IEC TR 60076-26:2020

IEC TR 60076-26 ®
Edition 1.0 2020-03
TECHNICAL
REPORT
colour
inside
Power transformers –
Part 26: Functional requirements of insulating liquids for use in power
transformers
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IEC TR 60076-26 ®
Edition 1.0 2020-03
TECHNICAL
REPORT
colour
inside
Power transformers –
Part 26: Functional requirements of insulating liquids for use in power

transformers
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.180 ISBN 978-2-8322-8016-4

– 2 – IEC TR 60076-26:2020 © IEC 2020
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 6
4 Explanation of entries used for the categorization . 7
5 Maintenance . 8
6 Categorized functional requirements of insulating liquids . 9
6.1 General (physical / chemical) . 9
6.2 Dielectric / insulation . 10
6.3 Thermal / cooling . 11
6.4 Ageing and stability . 12
6.5 Liquid-solid system . 13
6.6 Material compatibility . 14

Table 1 – General (physical / chemical) . 9
Table 2 – Dielectric / insulation . 10
Table 3 – Thermal / cooling . 11
Table 4 – Ageing and stability . 12
Table 5 – Liquid-solid system . 13
Table 6 – Material compatibility . 14

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER TRANSFORMERS –
Part 26: Functional requirements of insulating
liquids for use in power transformers

FOREWORD
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The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a Technical Report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC/TR 60076-26, which is a technical report, has been prepared by IEC technical
committee 14, Power transformers.
The text of this Technical Report is based on the following documents:
Draft TR Report on voting
14/1010/DTR 14/1018/RVDTR
Full information on the voting for the approval of this Technical Report can be found in the
report on voting indicated in the above table.

– 4 – IEC TR 60076-26:2020 © IEC 2020
This document 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 document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document 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.

INTRODUCTION
At the time of writing of this document, many new insulating liquids for power transformers are
being offered by various suppliers. The end users of insulating liquids in power transformers
assume that a particular liquid has been properly qualified to perform the functional
requirements as a coolant and an electrical insulating liquid without failure for the expected
lifetime of the specific device.
So far, there is no available IEC International Standard in the form of a roadmap that lays out
the many requirements of liquids for use in power transformers, reactors and other high voltage
equipment other than simply conforming to a liquid standard specification, as for example
IEC 60296, IEC 62770 or IEC 61099.
In this document, the functional requirements of an insulating liquid that are considered
necessary for use in a power transformer application, are assembled and listed in a structured
manner. Detailed technical information on the individual requirements and their validation is
purposely not given. This is because this document is intended to serve as a reference
document for the transformer industry, including liquid suppliers as well as relevant scientific
and technical bodies dealing with insulating liquids (materials).
Certain functional requirements of an insulating liquid are not independent from design aspects
and materials in contact with the liquid. For example, dielectric withstand capability/testing and
transformer systems ageing, widely require consideration of solid and liquid insulation materials
together as a system. For transformers with tap-changers, additional requirements not yet
included in standards are applicable.
To address this, a matrix of functional requirements, including their status of validation (testing)
has been developed and is presented in this document. It is recommended to consider the
requirements for any insulating liquid to be used in power transformers, including for example
reactors, HVDC transformers.
The individual requirements (parameters) in the matrix are given a relevance index as to their
importance for design and service. Furthermore, for each parameter the status of the method
is indicated as
– already existing as an IEC/ISO International Standard,
– existing as an IEC/ISO International Standard that requires updating / extension, or
– does not exist as an IEC/ISO International Standard, thus would require future development.
Some of the identified tests are only available as ASTM or IEEE standards. Such tests, as well
as missing tests, are recommended as future work items for the relevant CIGRE and IEC bodies.
The intention is for this document to be regularly updated based on results produced by the
previously mentioned bodies. This will ensure the availability of prevailing information on the
functional requirements of insulating liquids used in the transformer industry.

– 6 – IEC TR 60076-26:2020 © IEC 2020
POWER TRANSFORMERS –
Part 26: Functional requirements of insulating
liquids for use in power transformers

1 Scope
In this document, the functional requirements of insulating liquids that are considered necessary
for use in power transformers, including, for example, reactors and HVDC transformers, are
assembled and listed. A relevance index of importance for design and for service as well as the
status of validation is given for all individual requirements (parameters). All parameters are
assigned to one of the following categories:
– General (physical / chemical)
– Dielectric / Insulation
– Thermal / Cooling
– Ageing and Stability
– Liquid-solid system
– Material compatibility
The document is intended to serve as a general reference document for the transformer
industry, including liquid suppliers as well as relevant scientific and technical bodies dealing
with insulating liquids (materials).
2 Normative references
There are no normative refer
...