents - Application guide

Standards Content (Sample)

SLOVENSKI STANDARD
SIST-TS CLC/TS 60034-24:2011
01-april-2011
(OHNWULþQLURWDFLMVNLVWURMLGHO6SURWQRRGNULYDQMHLQGLDJQRVWLNDPRJRþLK
RGSRYHGLQDDNWLYQLKGHOLKHOHNWULþQLKURWDFLMVNLKVWURMHYLQOHåDMQLKWRNRY
1DYRGLOR]DXSRUDER,(&76
Rotating electrical machines - Part 24: Online detection and diagnosis of potential
failures at the active parts of rotating electrical machines and of bearing currents -
Application guide (IEC/TS 60034-24:2009)
Drehende elektrische Maschinen - Teil 24: Erkennung und Diagnose von möglichen
Schäden an den Aktivteilen drehender elektrischer Maschinen und von Lagerströmen -
Anwendungsleitfaden (IEC/TS 60034-24:2009)
Machines électriques tournantes - Partie 24: Détection et diagnostic en ligne de
défaillances potentielles des parties actives de machines électriques tournantes et de
courants de palier - Guide d'application (CEI/TS 60034-24:2009)
Ta slovenski standard je istoveten z: CLC/TS 60034-24:2011
ICS:
29.160.01 Rotacijski stroji na splošno Rotating machinery in
general
SIST-TS CLC/TS 60034-24:2011 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST-TS CLC/TS 60034-24:2011

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SIST-TS CLC/TS 60034-24:2011

TECHNICAL SPECIFICATION
CLC/TS 60034-24

SPÉCIFICATION TECHNIQUE
February 2011
TECHNISCHE SPEZIFIKATION

ICS 29.160


English version


Rotating electrical machines -
Part 24: Online detection and diagnosis of potential failures at the active
parts of rotating electrical machines and of bearing currents -
Application guide
(IEC/TS 60034-24:2009)


Machines électriques tournantes -  Drehende elektrische Maschinen -
Partie 24: Détection et diagnostic en ligne Teil 24: Erkennung und Diagnose von
de défaillances potentielles des parties möglichen Schäden an den Aktivteilen
actives de machines électriques drehender elektrischer Maschinen und
tournantes et de courants de palier - von Lagerströmen -
Guide d'application Anwendungsleitfaden
(CEI/TS 60034-24:2009) (IEC/TS 60034-24:2009)





This Technical Specification was approved by CENELEC on 2011-01-25.

CENELEC members are required to announce the existence of this TS in the same way as for an EN and to
make the TS available promptly at national level in an appropriate form. It is permissible to keep conflicting
national standards in force.

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, Romania, Slovakia, Slovenia,
Spain, Sweden, Switzerland and the United Kingdom.



CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Management Centre: Avenue Marnix 17, B - 1000 Brussels


© 2011 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. CLC/TS 60034-24:2011 E

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SIST-TS CLC/TS 60034-24:2011
CLC/TS 60034-24:2011 - 2 -
Foreword
The text of the Technical Specification IEC/TS 60034-24:2009, prepared by IEC TC 2, Rotating
machinery, was submitted to the formal vote and was approved by CENELEC as CLC/TS 60034-24 on
2011-01-25.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN and CENELEC shall not be held responsible for identifying any or all such patent
rights.
The following date was fixed:
– latest date by which the existence of the CLC/TS
has to be announced at national level (doa) 2011-07-25
__________
Endorsement notice
The text of the Technical Specification IEC/TS 60034-24:2009 was approved by CENELEC as a
Technical Specification without any modification.

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SIST-TS CLC/TS 60034-24:2011
IEC/TS 60034-24
®
Edition 1.0 2009-09
TECHNICAL
SPECIFICATION
SPÉCIFICATION
TECHNIQUE
Rotating electrical machines –
Part 24: Online detection and diagnosis of potential failures at the active parts of
rotating electrical machines and of bearing currents – Application guide

Machines électriques tournantes –
Partie 24: Détection et diagnostic en ligne de défaillances potentielles des
parties actives de machines électriques tournantes et de courants de palier –
Guide d'application

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
S
CODE PRIX
ICS 29.160 ISBN 978-2-88910-021-7
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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SIST-TS CLC/TS 60034-24:2011
– 2 – TS 60034-24 © IEC:2009
CONTENTS
FOREWORD.3
INTRODUCTION.5
1 Scope.6
2 Normative references .6
3 Terms and definitions .6
4 Basis of the diagnosis .7
5 Kinds of electrical signal analysis .10
5.1 General remarks.10
5.2 Stator current/voltage analysis .10
5.3 Induced voltages of auxiliary turns embedded into the stator slots or other
magnetic sensors sensing the air-gap flux .11
5.4 Induced voltages of search coils collecting axial fluxes.14
5.5 Shaft voltage analysis .14
6 Detection of bearing currents.14
Bibliography.16

Table 1 – Most important magnetic fields in the air-gap of a three-phase cage induction
motor with an integral slot stator winding under normal operating and fault conditions .8
Table 2 – Diagnosis of failures at a cage induction motor, equipped with two identical
auxiliary coil systems.13

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SIST-TS CLC/TS 60034-24:2011
TS 60034-24 © IEC:2009 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

ROTATING ELECTRICAL MACHINES –

Part 24: Online detection and diagnosis of potential failures
at the active parts of rotating electrical machines
and of bearing currents –
Application guide


FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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.
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 60034-24, which is a technical specification, has been prepared by IEC technical
committee 2: Rotating machinery.

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SIST-TS CLC/TS 60034-24:2011
– 4 – TS 60034-24 © IEC:2009
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
2/1537/DTS 2/1553A/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.
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 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.

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SIST-TS CLC/TS 60034-24:2011
TS 60034-24 © IEC:2009 – 5 –
INTRODUCTION
Progress in design and technology has resulted in an increasing reliability of rotating
electrical machines, but failures could not be eliminated completely. Since the demand for a
high availability is permanently increasing, it is essential to detect deficiencies at an early
stage and to recognize the origin and identify the severity of the fault in order to estimate the
risk of a continuation of operation.
It would be advantageous, if the signals which are obtained by the detection methods
presented in this guide, were suitable to distinguish the different failures from each other. By
this means, the signal analysis can be used as input data of a complete monitoring system.
The aim of this guide is to present possible tools which are available for the intended purpose
and to explain their advantages and disadvantages. The minimum requirements which shall
be met by the various sensors will be discussed, whereas the detailed design rules are
outside the scope of this technical specification.
This guide deals with the detection of failures at the active parts of multi-phase rotating
machines (all kinds of winding faults in stator and rotor, cage deficiencies, eccentricities) and
of bearing currents.

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SIST-TS CLC/TS 60034-24:2011
– 6 – TS 60034-24 © IEC:2009
ROTATING ELECTRICAL MACHINES –

Part 24: Online detection and diagnosis of potential failures
at the active parts of rotating electrical machines
and of bearing currents –
Application guide



1 Scope
This part of IEC 60034 is applicable to the on-line detection and diagnosis of failures at the
active parts of multi-phase rotating electrical machines (induction and synchronous machines)
and of bearing currents. The failure analysis includes:
– interturn faults;
– phase-to-phase short-circuits;
– double earth faults and single earth faults of motors with earth connection of the star-
point;
– static and dynamic eccentricities;
– cage imperfection or defects (e.g. broken bars or end-rings);
– bearing currents.
This can be achieved by tools like search coils or other magnetic sensors or partly by the
analysis of the terminal voltages and currents.
The detection of the following effects is excluded from the scope:
– vibration (covered by ISO standards, e.g. ISO 10816 and ISO 7919);
– partial discharge (covered by IEC 60034-27);
– single earth-faults of motors without earth connection of the star-point;
– core imperfection.
Also excluded are special methods applicable for specific applications only (e.g. turbo
generators).
2 Normative references
There are no normative references in this technical specification.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
distribution factor
the factor, related to a distributed winding, which takes into account the reduction in the
generated voltage due to the phase difference between the voltages generated in the coils in
different slots
[IEV 411-38-37]

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SIST-TS CLC/TS 60034-24:2011
TS 60034-24 © IEC:2009 – 7 –
3.2
chording (pitch) factor
the factor, related to a distributed winding, which takes into account the reduction in the
generated voltage, when the winding pitch is not 100 %
[IEV 411-38-38]
3.3
branch factor
the factor, related to a distributed winding, which takes into account the reduction in the
generated voltage due to the phase difference between the voltages generated in the series-
connected branches
4 Basis of the diagnosis
The ability of electrical machines to operate is based on the existence of a magnetic field in
the air-gap, which is looping in a cross-sectional area of the laminations of stator and rotor.
Flux components in the end-portions of the machine outside the cores are of a parasitic
nature. Therefore available signals suitable for the detection of potential faults originate from
the magnetic field in the air-gap, which shall be analyzed in order to distinguish between
those components which occur under regular operating conditions and those components
which are attributed to a specific failure and which do not exist in a healthy machine.
Since the winding producing the magnetic field consists of coils distributed symmetrically
around the circumference and since the sum of the supplying currents is usually zero, the air-
gap field forms also a periodic function along the circumference. The wave of the flux density
can be considered as the superposition of a sum of sinusoidally distributed waves, which are
characterized by the following features:
– amplitude,
– number of pole-pairs,
– angular velocity,
– phase-angle,
– type of wave (rotating or standing).
Table 1 shows the composition of the air-gap field in the case of a three-phase cage induction
motor, which is equipped with an integral slot winding. The table can easily be extended to be
valid also for fractional slot windings. Similar tables can be developed for slip-ring motors and
all kinds of synchronous machines.

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SIST-TS CLC/TS 60034-24:2011
– 8 –               TS 60034-24 © IEC:2009

Table 1 – Most important magnetic fields in the air-gap of a three-phase cage induction motor with an integral
slot stator winding under normal operating and fault conditions
Origin of the field Stator fields Rotor fields Item
winding fields type: rotating type: rotating 1
(slot harmonics) frequency: f
g Q
1 ⎧ ⎫
⎪ ⎪
2 r
frequency: f 1+ ()1– s
number of
1⎨ ⎬
p
⎪ ⎪
⎩ ⎭
pole pairs: ν = p (1 + 6g )
1 1
 g = 0; ± 1; ± 2; . g = 0; ± 1; ± 2; …
1 2
number of
(slot harmonics: ν = p + g Q )
1 1 s
pole pairs: ν = ν + g Q
2 1 2 r

saturation fields type: rotating type: rotating 2
frequency: 3f
⎧ g Q ⎫
1
⎪ ⎪
2 r
number of frequency: f 3 + ()1– s
⎨ ⎬
1
p
⎪ ⎪
⎩ ⎭
pole pairs: ν = 3p
1
g = 0; ± 1; ± 2; …
2
number of
pole pairs: ν = 3p + g Q
2 2 r

interturn faults type: superposition of reverse rotating type: superposition of reverse rotating 3
phase-to-phase faults fields of different amplitude fields of different amplitude
double earth faults frequency: f
g Q
1 ⎧ ⎫
⎪ ⎪
2 r
frequency: f ± 1+ ()1– s
number of
1⎨ ⎬
p
⎪ ⎪
⎩ ⎭
pole pairs: ν = 1; 2; 3; .
1

g = ± 1; ± 2; …
2
+ positive-sequence fields
– negative-sequence fields

number of
pole pairs: ν = ν + g Q
2 1 2 r

Additional fields under Fields under normal operating
fault conditions conditions

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SIST-TS CLC/TS 60034-24:2011
TS 60034-24 © IEC:2009                – 9 –

Origin of the field Stator fields Rotor fields Item
eccentricity type: 2 rotating fields type: 2 rotating fields 4
K
⎧ g Q ⎫
⎡ ⎤
⎪ K ⎪
2 r
frequency: f {1 ± (1 – s)}
frequency: f 1+ ± + ()1– s
1 ⎢ ⎥
1⎨ ⎬
p
p p
⎪ ⎢ ⎥ ⎪
⎣ ⎦
⎩ ⎭
K = 0: static eccentricity
number of
K = 1: dynamic eccentricity
pole pairs: ν = ν + g Q
2 1 2 r
number of
g = 0; ± 1; ± 2; …
2
pole pairs: ν = p ± 1
1

rotor asymmetry type: superposition of reverse rotating 5
fields of the same amplitude
⎧ ν ⎫
2
frequency: f ±s + ()1−s
⎨ ⎬
1
p
⎩ ⎭
number of
pole pairs: ν = 1; 2; 3; …
2

Symbols: f fundamental frequency Q number of stator slots
1 s
p number of pole pairs, Q number of rotor bars
r
 for which the motor is designed s slip
ν number of pole pairs in general

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SIST-TS CLC/TS 60034-24:2011
– 10 – TS 60034-24 © IEC:2009
5 Kinds of electrical signal analysis
5.1 General
A valuable detection method shall be able to detect failures at an early stage. Therefore
signals disclosing a rapid change in the case of small deficiencies, are optimal for the
intended purpose. By contrast signals which vary only insignificantly should not be used as
the basis of the diagnosis.
The signal processing needs the availability of appropriate electronic equipment. Although the
resolution of modern devices is high, signals which do not need excessive precision should be
preferred in this respect.
5.2 Stator current/voltage analysis
The analysis of the terminal voltages or currents of a rotating machine allows identification of
– different frequencies,
– positive-, negative-, and zero-sequence components,
– different amplitudes of the components.
In general, all waves of induction in the air-gap field can induce voltages of certain
frequencies in the stator winding and can cause currents of the same frequencies. The
additional current components which are generated by a specific failure are superimposed to
the supply values during undisturbed operation. All details shall be taken from the relevant
table, that is Table 1 in the case of three-phase cage induction motors.
Table 1 is worded for one single supply frequency f . However, in case of a converter
1
supplied machine, it is valid for each voltage/frequency component, which is contained in the
output spectrum of the converter.
Table 1 shows the components of the air-gap field. Whether a specific component induces a
voltage in the stator winding, depends on its winding factor for the number of pole pairs under
consideration. The winding factor is the product of the following terms:
– the distribution factor,
– the chording factor,
– the branch factor.
The branch factor is not generally known amongst engineers, but of fundamental importance
for the problem under consideration. Each symmetrical three-phase integral slot winding
consists of p (in case of a single-layer winding) or 2p (in case of a double-layer winding)
identical coil groups (branches), which are distributed symmetrically around the
circumference. They can be series-connected or connected to form parallel branches with the
maximum number a = 2p. The connecting method considerably influences the branch factor of
a specific number of pole pairs.
It can be shown that the branch factor is zero for the eccentricity fields ν =
p + 1 and ν = p – 1 for all windings with series-connection of the coil-groups. Consequently
both types of eccentricity cannot be detected for such machines by stator current analysis.
The branch factor of the harmonic fields according to item 1 to 4 of Table 1 depends also on
the individual configuration and in addition on the number of rotor slots. The design of a given
case is selected by the manufacturer of the machine for different reasons (e.g. to suppress
unbalanced magnetic pull, to avoid nasty magnetic tones, etc.) and unknown to the user. It is
therefore not advisable to use the harmonic rotor fields of items 3 and 4 as the signal for a
stator current analysis.

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SIST-TS CLC/TS 60034-24:2011
TS 60034-24 © IEC:2009 – 11 –
The group of winding faults in item 3 marks the most severe deficiencies at the active parts.
They all produce magnetic fields of fundamental frequency. Thus winding faults cannot be
detected by a frequency analysis of the stator currents.
The field waves, produced by winding faults, are of elliptic nature, which means the
superposition of two reverse rotating waves, having the same number of poles and the same
frequency, but different amplitudes. In principle such failures can be detected by exploring the
negative sequence component of the current of fundamental frequency.
Especially in case of the most dangerous failure, an interturn fault of a high-voltage machine,
when the high currents flow in only one of many turns per phase, this component is very
small. A negative-sequence component of the current may also be caused by an unavoidable
small asymmetry of the supply voltages (a negative sequence component of the voltage
results in a negative sequence component of the currents, which is 6 to 10-times higher).
Summing up, it is not recommendable to detect winding faults by means of a voltage/current
analysis.
Reliable detection of cage imperfection or defects (e.g. broken bars or end-rings) is possible
by use of stator current analysis.
Another disadvantage of the stator current analysis cannot be neglected. Statistics of
insurance companies manifest that most of the winding faults occur during transient
phenomena such as starting of motors, short-circuits at the terminals, etc., and cause high
inrush currents. It is unfeasible to detect failures by current analysis during the interval of the
transients.
5.3 Induced voltages of auxiliary turns embedded into the stator slots or other
magnetic sensors sensing the air-gap flux
An ideal diagnostic signal would be zero during operation of a healthy machine under steady-
state and transient conditions, it would rise with the amount of the deficiency for all kinds of
failures according to items 3 to 5 of Table 1 and would be able to distinguish between the
failures. Solutions close to the optimum have been developed.
These solutions are based on turns made by insulated wire, the diameter of which can be
selected under solely mechanical aspects. Both coil-sides are incorporated in the stator slots
of the main winding, usually during manufacturing of the machine between the upper layer of
the winding and the slot wedge. The assembly at a later stage is possible. The end-
connections are led close to the end of the core.
The same insight into the magnetic field at specific locations at the stator bore can eventually
be achieved by other kinds of magnetic sensors instead of measuring turns.
Usually several turns of the same pitch are series-connected and shifted against each other
by a predetermined angle. It is aimed to get finally a system of auxiliary measuring coils, for
which the resulting winding factor is zero for all air-gap fields, which exist during normal
undisturbed operation, and for which the winding factor is maximum for a field with that
number of pole pairs, which is intended to be used as the reference field of the diagnosis.
If a system of auxiliary coils can be found which fulfills the condition explained above for a
reference field, which is amongst the fields generated by all failures of items 3 to 5, the coil
system would be complete. But there is one remaining difficulty: The fields produced by a
winding fault according to item 3 of Table 1, are of an elliptic nature. If one of them is chosen
as reference field, the induced voltage of the coil system would vary with the location of the
fault at the circumference. Such a situation is of course unacceptable.
The problem can be eliminated by use of a second identical coil system, which is shifted
against the first one by the angle π/(2ν), when ν is the number of pole pairs of the reference
field. Then both coil groups form a symmetrical two-phase system, which easily allows the

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SIST-TS CLC/TS 60034-24:2011
– 12 – TS 60034-24 © IEC:2009
calculation of the symmetrical components (SC) of the two measured voltages. The SCs are
independent of the fault location.
This guide is the inappropriate place to explain the design rules for the coil system in detail. It
is mentioned only that the minimum number of turns per coil system usually varies between 6
and 12 depending on the data of the relevant machine and the claims to the sensibility of the
diagnosis.
The reference field is taken from the list of air-gap fields, which are generated by the fault
condition and which are zero during normal operation. Therefore the amplitude of the
reference field is nearly unchanged during transients. This statement is proven by tests.
The procedure of the diagnosis is executed in Table 2. Winding faults are characterized by
the criterion that both (positive and negative sequence) symmetrical components do exist and
have mains frequency. The voltages in case of static eccentricity have mains frequency too,
but the negative-sequence component U is zero. A dynamic eccentricity can be distinguished
n
from other fault conditions by the typical frequencies of the induced voltages. Rotor
asymmetries are marked by other typical frequencies; the induced voltages become zero,
when the machine is running at synchronous speed (s = 0), because then the rotor currents,
responsible for the reference field, disappear.
It can be concluded that a professionally designed system of auxiliary coils forms a useful tool
for the detection and diagnosis of faults.
For the purpose of completeness it should be mentioned that other types of search coils were
proposed in technical articles, which e.g. comprise one stator tooth only. They may be useful
to investigate a specific effect, but they are unsuitable to form a complete diagnosis and were
therefore not introduced into engineering practice.

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SIST-TS CLC/TS 60034-24:2011
TS 60034-24 © IEC:2009             – 13 –

Table 2 – Diagnosis of failures at a cage induction motor, equipped with two identical auxiliary coil
...