EN 60143-2:1994

SLOVENSKI STANDARD
01-september-2000
Series capacitors for power systems - Part 2: Protective equipment for series
capacitor banks
Series capacitors for power systems -- Part 2: Protective equipment for series capacitor
banks
Reihenkondensatoren für Starkstromanlagen -- Teil 2: Schutzeinrichtungen für
Reihenkondensatorbatterien
Condensateurs série destinés à être installés sur des réseaux -- Partie 2: Matériel de
protection pour les batteries de condensateurs série
Ta slovenski standard je istoveten z: EN 60143-2:1994
ICS:
31.060.70 0RþQRVWQLNRQGHQ]DWRUML Power capacitors
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

CEI
NORME
IEC
INTERNATIONALE
143-2
INTERNATIONAL
Première édition
STANDARD
First edition
1994-07
Condensateurs série destinés à être installés
sur des réseaux —
Partie 2:
Matériel de protection pour les batteries
de condensateurs série
—
Series capacitors for power systems
Part 2:
Protective equipment for series capacitor banks
réservés — Copyright — all rights reserved
© CEI 1994 Droits de reproduction
No part of this publication may be reproduced or utilized in
Aucune partie de cette publication ne peut être reproduite ni
any form or by any means, electronic or mechanical,
utilisée sous quelque forme que ce soit et par aucun pro-
including photocopying and microfilm, without permission
cédé, électronique ou mécanique, y compris la photocopie et
in writing from the publisher.
les microfilms, sans l'accord écrit de l'éditeur.
Genève, Suisse
Bureau Central de la Commission Electrotechnique Inte rnationale 3, rue de Varembé
Commission Electrotechnique Internationale CODE PRIX
Commission
International Electrotechnical XA
PRICE CODE
MewityHapoaHan 3nekrporexHH gecnaa HoMHCCHn
IEC
Pour prix, voir catalogue en vigueur
• •
For price, see current catalogue

143-2 ©IEC:1994 – 3 –
CONTENTS
Page
FOREWORD 7
Clause
SECTION 1: GENERAL
1.1 Scope and object
1.2 Normative references
1.3 Definitions
SECTION 2: QUALITY REQUIREMENTS AND TESTS
2.1 Overvoltage protector
2.1.1 Protective spark gap 27
2.1.1.1 Purpose 27
2.1.1.2 Classification
2.1.1.3 Tests
2.1.2 Non-linear resistor (varistor)
2.1.2.1 Purpose
2.1.2.2 Classification
2.1.2.3 Tests
2.2 By-pass circuit-breaker
2.2.1 Purpose
2.2.2 Classification
2.2.3 Tests
2.3 Disconnectors 49
2.3.1 Purpose 49
2.3.1.1 By-pass disconnector
2.3.1.2 Series disconnector
2.3.2 Classification
2.3.3 Tests 49
2.4 Current-limiting damping equipment
2.4.1 Purpose
2.4.2 Classification
2.4.3 Tests
2.5 Discharge reactor
2.5.1 Purpose
2.5.2 Classification
2.5.3 Tests
143-2 ©IEC:1994 — 5 —
Clause Page
61 2.6 Voltage transformer
2.6.1 Purpose
61 2.6.2 Classification
2.6.3 Tests
2.7 Current transformer
2.7.1 Purpose
2.7.2 Classification
2.7.3 Tests
2.8 Signal column
2.8.1 Purpose
2.8.2 Classification
2.8.3 Tests
2.9 Relay protection, control equipment and platform to ground
communication equipment
2.9.1 Purpose
2.9.2 Classification
2.9.3 Tests
SECTION 3: GUIDE
3.1 General
71 3.2 Specification data for series capacitors
73 3.3 Protective spark gap
75 3.4 Non-linear resistor (varistor)
3.5 By-pass circuit-breaker
3.6 Disconnectors 91
3.7 Current-limiting damping equipment 91
3.8 Discharge reactor 95
3.9 Voltage transformer
3.10 Current transformer 97
3.11 Relay protection, control equipment and platform to ground communication
equipment 97
3.12 Precommissioning tests
3.13 Commissioning tests 99
Annex A— Bibliography
143-2 ©IEC:1994 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
SERIES CAPACITORS
FOR POWER SYSTEMS -
Part 2: Protective equipment for series
capacitor banks
FOREWORD
The IEC (International Electrotechnical Commission) is a worldwide organization for standardization
1)
comprising all national electrotechnical committees (IEC National Committees). The object of the IEC is to
promote international cooperation on all questions concerning standardization in the electrical and
electronic fields. To this end and in addition to other activities, the IEC publishes International Standards.
Their preparation is entrusted to technical committees; any IEC National Committee interested in
the subject dealt with may participate in this preparatory work. International, governmental and
non-governmental organizations liaising with the IEC also participate in this preparation. The IEC
collaborates closely with the International Organization for Standardization (ISO) in accordance with
conditions determined by agreement between the two organizations.
The formal decisions or agreements of the IEC on technical matters, prepared by technical committees on
2)
which all the National Committees having a special interest therein are represented, express, as nearly as
possible, an international consensus of opinion on the subjects dealt with.
They have the form of recommendations for international use published in the form of standards, technical
3)
reports or guides and they are accepted by the National Committees in that sense.
In order to promote international unification, IEC National Committees undertake to apply IEC International
4)
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
5)
equipment declared to be in conformity with one of its standards.
International Standard IEC 143-2 has been prepared by IEC technical committee 33:
Power capacitors.
The text of this standard is based on the following documents:
DIS Report on Voting
33(CO)115 33(CO)124
Full information on the voting for the approval of this standard can be found in the report
on voting indicated in the above table.
IEC 143 consists of the following parts, under the general title: Power capacitors:
143: 1992, Series capacitors for power systems (when revised, this standard will become
–
IEC 143-1);
143-2: 1994, Series capacitors for power systems – Part 2: Protective equipment for series
–
capacitor banks.
Other parts are under consideration.

143-2 © IEC:1994 - 9 -
SERIES CAPACITORS
FOR POWER SYSTEMS -
Part 2: Protective equipment for series
capacitor banks
Section 1: General
1.1 Scope and object
This pa rt of IEC 143 covers protective equipment for series capacitor banks, with a size
larger than 10 Mvar per phase. Protective equipment is defined as the main circuit appa-
ratus and ancillary equipment, which are part of a series capacitor installation, but which
are external to the capacitor part itself. The recommendations for the capacitor part are
given in IEC 143. The protective equipment is mentioned in clauses 1.3 and 7.6 of
IEC 143.
The protective equipment, treated in this standard, comprises the following items listed
below.
- overvoltage protector,
- protective spark gap,
non-linear resistor (varistor),
- by-pass circuit-breaker,
disconnectors,
- current-limiting damping equipment,
- discharge reactor,
- voltage transformer,
- current transformer,
- signal column,
relay protection, control equipment and platform to ground communication
equipment.
See figure 1.
Principles involved in the application and operation of series capacitors are given in
section 3.
Examples of fault scenarios are given in section 3.
Examples of protective schemes utilizing different overvoltage protectors are given in
clause 2.1.
143-2 ©IEC:1994 -11 -
Module 1 Module N
Segment AN
Segment Al !
4 4 Phase
Phase A
• bank A
F
Segment B1 Segment BN
Phase
Phase B
bank B
°\
Segment CN
Segment Cl
Phase
Phase C
bank C
L L
IEC 673194
1 Assembly of capacitor units,
2 Main protective equipment for a segment,
3 By-pass disconnector,
4 Series disconnector.
Figure 1 - Series capacitor bank nomenclature
NOTE - Capacitor fuses are not treated in this standard, since they are treated in IEC 143 and IEC 595.
The object of this standard is:
to formulate uniform rules regarding pe rformance, testing and rating,
-
to illustrate different kinds of overvoltage protectors,
-
- to provide a guide for installation and operation.
1.2 Normative references
The following normative documents contain provisions which, through reference in this
text, constitute provisions of this part of IEC 143. At the time of publication, the editions
indicated were valid. All normative documents are subject to revision, and pa rties to agree-
ments based on this part of IEC 143 are encouraged to investigate the possibility of apply-
ing the most recent editions of the normative documents indicated below. Members of IEC
and ISO maintain registers of currently valid International Standards.
The following IEC publications and reports are quoted in this standard:

-13 -
143-2 ©IEC:1994
4: Measurement of pa rtial discharges
IEC 44-4: 1980, Instrument transformers - Pa rt
International Electrotechnical Vocabulary (IEV)- Chapter 436: Power
IEC 50(436): 1990,
Capacitors
High-voltage alternating-current circuit-breakers
IEC 56: 1987,
High-voltage test techniques - Part 1: General definitions and test
IEC 60-1: 1989,
requirements
Basic environmental testing procedures - Part 2: Tests - Test Db and
IEC 68-2-30: 1980,
guidance: Damp heat, cyclic (12 + 12 hour cycle)
IEC 76-1, 1993, Power transformers - Part 1: General
IEC 99-1: 1991, Surge arresters - Part 1 : Non-linear resistor type gapped arresters for
a.c. systems
IEC 99-4: 1991, Surge arresters - Part 4: Metal-oxide surge arresters without gaps for a.c.
systems
IEC 129: 1984, Alternating current disconnectors and earthing switches
Series capacitors for power systems
IEC 143: 1992,
IEC 185: 1987, Current transformers
Voltage transformers
IEC 186: 1987,
Electrical relays - Part 6: Measuring relays and protection equipment
IEC 255-6: 1988,
IEC 289: 1988, Reactors
rts 1-2): 1993, Tests on insulators of ceramic material or glass for overhead
IEC 383 (Pa
lines with a nominal voltage greater than 1 000 V
Internal fuses for series capacitors
IEC 595: 1977,
Amendment 2, 1987
IEC 654 (Parts 1-4): 1979-1987, Operating conditions for industrial-process measurement
and control equipment
Common clauses for high-voltage switchgear and controlgear standards
IEC 694: 1980,
1: Generic specification
IEC 794-1: 1993, Optical fibre cables - Part
2: Product specifications
IEC 794-2: 1989, Optical fibre cables - Part
NOTE - No standard exists for varistors for series capacitors (S.C.). The relevant tests for series
capacitors varistors are therefore dealt with in this standard.

– 15 --
143-2©IEC:1994
1.3 Definitions
of IEC 143, the following definitions apply:
For the purpose of this pa rt
1.3.0 definitions of capacitor parts and accessories: They are in accordance with
IEC 143.
Supplementary gap which may be set to spark over at a voltage
1.3.1 back-up gap:
level higher than the protective level of the primary protective device, and which is
normally placed in parallel with the primary protective device.
1.3.2 bank protection: General term for all protective equipment for a capacitor bank,
or part thereof.
1.3.3 by-pass current: Current flowing through the by-pass device or devices in
parallel with the series capacitor. This current can either be a fault current or a normal
current.
Device such as a switch or a circuit-breaker used in parallel with
1.3.4 by-pass device:
a series capacitor and its overvoltage protector to shunt line current for a specified time,
or continuously. Besides by-passing the capacitor, this device may also have the capabil-
ity of inserting the capacitor into a circuit and carrying a specified current.
Device to short-circuit the series capacitor after it is
1.3.5 by-pass disconnector:
by-passed by the by-pass device.
fault current: Current flowing through the by-passed series capacitor
1.3.6 by-pass
bank caused by a fault on the line.
gap): Gap, or system of gaps, to protect either the
1.3.7 by-pass gap (protective
capacitor (Type K) against overvoltage or the non-linear resistor (Type M) against
rts for a specified time.
overload by carrying load or fault current around the protected pa
Device that requires all three poles of the by-pass
1.3.8 by-pass interlocking device:
device to be in the same open or closed position.
1.3.9 capacitance unbalance protection: Device to detect unbalance in capacitance
between capacitor groups within a phase, such as that caused by blown capacitor fuses or
faulted capacitors, and to initiate an alarm or the closing of the by-pass device, or both.
s the capacitor/rack assemblies and all
1.3.10 capacitor platform: Structure that suppo rt
associated equipment and protective devices, and is supported on insulators compatible
with phase-to-earth insulation requirements.
1.3.11 capacitor switching step: See module.
1.3.12 continuous operating voltage (COV = MCOV) (U c) (of a varistor): The (Maximum)
value of power
Continuous Operating Voltage, COV, is the designated permissible r.m.s.

143-2 ©IEC:1994 – 17 –
r.m.s. frequency voltage that may be applied continuously between the varistor terminals.
NOTES
1 COV of the series capacitor varistor is usually equal to the rated voltage of the series capacitor. This
definition is different from the definition of COV for a ZnO arrester according to IEC 99-4.
2 Consideration to short-time overvoltages of the series capacitor, such as voltages produced by swing
currents and overload currents, should be taken into account when the protective level of the varistor is
determined.
limiting damping equipment: Reactor or a reactor with a parallel
1.3.13 current-
connected resistor to limit the current magnitude and frequency and to provide a sufficient
damping of the oscillation of the discharge of the capacitors upon operation of the by-pass
gap or the by-pass device (see figure 1).
1.3.14 discharge device: Device permanently connected across the terminals of the
capacitor or built into the capacitor unit, capable of reducing the residual voltage across
the capacitor after the capacitor has been disconnected from the supply.
residual voltage.
1.3.15 discharge voltage (of a varistor): See
1.3.16 external fault: Line fault occurring outside the protected line section containing
the series capacitor bank.
Fault appearing within the capacitor bank (for
1.3.17 fault within the capacitor bank:
example changes of the capacitance within a segment, platform fault, etc.). Such faults
should be handled by the protection of the series capacitor bank and cleared without the
interruption of the transmission line.
fault-to-platform protection: Device to detect insulation failure on the platform
1.3.18
that results in current flowing from normal current-carrying circuit elements to the platform
and to initiate the closing of the by-pass device.
Opening of the by-pass device to place the series capacitor in service
1.3.19 insertion:
with or without load current flowing.
current: Steady-state root-mean-square current that flows through the
1.3.20 insertion
series capacitor after the by-pass device has opened.
Steady-state root-mean-square voltage appearing across the
1.3.21 insertion voltage:
series capacitor upon interruption of the by-pass current with the opening of the by-pass
device.
internal fault: Line fault occurring within the protected line section containing the
1.3.22
series capacitor bank.
Combination of test voltage values (both power-frequency and
1.3.23 insulation level:
impulse) which characterizes the insulation of the capacitor bank with regard to its
capability of withstanding the electric stresses between platform and earth, between
phases, between terminals of all equipment and between platform-mounted equipment and
the platform.
lEC:1994 –19 –
143-2 ©
1.3.24 leakage current (of a varistor): The leakage current is the continuous current
flowing through the varistor when energized at a specified power-frequency voltage.
NOTE — At COV, and at a varistor element temperature equal to normal ambient temperature, the leakage
current is usually capacitive.
The maximum instantaneous voltage appearing between
1.3.25 limiting voltage (Utim):
the capacitor terminals divided by Irf. This voltage appears either during operating of the
varistor or immediately before ignition of the spark gap.
loss-of-control-power protection: A means to initiate the closing of the by-pass
1.3.26
device upon the loss of normal control power.
of the protective spark gap, that shall carry the fault current
1.3.27 main gap: That pa rt
during a specified time, comprising two or more heavy-duty electrodes.
continuous operating voltage (of a varistor).
1.3.28 MCOV: See
metal-oxide varistor: See varistor.
1.3.29
varistor element.
1.3.30 metal-oxide varistor element: See
metal-oxide varistor column: See varistor column.
1.3.31
1.3.32 metal-oxide varistor group: See varistor group.
-oxide varistor unit: See varistor unit.
1.3.33 metal
(of a varistor): The minimum permissible
1.3.34 minimum reference voltage
UMRef
reference voltage for a complete varistor or varistor unit measured at a specified
temperature, typically (23 ± 5) °C (see figure 3 and comments in section 3).
A three-phase function unit, that consists of
module (capacitor switching step):
1.3.35
one capacitor segment (possibly several) per phase with provision for interlocked
operation of the single-phase by-pass devices (see figure 1).
1.3.36 non-linear resistor (varistor): A device to act as overvoltage protection of the
capacitor consisting of resistors with a non-linear voltage-dependent resistance (normally
metal-oxide varistors).
1.3.37 overvoltage protection: A quick-acting device which limits the instantaneous
voltage across the series capacitor to a permissible value at power-system faults or other
abnormal network conditions.
control power: Energy source(s) available at platform potential for
1.3.38 platform
performing operational and control functions.
platform-to-ground communication equipment: Devices to transmit operating,
1.3.39
control and alarm signals between the platform and ground level, as a result of operation
or protective actions.
143-2 ©IEC:1994 - 21 -
1.3.40 protective gap: See by-pass gap.
1.3.41 protective level: The maximum instantaneous voltage appearing across the
capacitor immediately before or during operation of the by-pass gap (gap-scheme) or at a
specified instantaneous current through the varistor (varistor-scheme). In practice, the
protective level is equal to
Ulim.
The maximum energy the varistor can
1.3.42 rated short-time energy (of a varistor):
absorb within a short period of time, without being damaged due to thermal shock. The
short-time energy is usually expressed in J, kJ or MJ.
The peak value of the resistive component of a
1.3.43 reference current (of a varistor):
power-frequency current used to determine the reference voltage of the varistor. It is
chosen in the transition area between the leakage current and the conduction current
region, typically in the range 1 mA to 20 mA for a single varistor column (see figure 3 in
section 3).
The peak value of power-frequency voltage
1.3.44 reference voltage (of a varistor):
measured at the reference current of the varistor.
divided by
NOTE - Measurement of the reference voltage is necessary for the selection of correct test samples in
the type testing.
1.3.45 reinsertion: The restoration of load current to the series capacitor from the
by-pass path (see figure 1).
The transient current flowing through the series capacitor
1.3.46 reinsertion current:
during the reinsertion.
The transient voltage appearing across the series capacitor
1.3.47 reinsertion voltage:
during reinsertion.
residual voltage (of a capacitor): The voltage remaining between terminals of a
1.3.48
capacitor at a given time following disconnection of the supply.
The peak value of voltage that appears between
1.3.49 residual voltage (of a varistor):
the terminals of a varistor during passage of current.
section (of a varistor): A complete, suitably assembled pa rt of a varistor
1.3.50
necessary to represent the behaviour of a complete varistor with respect to a particular
test. A section of a varistor is not necessarily a unit of a varistor.
1.3.51 segment: Single-phase assembly of groups of capacitors which has its own
voltage-limiting devices and relays to protect the capacitors from overvoltages and
overloads (see figure 1).
Devices to disconnect the by-passed series capacitor from
1.3.52 series disconnector:
the line, for example for maintenance.
1.3.53 subharmonic protection: A device that detects subharmonic current of specified
frequency and duration and initiates an alarm signal or corrective action, usually
by-passing the capacitor bank.

143-2 © IEC:1994 – 23 –
A means to detect prolonged current flow
1.3.54 sustained by-pass current protection:
through the overvoltage protector and to initiate closing of the by-pass device.
A device that detects capacitor voltage above
1.3.55 sustained overload protection:
rating but below the operating level of the overvoltage protector and initiates an alarm
signal or corrective action.
A temporary power-frequency voltage higher than the
1.3.56 temporary overvoltage:
continuous rated voltage of the series capacitor.
A section assembled in a suitable housing with
1.3.57 thermal section (of a varistor):
the same heat transfer capability as the actual varistor.
thermal runaway (of a varistor): Varistor condition when the sustained power
1.3.58
losses of the varistor elements steadily increase due to increased temperature, when the
varistor is energized. The heat generated by the power losses of the varistor elements
exceeds the cooling capability of the varistor housing, which causes further temperature
rise and finally leads to a varistor failure.
thermal stability (of a varistor): Varistor condition after a temperature rise, due
1.3.59
to an energy discharge and/or temporary overvoltage, when the varistor is energized at its
COV under specified ambient conditions and the temperature of the varistor elements
decreases with time.
It is the opposite of a "thermal runaway".
A device to ignite the main gap at a specified voltage level or by
1.3.60 trigger circuit:
external command.
Term used, when it is not necessary to distinguish between varistor
1.3.61 varistor:
element, varistor unit or varistor group.
varistor element: A dense ceramic cylindrical body, with metallized parallel end
1.3.62
aces, constituting the smallest active component used in larger varistor assemblies.
su rf
"n" varistor elements connected in series.
1.3.63 varistor column: A column comprising
1.3.64 varistor unit: An assembly of varistor elements, comprising one or several
varistor columns mounted in a suitable housing.
1.3.65 varistor group: Single-phase group of varistor units connected in parallel and/or
in series, carefully matched together, to form an overvoltage-limiting device for a series
capacitor.
— 25 —
143-2 ©IEC:1994
Section 2: Quality requirements and tests
2.1 Overvoltage protector
a) Purpose
The overvoltage protector is a quick-acting device which limits the instantaneous voltage
across the series capacitor to a permissible value when that value would otherwise be
exceeded as a result of a power-system fault or other abnormal network condition.
Classification
b)
Four common alternatives are listed below.
single-protective spark gap;
—
two different set single-protective spark gaps forming a dual-gap system;
—
- non-linear resistor;
non-linear resistor with by-pass gap.
2.
See figure
Non-linear resistor
Single gap
IEC 674194
Non-linear resistor
Dual gap
with by-pass gap
Figure 2 — Classification of overvoltage protection

143-2 ©IEC:1994 - 27 -
2.1.1 Protective spark gap
2.1.1.1 Purpose
The main purpose of the protective spark gap is to act as overvoltage protector for the
capacitor (type K, type L). In certain applications, the purpose of the spark gap is to act as
back-up protection for the capacitor (type K) or protection for the non-linear resistor
(type M). Reference is made to subclause 7.6.2 of IEC 143.
2.1.1.2 Classification
The protective spark gaps can be classified as follows, with regard to the working
principle:
type K - spark gap with sustained arc
-
- type L - spark gap with repetitive arc
With regard to triggering principles, i.e. how spark over of the main gap is initiated, the
following two principles can be distinguished:
self triggering;
-
- forced triggering
See further IEC 143, subclause 7.6.2.
2.1.1.3 Tests
For practical reasons, certain tests could be performed on the main gap and trigger circuit
separately. However, a type test on the total gap assembly is also necessary. The test
shall verify that the complete gap, comprising main gap and trigger gap operates correctly.
2.1.1.3.1 Main gap
2.1.1.3.1.1 Type tests
Fault current test
The following factors shall be considered:
- the test shall be made only once;
magnitude of test current shall conform with maximum power-frequency fault cur-
rent (r.m.s.) through the protective gap;
duration of test current shall conform with duration of fault current through the gap
-
at the series capacitor bank location. Fault scenarios and maximum back-up line
circuit-breaker fault-clearing time shall be taken into account (typical fault scenarios are
given in section 3 of the guide);
- criteria for acceptance of the tests: No excessive erosion nor significant change in
spark over voltage of the gap shall occur.

143-2 ©IEC:1994 - 29 -
Discharge current test
The following factors shall be considered:
- the magnitude of the test current shall be the calculated sum of the high-frequency
discharge current component at maximum gap setting and the instantaneous value of
the power-frequency fault current component including offset;
- test current frequency shall conform with the discharge current frequency of the
actual series capacitor bank. A 50 Hz or 60 Hz half-current wave from a short-circuit
generator may also be used. In that case, the current amplitude shall be reduced
by 10 %. Such a test is considered more severe compared to a discharge test at the
actual discharge frequency;
the discharge current test shall normally be repeated 10 times. However, if the
-
capacitor in service is expected to be subjected to frequent discharges, the number of
discharges may, by agreement, be increased to 20 (see IEC 143, clause 2.13, note 2);
criteria for acceptance of the test: no mechanical damage, excessive erosion, nor
-
significant change in spark over voltage of the gap shall occur.
Recovery voltage test
The following factors shall be considered:
the gap shall be exposed to power-frequency fault currents of specified
-
magnitude(s) and duration(s) corresponding to external line faults and/or internal line
faults. The withstand voltage versus time for the gap shall be recorded at specified time
intervals;
the test shall demonstrate that the gap has sufficient recovery voltage withstand
-
taking into account the trigger circuit, to allow the capacitor to be reinserted after a
successful line auto reclosure.
Self-clearing ability of self-extinguishing gap:
The gap shall be able to reinsert the capacitor at 150 % of rated current within four cycles.
Routine tests
2.1.1.3.1.2
- dimensional inspection;
routine test and inspection of spark-gap components, for example electrodes,
-
porcelain housings, grading components, bushings and support insulators, according to
relevant IEC standards.
Trigger circuit
2.1.1.3.2
2.1.1.3.2.1 Self-triggered circuit type tests
A routine test shall be performed before the type test is carried out.
spark over test
The test shall demonstrate that spark over occurs within the specified tolerance range.

143-2 ©IEC:1994 - 31 -
Environmental test
The test shall demonstrate that the gap works correctly within its tolerance range,
for the specified ambient conditions, such as temperature, air pressure, etc. (see
IEC 60-1).
Self-triggered circuit routine test
2.1.1.3.2.2
- power-frequency spark over voltage test or power-frequency reference voltage test,
whichever is applicable;
- measurement of grading current or leakage current (if applicable);
check of internal corona (if applicable);
-
- gas filling and leakage test.
Forced-triggered circuit type test
2.1.1.3.2.3
See 2.1.1.3.3 below.
Forced-triggered circuit routine test
2.1.1.3.2.4
- power-frequency spark over voltage test or power-frequency reference voltage test,
whichever is applicable;
- measurement of grading current or leakage current (if applicable);
check of internal corona (if applicable);
-
- gas filling and leakage test.
2.1.1.3.3 Complete gap test (type test)
The test shall verify, that the complete gap, comprising main gap and trigger gap operates
correctly. The test circuit shall comprise the complete gap, and if applicable a varistor and
a capacitor in order to represent the typical voltage waveform caused by the varistor.
Oscillographic recordings shall be made.
2.1.2 Non-linear resistor (varistor)
2.1.2.1 Purpose
The main purpose of the non-linear resistor is to act as overvoltage protector for the
capacitor (type M). See IEC 143, subclause 7.6.2.
2.1.2.2 Classification
The varistors can be classified as follows, with regard to the working principle:
- varistor without a by-pass gap;
- varistor with a by-pass gap.
The tests for the two types are the same.

– 33 –
143-2 ©IEC:1994
2.1.2.3 Tests
2.1.2.3.1 Type tests
2.1.2.3.1.1 Test samples
Unless otherwise stated all type tests shall be performed on three sections of new varistor
elements which have not been subjected to any previous tests except for evaluation
purposes.
The scale factors in voltage, current and energy used to determine representative stresses
to be applied on the test samples are further described in section 3.
2.1.2.3.1.2 Residual voltage test
The aim of the residual voltage type test is to establish the ratio between residual voltages
at given impulse currents for the voltage level checked in the routine test. See section 3.
Power-frequency residual voltage test
2.1.2.3.1.2.1
The power-frequency residual voltage test shall be performed on sections with a reference
voltage of at least 3 kV. The sections shall consist of one single varistor column. The
varistor elements may not be encapsulated in any form and shall be exposed to open air
at an ambient temperature of (23 ± 5) °C.
A power-frequency voltage shall be applied to the section. To avoid damage at high
currents the voltage shall only be applied for one half-cycle or for a few cycles. By chang-
ing the voltage amplitude the residual voltage of the section shall be checked for
approximately 0,5, 1,0 and 1,5 times the maximum prospective current of the complete
nc.
varistor divided by the current scale factor
NOTE - Because it could be difficult to control the current amplitude exactly the residual voltage at
prospective maximum current may be determined from a plot of residual voltage versus current.
The residual voltage for the varistor group is determined according to 2.1.2.3.1.2 for the
section with the highest residual voltage.
Switching impulse residual voltage test
2.1.2.3.1.2.2
The test shall be performed on sections with a reference voltage of at least 3 kV. The sections
shall consist of one single column of varistor elements, which need not be encapsulated in
any form and shall be exposed to open air at an ambient temperature of (23 ± 5) °C.
The sections are subjected to a voltage and current impulse with a virtual front time of the
voltage wave of 1 ms ± 10 %. The time to half-value is not critical and may have any
value. The current amplitude is chosen to approximately 0,5, 1,0 and 1,5 times the
maximum prospective current of the varistor group divided by the current scale factor nc.

143-2 ©IEC:1994 – 35 –
The residual voltage for the complete varistor is determined according to 2.1.2.3.1.2 for
the section with the highest residual voltage.
2.1.2.3.1.3 Accelerated ageing procedure
An accelerated ageing test shall be performed for 1 000 h at a temperature of (115 ± 3) °C
on the new test samples and in the surrounding medium of the varistor. During these 1 000 h
the test samples shall be energized at a test voltage corresponding to the COV of the
varistor. The power losses after 1 h to 2 h (starting value) shall be compared to the power
losses after 1 000 h. If the power losses after 1 000 h are less than, or equal to the
starting value, no corrections are necessary and all type tests shall be performed on new
varistor elements.
If the power losses have increased, the power ratio shall be determined as the ratio
between the power losses after 1 000 h and the starting value. The corrections to be
applied on the COV in all type tests are then determined by measurements on three new
samples at ambient temperature. The test voltage level, starting at COV, is increased until
the above ratio of power losses is achieved. The voltage level determined in this way
corresponds to the new test voltage which shall be applied, instead of the COV, when
verifying thermal stability. See section 3.
2.1.2.3.1.4 Repeated energy withstand test
The purpose of this test is to verify that the varistor can withstand the current and energy
duties for which it is designed, keeping any possible changes of the characteristic within
tolerable limits.
The test shall be performed on sections with a reference voltage of at least 3 kV. The
sections shall consist of one single column of varistor elements which are not encapsulated in
any form and shall be exposed to open air at an ambient temperature of (23 ± 5) °C.
A power-frequency voltage shall be applied to the section giving an energy injection equal
to maximum prescribed varistor energy taking into account the energy scale factor, nW.
The voltage shall be applied for a time duration not longer than the shortest operating time
giving maximum energy for the varistor group.
The test shall be repeated 20 times with a time interval between operations sufficiently
long to permit the section to cool to ambient temperature.
Prior to the repeated energy withstand test the following measurements shall be made:
reference voltage measurement;
-
- residual voltage measurement with current amplitude 500 A and waveshape 8/20 µs.

143-2 ©IEC:1994 – 37 –
These measurements shall be repeated after the test and it shall be demonstrated that no
significant changes have occurred. The reference voltage shall not have decreased by
more than 5 % and the residual voltage shall not have changed by more than 5 %.
NOTES
1 The residual voltage is checked for 500 A 8/20 µs current impulse and not for power-frequency volt-
age. This depends on difficulties to exactly reproduce the same current in a power-frequency voltage test
and thus obtain a high accuracy in checking any changes.
2 For some applications the energy decisive case for the varistor may correspond to only one half-cycle
or a few cycles of power-frequency voltage. The power-frequency source may then be replaced by a
distributed constant generator giving an approximately rectangular current impulse through the test sample.
This test is considered equivalent if the energy absorption is the same as if the duration of the rectangular
current wave is not longer than the time during which a power-frequency current is supposed to flow
through the varistor.
2.1.2.3.1.5 Energy withstand and power-frequency voltage stability test
The purpose of this test is to verify that the varistor is able to withstand maximum
specified energy, followed by a possible temporary overvoltage sequence and thereafter
show thermal stability energized at COV and at highest ambient temperature.
The test shall be performed on sections with a reference voltage of at least 3 kV. The
sections shall consist of varistor elements encapsulated in such a way that the section
represents a true thermal model of the varistor group.
If the varistor group contains units with several parallel columns of varistor elements the
prorated sections shall have the same number of parallel columns.
Further, if the reference voltage in test 2.1.2.3.1.4 has decreased for any of the test
samples, the same varistor elements shall be used in this test. Otherwise new varistor
elements shall be selected.
Prior to the test the following measurements shall be made:
– reference voltage measurement;
residual voltage measurement with current amplitude 500 A and waveshape 8/20 µs.
These measurements shall be repeated after the test and it shall be demonstrated that no
significant changes have occurred. The reference voltage shall not have decreased by
more than 5 % and the residual voltage shall not have changed by more than 5 %.
The energy withstand and power-frequency voltage stability test starts with a preheating of
the test sections to (60 ± 3) °C in an oven.
Within 5 min after removing the test section from the heat source a power-frequency volt-
age shall be applied to the section giving an energy injection equal to maximum
nw.
prescribed varistor energy taking into account the energy scale factor,

143-2 © I EC:1994 – 39 –
The voltage shall be applied during a period not longer than the shortest operating time
giving maximum energy for the varistor group.
As soon as possible and in less than 5 s after the energy injection a power-frequency volt-
age equal to continuous operating voltage of the varistor group taking into account the
nv, shall be applied and maintained for 30 min. During the 30 min
voltage scale factor,
thermal stability shall be demonstrated i.e. resistive component of the leakage current
and/or the temperature of the varistor elements and/or the power losses shall be
measured and show a steady decrease.
If a temporary overvoltage sequence is specified for the varistor group after an energy
absorption, the same or equivalent sequence shall be applied to the test sections taking
the voltage scale factor into account.
If the temporary overvoltage is very high, the temperature may increase during this period.
However, when the voltage is reduced to continuous operating voltage or a level which
can be maintained during hours thermal stability shall be proved. For example after a fault
sequence the capacitor voltage can be 35 % higher than continuous operating voltage
for 30 min followed by an overload of 17 % for an additional 24 h. The varistor shall then
be thermally stable after maximum energy and 35 % overload during 30 min. i.e. the
varistor shall be able to cool down when subjected to the 24 h overload voltage.
NOTES
1 The power-frequency voltage giving the energy injection may be replaced by a distributed constant
generator if the same requirements as discussed in note 2 of 2.1.2.3.1.4 are valid.
2 The COV should, if necessary, be adjusted according to the result of the accelerated ageing procedure
of 2.1.2.3.1.3.
2.1.2.3.1.6 Verification of thermal sections
In order to prove that the section is a true thermal model of the varistor group, the cooling
curve of the section shall be compared to the cooling curve of the longest unit in the
varistor. The two cooling curves shall be determined from approximately 150 °C down to
the ambient temperature. The heating of the section and of the varistor unit shall be made
by the application of a power-frequency voltage. The heating period shall be approxi-
mately the same for both the section and the unit.
The cooling curves shall be determined either as mean value or by checking the
temperature of single varistor elements.
If it is chosen to check the temperature of one single varistor element, an element located
between 1/2 to 1/3 of the unit length from the top shall be chosen.
Finally to prove thermal equivalency, the test section shall for all instants during the
cooling period have a higher or equal temperature than the varistor unit.

143-2 ©IEC:1994 – 41 –
2.1.2.3.1.7 Pressure-relief test
In IEC 99-1 pressure-relief test procedures valid for conventional arresters are prescribed.
The intention of these tests is to show that an internal short-circuit of the arrester will not
cause explosive shattering of the housing which might cause accidental damage to
surrounding or personnel equipment.
Due regard has to be taken, that the pressure-relief test also covers discharge of the
capacitor bank from the protective level.
In the absence of an alternative procedure, pressure-relief tests with both high and low
current shall be performed as per IEC standards.
For varistor units of the same type differing from each other only in insulator length, a
successful test on the longest unit is regarded as valid also for all the shorter ones.
Accelerated life test
2.1.2.3.1.8
This is a sample test performed on individual varistor elements taken at random from each
manufacturing batch. Samples shall be energized at an a.c. voltage at an elevated
temperature of 120 °C during some weeks. The number of samples shall be agreed upon
between purchaser and manufacturer. The imposed voltage shall at least be equal to
1,05 times the COV of the varistor element. The power losses of the varistor elements at
the end of the testing period are not allowed to exceed a prescribed value. This test
provides an indication of the long-term stability and provides some confidence that the
ormance during its life time.
varistor will provide satisfactory pe rf
2.1.2.3.2 Routine tests
The routine tests are not described in detail, since many different test methods can
achieve the same quality regarding energy capability and protective level. A proposed test
programme is given here.
2.1.2.3.2.1 Energy withstand test
All varistor elements shall be subjected to an energy withstand test including repeated
sequences of energy injections with cooling time between. Each test sequence shall
expose the varistor element to an energy injection higher than or equal to the rated short-
time energy.
2.1.2.3.2.2 Residual voltage test
In order to achieve a given protective level a residual voltage test shall be performed on
all individual varistor elements or complete assembled varistor units. The test should
preferably be performed with a current amplitude of the same order of magnitude as
c, into
maximum prospective fault current for the varistor taking the current scale factor, n
account. The waveshape may have any front time from µs to ms.

143-2 ©IEC:1994 - 43 -
The protective level for the varistor group at actual cur
...