EN 60034-27-3:2016
(Main)Rotating electrical machines - Part 27-3: Dielectric dissipation factor measurement on stator winding insulation of rotating electrical machines
Rotating electrical machines - Part 27-3: Dielectric dissipation factor measurement on stator winding insulation of rotating electrical machines
IEC 60034-27-3:2015 provides guidelines for the test procedures and the interpretation of test results for dielectric dissipation factor measurements on the stator winding insulation of rotating electrical machines. These guidelines are valid for rotating electrical machines with conductive slot coatings operating at a rated voltage of 6 kV and higher. This standard applies to individual form-wound stator bars and coils outside a core (uninstalled), individual stator bars and coils installed in a core and complete form-wound stator winding of machines in new or aged condition. This edition includes the following significant technical changes with respect to the previous publication IEC TR 60894:1987: - inclusion of digital measurement of dissipation factor and capacitance; - inclusion of limits for dissipation factor values; - detailed description of measuring techniques; extension of scope to complete windings.
Drehende elektrische Maschinen - Teil 27-3: Messung des dielektrischen Verlustfaktors an der Ständerwicklungsisolierung drehender elektrischer Maschinen
Machines électriques tournantes - Partie 27-3: Mesure du facteur de dissipation diélectrique sur le système d'isolation des enroulements statoriques des machines électriques tournantes
L'IEC 60034-27-3:2015 fournit des lignes directrices pour les procédures d'essai et l'interprétation des résultats d'essai concernant les mesures du facteur de dissipation diélectrique sur l'isolation des enroulements statoriques des machines électriques tournantes. Ces lignes directrices sont valables pour les machines électriques tournantes à revêtement d'encoche conducteur dont la tension assignée est supérieure ou égale à 6 kV. Cette norme s'applique aux barres et bobines de stator individuelles préformées situées à l'extérieur d'un noyau (non installées), aux barres et bobines de stator individuelles installées dans un noyau et aux enroulements statoriques préformés complets des machines à l'état neuf ou vieilli. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'IEC TR 60894:1987: - intégration de la mesure numérique du facteur de dissipation et de la capacité; - indication de valeurs limites pour le facteur de dissipation; - description détaillée des techniques de mesure; - extension du domaine d'application aux enroulements complets.
Električni rotacijski stroji - 27-3. del: Merjenje faktorja dielektričnih izgub v izolaciji statorskega navitja električnih rotacijskih strojev (IEC 60034-27-3:2015)
Ta del standarda IEC 60034 podaja smernice za preskusne postopke in interpretacijo rezultatov merjenja faktorja dielektričnih izgub v izolaciji statorskega navitja električnih rotacijskih strojev. Te smernice se uporabljajo za električne rotacijske stroje s prevodno prevleko, ki obratujejo pri nazivni napetosti 6 kV ali več.
Ta standard se uporablja za posamezna predhodno oblikovana navitja statornih palic in navoje zunaj jedra (nemontirane), posamezne statorne palice in navoje, montirane v jedru, ter celotna predhodno oblikovana statorna navitja novih ali rabljenih strojev.
Ta mednarodni standard se uporablja za vse vrste vakuumsko impregniranih ali smolnatih (polno obremenjenih) zalepljenih palic, navojev in celotnih navitij. Ne uporablja se za neimpregnirane posamezne palice in navoje ali neimpregnirana celotna navitja.
Podane so zahteve glede lastnosti faktorja dielektričnih izgub posameznih predhodno navitih statornih palic in navojev strojev pod napetostjo 6 kV ali več pri preskušanju z izmenično napetostjo 50 Hz ali 60 Hz.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-november-2016
(OHNWULþQLURWDFLMVNLVWURMLGHO 0HUMHQMHIDNWRUMDGLHOHNWULþQLKL]JXEYL]RODFLML
VWDWRUVNHJDQDYLWMDHOHNWULþQLKURWDFLMVNLKVWURMHY ,(&
Rotating electrical machines - Part 27-3: Dielectric dissipation factor measurement on
stator winding insulation of rotating electrical machines (IEC 60034-27-3:2015)
Drehende elektrische Maschinen - Teil 27-3: Messung des dielektrischen Verlustfaktors
an der Ständerwicklungsisolierung drehender elektrischer Maschinen (IEC 60034-27-
3:2015)
Machines électriques tournantes - Partie 27-3: Mesure du facteur de dissipation
diélectrique sur le système d'isolation des enroulements statoriques des machines
électriques tournantes (IEC 60034-27-3:2015)
Ta slovenski standard je istoveten z: EN 60034-27-3:2016
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 60034-27-3
NORME EUROPÉENNE
EUROPÄISCHE NORM
June 2016
ICS 29.160
English Version
Rotating electrical machines - Part 27-3: Dielectric dissipation
factor measurement on stator winding insulation of rotating
electrical machines
(IEC 60034-27-3:2015)
Machines électriques tournantes - Partie 27-3: Mesure du Drehende elektrische Maschinen - Teil 27-3: Messung des
facteur de dissipation diélectrique sur le système d'isolation dielektrischen Verlustfaktors an der
des enroulements statoriques des machines électriques Ständerwicklungsisolierung drehender elektrischer
tournantes Maschinen
(IEC 60034-27-3:2015) (IEC 60034-27-3:2015)
This European Standard was approved by CENELEC on 2016-01-20. 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
© 2016 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 60034-27-3:2016 E
European foreword
The text of document 2/1803/FDIS, future edition 1 of IEC 60034-27-3, prepared by IEC/TC 2
"Rotating machinery" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC
as EN 60034-27-3:2016.
The following dates are fixed:
(dop) 2016-12-24
• latest date by which the document has to be implemented at
national level by publication of an identical national
standard or by endorsement
(dow) 2019-06-24
• latest date by which the national standards conflicting with
the 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 [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 60034-27-3:2015 was approved by CENELEC as a
European Standard without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated :
IEC TS 60034-27 NOTE Harmonized as CLC/TS 60034-27.
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 1 When 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.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60060-1 - High-voltage test techniques - EN 60060-1 -
Part 1: General definitions and test
requirements
IEC 60060-2 - High-voltage test techniques - EN 60060-2 -
Part 2: Measuring systems
IEC 60034-27-3 ®
Edition 1.0 2015-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Rotating electrical machines –
Part 27-3: Dielectric dissipation factor measurement on stator winding
insulation of rotating electrical machines
Machines électriques tournantes –
Partie 27-3: Mesure du facteur de dissipation diélectrique sur le système
d’isolation des enroulements statoriques des machines électriques tournantes
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.160 ISBN 978-2-8322-3061-9
– 2 – IEC 60034-27-3:2015 © IEC 2015
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Theory and measuring techniques . 8
4.1 Dielectric dissipation factor measurement . 8
4.2 Analogue Schering bridge . 10
4.3 Transformer ratio arm bridge. 11
4.4 Digital phase shift measurement . 12
5 Test procedures . 13
5.1 General . 13
5.2 Winding bars and coils . 15
5.2.1 Test object preparation . 15
5.2.2 Guarding techniques . 15
5.2.3 Measuring procedure . 17
5.3 Complete windings . 17
6 Test results . 18
6.1 General . 18
6.2 Winding bars and coils . 19
6.3 Complete windings . 20
7 Test report . 21
7.1 General . 21
7.2 New coils, bars and winding . 21
7.3 Operational aged winding . 22
Annex A (informative) Relationship between power factor and dissipation factor . 24
Bibliography . 26
Figure 1 – Parallel circuit and vector diagram . 8
Figure 2 – Series circuit and vector diagram . 9
Figure 3 – Dielectric losses with increasing voltage (schematic) . 10
Figure 4 – High voltage Schering bridge – Basic circuit . 11
Figure 5 – Transformer ratio arm bridge . 12
Figure 6 – Schematic test set-up of a digital dissipation factor measuring system with
principle current oscillogram . 13
Figure 7 – Example of a curve of tan δ versus voltage ratio U/ U measured in voltage
N
steps of 0,2 U . 14
N
Figure 8 – Arrangement with guard rings electrodes on test objects with insulation gap
(example of preferred insulation gap and guard ring electrode dimensions) . 16
Figure 9 – Application of guard ring electrodes on top of stress control coating . 17
Figure A.1 – Phasor diagram . 24
Table 1 – Maximum values of dielectric dissipation factor of single bars and coils in
new condition with guard ring electrodes up to a rated voltage of U = 21 kV . 19
N
IEC 60034-27-3:2015 © IEC 2015 – 3 –
Table A.1 – Comparison between correlating values of dielectric power factor cos φ
and dielectric dissipation factor tan δ and their difference . 25
– 4 – IEC 60034-27-3:2015 © IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ROTATING ELECTRICAL MACHINES –
Part 27-3: Dielectric dissipation factor measurement on stator
winding insulation of rotating electrical machines
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 interna-
tional 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, Tech-
nical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publica-
tion(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 Interna-
tional 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 inter-
ested 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 misinter-
pretation 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 be-
tween 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 ex-
penses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publica-
tions.
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 60034-27-3 has been prepared by IEC technical committee 2:
Rotating machinery.
This first edition cancels and replaces the first edition of IEC TR 60894 published in 1987.
This edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) digital measurement of dissipation factor and capacitance included;
b) limits for dissipation factor values given;
c) detailed description of measuring techniques;
d) extension of scope to complete windings.
IEC 60034-27-3:2015 © IEC 2015 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
2/1803/FDIS 2/1804/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.
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 publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data re-
lated to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
– 6 – IEC 60034-27-3:2015 © IEC 2015
INTRODUCTION
This International Standard provides guidelines for dielectric dissipation factor measurements
on form-wound stator bars or coils as well as for complete windings.
The dielectric dissipation factor is a measure of the dielectric losses in the stator winding in-
sulation. Measurement of dielectric dissipation factor is an appropriate means of assessing
the quality of new and also aged stator winding insulation of rotating electrical machines. Es-
pecially, the method is useful for assessing the uniform quality of manufacturing and the die-
lectric behaviour of the insulation as a whole. For aged stator windings, the dielectric dissipa-
tion factor provides information about insulation condition.
The dielectric dissipation factor measurements give no indication of the distribution of loss
within the insulation and – in contrast to off-line partial discharge measurements – do not
permit localization of weak points of the insulation system.
The main principle is to measure the dielectric dissipation factor over a range of voltages and
to derive different characteristic dielectric loss parameters as basis for the evaluation.
Empirical limits verified in practice can be used as a basis for evaluating the quality of stator
winding insulation systems in manufacturing. Furthermore, trend evaluation, e.g. diagnostic
tests as part of the functional evaluation of insulation systems or in connection with servicing
and overhaul of rotating machines, can also provide information on ageing processes, neces-
sary further measures and intervals between overhauls. However, such trend evaluations
cannot be used to predict the time to failure of a stator winding insulation.
IEC 60034-27-3:2015 © IEC 2015 – 7 –
ROTATING ELECTRICAL MACHINES –
Part 27-3: Dielectric dissipation factor measurement on stator
winding insulation of rotating electrical machines
1 Scope
This part of IEC 60034 provides guidelines for the test procedures and the interpretation of
test results for dielectric dissipation factor measurements on the stator winding insulation of
rotating electrical machines. These guidelines are valid for rotating electrical machines with
conductive slot coatings operating at a rated voltage of 6 kV and higher.
This standard applies to individual form-wound stator bars and coils outside a core (unin-
stalled), individual stator bars and coils installed in a core and complete form-wound stator
winding of machines in new or aged condition.
This International Standard applies to all kind of vacuum impregnated or resin-rich (fully-
loaded) taped bars, coils and complete windings. It is not applicable to non-impregnated indi-
vidual bars and coils or non-impregnated complete windings.
Requirements for the dielectric dissipation factor characteristics of individual form-wound sta-
tor bars and coils of machines with rating voltages from 6 kV and higher when tested with
50 Hz or 60 Hz alternating voltages are given.
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 amend-
ments) applies.
IEC 60060-1, High-voltage test techniques – Part 1: General definitions and test requirements
IEC 60060-2, High-voltage test techniques – Part 2: Measuring systems
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
rated voltage
U
N
voltage or voltage range between lines at the terminals (also called line-to-line voltage) as-
signed, generally by a manufacturer, for a specified operating condition of a machine
3.2
dielectric dissipation factor
tan δ
tangent of the dielectric loss angle δ (complement of the insulation power factor angle) at pre-
determined values of temperature, frequency, and voltage or dielectric stress
Note 1 to entry: Other terms sometimes used for this property are tan delta, loss tangent, dielectric loss factor or
dielectric power factor. Between the dielectric dissipation factor and the power factor (the cosine of power factor
– 8 – IEC 60034-27-3:2015 © IEC 2015
angle or the sine of the dielectric loss angle) a physical difference exists, but the two measurements are very near-
–3
ly the same, when the dielectric dissipation factor is lower than 100 × 10 (see 4.1).
Note 2 to entry: Although the dielectric dissipation factor tan δ is expressed in absolute value in this standard, it is
also expressed in percentage in other documents.
3.3
delta tan delta
∆ tan δ
the difference in dielectric dissipation factor measured at two successive test voltages in
steps of 0,2 U intervals
N
3.4
tan delta tip-up
and 0,2 U
the difference in dielectric dissipation factor measured at the two voltages 0,6 U
N N
Note 1 to entry: Dielectric dissipation factor differences with other voltage steps than mentioned in 3.3 and 3.4
may be used but the limits suggested in Table 1 will not be valid in that case.
4 Theory and measuring techniques
4.1 Dielectric dissipation factor measurement
As defined in 3.2, the dielectric dissipation factor tanδ is the tangent of the dielectric loss an-
gle δ (complement of the insulation power factor angle φ) at a predetermined voltage U, fre-
quency and temperature. The dielectric loss of the insulation system can be represented by
either a parallel (C , R ) or a series (R , C ) equivalent circuit diagram of elements respec-
p p s s
tively (see Figure 1 and Figure 2).
I
tanδ =
ωC R
p p
I
I I I = U/R
C R R p
I
C
I = ωC U
C p
C
p
R U
p
δ
ϕ
U
I
R
IEC
Key
C parallel capacitance
p
R parallel resistor
p
ω 2πf angular frequency
I current in capacitive path
C
I current in resistive path
R
U voltage at insulation system
I total current through insulation system
Figure 1 – Parallel circuit and vector diagram
IEC 60034-27-3:2015 © IEC 2015 – 9 –
U I
R
I
tanδ = ωC R
s s
U = IR
R s
U = I/ω C
C s
δ
U R
R s
U
U
C U
U C
C s
IEC
Key
C series capacitance
s
R series resistor
s
U voltage at insulation system
I total current through insulation system
U voltage at capacitance
C
U voltage at resistor
R
Figure 2 – Series circuit and vector diagram
Comparison of the dielectric dissipation factor tan δ and the sometimes otherwise used insula-
tion power factor cos φ show that these values are very nearly the same, if the dielectric dis-
–3
sipation factor tan δ is less than 100 × 10 , which may be presumed for all modern stator
winding insulation systems.
NOTE The preferred and exclusive used loss characteristic in this standard is the dielectric dissipation factor
tan δ. But in order to make possible a comparison between insulation power factor cos φ and dielectric dissipation
factor tanδ values, a table is given in Annex A.
As shown in Figure 1, the vector of insulation current I can be divided in two perpendicular
components, which represent a capacitive current I (90° leading to voltage U) and a resistive
C
current I (in phase with voltage U). The phase shift angle δ is caused by a resistive compo-
R
nent in addition to the capacitive component of the insulation. The dielectric dissipation factor
tanδ can be expressed in the following equation:
tanδ=ωC R =
s s
ωC R
p p
The capacitive component C or C represents the lossless capacitance of the tested insula-
S P
tion while the resistive component R or R summarizes the different kind of losses. The loss
S P
characteristics under consideration are those mainly relating to the main ground-wall insula-
tion between the conductor structure (including inner conductor shield, if such exists), the
conductive slot coating and the earthed enclosure. In the case of measurements on single
stator bars or coils, only that part of the insulation which is dielectrically in series with the
ground-wall insulation enters into the measurement result because guard ring electrodes can
be used. In the case of dissipation factor measurements on complete windings, the action of
the stress control coating and ambient surface condition have to be considered. These influ-
encing factors may be important when comparing test results from different measurements.
Dielectric dissipation factor measurement at voltages below the inception of partial discharges
represents the magnitude of dielectric losses in the solid insulation (dielectric absorption and
conductive losses) and the conditions of electrical contact to the earthed measuring electrode.
The dielectric dissipation factor component arising from the dielectric losses generally chang-
– 10 – IEC 60034-27-3:2015 © IEC 2015
es very little with voltage, but a significantly higher than normal loss measured indicates some
difference in the structure of the insulation, such as may arise from incorrect resin composi-
tion or inadequate cure.
When the test voltage is raised two different types of dielectric losses increase (see Figure 3):
• dielectric losses of the solid insulation material (polarization, conductivity);
• partial discharges within gaseous inclusions (voids) in the insulation structure cause an
increase in dielectric dissipation factor and increasingly larger number of voids begin to
undergo discharge with rising applied voltage. The value of dielectric loss and therefore
the value of tan δ will continue to increase.
Total dielectric loss
Ionization loss
Solid losses
(dielectric polarization
and conductivity)
Test voltage
IEC
Figure 3 – Dielectric losses with increasing voltage (schematic)
4.2 Analogue Schering bridge
Measurement is carried out by means of the analogue Schering bridge or an equivalent type
of bridge like a transformer ratio arm bridge (see 4.3) or by means of modern digital meas-
urement facilities (see 4.4). A variable amplitude alternating voltage supply is used, having
sufficient rating to provide the measured voltage across the capacitance of the test object and
complying with the requirements of IEC 60060-2. Figure 4 shows the basic circuit diagram for
a high voltage Schering bridge, when measuring a stator winding bar or coil with an assumed
lossless capacitance C and resistive losses of R , using a test circuit with guard ring elec-
x x
trodes. The high voltage branch of the bridge includes the high voltage standard capacitor
(C ) with very low dielectric losses. The Schering bridge instrument itself consists of the low
voltage branches with variable sets of resistive (R and R ) and capacitive (C ) decades of
1 2 1
high precision. The balanced condition of the bridge, which is a necessary requirement for
correct measurement, is monitored by a sensitive “Null indicator” (see Figure 4).
Dielectric losses
IEC 60034-27-3:2015 © IEC 2015 – 11 –
Test object with
guard ring electrodes
C
High voltage x
R
standard x
C
capacitor
Null indicator
High voltage
AC supply
G
C R
1 1
R
A B
IEC
Key
Positions of earthing switch: A for testing coils or bars not earthed
B for testing windings in earthed condition
C Capacitance of standard capacitor C Capacitance of test object
0 x
C Variable capacitance of balancing branch 1 R Variable resistance of balancing branch 2
1 2
R Variable resistance of balancing branch 1 R Resistance of test object
1 x
Figure 4 – High voltage Schering bridge – Basic circuit
The analogue Schering bridge is very sensitive to disturbances produced by stray capacitance
to earth potential. Therefore it is recommended to use double screened coaxial measuring
cables with an active screen potential compensator, i.e. Wagner earth circuit.
Today, most analogue bridges like high voltage Schering bridge use an automated balancing
procedure for that part of the bridge equipment which includes the low voltage branches with
the variable bridge elements C , R and R .
1 1 2
A high-voltage standard capacitor is used as a reference standard C in the bridge circuit. The
nominal value of the capacitance is typically 100 pF or 1 000 pF within a tolerance less than
5 % in long term behaviour. The dielectric dissipation factor of this standard capacitor should
–3
be less than 0,01 × 10 up to the maximum test voltage.
4.3 Transformer ratio arm bridge
Another typical example of the analogue bridge is the transformer ratio arm bridge. The bridge
is automated by applying a current comparator consisting of operational amplifiers and trans-
formers. An example circuit is shown in Figure 5. Windings under the standard capacitor C
and the capacitance of test object C are wound in the reverse direction with each other
x
around a magnetic core of high permeability. When the bridge is balanced by adjusting turn
number N and adjustable resistor R , the flux or magnetomotive force in the magnetic core
s d
becomes zero. Then the potential of the points a and b is developed by the voltage drop
across very small DC resistances of windings N and N and becomes virtually zero. This
x s
method eliminates influence of stray capacitances to the ground. Therefore this bridge method
does not require the Wagner earth circuit which the Schering bridge requires.
– 12 – IEC 60034-27-3:2015 © IEC 2015
C
x
C
R
x
Magnetic
core
a
b
High voltage
R
d
AC source
N N
x s
C
d
A
G
IEC
Key
C capacitance of test object
x
R insulation resistance of test object
x
C standard capacitor
N number of turns of coil in test object branch
x
N number of turns of coil in reference branch
s
R adjustable resistance for balancing the bridge
d
C adjustable capacitance for balancing the bridge
d
G instrument to check balanced condition of the bridge
A amplifier
Figure 5 – Transformer ratio arm bridge
4.4 Digital phase shift measurement
The development of digital electronics, particularly high resolution AD-converter and filter
devices, resulted in digital dissipation factor and capacitance measuring systems which are
completely computer controlled. One example of a test set-up with the high voltage circuit
consisting of the test object (C , R ) path and the reference path with standard capacitor C
x x 0
and the electronic measuring equipment on the low voltage side is shown in Figure 6. The
measuring principle is based on precise recording of the currents through the standard capac-
itor (reference) and the test object path with the high voltage as a reference marker. The die-
lectric dissipation factor is calculated from these currents, or by measurement of the phase
difference between these currents. High sensitivity digital equipment for dissipation factor
measurement can be characterised by the following parts:
• simultaneous measurement of sinusoidal wave current and voltage in both high voltage
paths with high amplitude and time precision;
• suppression of harmonics and external noise at current and voltage sine-wave with digital
filtering in time or frequency domain;
• sensitive and reliable measurement of current phase shift between reference path and test
object path;
• calculation of dissipation factor tan δ and capacitance C based on phase shift and ampli-
x
tude information extracted from digital current measurement;
IEC 60034-27-3:2015 © IEC 2015 – 13 –
δ and Cx values of stator winding insulation in correlation to the applied
• display actual tan
test voltage during computer controlled test procedure.
Lossfree
High voltage Test object with Current sine wave of reference
reference
source dielectric losses capacitor and of test object
capacitor
Reference current
Current from the
i (t)
test object
C R C
X X 0
t
Phase shift δ
A
D
Preprocessing with
digital measurement
IEC
Key
C capacitance of high precision standard capacitor without losses
C , R insulation capacitance and resistance of bars or coils with dielectric losses
x x
Figure 6 – Schematic test set-up of a digital dissipation factor
measuring system with principle current oscillogram
If the measurement system uses high voltage insulated tools like e.g. fibre optic data links
between measuring units and the control computer it can easily perform dissipation factor
measurements on permanently earthed test objects like rotating machines in the field. Be-
cause the fibre optic cables act as a HV insulator, the battery powered measuring devices
may be placed on high potential leads instead of low voltage connections to earth.
5 Test procedures
5.1 General
The dielectric dissipation factor test is applicable to stator winding components (bars or coils)
in which the insulation is cured. This test is usable for single vacuum pressure impregnated or
resin-rich (fully-loaded) bars, coils and complete windings including global vacuum pressure
impregnation (VPI) technology. The test is not applicable to non-impregnated individual bars
and coils or non-impregnated complete windings.
Dissipation factor measurement should be performed with AC line frequency voltage of sinus-
oidal wave shape and a low amount of harmonics according to IEC 60060-1.
Shunt
Shunt
Data acquisition
– 14 – IEC 60034-27-3:2015 © IEC 2015
The dielectric dissipation factor is usually measured over a specific range of voltage U/U
N
starting at 0,2 U and ending at rated voltage of 1,0 U . Values of tan δ may be obtained in
N N
succeeding intervals like 0,2 U . The diagram in Figure 7 gives an example of a stepped
N
measuring procedure. As defined in 3.3, delta tan delta (∆ tan δ) refers to the difference in
dielectric dissipation factor measured between two specified voltages (see Figure 7). Voltage
steps other than 0,2 U may also be used according to agreement between manufacturer and
N
client.
0 0,2 0,4 0,6 0,8 1,0
U/U
N
IEC
Figure 7 – Example of a curve of tan δ versus voltage ratio
U/U measured in voltage steps of 0,2 U
N N
The dielectric dissipation factor tan δ is measured on stator bars/coils or complete windings.
For coils, each coil side is to be measured separately and all results are recorded. The follow-
ing information is obtained:
• dielectric dissipation factor at low voltage of 0,2 U (tan δ );
N 0,2
• delta tan delta for each voltage interval to identify the maximum value of dielectric dissipa-
tion factor increase (∆tan δ / 0,2 U );
N
• characteristic tan delta tip-up as a difference between the two predefined voltage steps of
0,6 U and 0,2 U (tan δ – tan δ );
N N 0,6 0,2
δ versus test voltage U/U (Figure 7).
• shape of the curve of dielectric dissipation factor tan
N
It is recommended that the voltage is increased step by step according to the agreed intervals
like 0,2 U . At each step the voltage has to be held unchanged until stabilized tan δ values
N
can be taken. Unstable readings may be caused by measuring system problems and should
be investigated further.
If an automatic measuring system with continuously increased voltage is used, it shall also
stop at the given voltage steps for a sufficient period to ensure stable measuring values or it
shall provide an appropriate slow voltage increase to obtain reliable readings.
All dielectric dissipation factor measurements should be performed at ambient temperature
and air atmosphere because under these ambient test conditions the most reproducible infor-
mation about the condition of the insulation system can be achieved.
tanδ
tanδ 0,2
∆tanδ
tanδ 0,4
tanδ 0,6
tanδ 0,8
tanδ 1,0
IEC 60034-27-3:2015 © IEC 2015 – 15 –
The dielectric dissipation factor versus voltage characteristic is affected to some extent by the
temperature of the test object insulation. Stator winding temperature shall be uniform and
close to ambient temperature (it may be checked by means of stator winding RTDs). The tem-
perature of the main insulation, the ambient air temperature and the relative humidity shall be
recorded.
NOTE The stray-capacitance of the test object to earth can influence the results of measurements. The operating
instructions of the instrument usually describes how this stray capacitance to be handled in order to minimize the
negative impact.
5.2 Winding bars and coils
5.2.1 Test object preparation
The dielectric dissipation factor test is mainly used as a quality control test on newly manufac-
tured bars and coils. It is an important method to prove the main insulation quality and to de-
termine the consistency of the manufacturing process.
The test results are affected by the electrodes used to simulate the slot. To compare results
between individual bars or coils, or groups of bars or coils, identical electrode systems shall
be used.
In order to use the conductive slot coating as measuring electrode, it is not sufficient to con-
tact it at a few single points because the contact resistance to the conductive slot coating
would be much higher than in the slot. This high resistance would lead to unrealistic high die-
lectric dissipation factor measurements. Therefore, it is necessary to contact the conductive
slot coating with metal plates, wrapped metal foil or spiralled wires along the entire length.
Great care should be taken to minimize voids between the metal electrode and the conductive
slot coating surface.
The use of guard electrodes is necessary to prevent erroneous surface effects at the end of
the conductive slot coating on the dielectric dissipation factor readings (see Figures 8 and 9).
All strands shall be electrically connected to avoid breakdown of the insulation of individual
strands. The bar or coil to be tested should be suitably insulated from earth.
5.2.2 Guarding techniques
5.2.2.1 General
Various techniques of using guard electrodes are available to minimize measuring errors
caused by additional currents starting from the end of the conductive slot coating to the high
voltage side. A grounded guard ring electrode placed near the ends of the conductive slot
coating (varnish or tape) should be used in order to minimise the influence of these additional
currents on the dielectric dissipation factor measurement. The type of guard electrode (metal
foil or conductive paint) that would be the most suitable depends on the manufacturing pro-
cess of the bars or coils.
Depending on bar design, the conductive slot coating area may cover only the straight part of
the bar or may also include the bends and part of the involutes of the bar.
5.2.2.2 Guard ring electrodes with insulation gap
For the dielectric dissipation factor measurement, different options of conductive slot coating
and stress control may be used. Temporary grading tapes or capacitive grading electrodes
can be applied in electrical contact to the conductive slot coating. Alternatively, grading var-
nish could be painted to obtain stress control. A small temporary gap (max. 4,0 mm) has to be
created in the conductive slot coating about 10 mm from each end of the visible beginning of
the end winding stress control coating. It shall be noted that the insulation gap width will have
some influence on the measured dielectric dissipation factor values due to electric field en-
hancement and possible surface discharge activity at a broader insulation gap.
– 16 – IEC 60034-27-3:2015 © IEC 2015
A guard ring electrode has to be applied adjacent to the insulation gap on top of the short
remainder of conductive slot coating. The recommended material for the guard ring electrodes
is a metal foil with conductive adhesive. However, any material demonstrated to be effective
for the guard ring electrodes may be used. The guard ring electrode has to be applied adja-
cent to the small temporary insulation gap and shall not overlap the beginning of stress con-
trol coating as shown in Figure 8. The width of the metal guard ring electrode should be broad
enough to insure low contact current density.
Copper conductor
Insulation gap
Guard ring Guard ring
Insulation gap
4 mm max.
electrode electrode
4 mm max.
HV connection for
e.g. 10 mm e.g. 10 mm
Not less than core length
test voltage
Stress Stress
Conductive slot coating
control control
coating coating
Guard circuit (earth)
C bridge circuit
x
IEC
Figure 8 – Arrangement with guard rings electrodes on test objects with insulation gap
(example of preferred insulation gap and guard ring electrode dimensions)
After dielectric dissipation factor measurement has been completed, the guarding insulation
gap has to be carefully repainted with conductive slot coating varnish to avoid any inhomoge-
neity in the conductive slot coating system. Repainting the gap will require adequate cure time
before additional testing of the test object may be performed.
If a painted conductive slot coating and a painted stress control coating are used on the main
insulation, the guard ring electrodes can be provided together with the painting procedure for
the conductive slot coating.
The guard technique with an insulation gap can also be used together with taped slot and
stress control coatings. If not well controlled, the cutting the insulation gap could affect the
main insulation and therefore should not be the preferred method for production coils and
bars.
Also, temporary grading tapes or capacitive grading electrodes could be used before the final
stress grading system is applied. In this case, the same insulation gap and guard ring ar-
rangement as described above should be used.
5.2.2.3 Guard ring electrodes on top of stress control coating
For new test objects with taped conductive slot coating and stress control coating, the appli-
cation of guard ring electrodes as illustrated in Figure 9 should be used. It can also be used
for painted conductive slot coating and stress control coating.
IEC 60034-27-3:2015 © IEC 2015 – 17 –
Guard electrodes on top of
stress control coating
Stress control coating Stress control coating
Overlapped Overlapped
Conductive slot coating
IEC
Figure 9 – Application of guard ring electrodes on top of stress control coating
The guard ring electrode has to be fixed on top of the stress control layer near the overlapped
part of the conductive slot coating and the stress control coating. Locating the physical end of
the conductive slot coating can be difficult if it is overlapped with the stress control coating.
Nevertheless, the beginning of the guard ring
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...