IEC 60076-15:2015

IEC 60076-15 ®
Edition 2.0 2015-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Power transformers –
Part 15: Gas-filled power transformers

Transformateurs de puissance –
Partie 15: Transformateurs de puissance à isolation gazeuse

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IEC 60076-15 ®
Edition 2.0 2015-04
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Power transformers –
Part 15: Gas-filled power transformers

Transformateurs de puissance –

Partie 15: Transformateurs de puissance à isolation gazeuse

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 20.180 ISBN 978-2-8322-2626-1

– 2 – IEC 60076-15:2015 © IEC 2015
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references. 6
3 Terms and definitions . 7
3.5 Terms, definitions, symbols and units relating to gas and vacuum tightness . 8
4 Service conditions . 8
5 Rating and general requirements . 8
5.1 Rated power . 8
5.1.1 General . 8
5.1.2 Preferred values of rated power . 9
5.1.3 Minimum power under alternative cooling modes . 9
5.1.4 Loading beyond rated power . 9
5.2 Cooling mode . 9
5.2.1 General . 9
5.2.2 Identification symbols . 10
5.2.3 Transformers with alternative cooling methods. 10
5.3 Temperature-rise limits . 10
5.3.1 Classification and insulation system temperature . 10
5.3.2 Normal temperature-rise limits . 11
5.3.3 Reduced temperature-rises for transformers designed for high cooling air
temperatures or special air cooling conditions . 11
5.3.4 High altitude temperature-rise correction . 11
5.3.5 Reduced temperature-rise for transformers designed for high cooling
water temperatures . 12
5.3.6 Temperature rise during specified load cycle . 12
5.4 Insulation level . 12
5.5 Load rejection on transformers directly connected to a generator . 12
5.6 Rated voltage and rated frequency . 12
5.7 Provision for unusual service conditions . 12
5.8 Highest voltage for equipment U and dielectric tests levels . 12
m
5.9 Additional information required for enquiry . 12
5.10 Components and materials . 12
5.11 Requirements for gases and gas tightness . 13
5.11.1 Requirements for gases . 13
5.11.2 Gas tightness . 13
6 Requirements for transformers having a tapped winding . 13
7 Connection phase displacement symbols . 13
8 Rating plates . 13
8.1 General . 13
8.2 Information to be given in all cases . 13
8.3 Additional information to be given when applicable . 14
9 Safety, environmental and other requirements . 15
9.1 Safety and environmental requirements . 15
9.1.1 Gas leaks . 15
9.1.2 Safety considerations . 15
9.2 Dimensioning of neutral connection . 16

9.3 Handling procedure for SF . 16
9.4 d.c. currents in neutral circuits . 16
9.5 Centre of gravity marking . 16
10 Tolerances . 16
11 Tests . 16
11.1 General requirements for routine, type and special tests . 16
11.1.1 General . 16
11.1.2 Routine tests. 17
11.1.3 Type tests . 18
11.1.4 Special tests . 18
11.2 Measurement of short-circuit impedance and load loss . 19
11.3 Leak testing with pressure (tightness test) . 19
11.4 Pressure tests for tanks . 19
11.5 Temperature-rise test . 20
11.5.1 General . 20
11.5.2 Corrections . 20
11.6 Measurement of sound level . 20
11.6.1 General . 20
11.6.2 Prescribed contour . 21
12 Electromagnetic compatibility (EMC) . 21
13 High frequency switching transients . 21
14 Earthing terminal . 21
15 Information required with enquiry and order . 21
Annex A (informative) Check list of information to be provided with enquiry and order . 22
A.1 Rating and general data . 22
A.1.1 Normal information . 22
A.1.2 Special information . 23
A.2 Parallel operation . 25
Annex B (informative) Transient loading – Mathematical model . 26
B.1 General . 26
B.2 Mathematical model for temperature distribution in a winding of a gas-filled
power transformer – The hot-spot concept . 26
Annex C (informative) Gauges, indicators and relays for gas-filled power transformers . 28
Bibliography . 29

Figure B.1 – Temperature distribution model . 26

Table 1 – Classification and insulation system temperature . 11
Table 2 – Winding temperature-rise limits . 11
Table 3 – Exponents for the corrections of temperature rise test results . 20
Table C.1 – Comparison of gauges, indicators and relays between gas-filled power
transformers and oil-immersed power transformers . 28

– 4 – IEC 60076-15:2015 © IEC 2015
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER TRANSFORMERS –
Part 15: Gas-filled power transformers

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,
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6) All users should ensure that they have the latest edition of this publication.
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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 60076-15 has been prepared by IEC technical committee 14: Power
transformers.
This second edition of IEC 60076-15 cancels and replaces the first edition published in 2008 and
constitutes a technical revision.
The following main technical changes from the first edition are:
– Modified in accordance with the related revised standards of IEC 60076-1, IEC 60076-2,
IEC 60076-3 and related items of SF gas in the revised standard of “High-voltage
switchgear and controlgear”
– Added the clause “minimum power under alternative cooling modes”
– Added the clause “safety, environmental and other requirements”
– Added the clause “d.c. currents in neutral circuits”
– Added the clause “electromagnetic compatibility (EMC)”
– Added the clause “high frequency switching transients”

The text of this standard is based on the following documents:
FDIS Report on voting
14/811/FDIS 14/818/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 60076 series, published under the general title Power transformers,
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 website 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.
– 6 – IEC 60076-15:2015 © IEC 2015
POWER TRANSFORMERS –
Part 15: Gas-filled power transformers

1 Scope
This part of IEC 60076 applies to three-phase and single-phase gas-filled power transformers
(including auto-transformers) with the exception of certain categories of small and special
transformers such as:
– single-phase transformers with rated power less than 1 kVA and three-phase transformers
less than 5 kVA;
– transformers, which have no windings with rated voltage higher than 1 000 V;
– instrument transformers;
– traction transformers mounted on rolling stock;
– starting transformers;
– testing transformers;
– welding transformers.
When IEC standards do not exist for such categories of transformers (in particular transformer
having no winding exceeding 1 000 V for industrial applications), this part of IEC 60076 may
still be applicable either as a whole or in part. This standard does not address the requirements
that would make a transformer suitable for mounting in a position accessible to the general
public. For those categories of power transformers and reactors which have their own IEC
standards, this part is applicable only to the extent in which it is specifically called up by
cross-reference in the other standard. Such standards exist for:
– reactors in general (IEC 60076-6);
– self-protected transformers (IEC 60076-13);
– transformers for wind turbine applications (IEC 60076-16);
– traction transformers and traction reactors (IEC 60310);
– converter transformers for industrial applications (IEC 61378-1);
– converter transformers for HVDC applications (IEC 61378-2).
At several places in this part it is specified or recommended that an 'agreement' should be
reached concerning alternative or additional technical solutions or procedures. Such
agreement is made between the manufacturer and the purchaser. The matters should
preferably be raised at an early stage and the agreements included in the contract
specification.
NOTE This standard can be applicable to the gas parts of a transformer in which an insulating gas is used with an
insulating liquid.
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 60076-1:2011, Power transformers – Part 1: General

IEC 60076-2:2011, Power transformers – Part 2: Temperature rise for liquid-immersed
transformers
IEC 60076-3, Power transformers – Part 3: Insulation levels, dielectric tests and external
clearances in air
IEC 60076-5, Power transformers – Part 5: Ability to withstand short circuit
IEC 60076-10, Power transformers – Part 10: Determination of sound levels
IEC 60137, Insulated bushings for alternating voltages above 1 000 V
IEC 60376, Specification of technical grade sulfur hexafluoride (SF6) for use in electrical
equipment
IEC 60480, Guidelines for the checking and treatment of sulfur hexafluoride (SF6) taken from
electrical equipment and specification for its re-use
IEC 62271-1, High-voltage switchgear and controlgear – Part 1: Common specifications
IEC 62271-4:2002, High-voltage switchgear and controlgear – Part 4: Handling procedures for
sulphur hexafluoride (SF6) and its mixtures
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE Other terms use the meanings ascribed to them in IEC 60076-1, 2, 3, 5 and 10, or in the IEC 60050 series.
3.1
gas-filled power transformer
transformer of which the magnetic circuit and windings are placed in an enclosure filled with an
insulating gas
Note 1 to entry: Generally sulfur hexafluoride (SF ) gas is used, and sometimes this transformer is called a
gas-insulated transformer.
3.2
rated gas pressure
gas pressure (gauge pressure) at 20 °C designed for use in a gas-filled power transformer
3.3
guaranteed minimum gas pressure
minimum gas pressure (gauge pressure) at 20 °C, which is able to guarantee the insulation of a
gas-filled power transformer
Note 1 to entry: Transformer of which the magnetic circuit and windings are placed in an enclosure or a vessel filled
with an insulating liquid such as perfluorocarbon, natural ester, synthetic ester, silicon oil and vegetable oil should be
considered a liquid-immersed type transformer.
3.4
design pressure of tanks
relative pressure used to determine the design of the tanks
Note 1 to entry: It is at least equal to the maximum pressure in the tank at the highest temperature that the gas can
reach under specified maximum service condition.

– 8 – IEC 60076-15:2015 © IEC 2015
3.5 Terms, definitions, symbols and units relating to gas and vacuum tightness
3.5.1
absolute leakage rate
F
amount of gas escaped by time unit at rated filling pressure (or density), expressed in Pa m /s
3.5.2
permissible leakage rate
F
p
maximum permissible absolute leakage rate of gas at rated filling pressure (or density)
specified by the manufacturer, expressed in Pa m /s
3.5.3
relative leakage rate
F
rel
absolute leakage rate related to the total amount of gas in the transformer at rated filling
pressure (or density)
Note 1 to entry: It is expressed in percentage per year or per day.
4 Service conditions
Service conditions in IEC 60076-1 apply. As far as cooling conditions are concerned, see
IEC 60076-2.
5 Rating and general requirements
5.1 Rated power
5.1.1 General
The rated power for each winding shall either be specified by the purchaser or the purchaser
shall provide sufficient information to the manufacturer to determine the rated power at the
enquiry stage.
The transformer shall have an assigned rated power for each winding which shall be marked on
the rating plate. The rated power refers to continuous loading. This is a reference value for
guarantees and tests concerning load losses and temperature rises.
If different values of apparent power are assigned under different circumstances, for example,
with different methods of cooling, the highest of these values is the rated power.
A two-winding transformer has only one value of rated power, identical for both windings.
For multi-winding transformers, the purchaser shall specify the required power-loading
combinations, stating, when necessary, the active and reactive outputs separately.
When the transformer has rated voltage applied to a primary winding, and rated current flows
through the terminals of a secondary winding, the transformer receives the relevant rated
power for that pair of windings.
The transformer shall be capable of carrying, in continuous service, the rated power (for a
multi-winding transformer: the specified combination(s) of winding rated power(s) under
conditions listed in Clause 4 of IEC 60076-1:2011 and without exceeding the temperature-rise
limitations specified in 5.3.
NOTE 1 The interpretation of rated power according to this subclause implies that it is a value of apparent power
input to the transformer – including its own absorption of active and reactive power. The apparent power that the
transformer delivers to the circuit connected to the terminals of the secondary winding under rated loading differs
from the rated power. The voltage across the secondary terminals differs from rated voltage by the voltage drop (or
rise) in the transformer. Allowance for voltage drop, with regard to load power factor, is made in the specification of
the rated voltage and the tapping range (see Clause 7 of IEC 60076-8:1997).
National practices can be different.
NOTE 2 For a multi-winding transformer, half the arithmetic sum of the rated power values of all windings (separate
windings, not auto-connected) gives a rough estimate of its physical size as compared with a two winding
transformer.
5.1.2 Preferred values of rated power
Preferred values of rated power in IEC 60076-1 apply.
5.1.3 Minimum power under alternative cooling modes
Where the user has a particular requirement for a minimum power under a particular cooling
mode other than the cooling mode for rated power, this shall be stated and subjected to
agreement between the supplier and the purchaser in the tender stage.
The transformer shall be capable of carrying, in continuous service, the specified minimum
power (for a multi-winding transformer: the specified combination(s) of winding rated power(s)
under conditions listed in Clause 4 of IEC 60076-1:2011, and under the specified cooling mode,
without exceeding the temperature-rise limitations specified in 5.3.
NOTE An example of this is where the transformer is required to operate at a particular minimum percentage of
rated power with the forced cooling out of service (GNAN) to allow for the loss of auxiliary supply and large GNAN
rating will be pushed up the transformer cost. A minimum percentage of rated power is determined with consideration
of the cost-effectiveness.
5.1.4 Loading beyond rated power
Temporary loading beyond nameplate rating capability is subjected to agreement between the
supplier and the purchaser in the tender stage.
NOTE 1 The concept of IEC 60076-7 can be applicable to the consideration of the loading beyond rated power of
gas-filled power transformers, but constants and/or factors may not be applicable.
Any specific requirements for loading beyond rated power, operation at higher external cooling
medium temperatures or reduced temperature rise limits shall be specified by the purchaser in
the enquiry and the contract. Any additional tests or calculations required to verify compliance
with these specific requirements shall also be specified.
NOTE 2 This option is intended to be used in particular to give a basis for design and guarantees concerning
temporary emergency loading of power transformers.
The bushings, tap-changers, current transformers and other auxiliary equipment shall be
selected so as not to restrict the loading capability of the transformer.
NOTE 3 The relevant component standards IEC 60137 for bushings and IEC 60214-1 for tap-changers are
consulted for the loading capability of those components.
NOTE 4 These requirements do not apply to transformers for special applications, which do not need a loading
capability beyond rated power. For these transformers, if such a capability is required, It is specified.
5.2 Cooling mode
5.2.1 General
The user shall specify the cooling medium (air or water). If the user has particular requirements
for the cooling method(s) or cooling equipment, this shall be stated in the enquiry and the
contract.
– 10 – IEC 60076-15:2015 © IEC 2015
5.2.2 Identification symbols
Transformers shall be identified according to the cooling method employed. For gas-filled
power transformers, this identification is expressed by a four-letter code as described below.
First letter: Internal cooling medium:
– G: insulating gas;
Second letter: Circulation mechanism for internal cooling medium:
– N: natural/thermosiphon flow through cooling equipment and in windings;
– F: forced circulation through cooling equipment (e.g., gas blower), thermosiphon flow in
windings;
– D: forced circulation through cooling equipment, directed from the cooling equipment into at
least the main windings.
Third letter: External cooling medium:
– A: air;
– W: water.
Fourth letter: Circulation mechanism for external cooling medium:
– N: natural convection;
– F: forced circulation (fans, air blowers, water pumps).
5.2.3 Transformers with alternative cooling methods
A transformer may be specified with alternative cooling methods. In this case, the specification
and the nameplate shall then carry information about the power values at which the transformer
fulfils the temperature rise limitations when these alternatives apply.
The power value for the alternative with the highest cooling capacity is the rated power of the
transformer (or of an individual winding of a multi-winding transformer). The alternatives are
conventionally listed in rising order of cooling capacity.
EXAMPLE
GNAN/GDAF. The transformer has cooling equipment with blowers and fans but is also specified with a reduced
power-carrying under natural cooling.
NOTE The percentage of natural cooling capacity to forced cooling capacity of gas-filled transformers is smaller
than that of oil-immersed transformers. It is not difficult generally in oil-immersed transformers to achieve ONAN
capacity as 50 % of the OFAF or ODAF capacity. But in gas-filled transformers, it is sometimes difficult and not
economical to achieve GNAN capacity as 50 % of the GDAF capacity. The purchaser consults with the manufacturer
about natural cooling capacity to forced cooling capacity.
5.3 Temperature-rise limits
5.3.1 Classification and insulation system temperature
Transformers are classified by the insulation systems shown in Table 1.
An approximate value for practical purposes of hot-spot temperature can be calculated by
using the concept of Annex B.
The application of insulating materials with different thermal classes leads to unconventional
insulation systems (see the examples of unconventional insulation systems as described in
Clause 5 of IEC 60076-14:2013).

Table 1 – Classification and insulation system temperature
Thermal class
a
Letter designation (insulation system
temperature °C)
A 105
E 120
B 130
F 155
H 180
N 200
R 220
a
Temperature classifications are given in IEC 60085.

5.3.2 Normal temperature-rise limits
The temperature rise of each winding of the transformer, designed for operation at normal
service conditions, shall not exceed the corresponding limit specified in Table 2 when tested in
accordance with 11.5.
The temperature of the core, metallic parts and adjacent materials shall not reach a value that
will cause damage to any part of the transformer.
In most of the gases, the temperature-rise limit of gas is higher than the temperature-rise limit
of winding, so that the temperature-rise limit of gas is not necessary to be specified. If
necessary, it is subjected to agreement between the supplier and the purchaser.
Table 2 – Winding temperature-rise limits
Thermal class Average winding temperature-rise
(insulation system temperature °C) limits K (see note)
105 60
120 75
130 80
155 100
180 125
200 135
220 150
NOTE Temperature-rise measured in accordance with 11.5.

5.3.3 Reduced temperature-rises for transformers designed for high cooling air
temperatures or special air cooling conditions
Reduced temperature-rises for transformers designed for high cooling air temperatures or
special air cooling conditions in IEC 60076-2 apply.
5.3.4 High altitude temperature-rise correction
Unless otherwise agreed between the supplier and the purchaser, for transformers designed
for operation at an altitude greater than 1 000 m but tested at normal altitudes, the limits of
temperature-rise given in Table 2 shall be reduced by the following amounts for each 500 m by
which the intended working altitude exceeds 1 000 m:

– 12 – IEC 60076-15:2015 © IEC 2015
– natural-air-cooled transformers: 2 %;
– forced-air-cooled transformers: 3 %.
A corresponding reverse correction may be applied in cases where the altitude of the factory is
above 1 000 m and the altitude of the installation site is below 1 000 m.
Any temperature-rise correction in dependence on altitude shall be rounded to the nearest
whole number of Kelvin.
The influence of differing ambient temperature or altitude on the air cooling of the tank is
disregarded for the water-cooled transformers.
5.3.5 Reduced temperature-rise for transformers designed for high cooling water
temperatures
Reduced temperature-rise for transformers designed for high cooling water temperatures in
IEC 60076-2 apply.
5.3.6 Temperature rise during specified load cycle
By agreement between manufacturer and purchaser, temperature rise limits can be guaranteed
and/or a special test regarding load cycle operation specified (see IEC 60076-7).
5.4 Insulation level
Insulation level described in IEC 60076-3 apply.
5.5 Load rejection on transformers directly connected to a generator
The requirements for transformer connected directly to generators described in IEC 60076-1
apply.
5.6 Rated voltage and rated frequency
Rated voltage and rated frequency in IEC 60076-1 apply.
5.7 Provision for unusual service conditions
Any service conditions not covered by the normal service conditions shall be identified by the
purchaser as described in IEC 60076-1.
and dielectric tests levels
5.8 Highest voltage for equipment U
m
Highest voltage for equipment U and dielectric tests levels in IEC 60076-1 apply.
m
5.9 Additional information required for enquiry
Additional information required for enquiry that is described in IEC 60076-1 apply.
5.10 Components and materials
All components and materials used in the construction of the transformer shall comply with the
requirements of the relevant IEC standards where they exist unless otherwise agreed or
specified. In particular bushings shall comply with IEC 60137 and tap-changers shall comply
with IEC 60214-1. Insulating gas shall comply with IEC 60376 and 60480 for new and used SF
or as agreed for other gases.
5.11 Requirements for gases and gas tightness
5.11.1 Requirements for gases
The manufacturer shall specify the type and the required quantity, quality and density of the
gas to be used in a gas-filled power transformer.
The maximum allowable moisture content within gas-filled power transformer filled with gas at
rated gas pressure shall be such that the dew-point is not higher than –20 °C for a
measurement at 20 °C. Adequate correction shall be made for measurement made at other
temperatures.
NOTE 1 A dew point of –5 °C for measurement at 20 °C is acceptable for the gas-filled compartments other than
main tank.
NOTE 2 The requirement level for the purity of SF before filling transformers is equal and more than 97 %.
NOTE 3 For the measurement and determination of the dew point, see IEC 60376 and IEC 60480.
5.11.2 Gas tightness
IEC 62271-1 gives general rules to the gas tightness of high-voltage switchgears. This rule can
be applicable to the gas-filled power transformers.
The tightness characteristic shall be consistent with a minimum maintenance and inspection
philosophy. The tightness for gas is specified by the relative leakage rate F .
rel
For SF -filled transformers, the relative leakage rate of SF shall not exceed 0,5 percent per
6 6
year. For transformers filled with the mixture, consisting of SF and other gases, the relative
leakage rate of the mixture shall not exceed 0,5 % per year.
6 Requirements for transformers having a tapped winding
Requirements for transformers having a tapped winding in IEC 60076-1 apply.
7 Connection phase displacement symbols
Connection phase displacement symbols in IEC 60076-1 apply.
8 Rating plates
8.1 General
The transformer shall be provided with a rating plate of weatherproof material, fitted in a visible
position, showing the appropriate items indicated below. The entries on the plate shall be
indelibly marked.
8.2 Information to be given in all cases
The information listed below shall be included on the rating plate in all cases.
a) Kind of gas-filled power transformer (for example gas-filled power transformer, gas-filled
auto-transformer, gas-filled series transformer, etc.).
b) Number of this standard.
c) Manufacturer's name, country and town where the transformer was assembled.
d) Manufacturer's serial number.
e) Year of manufacture.
– 14 – IEC 60076-15:2015 © IEC 2015
f) Number of phases.
g) Rated power (in kVA or MVA). (For multi-winding transformers, the rated power of each
winding shall be given. The loading combinations shall also be indicated unless the rated
power of one of the windings is the sum of the rated powers of the other windings.)
h) Rated frequency (in Hz).
i) Rated voltages (in V or kV) and tapping range.
j) Rated currents (in A or kA).
k) Connection and phase displacement symbol.
l) Short-circuit impedance, measured value in percentage. For multi-winding transformers,
several impedances for different two-winding combinations are to be given with the
respective reference power values. For transformers having a tapped winding, see also 5.5
and item b) of 8.3 in IEC 60076-1:2011.
m) Type of cooling. (If the transformer has several assigned cooling methods, the respective
power values may be expressed as percentages of rated power, for example GNAN/GNAF
30/100 %.)
n) Total mass.
o) Mass and type of insulating gas with reference to the relevant IEC standard.
p) Maximum system short-circuit power or current used to determine the transformer withstand
capability if not infinite.
q) Insulation system temperature for each winding (for multi-winding transformers, the
insulation system temperature of each winding should be given).
r) Rated gas pressure (in MPa-gauge.)
s) Guaranteed minimum gas pressure (in MPa-gauge).
If the transformer has more than one set of ratings, depending upon different connections of
windings which have been specifically allowed for in the design, the additional ratings shall all
be given on the rating plate, or separate rating plates shall be fitted for each set.
8.3 Additional information to be given when applicable
The information listed below shall be included on the rating plate when it is applicable to a
particular transformer.
a) For transformers having one or more windings with 'highest voltage for equipment' U
m
equal to or above 3,6 kV:
– short notation of insulation levels (withstand voltages) as described in IEC 60076-3.
b) Tapping designations
– For transformers with highest rated voltage less than or equal to 72,5 kV and with rated
power less than or equal to 20 MVA (three phase) or 6,7 MVA (single phase) having a
tapping range not exceeding ±5 %, tapping voltages on the tapped winding for all
tappings.
– For all other transformers
• a table stating tapping voltage and maximum allowable tapping service voltage,
tapping current, tapping power, and internal connection for all tappings,
• a table showing the
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