IEC 60143-2:2012

IEC 60143-2 ®
Edition 2.0 2012-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Series capacitors for power systems –
Part 2: Protective equipment for series capacitor banks

Condensateurs série destinés à être installés sur des réseaux –
Partie 2: Matériel de protection pour les batteries de condensateurs série

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IEC 60143-2 ®
Edition 2.0 2012-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Series capacitors for power systems –

Part 2: Protective equipment for series capacitor banks

Condensateurs série destinés à être installés sur des réseaux –

Partie 2: Matériel de protection pour les batteries de condensateurs série

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XA
ICS 29.240.99; 31.060.70 ISBN 978-2-83220-546-4

– 2 – 60143-2  IEC:2012
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 7
3 Terms and definitions . 9
4 Quality requirements and tests . 15
4.1 Overvoltage protector . 15
4.2 Protective spark gap . 16
4.2.1 Purpose . 16
4.2.2 Classification of triggering principles . 16
4.2.3 Tests . 16
4.3 Varistor . 21
4.3.1 Purpose . 21
4.3.2 Classification . 21
4.3.3 Tests . 22
4.4 Bypass switch . 26
4.5 Disconnectors and earthing switches . 26
4.5.1 Purpose . 26
4.5.2 Classification . 27
4.5.3 Tests . 27
4.6 Discharge current-limiting and damping equipment (DCLDE) . 28
4.6.1 Purpose . 28
4.6.2 Classification . 28
4.6.3 Tests . 28
4.7 Voltage transformer . 32
4.7.1 Purpose . 32
4.7.2 Classification . 32
4.7.3 Tests . 32
4.8 Current sensors . 33
4.8.1 Purpose . 33
4.8.2 Classification . 33
4.8.3 Current transformer tests . 33
4.8.4 Electronic transformer tests . 33
4.8.5 Optical transducer tests . 33
4.9 Coupling capacitor. 34
4.9.1 Purpose . 34
4.9.2 Tests . 34
4.10 Signal column . 34
4.10.1 Purpose . 34
4.10.2 Tests . 34
4.11 Fibre optical platform links . 34
4.11.1 Purpose . 34
4.11.2 Tests . 35
4.12 Relay protection, control equipment and platform-to-ground communication
equipment . 35
4.12.1 Purpose . 35
4.12.2 Classification . 35

60143-2  IEC:2012 – 3 –
4.12.3 Tests . 35
5 Guide . 36
5.1 General . 36
5.2 Specification data for series capacitors . 36
5.3 Protective spark gap . 37
5.4 Varistor . 38
5.4.1 General . 38
5.4.2 Varistor voltage-current characteristic . 39
5.4.3 Varistor current and voltage waveforms during a system fault . 40
5.4.4 Comments on varistor definitions and type tests . 41
5.5 Bypass switch . 44
5.6 Disconnectors . 44
5.7 Discharge current-limiting and damping equipment . 44
5.7.1 Purpose of the Discharge Current-Limiting and Damping Equipment . 44
5.7.2 Location of the DCLDE . 45
5.7.3 Configuration of the DCLDE. 47
5.7.4 Miscellaneous comments regarding the DCLDE . 48
5.8 Voltage transformer . 49
5.9 Current transformer . 49
5.10 Relay protection, control equipment and platform-to-ground communication
equipment . 49
5.11 Protection redundancy . 51
5.12 Commissioning tests . 52
5.13 Energization tests . 52
Bibliography . 54

Figure 1 – Typical nomenclature of a series capacitor installation . 7
Figure 2 – Classification of overvoltage protection . 16
Figure 3 – Illustration of waveforms in recovery voltage test . 19
Figure 4 – Typical voltage-current characteristics of one specific metal oxide varistor
element (95 mm diameter) . 40
Figure 5 – Current, voltage and energy waveforms for a phase-to-earth fault . 41
Figure 6 – Conventional location in the bypass branch . 45
Figure 7 – DCLDE in series with the capacitor and the parallel connected MOV . 45
Figure 8 – DCLDE in series with the capacitor and parallel to the MOV . 45
Figure 9 – Only a discharge current-limiting reactor . 47
Figure 10 – Discharge current-limiting reactor connected in parallel with a damping
resistor. A varistor is connected in series with the resistor . 47
Figure 11 – Discharge current-limiting reactor connected in parallel with a damping
resistor. A small spark gap is connected in series with the resistor . 47
Figure 12 – Current-limiting and damping equipment with and without damping resistor . 48

Table 1 – Summary of varistor energy absorption design criteria (example) . 38
Table 2 – Overview of typical series capacitor bank protections . 51

– 4 – 60143-2  IEC:2012
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SERIES CAPACITORS FOR POWER SYSTEMS –

Part 2: Protective equipment for series capacitor banks

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,
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Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
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with the International Organization for 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
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60143-2 has been prepared by IEC technical committee 33: Power
capacitors and their applications.
This second edition cancels and replaces the first edition published in 1994. It constitutes a
technical revision. The main changes with respect to the previous edition are:
• updated with respect to new and revised component standards;
• updates with respect to technology changes. Outdated technologies have been removed,
i.e. series capacitors with dual self-triggered gaps. New technologies have been added,
i.e. current sensors instead of current transformers;
• the testing of spark gaps has been updated to more clearly specify requirements and
testing procedures. A new bypass making current test replaces the old discharge current
test;
• Clause 5, Guide, has been expanded with more information about different damping
circuits and series capacitor protections

60143-2  IEC:2012 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
33/517/FDIS 33/521/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 60143 series, under the general title Series capacitors for
power systems, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – 60143-2  IEC:2012
SERIES CAPACITORS FOR POWER SYSTEMS –

Part 2: Protective equipment for series capacitor banks

1 Scope
This part of IEC 60143 covers protective equipment for series capacitor banks, with a size
larger than 10 Mvar per phase. Protective equipment is defined as the main circuit apparatus
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 60143-1:2004. The protective equipment is mentioned in Clause 3 and 10.6 of
IEC 60143-1:2004.
The protective equipment, treated in this standard, comprises the following items listed below:
– overvoltage protector,
– protective spark gap,
– varistor,
– bypass switch,
– disconnectors and earthing switches,
– discharge current-limiting and damping equipment,
– voltage transformer,
– current sensors,
– coupling capacitor,
– signal column,
– fibre optical platform links,
– 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 Clause 5.
Examples of fault scenarios are given in Clause 5.
Examples of protective schemes utilizing different overvoltage protectors are given in 4.1.

60143-2  IEC:2012 – 7 –
Key
1 assembly of capacitor units
2-7 main protective equipment
9 isolating disconnector
10 bypass disconnector
11 earth switch
Figure 1 – Typical nomenclature of a series capacitor installation
NOTE Most series capacitors are configured with a single module, unless the reactance and current requirements
result in a voltage across the bank that is impractical for the supplier to achieve with one module. Normally each
module has its own bypass switch but a common bypass switch can be used for more than one module. See 10.2.3
of IEC 60143-1:2004 for additional details.
The object of this standard is:
– to formulate uniform rules regarding performance, testing and rating,
– to illustrate different kinds of overvoltage protectors,
– to provide a guide for installation and operation.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60044 (all parts), Instrument transformers
IEC 60044-1, Instrument transformers – Part 1: Current transformers
IEC 60044-8, Instrument transformers – Part 8: Electronic current transformers

– 8 – 60143-2  IEC:2012
IEC 60060 (all parts), High-voltage test techniques
IEC 60076-1, Power transformers – Part 1: General
IEC 60076-6:2007, Power transformers – Part 6: Reactors
IEC 60099-4:2009, Surge arresters – Part 4: Metal-oxide surge arresters without gaps for a.c.
systems
IEC 60143-1:2004, Series capacitors for power systems – Part 1: General
IEC 60255-5, Electrical relays – Part 5: Insulation coordination for measuring relays and
protection equipment – Requirements and tests
IEC 60255-21, Electrical relays – Part 21: Vibration, shock, bump and seismic test on
measuring relays and protection equipment – Section One – Vibration tests (sinusoidal)
IEC 60270, High-voltage test techniques – Partial discharge measurements
IEC 60358-1, Coupling capacitors and capacitor dividers – Part 1: General rules
IEC 60358-2, Coupling capacitors and capacitor dividers – Part 2: AC or DC single-phase
coupling capacitor connected between line and ground for power line carrier frequency (PLC)
application
IEC 60794-1-1, Optical fibre cables - Part 1: Generic specification – General
IEC 60794-2, Optical fibre cables - Part 2: Indoor cables – Sectional specification
IEC 61000-4-29, Electromagnetic compatibility (EMC) – Part 4-29: Testing and measurement
techniques – Voltage dips, short interruptions and voltage variations on d.c. input port
immunity tests
IEC 61109, Insulators for overhead lines – Composite suspension and tension insulators for
a.c. systems with a nominal voltage greater than 1 000 V – Definitions, test methods and
acceptance criteria
IEC 61300-3-4, Fibre optic interconnecting devices and passive components – Basic test and
measurement procedures – Part 3-4: Examinations and measurements – Attenuation
IEC 61869-3, Instrument transformers – Part 3: Additional requirements for inductive voltage
transformers
IEC 61869-5, Instrument transformers – Part 5: Additional requirements for capacitor voltage
transformers
IEC 62271-1, High-voltage switchgear and controlgear – Part 1: Common specifications
IEC 62271-102:2001, High-voltage switchgear and controlgear – Part 102: Alternating current
disconnectors and earthing switches
IEC 62271-109:2008, High-voltage switchgear and controlgear – Part 109: Alternating current
series capacitor bypass switches
—————————
To be published.
60143-2  IEC:2012 – 9 –
NOTE No standard exists for varistors for series capacitors (SC). The relevant tests for series capacitors varistors
are therefore dealt with in this standard.
3 Terms and definitions
For the purpose of this document, the following terms and definitions apply:
NOTE The definitions of capacitor parts and accessories in this standard are in accordance with
IEC 60143-1:2004.
3.1
back-up gap
supplementary gap which may be set to spark over at a voltage level higher than the
protective level of the primary protective device, and which is normally placed in parallel with
the primary protective device
3.2
bank protection
general term for all protective equipment for a capacitor bank, or part thereof
3.3
bypass current
current flowing through the bypass switch or spark gap in parallel with the series capacitor
3.4
bypass switch
device such as a switch or a circuit-breaker used in parallel with a series capacitor and its
overvoltage protector to shunt line current for a specified time, or continuously
Note 1 to entry: Besides bypassing the capacitor, this device may also have the capability of inserting the
capacitor into a circuit and carrying a specified current.
Note 2 to entry: This device shall also have the capability of bypassing the capacitor during specified power
system fault conditions. The operation of the device is initiated by the capacitor control, remote control or an
operator. The device may be mounted on the platform or on the ground near the platform.
3.5
bypass disconnector
device to short-circuit the series capacitor after it is bypassed by the bypass switch
Note 1 to entry: Installed to keep the line in service while the bypass switch or series capacitor bank are
maintained.
3.6
bypass fault current
current flowing through the bypassed series capacitor bank caused by a fault on the line
Note 1 to entry: See also “through fault current” and “partial fault current”.
3.7
bypass gap (protective gap)
gap, or system of gaps, to protect either the capacitor (type K) against overvoltage or the
varistor (type M) against overload by carrying load or fault current around the protected parts
for a specified time
3.8
bypass interlocking device
device that requires all three poles of the bypass switch to be in the same open or closed
position
– 10 – 60143-2  IEC:2012
3.9
capacitor unbalance protection
device to detect unbalance in capacitance between capacitor groups within a phase, such as
that caused by blown capacitor fuses or faulted capacitor elements, and to initiate an alarm or
the closing of the bypass switch, or both
3.10
capacitor platform
structure that supports the capacitor/rack assemblies and all associated equipment and
protective devices, and is supported on insulators compatible with phase-to-earth insulation
requirements
3.11
continuous operating voltage
COV
MCOV of a varistor
(maximum) continuous operating voltage, COV is the designated permissible r.m.s. value of
power frequency voltage that may be applied continuously between the varistor terminals
Note 1 to entry: 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 (U ) for a ZnO arrester according to IEC 60099-4:2009.
c
Note 2 to entry: In IEC 60099-4:2009 U is used to designate “continuous operating voltage”. However, in this
C
standard, COV is used to designate “continuous operating voltage”. The reason is that U is used to designate
C
“capacitor voltage” in the IEC 60143 series.
Note 3 to entry: Consideration of 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.
3.12
discharge current-limiting and damping equipment
reactor or reactor with a parallel 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 bypass gap or the bypass switch
3.13
external fault
line fault occurring outside the protected line section containing the series capacitor bank
3.14
fault-to-platform protection
device to detect insulation failure on the platform that results in current flowing from normal
current-carrying circuit elements to the platform and to initiate the closing of the bypass
switch
3.15
forced-triggered bypass gap
bypass gap that is designed to operate on external command on quantities such as MOV
energy, current magnitude, or rate of change of such quantities
Note 1 to entry: The sparkover of the gap is initiated by a trigger circuit. After initiation, an arc is established in
the power gap. Forced-triggered gaps typically operate only during internal faults.
3.16
insertion
opening of the bypass switch to place the series capacitor in service
3.17
insertion current
r.m.s. current that flows through the series capacitor bank after the bypass switch has opened

60143-2  IEC:2012 – 11 –
Note 1 to entry: This current may be at the specified continuous, overload or swing current magnitudes.
3.18
insertion voltage
peak voltage appearing across the series capacitor bank upon the interruption of the bypass
current with the opening of the bypass switch
3.19
internal fault
line fault occurring within the protected line section containing the series capacitor bank
3.20
isolating disconnector
devices to connect or disconnect the bypassed series capacitor from the line
SEE: Figure 1.
3.21
leakage current (of a varistor)
continuous current flowing through the varistor when energized at a specified power-
frequency voltage
Note 1 to entry: At COV, and at a varistor element temperature equal to normal ambient temperature, the leakage
current is usually mainly capacitive.
3.22
limiting voltage
maximum peak of the power frequency voltage occurring between capacitor unit terminals
immediately before or during operation of the overvoltage protector, divided by √2
Note 1 to entry: This voltage appears either during conduction of the varistor or immediately before ignition of the
spark gap. See IEC 60143-1:2004 for details.
3.23
loss-of-control power protection
means to initiate the closing of the bypass switch upon the loss of normal control power
3.24
main gap
part of the protective spark gap, that shall carry the fault current during a specified time,
comprising two or more heavy-duty electrodes
3.25
minimum reference voltage (of a varistor)
U
MRef
minimum permissible reference voltage for a complete varistor or varistor unit measured at a
specified temperature, typically (20 ± 15) °C
Note 1 to entry: See Figure 4 and comments in Clause 5.
3.26
module
capacitor switching step
three-phase function unit, that consists of one capacitor segment (possibly several) per phase
with provision for interlocked operation of the single-phase bypass switches
SEE: Figure 1.
Note 1 to entry: The bypass switch of a module is normally operated on a three-phase basis. However, in some
applications for protection purposes, the bypass switch may be required to temporarily operate on an individual
phase basis.
– 12 – 60143-2  IEC:2012
3.27
overvoltage protector
quick-acting device (usually MOV or voltage triggered spark gap) which limits the
instantaneous voltage across the series capacitor to a permissible value at power-system
faults or other abnormal network conditions
3.28
platform
structure that supports one or more segments of the bank and is supported on insulators
compatible with phase-to-ground insulation requirements
3.29
platform control power
energy source(s) available at platform potential for performing operational and control
functions
3.30
platform-to-ground communication equipment
devices to transmit operating, control and alarm signals between the platform and ground
level, as a result of operation or protective actions
3.31
protective level
U
pl
maximum peak of the power frequency voltage appearing across the overvoltage protector
during a power system fault
Note 1 to entry: The protective level may be expressed in terms of the actual peak voltage across a segment or in
terms of the per unit of the peak of the rated voltage across the capacitor segment. This voltage appears either
during conduction of the varistor or immediately before ignition of the spark gap.
3.32
rated short-time energy (of a varistor)
maximum energy the varistor can absorb within a short period of time, without being damaged
due to thermal shock
Note 1 to entry: The short time energy is usually expressed in J, kJ or MJ.
3.33
reference current (of a varistor)
peak value of the resistive component of a power-frequency current used to determine the
reference voltage of the varistor
Note 1 to entry: The reference current 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 4).
3.34
reference voltage (of a varistor)
peak value of power-frequency voltage divided by √2 measured at the reference current of the
varistor
Note 1 to entry: Measurement of the reference voltage is necessary for the selection of correct test samples in
the type testing.
3.35
reinsertion
restoration of line current through the series capacitor from the bypass path

60143-2  IEC:2012 – 13 –
3.36
reinsertion current
transient current flowing through the series capacitor after the opening of the bypass path
during reinsertion
3.37
reinsertion voltage
transient voltage appearing across the series capacitor after the opening of the bypass path
during reinsertion
3.38
residual voltage (of a capacitor)
voltage remaining between terminals of a capacitor at a given time following disconnection of
the supply
3.39
residual voltage (of a varistor)
peak value of voltage that appears between the terminals of a varistor during passage of
current
3.40
section (of a varistor)
complete, suitably assembled part of a varistor necessary to represent the behaviour of a
complete varistor with respect to a particular test
Note 1 to entry: A section of a varistor is not necessarily a unit of a varistor.
3.41
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.
3.42
subharmonic protection
device that detects subharmonic current of specified frequency and duration and initiates an
alarm signal or corrective action, usually bypassing the capacitor bank
3.43
sustained bypass current protection
means to detect prolonged current flow through the overvoltage protector and to initiate
closing of the bypass switch
3.44
sustained overload protection
device that detects capacitor voltage above rating but below the operating level of the
overvoltage protector and initiates an alarm signal or corrective action
3.45
swing current
highest value of the oscillatory portion of the current during the transient period following a
large disturbance
Note 1 to entry: The swing current is measured in A r.m.s. and is characterized by a specified amplitude,
frequency and decay time-constant. The swing current is propagated from electromechanical oscillations of the
synchronous machines in the actual power system. The frequency of these oscillations is typically in the range 0,5
Hz to 2 Hz.
– 14 – 60143-2  IEC:2012
3.46
temporary overvoltage
temporary power-frequency voltage across the capacitor higher than the continuous rated
voltage U of the series capacitor
N
3.47
thermal section (of a varistor)
section assembled in a suitable housing with the same heat transfer capability as the actual
varistor
3.48
thermal runaway (of a varistor)
varistor condition when the sustained power losses of the varistor elements steadily increase
due to increased temperature, while the varistor is energized
Note 1 to entry: 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 if the process is
not interrupted, e.g. the voltage is decreased or the varistor is bypassed.
3.49
thermal stability (of a varistor)
varistor condition after a temperature rise, due 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
Note 1 to entry: This is the opposite of a "thermal runaway".
3.50
through fault current
partial fault current
component of the fault current that flows through the SC bank and not the total fault current
(bus fault current)
Note 1 to entry: The component of the fault current which flows through the SC bank is called “through fault
current” or “partial fault current”.
Note 2 to entry: See IEC 60909.
3.51
trigger circuit
device to ignite the main gap at a specified voltage level or by external command
3.52
varistor
metal oxide varistor
non-linear resistor
device to act as overvoltage protection of the capacitor consisting of resistors with a non-
linear voltage-dependent resistance (normally metal-oxide varistors)
Note 1 to entry: The term varistor is used when it is not necessary to distinguish between varistor element,
varistor unit or varistor group.
3.53
varistor element
metal-oxide varistor element
dense ceramic cylindrical body, with metallized parallel end surfaces, constituting the smallest
active component used in larger varistor assemblies
3.54
varistor column
metal-oxide varistor column
column comprising "n" varistor elements connected in series

60143-2  IEC:2012 – 15 –
3.55
varistor unit
metal-oxide varistor unit
assembly of varistor elements, comprising one or several varistor columns mounted in a
suitable housing
3.56
varistor group
metal-oxide 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
3.57
varistor coordinating current
magnitude of the maximum peak of power frequency varistor current associated with the
protective level
Note 1 to entry: The varistor coordinating current waveform is considered to have a virtual front time of 30 µs to
50 µs. The tail of the waveform is not significant in establishing the protective level.
3.58
voltage triggered bypass gap
bypass gap that is designed to spark over on the voltage that appears across the gap
terminals
Note 1 to entry: The spark over of the gap is normally initiated by a trigger circuit set at a specified voltage level.
A voltage-triggered bypass gap may be used for the primary protection of the capacitor and may spark over during
external as well as internal faults.
4 Quality requirements and tests
4.1 Overvoltage protector
The purpose and classification of an overvoltage protector are as follows.
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.
b) Classification
Three common alternatives of overvoltage protectors are listed below:
– single-protective spark gap (type K1). See Figure 2a).
– varistor (gapless) (type M1). See Figure 2b).
– varistor with bypass gap (type M2). See Figure 2c).
X
C
D
SG
B
IEC  2336/12
2a) Single gap (type K1)
– 16 – 60143-2  IEC:2012
X X
C C
MOV
MOV
D
D
SG
B
B
IEC  2337/12 IEC  2338/12
2b) MOV (type M1) 2c) MOV + bypass gap (type M2)
Key
X Capacitor
c
SG Spark gap
D Current-limiting damping circuit
B Bypass switch
Figure 2 – Classification of overvoltage protection
4.2 Protective spark gap
4.2.1 Purpose
The purpose of the protective spark gap is to act as overvoltage protector for the capacitor
(protection scheme K1) or as protection for the varistor (protection scheme M2), see also 5.3.
4.2.2 Classification of triggering principles
The protective spark gaps can be classified as follows:
– self-triggering (used in type K1)
– forced triggering (used in type M2)
4.2.3 Tests
4.2.3.1 General
For practical reasons, certain tests could be performed on the main gap and trigger circuit
separately.
For forced triggered spark gaps, a type test on the total gap assembly is required. The test
shall verify that the overvoltage protector comprising the main gap, trigger circuit and varistor
overload protection operate correctly. See 4.2.3.4.2 below.
4.2.3.2 Main gap
4.2.3.2.1 Routine tests
Routine tests are as follows.
a) dimensional inspection;
b) routine test and inspection of spark-gap components.
Examples of components are electrodes, porcelain housings, grading components, bushings
and support insulators, according to relevant IEC standards.

60143-2  IEC:2012 – 17 –
4.2.3.2.2 Type tests
Type tests are as follows.
a) Fault current test
A fault current test shall be performed to demonstrate that the main gap will withstand the
rated power frequency byp
...