IEC TS 63042-301:2026

IEC TS 63042-301 ®
Edition 2.0 2026-02
TECHNICAL
SPECIFICATION
UHV AC transmission systems -
Part 301: On-site acceptance tests
ICS 29.240.01  ISBN 978-2-8327-0978-8

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CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 General . 9
5 Power transformers . 9
5.1 General . 9
5.2 Leak testing with pressure (tightness test) . 10
5.3 Winding resistance measurement . 10
5.4 Ratio test . 10
5.5 Polarity check . 10
5.6 Insulation resistance test on each winding to earth and between windings
including bushings . 11
5.7 Dissipation factor (tan δ) and capacitance measurement on each winding to
earth and between windings . 11
5.8 Core and frame insulation check . 11
5.9 Tests on bushings . 11
5.9.1 Visual inspection . 11
5.9.2 Tan δ and capacitance measurement . 11
5.9.3 Tap withstand voltage . 11
5.10 Insulating oil tests . 11
5.11 Dissolved gas analysis (DGA) test . 12
5.12 Excitation current measurements at reduced voltage . 12
5.13 Frequency-response analysis (FRA) . 12
5.14 Short-circuit impedance measurement at reduced current . 12
5.15 Induced voltage tests with partial discharge measurement . 12
5.16 Applied voltage tests . 13
5.17 Measurement of short-circuit impedance and load loss (for an on-site
assembly transformer) . 13
5.18 Measurement of no-load loss and current (for an on-site assembly
transformer) . 13
6 Circuit-breakers (CB) . 13
6.1 General . 13
6.2 Dielectric test on main circuit . 14
6.3 Dielectric test on auxiliary circuit . 14
6.4 Measurement of the resistance of the main circuit . 14
6.5 Checks after installation including gas tightness tests, gas quality, insulation
resistance test . 14
6.5.1 General . 14
6.5.2 General checks . 14
6.5.3 Checks of electrical circuits . 14
6.5.4 Checks of the insulation and/or extinguishing fluid(s) . 15
6.5.5 Checks on operating fluid(s), where filled or added to on-site . 15
6.5.6 Site operations . 15
6.6 Mechanical test and measurement . 15
6.7 Test of accessories . 16
7 GIS and GIL . 16
7.1 General . 16
7.2 Dielectric tests on the main circuits . 17
7.3 Dielectric tests on auxiliary circuits . 17
7.4 Measurement of the resistance of the main circuit . 18
7.5 Gas tightness tests . 18
7.6 Checks and verifications . 18
7.7 Gas quality verifications . 18
8 Surge arresters . 19
8.1 General . 19
8.2 Insulation resistance test . 19
8.3 Insulation resistance test of the base insulator . 19
8.4 Leakage current test . 19
8.5 Checks and verifications . 19
8.6 Tests of accessories . 19
9 Voltage and current transformers . 20
9.1 Capacitive voltage transformers (CVTs) . 20
9.1.1 General . 20
9.1.2 Insulation resistance measurement of low voltage terminal to earth
terminal . 20
9.1.3 Capacitance and dissipation factor (tan δ) measurement . 20
9.1.4 Tightness of the liquid-filled capacitor voltage dividers . 20
9.1.5 Winding resistance measurement of electromagnetic units . 21
9.1.6 Insulation resistance measurement of each component of
electromagnetic units . 21
9.1.7 Connection check between components of electromagnetic units . 21
9.1.8 Tightness of electromagnetic units . 21
9.1.9 Accuracy check (determination of error). 21
9.1.10 Damper check . 22
9.2 Bushing-type current transformers (CT) . 22
9.2.1 General . 22
9.2.2 Insulation resistance test . 22
9.2.3 Resistance measurement . 22
9.2.4 Applied voltage test on secondary windings . 22
9.2.5 Determination of error and polarity check . 22
9.2.6 Excitation test . 22
10 Shunt reactors . 23
10.1 General . 23
10.2 Leak testing with pressure (tightness test) . 23
10.3 Winding resistance measurement . 23
10.4 Insulation resistance tests on each winding to earth and between windings
including bushings . 23
10.5 Dissipation factor (tan δ) and capacitance measurement on each winding to
earth and between windings . 24
10.6 Core and frame insulation check . 24
10.7 Tests on bushings . 24
10.7.1 Visual inspection . 24
10.7.2 Tan δ and capacitance measurement . 24
10.7.3 Tap withstand voltage . 24
10.8 Insulating oil tests . 24
10.9 DGA test . 24
10.10 Applied voltage tests . 24
11 Series compensators . 25
11.1 General . 25
11.2 Test on capacitors . 25
11.3 Tests on metal oxide varistors . 25
11.4 Tests on damping equipment . 26
11.5 Tests on spark gaps . 26
11.6 Tests on current transformers . 27
11.7 Tests on by-pass switches . 28
11.8 Tests on disconnectors . 29
11.9 Tests on insulators . 29
11.10 Tests on control and protection systems of series compensator . 29
12 Insulators . 30
12.1 General . 30
12.2 On-site acceptance tests of suspension insulators . 30
12.3 On-site acceptance tests of post insulators . 30
13 Air-insulated disconnectors and earthing switches . 30
13.1 Air-insulated disconnectors . 30
13.1.1 General . 30
13.1.2 Dielectric test on control and auxiliary circuits . 30
13.1.3 Measurement of the resistance of the main circuit . 31
13.1.4 Design and visual checks . 31
13.1.5 Mechanical test . 31
13.2 Air-insulated earthing switches . 31
13.2.1 General . 31
13.2.2 Design and visual checks . 31
13.2.3 Dielectric tests on control and auxiliary circuits . 31
13.2.4 Mechanical test . 31
14 High-speed earthing switches (HSES) . 31
14.1 General . 31
14.2 Dielectric test on main circuit . 31
14.3 Dielectric test on auxiliary circuit . 32
14.4 Measurement of the resistance of the main circuit . 32
14.5 Checks and verifications after installation including gas tightness tests, gas
quality, insulation resistance test . 32
14.6 Mechanical tests and measurements . 32
14.7 Tests of accessories . 32
14.8 CB and HSES operating sequence test . 32
15 Protection and control system . 32
15.1 General . 32
15.2 Visual inspection . 33
15.3 Wiring check . 33
15.4 Insulation test . 33
15.5 AC/DC power supply check . 33
15.6 Device current and voltage sampling test . 33
15.7 Binary input/output contact and signal check . 33
15.8 Protection function verification . 33
15.9 Control function verification . 33
15.10 Auxiliary relay test . 33
Bibliography . 34

Figure 1 – Delay time of opening resistor and pre-insertion time of closing resistor . 16

Table 1 – Requirements of insulating oil . 12
Table 2 – Tan δ (%) of bushings. 27
Table 3 – Limiting value of tan δ (%) . 28

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
UHV AC transmission systems -
Part 301: On-site acceptance tests

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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preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
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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
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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) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC takes no position concerning the evidence, validity or applicability of any claimed patent rights in
respect thereof. As of the date of publication of this document, IEC had not received notice of (a) patent(s), which
may be required to implement this document. However, implementers are cautioned that this may not represent
the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC TS 63042-301 has been prepared by IEC technical committee 122: UHV AC transmission
systems. It is a Technical Specification.
This second edition cancels and replaces the first edition published in 2018. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
a) new subclause with measurement of short-circuit impedance and load loss for on-site
assembly transformer has been added;
b) new subclause with measurement of no-load loss and current for on-site assembly
transformer has been added;
c) on-site acceptance test requirement for GIL has been added;
d) new clause with protection and control system on-site acceptance tests has been added.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
122/199/DTS 122/211/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.
A list of all parts in the IEC 63042 series, published under the general title UHV AC transmission
systems, can be found on the IEC website.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
– reconfirmed,
– withdrawn, or
– revised.
INTRODUCTION
With the increase in voltage levels, the reliability and safety of high-voltage electric equipment
is facing new challenges. There is a need to have consensus on a series of technical criteria
and requirements for on-site acceptance tests for electrical equipment of ultra-high voltage
(UHV) AC transmission systems exceeding 800 kV to detect the damages or abnormal
conditions that can occur during the transportation and installation processes and to determine
whether equipment can be put into operation reliably and safely for power systems.
This document proposes on-site acceptance tests, relevant test items, test methods, and
evaluation criteria for transformers, circuit-breakers, gas insulated switchgear (GIS) and gas
insulated transmission line (GIL), surge arresters, voltage and current transformers, shunt
reactors, series compensators, insulators, disconnectors, earthing switches and high-speed
earthing switches.
1 Scope
This part of IEC 63042, which is a technical specification, applies to on-site acceptance tests
of electrical equipment with the highest voltages of AC transmission system exceeding 800 kV
and its protection and control system.
The electrical equipment exceeding 800 kV includes the following items:
– power transformers;
– circuit-breakers (CBs);
– gas insulated switchgear (GIS);
– gas insulated transmission line (GIL);
– surge arresters;
– voltage and current transformers;
– shunt reactors;
– series compensators;
– insulators;
– disconnectors and earthing switches;
– high-speed earthing switches (HSES).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 60076-18, Power transformers – Part 18: Measurement of frequency response
IEC 60137:2017, Insulated bushings for alternating voltages above 1 000 V
IEC 60383-1:2023, Insulators for overhead lines with a nominal voltage above 1 000 V – Part 1:
Ceramic or glass insulator units for a.c. systems – Definitions, test methods and acceptance
criteria
IEC 60480, Specifications for the re-use of sulphur hexafluoride (SF ) and its mixtures in
electrical equipment
IEC 62271-1:2017, High-voltage switchgear and controlgear – Part 1: Common specifications
for alternating current switchgear and controlgear
IEC 62271-1:2017/AMD1:2021
IEC 62271-4, High-voltage switchgear and controlgear – Part 4: Handling procedures for gases
for insulation and/or switching
IEC 62271-100:2021, High-voltage switchgear and controlgear – Part 100: Alternating-current
circuit-breakers
IEC 62271-100:2021/AMD1:2024
IEC 62271-102:2018, High-voltage switchgear and controlgear – Part 102: Alternating current
disconnectors and earthing switches

IEC 62271-203:2022, High-voltage switchgear and controlgear – Part 203: AC gas-insulated
metal-enclosed switchgear for rated voltages above 52 kV

IEC 62271-204:2022, High-voltage switchgear and controlgear – Part 204: Rigid gas-insulated
transmission lines for rated voltage above 52 kV
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
– IEC Electropedia: available at http://www.electropedia.org/
– ISO Online browsing platform: available at http://www.iso.org/obp
3.1
on-site acceptance test
inspection and test performed (or checked) in order to verify the correct operation and dielectric
integrity of the equipment after shipping and on-site installation
3.2
UHV AC
ultra-high voltage alternating current
highest voltage of AC transmission system exceeding 800 kV
3.3
on-site assembly transformer
power transformer that is assembled at the installation site, including the assembly of the
windings and either a complete or partial assembly of the core
4 General
On-site acceptance tests for newly installed electrical equipment are an important approach to
judge whether equipment is normal or abnormal after transportation and installation. Repetition
of the full programme of routine tests already performed at the factory is not required; however,
some tests should be repeated to confirm the correct operation of the equipment, taking into
account the conditions after transportation and installation.
On-site acceptance test results should be analysed and compared carefully with those from the
factory test. The influence of different test conditions, such as humidity and the ambient
temperature and pressure, should be taken into consideration when making comparisons.
5 Power transformers
5.1 General
UHV power transformers have special characteristics of very high voltage level, large capacity
and large size. When the split-type installation is used on site, it is recommended to carry out
separate tests on the main transformer, and the voltage regulating and compensating
transformer respectively.
NOTE 1 For the procedure followed for on-site tests, the test method refers to the same kind of tests described in
relevant publications for factory tests, such as IEC 60076 and/or the IEC 60599 series.
UHV power transformers should be subjected to on-site acceptance tests as specified below:
– leak testing with pressure (tightness test);
– winding resistance measurement;
– ratio test;
– polarity check;
– insulation resistance test on each winding to earth and between windings including bushings;
– dissipation factor (tan δ) and capacitance measurement on each winding to earth and
between windings including bushings;
– core and frame insulation check;
– tests on bushings;
– insulating oil test;
– dissolved gas analysis (DGA) test;
– excitation current measurement at low voltage;
– frequency-response analysis (FRA);
– short-circuit impedance measurement.
The following items are optional:
– induced voltage test with partial discharge measurement;
– applied voltage test;
– measurement of short-circuit impedance and load loss (on-site assembly transformer);
– measurement of no-load loss and current (on-site assembly transformer).
NOTE 2 The above optional test items are based on agreement between supplier and purchaser.
5.2 Leak testing with pressure (tightness test)
The transformer main tank should withstand a pressure of 30 kPa, or any specified value,
applied on the top-level of oil in the oil conservator and maintained for 24 h or any specified
period without any leakage and damage.
5.3 Winding resistance measurement
Winding resistance measurement tests should include the following:
– measurement should be performed for all windings at all tap positions (if any);
– measured values should be compared with the factory test results. The deviation should be
within ± 5 % or otherwise specified;
– measured values should be compared with the average value of three phase windings. The
deviation should be within ± 3 % or otherwise specified.
5.4 Ratio test
Ratio tests should include the following:
– the voltage ratio should be measured on each tap;
– voltage ratio should correspond to the value on nameplate and the factory test result.
5.5 Polarity check
The polarity of single-phase transformers should be checked. The polarity should be the same
as that identified on the nameplate.
5.6 Insulation resistance test on each winding to earth and between windings
including bushings
Insulation resistance tests should be conducted for each winding with respect to earth and
between windings.
5.7 Dissipation factor (tan δ) and capacitance measurement on each winding to earth
and between windings
Dissipation factor (tan δ) and capacitance measurement on each winding to earth and between
windings should include the following:
– terminals to be tested should be connected to the test instrument and the terminals not
being tested should be short-circuited and connected to earth. Test voltage should be 10 kV
or agreement between supplier and purchaser;
– tan δ measurement results should be compared with the factory test result considering the
temperature difference and the difference should be within ± 0,001 or otherwise specified.
The difference of the capacitance value should be within ± 1 % of the factory test result or
otherwise specified.
5.8 Core and frame insulation check
Insulation resistance check should be conducted between core to frame, core to tank and frame
to tank. For details see IEC 60076-1.
5.9 Tests on bushings
5.9.1 Visual inspection
Visual inspections should be conducted on each bushing. Visual inspections shall be in
accordance with IEC 60137:2017, 9.11.
5.9.2 Tan δ and capacitance measurement
– The measurement is only applicable to capacitance-graded bushings. After installation of
the transformer and reactor bushings, tan δ and capacitance of the insulation should be
measured. The test voltage should be 10 kV or as agreed between supplier and purchaser.
Voltage tap (if any) should be short-circuited with the test tap.
– The deviation between measured capacitance value and factory test value should be lower
than ± 1 %, depending on the number of layers up to 5 % or agreement between supplier
and purchaser.
For details, see IEC 60137:2017, 9.2.
5.9.3 Tap withstand voltage
A rated frequency voltage withstand test should be applied to or induced at the tap for 1 min
with the bushing mounting flange earthed. The voltage tap should be tested at 20 kV or
agreement between purchaser and supplier. The test tap should be tested at 2 kV or agreement
between purchaser and supplier.
For voltage tap, different suppliers can give different suggested value of test voltage. It is
advised to refer to the product specification or consult the supplier before testing.
5.10 Insulating oil tests
The test requirements of insulating oil filling into electrical equipment should be as per Table 1
or agreement between purchaser and supplier.
Table 1 – Requirements of insulating oil
No. Item Requirements
1 Visual examination Transparent, inclusion-free, no suspended matter
2 Particle count in oil Granularity (5 µm ~ 100 µm): ≤ 1 000/100 mL
Granularity (> 100 µm): None
3 Dielectric strength (kV) ≥ 70 (2.5 mm gap, spherical electrode)
4 Dissipation factor (90 °C) % After filling into equipment ≤ 0,7
5 Water content mg/ kg (50 °C) ≤ 10 after filling
6 Total dissolved gas ≤ 0,5
(volume fraction) %
7 DGA Refer to relevant clauses of this document
NOTE For details see IEC 60422 and IEC 60296.

5.11 Dissolved gas analysis (DGA) test
The DGA test should be carried out after the completion of oil treatment. If a dielectric test, load
loss or no-load loss test is required, the DGA test should be carried out after the test. For details,
see IEC 60599.
5.12 Excitation current measurements at reduced voltage
Excitation current measurements at low voltage should include the following:
– the excitation current should be measured at the same low test voltage as the factory test.
The test should be carried out before the winding resistance measurement to avoid the
influence of residual flux in the core;
– the value of excitation current at low test voltage should be compared with the factory test
results. The difference should be less than 30 % or agreement between supplier and
purchaser.
NOTE If a higher excitation current is needed a higher voltage could be applied.
5.13 Frequency-response analysis (FRA)
The FRA should be performed for each winding of transformers. Test requirements shall be in
accordance with IEC 60076-18.
5.14 Short-circuit impedance measurement at reduced current
A short-circuit impedance measurement at reduced current should include the following:
– the short-circuit impedance should be measured at the same reduced current as in the
factory test;
– the value of short-circuit impedance at reduced current should be compared with the factory
test result. The difference should be less than ±5 % or agreement between supplier and
purchaser.
As an option, if supplier and purchaser agree, 5.15, 5.16, 5.17 or 5.18 may be applicable.
5.15 Induced voltage tests with partial discharge measurement
The induced voltage test may be conducted on-site. For details see IEC 60076-3. The test
voltage, value of the accepted partial discharge may be agreed between supplier and purchaser.
5.16 Applied voltage tests
The applied voltage test may be conducted on-site. For details see IEC 60076-3. The applied
voltage test may include the following:
– apply the test voltage across all terminals of the winding being tested and all terminals of
the remaining windings, core, frame and tank of the transformer, connected together to
earth;
– test voltage may be 80 % of the factory test value and the time duration may be 1 min, or in
accordance with the agreement between purchaser and supplier;
– the test voltage may be as nearly as possible to a sine-wave form. The peak value divided
by √2 may be equal to the test value;
– the test is successful if no collapse of the test voltage occurs.
5.17 Measurement of short-circuit impedance and load loss (for an on-site assembly
transformer)
The test should be performed for on-site assembly UHV transformers. For details, see
IEC 60076-1. Measurement of short-circuit impedance and load loss should include the
following:
– the supplied current should be equal to the relevant rated current but shall not be less than
50 % thereof or as agreed between supplier and purchaser;
– the value of short-circuit impedance and load loss should be compared with the factory test
result. The difference should be less than ±2 % of the factory test result or as agreed
between supplier and purchaser.
5.18 Measurement of no-load loss and current (for an on-site assembly transformer)
The test should be performed for on-site assembly UHV transformers. For details, see
IEC 60076-1. Measurement of no-load loss and current should include the following:
– the no-load loss and current should be measured at rated voltage;
– the value of no-load loss should be compared with the factory test result. The difference
should be less than ±3 % of the factory test result or as agreed between supplier and
purchaser;
– the value of no-load current should be compared with the factory test result. The difference
should be agreed between supplier and purchaser.
6 Circuit-breakers (CB)
6.1 General
After installation, and before being put into service, the circuit-breaker (CB) should be tested in
order to check the correct operation and the dielectric integrity of the equipment.
A programme of site commissioning checks and tests should be agreed between supplier and
purchaser. Full repetition of routine tests, already conducted in the factory, is not mandatory.
However some of the tests should be repeated for confirmation of
– absence of damage;
– compatibility of separate units;
– correct assembly;
– correct performance of the assembled circuit-breaker.
In general, this is achieved when the commissioning tests include, but are not limited to the
following test program with a record of the test results in a test report:
– dielectric test on main circuit;
– dielectric test on auxiliary circuit;
– measurement of the resistance of the main circuit;
– checks after installation, including gas tightness test, gas quality, insulation resistance test;
– mechanical test and measurement;
– test of accessories.
The supplier and purchaser should agree on a commissioning test plan for tests on site.
6.2 Dielectric test on main circuit
For dielectric tests on the main circuit of circuit-breaker, the power frequency voltage test should
be performed and the test voltage and procedure on main circuit for circuit-breaker are the
same as that for the metal-enclosed switchgear and controlgear. See 7.2.
6.3 Dielectric test on auxiliary circuit
Dielectric tests on auxiliary circuits should be performed to verify that circuit-breakers have not
been damaged during transport and storage. However, it is recognized that such circuits contain
vulnerable sub-components and the application of the full testing voltage for the full duration
can cause damage. In order to avoid this, and to avoid the temporary removal of proven
connections, the supplier should detail the test process that demonstrates that damage has not
occurred as well as the method of recording the results from this test process.
For details, see also IEC 62271-100:2021, 11.3.102.3.1.
6.4 Measurement of the resistance of the main circuit
Measurement of the resistance of the main circuit need only be conducted if interrupting units
have been assembled on site. The measurement shall be conducted with a direct current in
accordance with IEC 62271-100:2021, 11.3.102.3.2.
Dynamic resistance measurements (DRM) could be carried out as an additional tool for the
assessment of the condition of the circuit-breaker during its lifetime.
6.5 Checks after installation including gas tightness tests, gas quality, insulation
resistance test
6.5.1 General
The supplier should produce a programme of commissioning checks and tests. This should be
based on, but is not limited to, the programme of checks and tests given in this document.
6.5.2 General check
...