IEC TS 63042-401:2026

IEC TS 63042-401 ®
Edition 1.0 2026-01
TECHNICAL
SPECIFICATION
UHV AC transmission systems -
Part 401: Substation maintenance
ICS 29.240.01; 29.240.10 ISBN 978-2-8327-0954-2

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CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Considerations for maintenance oriented to UHV AC transmission systems . 8
4.1 General . 8
4.2 Maintenance needs for substation design . 8
4.3 Spare parts . 9
4.4 Tools . 9
4.5 Maintenance plan . 10
4.6 Failure and operation database . 10
4.7 Resiliency against natural disasters . 11
4.8 Standardization of equipment dimensions and specifications . 11
4.9 Other . 11
5 Substation maintenance . 11
5.1 General . 11
5.2 Power transformers . 12
5.3 CBs . 14
5.4 GIS and GIL . 15
5.5 Surge arresters . 15
5.6 Voltage and current transformers . 16
5.7 Shunt reactors . 17
5.8 Series compensators . 18
5.9 Insulators . 19
5.10 Air-insulated disconnectors and earthing switches. 19
5.11 HSESs . 20
5.12 Protection and control system . 22
Annex A (informative) Maintenance experiences in China . 24
A.1 Maintenance experience at the substation design stage. 24
A.2 Maintenance experience of UHV substation . 25
A.2.1 General . 25
A.2.2 Maintenance experience of UHV transformers . 25
A.2.3 Maintenance experience of switch equipment . 28
Annex B (informative) Maintenance experiences in Japan. 31
B.1 Examples of maintenance optimisation based on results of UHV test
equipment . 31
B.1.1 General . 31
B.1.2 Rare-frequency characteristics of CBs . 32
B.1.3 HSES-CB operation coordination test . 33
B.1.4 Ease of maintenance verification . 34
B.1.5 Advancement of design and maintenance technology for static electrification
in transformers . 35
B.2 Reducing outage time through layout design of entire substations . 35
B.2.1 Gas-insulated busbar (GIB) cross-retracting and flat placement. 35
B.2.2 Considerations for the arrangement of GIS detachable devices . 36
Annex C (informative) Maintenance experiences in India . 38
C.1 Maintenance experience in India . 38
C.2 Modification in 1 200 kV bushing type from oil impregnated paper bushings
(OIP) to resin impregnated paper bushings (RIP) . 41
C.3 Validation of electric and magnetic field in 1 200 kV National Test Station,
Bina . 41
Bibliography . 45

Figure 1 – Example of standardization of dimension of GIS bushing . 11
Figure A.1 – Operation space of UHV shunt reactor . 24
Figure A.2 – Example of 1 000 kV transformer arrangement. 25
Figure B.1 – Overview of verification contributing to optimisation of maintenance at the
UHV equipment test site . 32
Figure B.2 – Opening time characteristic of 1 000 kV CB . 33
Figure B.3 – Oscilloscope waveform example of HSES operation coordination test
results . 34
Figure B.4 – Example of 1 000 kV substation arrangement . 36
Figure B.5 – Bus-tie system applied to 1 000 kV substations (double busbar with 4
bus-coupler) . 36
Figure B.6 – Locations of detachable devices . 37
Figure C.1 – Layout of 1 200 kV National Test Station Bina . 43

Table 1 – Examples of tools for maintenance of an UHV substation . 9
Table 2 – Major equipment in the UHV substation . 12
Table 3 – Maintenance items of UHV power transformers . 12
Table 4 – Maintenance items of CBs . 14
Table 5 – Maintenance items of GIS and GIL . 15
Table 6 – Maintenance items of surge arresters . 16
Table 7 – Maintenance items of CVTs. 16
Table 8 – Maintenance items of bushing-type current transformers . 17
Table 9 – Maintenance items of shunt reactors . 17
Table 10 – Maintenance items of series compensators . 19
Table 11 – Maintenance items of insulators . 19
Table 12 – Maintenance items of air-insulated disconnectors and earthing switches . 20
Table 13 – Maintenance items of HSESs . 21
Table 14 – Maintenance items of protection and control system . 22
Table A.1 – Preventive tests of main transformer . 26
Table A.2 – Preventive tests of voltage regulating and compensation transformer . 27
Table A.3 – Preventive tests of whole transformer . 28
Table A.4 – Preventive tests of GIS (mixed technology switchgear) . 28
Table A.5 – Preventive tests of disconnector . 30
Table B.1 – HSES operation coordination test results . 33
Table B.2 – Workability test result of disassembly and reassembly of CB . 34
Table B.3 – Workability test result of disassembly and reassembly of HSES . 35
Table B.4 – Arrangement of detachable devices . 37
Table C.1 – Maintenance schedule for 1 200 kV transformers . 38
Table C.2 – Maintenance schedule for 1 200 kV circuit breakers . 39
Table C.3 – Maintenance schedule for 1 200 kV CVTs . 40
Table C.4 – Maintenance schedule for 1 200 kV Disconnectors . 40
Table C.5 – Surge arresters. 41
Table C.6 – Occupational and public exposure limits . 42

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
UHV AC transmission systems -
Part 401: Substation maintenance

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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
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shall not be held responsible for identifying any or all such patent rights.
IEC TS 63042-401 has been prepared by IEC technical committee 122: UHV AC transmission
systems. It is a Technical Specification.
The text of this Technical Specification is based on the following documents:
Draft Report on voting
122/201/DTS 122/210/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
A UHV AC transmission system features large capacity and high voltage, which necessitates
high level requirements for reliability and safety of its equipment, transmission lines, protection
and control system. In order to obtain the operation condition and maintain the transmission
system soundness during its service life, necessary maintenance is required. Until now, several
UHV AC test bases and transmission projects have been constructed in several countries.
Maintenance for UHV AC equipment, transmission lines, and the control and protection system
is needed.
This document provides guidance for UHV AC substation maintenance considering system-
oriented maintenance issues of UHV AC transmission systems.

1 Scope
This part of IEC 63042, which is a Technical Specification, gives guidance on UHV AC
substation maintenance considering system-oriented maintenance issues of UHV AC
transmission systems.
It is based on the development and on-site practice of maintenance technology involved in UHV
AC transmission systems. It applies to power system planners, equipment suppliers,
engineering contractors, maintenance staff and power grid operators.
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 60422:2024, Mineral insulating oils in electrical equipment - Supervision and maintenance
guidance
IEC 60599, Mineral oil-filled electrical equipment in service – Guidance on the interpretation of
dissolved and free gases analysis
IEC TS 63042-301, UHV AC transmission systems – Part 301: On-site acceptance tests
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
maintenance
combination of all technical and management actions intended to retain an item in, or restore it
to, a state in which it can perform as required
Note 1 to entry: Maintenance includes maintenance test, diagnostic test, repair and overhaul to establish the
soundness of equipment or system during its service life.
Note 2 to entry: The term “item” means equipment and system.
[SOURCE: IEC 60050-192:2015, 192-06-01, modified – Note 1 to entry has been replaced with
a new note, and Note 2 has been added.]
3.2
maintenance test
test carried out periodically on an item to verify that its performance remains within specified
limits
Note 1 to entry: Maintenance test includes examination and periodical inspection.
[SOURCE: IEC 60050-151:2001, 151-16-25, modified – The wording “after having made certain
adjustments, if necessary” has been deleted from the definition, and Note 1 to entry has been
added.]
3.3
diagnostic test
test carried out in order to make a diagnosis for equipment conditions
[SOURCE: IEC 60050-192:2015, 192-09-21, modified – The wording “for equipment conditions”
has been added to the definition.]
3.4
overhaul
action to restore to a fully serviceable condition equipment that has been in use, out of use or
in storage for a period of time
[SOURCE: IEC 60050-426:2020, 426-15-17, modified – The wording “out of use” has been
added to the definition and “but which is not faulty” has been omitted.]
4 Considerations for maintenance oriented to UHV AC transmission systems
4.1 General
The maintenance oriented to UHV AC transmission systems should be considered for UHV AC
substations. The factors to be considered for maintenance should follow the recommendations
of power system planners, equipment suppliers, engineering contractors, maintenance staff and
power grid operators. National regulations can also apply.
The impact of planned or faulty power outages on a UHV system which features large capacity
and high voltage is greater than those for lower voltage systems. UHV systems requires higher
reliability and availability. The maintenance policy for UHV substations must meet the reliability
requirements of the UHV AC transmission system.
Considering the reliability of the UHV AC transmission system, it is necessary to carry out a
wide range of studies, mainly from the point of view of reducing outage times. The following are
examples:
– layout design of the entire substation;
– methods of stocking spare parts;
– planning of equipment and facilities for installation and maintenance used in substation;
– periodic reviews and preliminary studies of transportation routes and methods for large
equipment to and from the site in the event of failure or natural disasters such as floods and
earthquakes.
4.2 Maintenance needs for substation design
The maintenance needs should be considered in the design of the substation, generally
including the following:
a) adequate working space of the staff and the enough safe distance from the adjacent live
part during any maintenance work;
b) transportation route and facilities, including overhaul and installation;
c) space for equipment disassembly and assembly;
d) security and protection system, e.g. firefighting, intelligence patrol, monitoring, etc.;
e) living facilities for staff, such as rest room, water supply, air conditioner, etc.;
f) spare parts warehouse and maintenance room (if required);
g) auxiliary power supply system.
4.3 Spare parts
The recommendations for substation spare parts should be determined at the design stage.
Generally, the spare parts scheme is recommended according to the experience of the
equipment supplier. Users and owners can select and evaluate their spare parts
recommendations according to reliability requirements. When determining the demand for spare
parts, the following should be considered:
a) replacement of spare parts and maintenance working time of different equipment;
b) lead time for manufacturing and transportation of equipment;
c) distance between adjacent UHV substations and transportation conditions;
d) grid scale and preparation scale at different grid construction stages.
An example of spare parts configuration for a substation is listed below. Users may clearly
specify the requirements for specific project equipment suppliers.
1) spare parts of UHV transformer;
2) spare parts of UHV shunt reactor;
3) UHV bushing;
4) UHV capacitive voltage transformers (CVTs);
5) UHV surge arrester;
6) capacitors;
7) switchgear component;
8) printed circuit boards used by the control and protection system.
4.4 Tools
The tools that may be used for maintenance of an UHV substation are listed in Table 1.
Table 1 – Examples of tools for maintenance of an UHV substation
Equipment Purpose Name
Telescopic boom truck crane
Operating vehicles
Electric counter-balanced truck
Insulation test set
Test apparatus
General DC resistance tester
Infrared camera
Special tools Ultraviolet imaging meter
Ultrasonic partial discharge tester
Operating vehicles Cart to move the transformer / shunt reactor
Transformer oil dissolved gas analyser
Partial discharge meter
Frequency response analyzer
Test apparatus Transformation ratio tester
Capacitance and tan delta tester
Power transformer / Shunt
reactor
Oil breakdown voltage tester
Oil moisture tester
Oil filter
Dry air generator
Special tools
Transformer bushing lifting tools
Jacking bracket
Equipment Purpose Name
Endoscope
Sulphur Hexafluoride (SF6) decomposition
analyser
SF leakage detector
Test apparatus
SF moisture meter
Gas insulated switchgears
(GIS)
Timing tester
UHF PD detector
Endoscope
Special tools
SF gas recovery unit
Voltage transformer and
Test apparatus Transformer calibrator
current transformer
Operating vehicles Lifting platform of capacitor tower
Series compensators Capacitive bridge
Test apparatus
Inductance measuring device
Insulators Test apparatus Insulator flaw detection device
Test apparatus Protection relay test device
Protection and control
system
Special tools Input/output board program download tools

4.5 Maintenance plan
When preparing a maintenance plan, the following should be considered:
a) condition of maintenance object;
b) power outage area and load dropout during maintenance;
c) neighbouring equipment which needs to be powered off together for safety reasons in
substations;
d) working time of maintenance objects, difference in working conditions between factory and
substation because of the size and working space of equipment and related system;
e) for some tests, the time of skill training should be considered;
f) on-site operation conditions, environment and other danger risk factors;
g) for outage equipment, safety measures such as power cut, earthing, voltage detecting,
installing barriers and signboards should be taken;
h) when the equipment is not powered off, the distance between the staff on the site and the
live parts should meet the safety-distance criteria;
i) some maintenance tasks require authorization. Maintenance staff require corresponding
competence, skills, experience, and special training if necessary.
4.6 Failure and operation database
UHV AC transmission systems may use technologies that are not commonly used in lower
voltage systems. Therefore, an operation and maintenance database should be established in
advance on failures and phenomena specific to UHV AC transmission systems and their
equipment, and how to deal with them so that information can be shared in order to support
maintenance planning.
For matters specific to UHV power systems and UHV transmission and substation equipment,
suppliers should provide the basic information, operating and maintenance manual, drawings,
fault analysis and troubleshooting.
Utilities should keep records of past operation and maintenance of the equipment, tracking and
recording of abnormal events, and relevant reports, disposal methods and results of defects or
failures.
Users should feedback to manufacturers about failure, repair and maintenance equipment
information.
4.7 Resiliency against natural disasters
Floods, earthquakes and other natural disasters should be studied periodically to predict
immediate maintenance activities.
4.8 Standardization of equipment dimensions and specifications
Standardization of equipment dimensions and specifications should be considered in order to
more effectively replace faulty equipment or components. Figure 1 shows an example of
standardization dimensions of GIS bushing.

Figure 1 – Example of standardization of dimension of GIS bushing
4.9 Other
Regular inspection of equipment transportation routes should be considered.
5 Substation maintenance
5.1 General
Maintenance of UHV AC electrical equipment is performed in four ways: maintenance tests,
diagnostic tests, repair and overhaul. The major equipment in the UHV substation is listed in
Table 2.
The effectiveness of maintenance mainly depends on the way instructions are prepared by the
manufacturer and implemented by the user.
Maintenance of UHV AC electrical equipment is performed periodically. The interval between
maintenance depends on the instructions prepared by the manufacturer and implemented by
the user. The equipment manager may extend or shorten the cycle according to the equipment
status and regional environment, or specify different cycles for similar equipment according to
the actual difference of equipment status.
To evaluate the soundness of UHV equipment during operation, monitoring methods and
intelligent inspection measures are recommended. Online monitoring devices should be
inspected and the data should be analysed to assess equipment performance.
To diagnose equipment defects during power outages, some special diagnostic tests are
conducted on-site if necessary.
See Annex A, Annex B and Annex C for maintenance experiences in China, Japan and India.
Table 2 – Major equipment in the UHV substation
No. Major equipment in the UHV substation
1 Power transformers
2 Circuit-breakers (CBs)
3 GIS and gas insulated transmission lines (GIL)
4 Surge arresters
5 Voltage and current transformers
6 Shunt reactors
7 Series compensators
8 Insulators
9 Air-insulated disconnectors and earthing switches
10 High-speed earthing switches (HSESs)
11 Protection and control system

5.2 Power transformers
Maintenance items of UHV power transformers in general are listed in Table 3. For maintenance
test and diagnostic test, the test method shall refer to the same kind of tests described in
IEC TS 63042-301, IEC 60076-18, IEC 60599 and IEC 60422.
Table 3 – Maintenance items of UHV power transformers
No. Category Item Recommendations
The silica-gel breather, the oil level
indicators, the gas relays, the control
1 Visual inspection
cabinet, and other auxiliary devices of
transformer should be in good condition.
2 Infrared detection The equipment should not overheat.
Test should meet the agreement
3 Oil temperature
between supplier and user.
Maintenance test
The oil level should match the oil
4 Oil level
temperature
Online monitoring data of dissolved Test should meet the agreement
gas analysis (DGA) between supplier and user.
Test should meet the agreement
6 Monitoring data of partial discharge
between supplier and user.
No. Category Item Recommendations
Test should be in accordance with
7 DGA test
IEC 60599.
Test should be in accordance with
8 Insulating oil tests IEC 60422:2024, Clause 7, or meet the
agreement between supplier and user.
Check of core and frame earthing Test should meet the agreement
current between supplier and user.
Test requirements should be in
accordance with IEC 60076-1:2011,
10 Winding resistance measurement 11.2, and IEC TS 63042-301:2018, 5.3,
or meet the agreement between supplier
and user.
Test should be in accordance with
11 Ratio test IEC 60076-1:2011, 11.3, or meet the
agreement between supplier and user.
The polarity should be the same as that
12 Polarity check
identified on the nameplate.
Insulation resistance test on each
Test should meet the agreement
13 winding to earth and between
between supplier and user.
windings including bushings
Dissipation factor (tan δ) and Test should be in accordance with
capacitance measurement on each IEC TS 63042-301:2018, 5.7, or meet
winding to earth and between the agreement between supplier and
windings user.
Test should be in accordance with
IEC 60076-3:2013, Clause 10, or meet
15 Applied voltage tests
the agreement between supplier and
user.
Test should be in accordance with
Induced voltage tests with partial IEC 60076-3:2013, Clause 11 or meet
discharge measurement the agreement between supplier and
user.
Test should be in accordance with
Short-circuit impedance measurement IEC TS 63042-301:2018, 5.14 or meet
Diagnostic test
at reduced current the agreement between supplier and
user.
Test should be in accordance with of
18 No-load current and no-load loss test IEC 60076-1:2011, 11.5 or meet the
agreement between supplier and user.
Test should be in accordance with
19 Frequency-response analysis IEC 60076-18 or meet the agreement
between supplier and user.
Test should be in accordance with 11.8
Leak testing with pressure (tightness
20 of IEC 60076-1:2011 or meet the
test)
agreement between supplier and user.
Test should be in accordance with
IEC 60137:2017, 9.2, 9.6 and 9.11 or
21 Tests on bushings
meet the agreement between supplier
and user.
Test should meet the agreement
22 Tests on tap-changers
between supplier and user.
Test should be in accordance with
23 Tests on built-in current transformers IEC TS 63042-301:2018, 9.2 or meet the
agreement between supplier and user.
Buchholz relay and auxiliary circuit Test should meet the agreement
test between supplier and user.
Test should meet the agreement
25 Pressure relief device replacement
between supplier and user.
Check of cooler Test should meet the agreement
between supplier and user.
No. Category Item Recommendations
Check of thermometer and auxiliary Test should meet the agreement
circuit test between supplier and user.
Test should be in accordance with
28 Check of core and frame insulation IEC 60076-1:2011, 11.12 or meet the
agreement between supplier and user.
Test should meet the agreement
29 The content of furfural in oil
between supplier and user.
Refer to the instructions prepared by
Overhaul should meet the agreement
30 Overhaul the manufacturer and implemented by
between supplier and user.
the user.
5.3 CBs
Maintenance items of CBs in general are listed in Table 4. For maintenance test and diagnostic
test, the test method shall refer to the same kind of tests described in IEC TS 63042-301.
Table 4 – Maintenance items of CBs
No. Category Item Recommendations
Appearance should show no visible
1 Visual inspection
damage.
2 Infrared detection The equipment should not overheat.
Maintenance test
Test should meet the agreement
3 Gas pressure check
between supplier and user.
Dielectric tests on the main circuit Test should be in accordance with
IEC 62271-203:2022, 11.101.2, and
IEC TS 63042-301:2018, 7.2 or meet the
agreement between supplier and user.
Measurement of resistance of main Test should be in accordance with
circuit IEC 62271-203:2022, 11.101.4 or meet
the agreement between supplier and
user.
Measurement of the resistance of Test should be in accordance with
6 auxiliary contacts IEC 62271-1:2017, 7.4 or meet the
agreement between supplier and user.
Test should be in accordance with
7 Tests on auxiliary and control circuits IEC 62271-1:2017, 8.3 or meet the
agreement between supplier and user.
Test should be in accordance with
IEC 62271-100:2021, 8.101, and
IEC 62271-100:2021/AMD1:2024, 8.101,
8 Mechanical test and measurement
Diagnostic test
and IEC TS 63042-301:2018, 6.6 or
meet the agreement between supplier
and user.
Gas quality verification Test should be in accordance with
IEC 62271-203:2022, 11.101.7 or meet
the agreement between supplier and
user.
Tightness test Test should be in accordance with
10 IEC 62271-1:2017, 8.5 or meet the
agreement between supplier and user.
Test should be in accordance with
11 Test of accessories IEC TS 63042-301:2018, 6.7 or meet the
agreement between supplier and user.
Hydraulic pump or spring mechanism Test should meet the agreement
charging time test between supplier and user.
Test should meet the agreement
13 Greasing in operating mechanism
between supplier and user.
No. Category Item Recommendations
Check interrupting chamber
Test should meet the agreement
14 (dismantling the interrupting
between supplier and user.
chamber)
Safety valve operation check of Test should meet the agreement
hydraulic mechanism between supplier and user.
Refer to the instructions prepared by
Overhaul should meet the agreement
16 Overhaul the manufacturer and implemented by
between supplier and user.
the user.
5.4 GIS and GIL
Maintenance items of GIS and GIL in general are listed in Table 5. For the maintenance test
and diagnostic test, the test method shall refer to the same kind of tests described in
IEC TS 63042-301.
Table 5 – Maintenance items of GIS and GIL
No. Category Item Recommendations
1 Visual inspection Appearance should show no visible damage.
2 Infrared detection The equipment should not overheat.
Maintenance
Test should meet the agreement between supplier and
3 Gas pressure check
test
user.
Online monitoring data of Test should meet the agreement between supplier and
partial discharge user.
Test should be in accordance with
IEC 62271-203:2022, 11.101.2, and
Dielectric tests on the main
circuit IEC TS 63042-301:2018, 7.2 or meet the agreement
between supplier and user.
Test should be in accordance with
Measurement of the resistance
6 IEC 62271-203:2022, 11.101.4 or meet the agreement
of the main circuit
between supplier and user.
Tests on auxiliary and control Test should be in accordance with IEC 62271-1:2017,
circuits 8.3 or meet the agreement between supplier and user.
Diagnostic
test
Test should be in accordance with
Mechanical test and
8 IEC 62271-203:2022, 8.102 or meet the agreement
measurement
between supplier and user.
Test should be in accordance with
9 Gas quality verification IEC 62271-203:2022, 11.101.7 or meet the agreement
between supplier and user.
Test should be in accordance with
10 Tightness tests IEC 62271-203:2022, 11.101.5 or meet the agreement
between supplier and user.
Refer to the instructions
Overhaul should meet the agreement between supplier
11 Overhaul prepared by the manufacturer
and user.
and implemented by the user.
5.5 Surge arresters
Maintenance items of surge arresters in general are listed in Table 6. For the maintenance test
and diagnostic test, the test method shall refer to the same kind of tests described in
IEC TS 63042-301.
Table 6 – Maintenance items of surge arresters
No. Category Item Recommendations
a) Check the value of discharge
counter;
b) Check the value of leakage current
Visual inspection
meter;
1 Maintenance test
c) Appearance should show no visible
damage.
Infrared detection The equipment should not overheat.
Test should meet the agreement between
2 Insulation resistance test
supplier and user.
Test should meet the agreement between
Insulation resistance test of the base
supplier and user.
insulator
Diagnostic test
Test should meet the agreement between
5 Leakage current test
supplier and user.
Test should be in accordance with
IEC 60099-4:2014, 7.2 or meet the
6 Reference voltage measurements
agreement between supplier and user.
Refer to the instructions prepared by
Overhaul should meet the agreement
7 Overhaul the manufacturer and implemented
between supplier and user.
by the user.
5.6 Voltage and current transformers
Maintenance items of voltage and current transformers in general are listed in Table 7 and
Table 8. For the maintenance test and diagnostic test, the test method shall refer to the same
kind of test described in IEC TS 63042-301, IEC 60599, and IEC 60422.
Table 7 – Maintenance items of CVTs
No. Category Item Recommendations
Appearance should show no visible
1 Visual inspection
damage.
Maintenance test
2 Infrared detection The equipment should not overheat.
Test should be in accordance with
Insulation resistance measurement
IEC TS 63042-301:2018, 9.1.2 or meet
3 of low voltage terminal to earth
the agreement between supplier and
terminal
user.
Test should be in accordance with
Capacitance and dissipation factor IEC TS 63042-301:2018, 9.1.3 or meet
(tan δ) measurement the agreement between supplier and
user.
Test should be in accordance with
Winding resistance measurement of IEC TS 63042-301:2018, 9.1.5 or meet
electromagnetic units the agreement between supplier and
user.
Diagnostic test
Test should be in accordance with
Insulation resistance measurement
IEC TS 63042-301:2018, 9.1.6 or meet
6 of each component of
the agreement between supplier and
electromagnetic units
user.
DGA of electromagnetic unit Test should be in accordance with
7 IEC 60599 or meet the agreement
between supplier and user.
Test should be in accordance with
8 Oil moisture of electromagnetic unit IEC 60422:2024, 7.5, or meet the
agreement between supplier and user.
Damper check Test should meet the agreement between
supplier and user.
Refer to the instructions prepared by
Overhaul should meet the agreement
the manufacturer and implemented
10 Overhaul
between supplier and user.
by the user.
Table 8 – Maintenance items of bushing-type current transformers
No. Category Item Recommendations
1 Maintenance test / /
Test should be in accordance with
IEC TS 63042-301:2018, 9.2.2 or meet
2 Insulation resistance measurement
the agreement between supplier and
user.
Test should be in accordance with
IEC TS 63042-301:2018, 9.2.3 or meet
3 Winding resistance measurement
the agreement between supplier and
user.
Test should be in accordance with
Applied voltage test on secondary IEC TS 63042-301:2018, 9.2.4 or meet
4 Diagnostic test
windings the agreement between supplier and
user.
Test should be in accordance with
Determination of error and polarity IEC TS 63042-301:2018, 9.2.5 or meet
check the agreement between supplier and
user.
Excitation test Test should be in accordance with
IEC TS 63042-301:2018, 9.2.6 or meet
the agreement between supplier and
user.
Refer to the instruc
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