IEC 60076-16:2011

Power transformers - Part 16: Transformers for wind turbine applications

IEC 60076-16:2011 applies to dry-type and liquid-immersed transformers for rated power 100 kVA up to 10 000 kVA for wind turbine applications having a winding with highest voltage for equipment up to and including 36 kV and at least one winding operating at a voltage greater than 1,1 kV.

Transformateurs de puissance - Partie 16: Transformateurs pour applications éoliennes

La CEI 60076-11:2011 s'applique aux transformateurs de type sec et immergés dans un liquide, pour une puissance assignée comprise entre 100 kVA et 10 000 kVA, destinés à des applications éoliennes, ayant un enroulement avec une tension la plus élevée pour le matériel inférieure ou égale à 36 kV et au moins un enroulement fonctionnant à une tension supérieure à 1,1 kV.

General Information

• Status: Replaced
• Publication Date: 24-Aug-2011
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: TC 14 - Power transformers
• Drafting Committee: WG 31 - TC 14/WG 31
• Current Stage: DELPUB - Deleted Publication
• Completion Date: 02-Oct-2018

Relations

• Replaced By: IEC/IEEE 60076-16:2018 - Power transformers - Part 16: Transformers for wind turbine applications
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 60076-16


®


Edition 1.0 2011-08



INTERNATIONAL



STANDARD



NORME
INTERNATIONALE
colour
inside


Power transformers –
Part 16: Transformers for wind turbine applications

Transformateurs de puissance –
Partie 16: Transformateurs pour applications éoliennes



IEC 60076-16:2011

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IEC 60076-16


®


Edition 1.0 2011-08



INTERNATIONAL



STANDARD



NORME
INTERNATIONALE
colour
inside


Power transformers –
Part 16: Transformers for wind turbine applications

Transformateurs de puissance –
Partie 16: Transformateurs pour applications éoliennes


INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX W
ICS 29.180 ISBN 978-2-88912-670-5

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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– 2 – 60076-16 © IEC:2011


CONTENTS


FOREWORD . 4

INTRODUCTION . 6


1 Scope . 7

2 Normative references . 7

3 Terms and definitions . 8

4 Service conditions . 8

4.1 Normal service conditions . 8

4.2 Altitude . 8
4.3 Temperature of cooling air . 8
4.4 Content of harmonic currents in the transformer . 9
4.5 Wave-shape of supply voltage . 9
4.6 Transient over and under voltages . 9
4.7 Humidity and salinity . 10
4.8 Special electrical and environmental conditions around the transformer . 10
4.9 Level of vibration . 11
4.10 Provision for unusual service conditions for transformers for wind turbine
applications . 11
4.11 Transportation and storage conditions . 11
4.12 Corrosion protection . 11
5 Electrical characteristics . 11
5.1 Rated power . 11
5.2 Highest voltage for equipment . 11
5.3 Tappings . 12
5.4 Connection group . 12
5.5 Dimensioning of neutral terminal . 12
5.6 Short circuit impedance . 12
5.7 Insulation levels for high voltage and low voltage windings . 12
5.8 Temperature rise guaranteed at rated conditions . 12
5.9 Overload capability . 13
5.10 Inrush current . 13
5.11 Ability to withstand short circuit . 13
5.12 Operation with forced cooling . 13
6 Rating plate . 13

7 Tests . 13
7.1 List and classification of tests (routine, type and special tests) . 13
7.2 Routine tests . 13
7.3 Type tests . 14
7.4 Special tests . 14
7.4.1 General . 14
7.4.2 Chopped wave test . 14
7.4.3 Electrical resonance frequency test . 14
7.4.4 Climatic tests . 14
7.4.5 Environmental test E3 . 14
7.4.6 Fire behavior test . 15
Annex A (informative) Calculation method and tables . 16
Bibliography . 36

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60076-16 © IEC:2011 – 3 –




Figure A.1 – Heat dissipation in a natural ventilated room . 17


Figure A.2 – Schematic diagram of power frequency current injection apparatus . 30

Figure A.3 – Switched transformer winding voltage responses with capacitor injection . 31

Figure A.4 – HV Injection test figure . 32


Figure A.5 – Example of measurement device . 33



Table 1 – Insulation levels . 10


Table A.1 – Impact of harmonics content on liquid-immersed transformer losses . 23
Table A.2 – Impact of harmonics content on dry type transformers losses. 26
Table A.3 – Example of voltage harmonic order . 29

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INTERNATIONAL ELECTROTECHNICAL COMMISSION


____________




POWER TRANSFORMERS –



Part 16: Transformers for wind turbine applications





FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.

International Standard IEC 60076-16 has been prepared by IEC technical committee 14:
Power transformers.
The text of this standard is based on the following documents:
FDIS Report on voting
14/690/FDIS 14/698/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.

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60076-16 © IEC:2011 – 5 –


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.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.

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INTRODUCTION


This part of IEC 60076 is intended to specify the additional requirements for the transformers

for installation in wind turbine applications.


Wind turbines use generator step-up transformers to connect the turbines to a network. These

transformers can be installed in the nacelle or in the tower or outside close to the wind

turbine.


This standard covers transformers for wind turbine applications or wind farms where the

constraints on transformers exceed the requirement of the present IEC 60076 series. The

constraints are not often known or recognized by the transformer manufacturers, wind turbine
manufacturers and operators and as a result the level of reliability of these transformers can
be lower than those used for conventional applications.
The transformers for wind turbine applications are not included in the present list of
IEC 60076 standard series.
The purpose of this standard is help to obtain the same level of reliability as transformers for
more common applications.
This standard deals particularly with the effects of repeated high frequency transient over-
voltages, electrical, environmental, thermal, loading, installation and maintenance conditions
that are specific for wind turbines or wind farms.
On site measurements, investigations and observations in wind turbines have detected risks
for some different kind of installations:
– repeated high frequency transient over or under voltages in the range of kHz;
– over and under frequency due to turbine control;
– values of over voltage;
– over voltage or under voltage coming from LV side;
– high level of transient over voltages due to switching;
– presence of partial discharge around the transformer;
– harmonic contents current and voltage;
– overloading under ambient conditions;
– fast transient overload;
– clearances not in compliance with the minimum prescribed;

– installation conditions and connections;
– restricted conditions of cooling;
– water droplets;
– humidity levels that exceed the maximum permissible values;
– salt and dust pollution and extreme climatic conditions;
– high levels of vibration;
– mechanical stresses.
Therefore it is necessary to take into account in the design of the transformer the constraints
of this application, or to define some protective devices to protect the transformer. Additional
or improved routine, type or special tests for these transformers have to be specified to be in
compliance with the constraints on the network.

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60076-16 © IEC:2011 – 7 –


POWER TRANSFORMERS –



Part 16: Transformers for wind turbine applications








1 Scope


This part of IEC 60076 applies to dry-type and liquid-immersed transformers for rated power

100 kVA up to 10 000 kVA for wind turbine applications having a winding with highest voltage
for equipment up to and including 36 kV and at least one winding operating at a voltage
greater than 1,1 kV.
Transformers covered by this standard comply with the relevant requirements prescribed in
the IEC 60076 standards.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60076-1:2011, Power transformers – Part 1: General
IEC 60076-2:2011, Power transformers – Part 2: Temperature rise for liquid-immersed
transformers
IEC 60076-3:2000, Power transformers – Part 3: Insulation levels, dielectric tests and external
clearances in air
IEC 60076-5:2006, Power transformers – Part 5: Ability to withstand short circuit
IEC 60076-7:2005, Power transformers – Part 7: Loading guide for oil-immersed power
transformers
IEC 60076-8:1997, Power transformers – Application guide
IEC 60076-11:2004, Power transformers – Part 11: Dry-type transformers

IEC 60076-12:2008, Power transformers – Part 12: Loading guide for dry-type power
transformers
IEC 60076-13:2006, Power transformers – Part 13: Self-protected liquid-filled transformers
IEC 61100, Classification of insulating liquids according to fire-point and net calorific value
IEC 61378-1:2011, Converter transformers – Part 1: Transformers for industrial applications
IEC 61378-3:2006, Converter transformers – Part 3: Application guide
IEC 61400-1:2005, Wind turbines – Part 1: Design requirements

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ISO 12944 (all parts), Paints and varnishes – Corrosion protection of steel structures by

protective paint systems



3 Terms and definitions


For the purposes of this document, the following terms and definitions apply.


3.1

wind turbine transformer

generator step up transformer connecting the wind turbine to the power collection network of

the wind farm
3.2
tower
part of the supporting structure of wind turbine on top of which the nacelle with generator and
other equipments are located
3.3
nacelle
housing that contains the drive-train and other elements on top of a horizontal-axis wind
turbine tower
4 Service conditions
4.1 Normal service conditions
Unless otherwise stated in this standard, the service conditions in IEC 60076-11 and
IEC 60076-1 apply.
4.2 Altitude
IEC 60076 series applies.
4.3 Temperature of cooling air
The installation of transformers inside an enclosure without active cooling systems increases
the transformer temperature.
The purchaser shall specify the maximum cooling air temperatures if they are different from
those stated in IEC 60076-2.

The transformer shall be designed according to real ambient temperatures and installation
real conditions as described by the purchaser at enquiry stage.
Clause A.1 provides considerations for transformers installed in a naturally ventilated area
like at the rear of the nacelle or in a separate enclosure installed outside the tower and
equipped with air inlet and outlet.
In case of transformer installed in the tower or in an enclosure where natural ventilation is not
provided the formula in A.1 is not applicable. For transformers operating under these
conditions, the effects of air inlet and outlet, cooling conditions, efficiency of air cooling and
ventilation shall be considered.
The purchaser shall prescribe the air ambient temperature and air flow inside the tower at the
enquiry stage. If no temperature or air flow is specified, an internal ambient temperature
inside the tower of 10 K higher than external temperature shall be assumed and not limited air
circulation around the transformers.

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60076-16 © IEC:2011 – 9 –


The effect of external direct solar radiation is not taken into account at the design stage. This

can increase the temperature of transformers parts and therefore information should be given

by purchaser at enquiry time.


4.4 Content of harmonic currents in the transformer


At the enquiry stage the purchaser shall specify the magnitude and frequency of all harmonic

currents supplied to the transformer. The manufacturer shall take the losses caused by these

harmonic currents into account in the transformer design to prevent that the winding and
liquid temperature rises exceed the permissible limits.


A method to calculate the impact of the harmonic currents on the design of the transformer is
given in A.2.
The transformer shall be designed to take into account the increased rating required due to
the harmonic currents. The temperature rise test shall be carried out with the equivalent rated
power due to the harmonics defined in A.2. The result of the test shall be in compliance with
temperature limits guaranteed for the transformer and related to the transformer insulation
thermal class.
4.5 Wave-shape of supply voltage
U
Within the prescribed value of a transformer shall be capable of continuous service at full
m
load without damage under conditions of ‘overfluxing’ where the ratio of voltage over
frequency exceeds the corresponding ratio at rated voltage and rated frequency according to
IEC 60076-1.
The wind turbine manufacturer shall state at enquiry stage the maximum ratio between the
voltage and the frequency. The transformer manufacturer shall take into account this value in
the design of the transformer.
The purchaser shall specify in the inquiry the magnitude and frequency of any harmonic
voltages present in the supply. A method to calculate the impact of the voltage harmonics on
the design of the transformer is given in A.3.
4.6 Transient over and under voltages
The risk of failures of a wind turbine transformer is higher due to the fact of repeated transient
over and under voltages on each side on transformer.
Several solutions are available to increase the reliability of the transformer against these fast
transient interactions:
– to evaluate the insulation level of the transformer and if necessary apply one or more of
the following solutions. This can be done by modeling or measuring the system by high
frequency resonance analysis. The resonance frequency test is a special test. The test
method shall be agreed between manufacturer and purchaser. One method is described in
A.4;
– to install standard protection technique such as surge arresters (HV, LV), or RC circuit or
surge capacitor.
The choice of the lists 2 or 3 in Table 1 shall be the responsibility of the system engineer
based on specific insulation co-ordination (IEC 60071-1 and -2) and risk assessment.
The list 3 covers transformers with increased ability to withstand repeated transient over
voltages and increases the reliability of the transformer.

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Table 1 – Insulation levels


Highest voltage Rated short Rated lightning impulse

for equipment duration withstand voltage (peak
separated source value) in kV

U
(rms) kV
m
AC withstand

List 2 List 3
voltage (RMS) kV

≤ 1,1 3 - 20

3,6 10 40 50


7,2 20 60 75

12 28 75 95

17,5 38 95 125
24 50 125 150
36 70 170 200

High frequency steep surges can be generated by switching operation on LV or HV side.
These surges are transferred by cables to the terminals of the transformer. Transformers have
different values of resonance frequency. See A.4.
If the high frequency steep surges generated by switching operation on LV and HV side
coincide with the internal frequency of the winding, the result of these surges can resonate
with the winding internal frequencies and cause higher electric stresses than the dielectric
withstand strength of the windings
NOTE For U ≤ 1,1 kV a.c. withstand voltage should have higher value as 10 kV.
m
4.7 Humidity and salinity
An abnormal level of humidity and salinity can lead to failures of dry type transformers and
problems on open type bushings of liquid-immersed transformers or dry type transformers in
enclosures.
The standard pollution levels for open type bushing for liquid-immersed transformers are
defined in IEC 60815 series. There are also simulated rain tests defined in IEC 60137.
According to IEC 60076-11, the relative humidity in the test chamber shall be maintained
above 93 % for environmental class E2 transformers. Salinity shall be such as the
conductivity of the water in E2 test shall be in the range of 0,5 to1,5 S/m.
If a dry type transformer shall operate under more severe conditions than corresponding to

class E2 without a protective enclosure against humidity and salinity, the capability of the
transformer design shall be demonstrated by the test according to class E3 described in 7.4.5
in this standard.
IEC 61400-1 states that relative humidity up to 95 % shall be taken into account as a normal
environmental condition.
Higher values of humidity and salinity shall be given at enquiry stage.
4.8 Special electrical and environmental conditions around the transformer
IEC 60076-3 recommends general minimum clearances between transformer live parts and
conductive parts of the wind turbine.

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60076-16 © IEC:2011 – 11 –


Any part of the wind turbine made of insulation material becomes conductive when moistened

with rain water, salt water or other conductive liquids. Partial discharges in the surroundings

of the transformer can decrease the dielectric strength of the air.


Therefore the clearances between these wind turbine parts and the live parts of the

transformer shall not be less than the
...