IEC 60076-14:2013
(Main)Power transformers - Part 14: Liquid-immersed power transformers using high-temperature insulation materials
Power transformers - Part 14: Liquid-immersed power transformers using high-temperature insulation materials
IEC 60076-14:2013 applies to liquid-immersed power transformers employing either high-temperature insulation or combinations of high-temperature and conventional insulation, operating at temperatures above conventional limits. It is applicable to:
- power transformers in accordance with IEC 60076-1;
- convertor transformers according to IEC 61378 series;
- transformers for wind turbine applications in accordance with IEC 60076-16;
- arc furnace transformers;
- reactors in accordance with IEC 60076-6. This part of IEC 60076 may be applicable as a reference for the use of high-temperature insulation materials in other types of transformers and reactors. This first edition of IEC 60076-14 cancels and replaces the second edition of the Technical Specification IEC/TS 60076-14 published in 2009. It constitutes a technical revision.
Transformateurs de puissance - Partie 14: Transformateurs de puissance immergés dans du liquide utilisant des matériaux isolants haute température
La CEI 60076-14:2013 s'applique aux transformateurs immergés dans un liquide qui utilisent soit des isolants haute température soit des combinaisons d'isolants conventionnels et haute température, fonctionnant à des températures au-dessus des limites conventionnelles. Elle s'applique aux:
- transformateurs de puissance conformes à la norme CEI 60076-1;
- transformateurs de convertisseur conformes à la série CEI 61378;
- transformateurs pour applications éoliennes conformes à la norme CEI 60076-16;
- transformateurs de four à arc;
- bobines d'inductance conformes à la norme CEI 60076-6. La présente partie de la norme CEI 60076 peut s'appliquer comme référence pour l'utilisation de matériaux isolants haute température dans d'autres types de transformateurs et bobines d'inductance. Cette première édition de la CEI 60076-14 annule et remplace la deuxième édition de la Spécification technique CEI/TS 60076-14 publiée en 2009. Elle constitue une révision technique.
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Standards Content (Sample)
IEC 60076-14 ®
Edition 1.0 2013-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Power transformers –
Part 14: Liquid-immersed power transformers using high-temperature insulation
materials
Transformateurs de puissance –
Partie 14: Transformateurs de puissance immergés dans du liquide utilisant des
matériaux isolants haute température
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IEC 60076-14 ®
Edition 1.0 2013-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Power transformers –
Part 14: Liquid-immersed power transformers using high-temperature insulation
materials
Transformateurs de puissance –
Partie 14: Transformateurs de puissance immergés dans du liquide utilisant des
matériaux isolants haute température
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XA
ICS 29.180 ISBN 978-2-8322-1096-3
– 2 – 60076-14 © IEC:2013
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Insulation systems . 11
4.1 General . 11
4.2 Winding insulation types . 12
4.2.1 General . 12
4.2.2 Summary of winding/system insulation types . 13
4.2.3 Hybrid winding types . 13
4.2.4 High-temperature insulation winding . 16
5 Temperature rise limits . 17
5.1 General . 17
5.2 Thermally upgraded paper (TUP) . 19
5.3 Cellulose used in ester liquid . 19
6 Components and materials . 19
6.1 General . 19
6.2 Leads and cables . 19
7 Special design considerations . 20
7.1 Short-circuit considerations . 20
7.2 Dielectric requirements . 20
7.3 Temperature requirements . 20
7.4 Overload . 22
8 Required information . 23
8.1 Information to be provided by the purchaser . 23
8.1.1 Ambient temperatures and loading cycle . 23
8.1.2 Other unusual service conditions . 23
8.2 Information to be provided by the manufacturer . 23
8.2.1 Thermal characteristics . 23
8.2.2 Guarantees . 23
9 Rating plate and additional information . 23
9.1 Rating plate . 23
9.2 Transformer manual . 24
10 Test requirements. 24
10.1 Routine, type and special tests . 24
10.2 Dissolved gas analysis . 24
10.3 OD cooled compact transformers . 24
10.4 Evaluation of temperature-rise tests for windings with multiple hot-spots . 24
10.5 Dielectric type tests . 26
11 Supervision, diagnostics, and maintenance . 27
11.1 General . 27
11.2 Transformers filled with mineral insulating oil . 27
11.3 Transformers filled with high-temperature insulating liquids . 27
Annex A (informative) Insulation materials . 28
60076-14 © IEC:2013 – 3 –
Annex B (informative) Rapid temperature increase and bubble generation . 35
Annex C (informative) Ester liquid and cellulose . 38
Annex D (normative) Insulation system coding . 52
Bibliography . 55
Figure 1 – Example of semi-hybrid insulation windings . 14
Figure 2 – Example of a mixed hybrid insulation winding . 15
Figure 3 – Example of full hybrid insulation windings . 16
Figure 4 – Example of high-temperature insulation system . 17
Figure 5 – Temperature gradient conductor to liquid . 21
Figure 6 – Modified temperature diagram for windings with mixed hybrid insulation
system . 26
Figure A.1 – Example of a thermal endurance graph . 29
Figure B.1 – Bubble evolution temperature chart. 36
Figure C.1 – Tensile strength ageing results of TUP in mineral oil and natural ester
liquid. 39
Figure C.2 – Composite tensile strength ageing results of TUP in mineral oil and
natural ester liquid . 40
Figure C.3 – DP ageing results of TUP in mineral oil and natural ester liquid . 41
Figure C.4 – Composite DP ageing results of TUP in mineral oil and natural ester liquid. 42
Figure C.5 – Tensile strength ageing results of kraft paper in mineral oil and natural
ester liquid . 42
Figure C.6 – Composite tensile strength ageing results of kraft paper in mineral oil and
natural ester liquid . 43
Figure C.7 – DP ageing results of kraft paper in mineral oil and natural ester liquid . 43
Figure C.8 – Composite DP ageing results of kraft paper in mineral oil and natural
ester liquid . 44
Figure C.9 – Infrared spectra of kraft paper aged in liquid at 110 °C for 175 days . 46
Figure C.10 – Unit life versus temperature of TUP ageing data (least squares fit) . 48
Figure C.11 – Unit life versus temperature of kraft paper ageing data (least squares fit) . 48
Table 1 – Preferred insulation system thermal classes . 12
Table 2 – Winding/system insulation comparison . 13
Table 3 – Maximum continuous temperature rise limits for transformers with hybrid
insulation systems . 18
Table 4 – Maximum continuous temperature rise limits for transformers with high-
temperature insulation systems . 19
Table 5 – Suggested maximum overload temperature limits for transformers with
hybrid insulation systems . 22
Table 6 – Suggested maximum overload temperature limits for transformers with high-
temperature insulation systems . 22
Table A.1 – Typical properties of solid insulation materials . 32
Table A.2 – Typical enamels for wire insulation . 33
Table A.3 – Typical performance characteristics of unused insulating liquids . 34
Table C.1 – Effect of moisture solubility limits on cellulose moisture reduction . 46
Table C.2 – Comparison of ageing results. 47
– 4 – 60076-14 © IEC:2013
Table C.3 – Maximum temperature rise for ester liquid/cellulose insulation systems . 49
Table C.4 – Suggested maximum overload temperature limits for ester liquid/cellulose
insulation systems . 49
60076-14 © IEC:2013 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER TRANSFORMERS –
Part 14: Liquid-immersed power transformers
using high-temperature insulation materials
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60076-14 has been prepared by IEC technical committee 14:
Power transformers.
This first edition of IEC 60076-14 is an International Standard which cancels and replaces the
second edition of the Technical Specification IEC/TS 60076-14 published in 2009. It
constitutes a technical revision.
This International Standard includes the following significant technical changes with respect to
the Technical Specification:
a) the hot-spot relationship to thermal class is now defined;
b) a new 140 thermal class is defined;
c) the number of insulation systems is reduced to only three: conventional, hybrid and high-
temperature;
– 6 – 60076-14 © IEC:2013
d) homogeneous high-temperature insulation system has been changed to just high-
temperature insulation system;
e) winding definitions were introduced to define variations in the hybrid insulation system;
f) the system example drawings have been revised for clarity;
g) all suggested limits corresponding to Part 7 loading guide have been defined in a similar
format;
h) moisture equilibrium curves for high-temperature materials have been added to the
moisture and bubble generation annex;
i) an annex has been added to introduce the concept of thermal enhancement of cellulose
by ester;
j) some guide information, such as overload temperature limit suggestions was retained, but
most of the other informative text was moved into informative annexes.
The text of this standard is based on the following documents:
FDIS Report on voting
14/755/FDIS 14/759/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 of the IEC 60076 series can be found, under the general title Power
transformers, on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
60076-14 © IEC:2013 – 7 –
INTRODUCTION
This part of IEC 60076 standardizes liquid-immersed transformers that use high-temperature
insulation. As a system, the solid insulation may encompass a broad range of materials with
varying degrees of thermal capability. The insulating and cooling liquids also vary
substantially, ranging from mineral oil to a number of liquids that also have a range of thermal
capability.
This international standard is not intended to stand alone, but rather builds on the information
and guidelines documented in other parts of the IEC 60076 series. Accordingly, this document
follows two guiding principles. The first principle is that liquid-immersed transformers are well
known and are well defined in other parts of this series and therefore, the details of these
transformers are not repeated in this international standard, except where reference has
value, or where repetition is considered appropriate for purposes of emphasis or comparison.
The second principle is that the materials used in normal liquid-immersed transformers,
typically kraft paper, pressboard, wood, mineral oil, paint and varnish, which operate within
temperature limits given in IEC 60076-2, are well known and are considered normal or
conventional. All other insulation materials, either solid or liquid that have a thermal capability
higher than the materials used in this well-known system of insulation materials are
considered high-temperature. Consequently, this standard or normal insulation system is
defined as the “conventional” insulation system for comparison purposes and these normal
thermal limits are presented for reference to illustrate the differences between other higher-
temperature systems.
This international standard addresses loading, overloading, testing and accessories in the
same manner. Only selected information for the “conventional” transformers is included for
comparison purposes or for emphasis. All other references are directed to the appropriate IEC
document.
– 8 – 60076-14 © IEC:2013
POWER TRANSFORMERS –
Part 14: Liquid-immersed power transformers
using high-temperature insulation materials
1 Scope
This part of IEC 60076 applies to liquid-immersed power transformers employing either high-
temperature insulation or combinations of high-temperature and conventional insulation,
operating at temperatures above conventional limits.
It is applicable to:
– power transformers in accordance with IEC 60076-1;
– convertor transformers according to IEC 61378 series;
– transformers for wind turbine applications in accordance with IEC 60076-16;
– arc furnace transformers;
– reactors in accordance with IEC 60076-6.
This part of IEC 60076 may be applicable as a reference for the use of high-temperature
insulation materials in other types of transformers and reactors.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60076-1, Power transformers – Part 1: General
IEC 60076-2, Power transformers – Part 2: Temperature rise
IEC 60076-5, Power transformers – Part 5: Ability to withstand short-circuit
IEC 60076-7, Power transformers – Part 7: Loading guide for oil-immersed power
transformers
IEC 60076-16, Power transformers – Part 16: Transformers for wind turbine applications
IEC 60085, Electrical insulation – Thermal evaluation and designation
IEC 60137, Insulated bushings for alternating voltages above 1 000 V
IEC 60214-1, Tap-changers – Part 1: Performance requirements and test methods
IEC 60296, Fluids for electrotechnical applications – Unused mineral insulating oils for
transformers and switchgear
IEC 60836, Specifications for unused silicone insulating liquids for electrotechnical purposes
60076-14 © IEC:2013 – 9 –
IEC 61099, Specifications for unused synthetic organic esters for electrical purposes
IEC 61378-1, Convertor transformers – Part 1: Transformers for industrial applications
IEC 61378-2, Convertor transformers – Part 2: Transformers for HVDC applications
3 Terms and definitions
For the purposes of this document, the following terms and definitions, as well as those given
in IEC 60076-1 and IEC 60076-2 apply.
3.1
insulation system
system composed of solid insulating materials and an insulating liquid
3.2
temperature index
TI
numerical value of the temperature in degrees Celsius derived from the thermal endurance
relationship at a time of 20 000 h (or other specified time)
[SOURCE: IEC 60050-212:2010, 212-12-11, modified – Notes 1 and 2 have been deleted]
3.3
thermal class
designation of Electrical Insulation Materials (EIM) or Electrical Insulation Systems (EIS)
equal to the numerical value of the maximum used temperature in degrees Celsius for which
the EIM/EIS is appropriate
Note 1 to entry: See IEC 60085.
3.4
conventional
modifier applied to temperature-rise limits, insulation materials or insulation systems
operating at temperature limits defined by IEC 60076-2
3.5
kraft paper
paper made almost entirely from pulp of high mechanical strength, manufactured from soft-
wood by the sulphate process
[SOURCE: IEC 60050-212:2010, 212-16-03]
3.6
thermally upgraded paper
TUP
cellulose-based paper which has been chemically modified to reduce the rate at which the
paper decomposes
Note 1 to entry: See IEC 60076-2 for the complete definition.
Note 2 to entry: This note applies to the French language only.
3.7
high-temperature
temperature rise limits and/or insulation materials applied in systems consisting of solid
materials and/or liquid, capable of operating at higher temperatures than conventional
– 10 – 60076-14 © IEC:2013
3.8
conventional insulation system
insulation system consisting of solid insulation materials used throughout the transformer and
insulating liquid operating at temperatures within the normal thermal limits specified in
IEC 60076-2
3.9
high-temperature insulation system
insulation system consisting of high-temperature insulation used throughout the transformer,
except for some insulation components in lower temperature areas, together with high-
temperature insulating liquid, capable of operating at higher than conventional top liquid,
average winding and hot-spot temperature rises
3.10
high-temperature insulation winding
winding with high-temperature insulation used throughout, to allow higher than conventional
average winding and hot-spot temperature rises
3.11
hybrid insulation system
insulation system consisting of high-temperature solid insulation capable of operating above
conventional temperatures, combined with conventional solid insulation and an insulating
liquid, operating at conventional temperatures
3.12
full hybrid insulation winding
winding with high-temperature solid insulation used for all parts in thermal contact with the
conductor, combined with conventional solid insulation to allow higher than conventional
average winding and hot-spot temperature rises
3.13
semi-hybrid insulation winding
winding with high-temperature solid insulation used only for the conductor insulation to allow
higher than conventional average winding and hot-spot temperature rises
3.14
mixed hybrid insulation winding
winding with high-temperature solid insulation used only selectively, combined with
conventional solid insulation to allow higher than conventional hot-spot temperature rises,
while operating at conventional average winding temperature rises
3.15
normal cyclic loading
loading and ambient temperature cycle which, from the point of view of relative thermal
ageing rate (according to the mathematical model), is equivalent to the rated load at yearly
average ambient temperature.
Note 1 to entry: Higher ambient temperature or a higher-than-rated load current may be applied during part of the
cycle. This is achieved by taking advantage of low ambient temperatures or low load currents during the rest of the
load cycle.
Note 2 to entry: For planning purposes, this principle can be extended to provide for long periods of time whereby
cycles with relative thermal ageing rates greater than unity are compensated for by cycles with thermal ageing
rates less than unity.
[SOURCE: IEC 60076-7:2005, 3.5]
60076-14 © IEC:2013 – 11 –
3.16
long-time emergency loading
loading resulting from the prolonged outage of some system elements that will not be
reconnected before the transformer reaches a new and higher steady-state temperature
[SOURCE: IEC 60076-7:2005, 3.6]
3.17
short-time emergency loading
unusually heavy loading of a transient nature (less than 30 min) due to the occurrence of one
or more unlikely events which seriously disturb normal system loading
[SOURCE: IEC 60076-7:2005, 3.7]
3.18
rated average winding temperature rise
contractually agreed upon average winding temperature rise as defined on the nameplate in
contrast to calculated or actual tested value
3.19
reference temperature
rated average winding temperature rise +20 °C, or rated average winding temperature rise +
yearly external cooling medium average temperature, whichever is higher
Note 1 to entry: When there is more than one power rating specified, the highest rating shall be used to determine
the reference temperature.
Note 2 to entry: For transformers that have more than one rated average winding temperature rise, assigned for
different windings at the same power rating, the highest average winding rise shall be used to determine the
reference temperature for this power rating. In this case the losses in service will be lower than calculated.
Note 3 to entry: See IEC 60076-1 for complete details on reference temperature.
Note 4 to entry: The term “rated average temperature rise” is meant to be the same as guaranteed temperature
rise.
4 Insulation systems
4.1 General
An insulation system used in liquid-immersed transformers contains one or more solid
materials for insulating the conductive parts and a liquid, for insulation and heat transfer. This
insulation shall withstand the electrical, mechanical, and thermal stresses for the expected life
of the device. The thermal class ratings for solid insulation and wire enamels determined by
test procedures performed in air are not acceptable for use in transformers conforming to this
standard.
The solid insulation used in transformers covered by this standard shall have thermal
performance and temperature ratings evaluated in combination with the intended liquid. The
procedure for evaluating a combined solid and liquid insulation is described in IEC/TS 62332-
1, which results in a thermal index, from which the thermal class is determined. By agreement
between manufacturer and purchaser, service experience or other suitable test procedures
are acceptable to verify thermal class. See Table 1 for a list of preferred insulation system
thermal classes and the associated hot-spot temperature. Refer to IEC 60085 for more
information on thermal evaluation procedures.
– 12 – 60076-14 © IEC:2013
Table 1 – Preferred insulation system thermal classes
Thermal class Hot-spot temperature
°C
105 98
120 110
130 120
140 130
155 145
180 170
200 190
220 210
Since ageing and lifetime of the insulation system so strongly depend on the temperature,
combinations of insulating materials with different thermal capabilities are used within a unit in
order to optimise the thermal and economical design of the transformer. In order to simplify
and standardize, three distinct insulation systems are defined, based on the degree of high-
temperature insulation content. The conventional insulation system is the basis for reference
and contains no high-temperature insulation. This system is used as a reference only in this
document.
Although a winding with radial spacers, typical for a core-type power transformer is used to
illustrate the various insulation systems, the application is not limited to this type of
transformer. Each of the insulation systems described is an illustration of the definition and
the description is applicable to any other type of transformer with different types of windings,
such as layer-type and shell-type pancake windings.
4.2 Winding insulation types
4.2.1 General
The transformer winding insulation is a component of the insulation system. Subclauses 4.2.3
to 4.2.4 illustrate different low voltage (LV) and high voltage (HV) winding types with
examples based on power transformers, which have a high degree of winding separation.
Table 2 summarizes and compares the different variations.
The barrier insulation between the individual windings shall be treated as a separate entity
when properly designed cooling channels separate the material from the winding itself. In this
case, the liquid circulation provides sufficient cooling to avoid exceeding the thermal
capability of the barrier insulation. If the barrier insulation touches the winding then it shall be
considered part of that winding. This is especially important for layer type windings when the
layer insulation touches the winding conductor. In this application, the layer insulation shall be
treated in the same manner as the winding conductor insulation.
Sufficient testing shall be performed to verify the thermal profile. This shall be accomplished
by actual thermal measurement of critical locations taken during prototype and unit testing.
Once thermally mapped, materials shall be selected appropriate to the temperature
requirements of the specific location. Supporting test data sufficient to validate the
manufacturer’s thermal model shall be available upon request as part of the type testing.
NOTE The different insulation systems can be explained by considering the transformer as an assembly of
individual isolated windings, separated by insulation barriers and cooling channels. A series of winding types could
then be used to illustrate how parts of different insulation systems can be combined in a single transformer. In
some cases it might not be necessary to use high-temperature insulation in the same way for all windings.
60076-14 © IEC:2013 – 13 –
4.2.2 Summary of winding/system insulation types
Table 2 summarizes the key attributes that identify the different winding types. These same
attributes also define the corresponding insulation systems.
Table 2 – Winding/system insulation comparison
Hybrid insulation systems
High-
Conventional
temperature
Semi- Mixed Full
insulation
insulation
hybrid hybrid hybrid
system
b
system
winding winding winding
Liquid C or H C or H C or H C or H H
Type of
insulating Conductor C and H
C H H H
a
insulation combination
component
Conventional Spacers/strips C and H
C C H H
(C) or high-
combination
temperature (H)
Barrier solid
C C C C H
Insulating Top liquid
C C C C H
component rise
application
Average
temperature
C H C H H
winding rise
Conventional
Hot-spot
(C) or high-
C H H H H
winding rise
temperature (H)
a Only basic transformer parts are shown and the temperature of other parts will depend on the results of the
thermal mapping.
b Since thermal gradients exist in all transformers, some conventional insulation is acceptable in locations
where conventional temperatures are maintained.
4.2.3 Hybrid winding types
4.2.3.1 General
Three hybrid winding types share the use of conventional barrier insulation and the use of
high-temperature insulation on the windings.
4.2.3.2 Semi-hybrid insulation winding
The semi-hybrid insulation winding shall use high-temperature insulation only on the winding
conductor. For layer windings, the layer insulation shall also be high-temperature.
Conventional cellulose-based insulation may be used in all other areas. See Figure 1 for an
illustration of this winding style.
Type of material in winding
High-temperature for conductor insulation only
Type of material in barriers
Conventional
Winding temperature rise limits
Average winding: Higher than conventional
Winding hot-spot: Higher than conventional
– 14 – 60076-14 © IEC:2013
IEC 2247/13
Key
LV low voltage
HV high voltage
1 conventional axial spacers against the winding 4 conventional static rings
2 conventional radial spacers 5 conventional angle rings
3 high-temperature conductor insulation 6 conventional barriers
Figure 1 – Example of semi-hybrid insulation windings
4.2.3.3 Mixed hybrid insulation winding
The mixed hybrid winding shall use high-temperature insulation for certain components or
parts of windings, such as the conductors in regions operating at hot-spot temperatures above
conventional limits. However, the majority of the solid insulation may be conventional. The
average winding temperature is conventional while a portion of the winding exceeds
conventional hot-spot temperatures. See Figure 2 for an illustration of this type of winding.
NOTE This winding type uses high-temperature insulation only for the purpose of protecting a portion of the
winding from temperatures that exceed the conventional hot-spot temperature limit. The key to this winding type is
that the average winding temperature remains equal to or below conventional limits and only a portion of the
winding exceeds the conventional hot-spot temperature limit. Examples of winding zones with extra losses and
higher heat development that could benefit from high-temperature insulation are winding ends due to the radial
component of the magnetic leakage field and zones of convertor transformer windings, where harmonic currents
are concentrated.
Type of material in winding
High-temperature applied to minor selected areas of the winding and used with the specific
intent to protect strategic locations from excessive ageing
Type of material in barriers
Conventional
Winding temperature rise limits
Average winding: Conventional
Winding hot-spot: Higher than conventional
60076-14 © IEC:2013 – 15 –
IEC 2248/13
Key
LV low voltage
HV high voltage
1 conventional axial spacers against the winding 5 conventional angle rings
2 conventional radial spacers 6 conventional barriers
3 conventional conductor insulation 7 high-temperature radial spacers
4 conventional static rings 8 high-temperature conductor insulation in the hottest
areas
Figure 2 – Example of a mixed hybrid insulation winding
4.2.3.4 Full hybrid insulation winding
The full hybrid insulation winding shall use high-temperature material throughout the winding,
which operates above conventional temperatures. The conductor insulation and the radial and
axial spacers separating the coil disks shall be composed of high-temperature materials.
Other insulation components shall also be composed of high-temperature materials, where
conventional temperatures are exceeded. Conventional cellulose-based insulation may be
used in all other areas, such as barrier cylinders and angle rings that operate at conventional
temperatures. See Figure 3 for an example of this winding style.
Type of material in winding
High-temperature for all insulation operating at temperatures higher than conventional
Type of material in barriers
Conventional
Winding temperature rise limits
Average winding: Higher than conventional
Winding hot-spot: Higher than conventional
– 16 – 60076-14 © IEC:2013
IEC 2249/13
Key
LV low voltage
HV high voltage
1 high-temperature axial spacers against the winding 4 conventional static rings
2 high-temperature radial spacers 5 conventional angle rings
3 high-temperature conductor insulation 6 conventional barriers
Figure 3 – Example of full hybrid insulation windings
4.2.4 High-temperature insulation winding
The high-temperature insulation winding shall use high-temperature insulation material
throughout the winding. The high-temperature insulation may include different temperature
classes, all above conventional. See Figure 4 for an example of this winding style.
Type of material in winding
High-temperature
Type of material in barriers
High-temperature
Winding temperature rise limits
Average winding: Higher than conventional
Winding hot-spot: Higher than conventional
60076-14 © IEC:2013 – 17 –
IEC 2250 /13
Key
LV low voltage
HV high voltage
1 high-temperature axial spacers against the winding 4 high-temperature static rings
2 high-temperature radial spacers 5 high-temperature angle rings
3 high-temperature conductor insulation 6 high-temperature barriers
Figure 4 – Example of high-temperature insulation system
5 Temperature rise limits
5.1 General
Maximum temperature rise limits for continuous operation for various combinations of solid
and liquid insulating materials are presented in Tables 3 and 4. Rated temperature-rise values
that are selected lower than the maximum shown shall be selected on 5 K increments. An
accurate thermal model verified by adequate test data shall be required to determine the
actual maximum values of any specific transformer design.
The many different dielectric liquids available offer a range of thermal capabilities. However,
for simplification this standard recognizes only three liquid categories represented by mineral
oil, ester and silicone liquids, each characterized by different top liquid temperature rises.
This standard does not make a distinction between ester liquids based on the source of the
product. Consequently, both synthetic and natural ester are considered thermally equivalent.
Note that other liquids are not intended to be excluded and limits appropriate to specific
thermal capability shall be applied according to the thermal capability of the liquid.
NOTE 1 Some of the limiting factors to be considered in determining the permissible maximum temperatures are:
– freely breathing units t
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