IEC 60871-4:2014

Shunt capacitors for AC power systems having a rated voltage above 1 000 V - Part 4: Internal fuses

IEC 60871-4:2014 applies to internal fuses which are designed to isolate faulty capacitor elements, in order to allow operation of the remaining parts of that capacitor unit and the bank in which the capacitor unit is connected. Such fuses are not a substitute for a switching device such as a circuit-breaker, or for external protection of the capacitor bank or any part thereof. The object of this part of IEC 60871 is to formulate requirements regarding performance and testing and to provide a guide for coordination of fuse protection. This second edition cancels and replaces the first edition published in 1996. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: The disconnecting requirements have been modified. Keywords: internal fuses, faulty capacitor elements, fuse protection

Condensateurs shunt pour réseaux à courant alternatif de tension assignée supérieure à 1 000 V - Partie 4: Fusibles internes

L'IEC 60871-4:2014 s'applique aux fusibles internes qui sont destinés à isoler les éléments de condensateur en défaut et permettre ainsi le maintien en service de la partie saine de l'unité et de la batterie à laquelle cette unité est raccordée. Ils ne sont pas destinés à se substituer à un dispositif de coupure, par exemple un disjoncteur ou une protection externe de la batterie de condensateurs ou une partie de celle-ci. La présente partie de l'IEC 60871 a pour objet de formuler des exigences relatives aux performances et aux essais et de fournir un guide pour la coordination de la protection par fusibles internes. Cette deuxième édition annule et remplace la première édition parue en 1996. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente: Les exigences concernant la déconnexion ont été modifiées. Mots clés: fusibles internes, éléments de condensateur en défaut, protection par fusibles internes

General Information

• Status: Published
• Publication Date: 26-Mar-2014
• ICS: 29.240.99 - Other equipment related to power transmission and distribution networks
• ICS: 31.060.70 - Power capacitors
• Technical Committee: TC 33 - Power capacitors and their applications
• Drafting Committee: MT 19 - TC 33/MT 19
• Current Stage: PPUB - Publication issued
• Start Date: 27-Mar-2014
• Completion Date: 30-Apr-2014

IEC 60871-4:2014 – Internal Fuses for Shunt Capacitors Above 1000 V

Overview

IEC 60871-4:2014 is an international standard published by the International Electrotechnical Commission (IEC) that specifies requirements for internal fuses used in shunt capacitors designed for AC power systems with rated voltages above 1,000 V. This standard focuses on the performance, testing, and coordination of internal fuse protection to isolate faulty capacitor elements within capacitor units and banks. It ensures reliable operation of non-faulty elements while preventing damage and enhancing overall system safety. This edition is a technical revision of the original 1996 standard, introducing updated disconnecting requirements.

Key Topics

• Internal Fuse Purpose
  Internal fuses are designed to disconnect faulty capacitor elements without interrupting the operation of the remaining capacitor unit or bank. They serve as an essential safety component but do not replace external protective devices like circuit-breakers.

• Performance and Disconnecting Requirements
  The standard defines the voltage and current levels at which internal fuses must operate. The fuse should disconnect capacitor elements when breakdown occurs within a specified voltage range based on rated element voltage, taking into account transient overvoltages and power-frequency fault currents.

• Withstand and Continuous Operation
  Fuses must withstand the full voltages after operation, including any unbalanced voltages caused by fuse action. They must carry continuous currents corresponding to maximum permissible unit current divided by parallel fuse paths, handle switching inrush currents, discharge currents from element breakdown, and short-circuit fault currents at peak voltages of up to 2.5 times the rated voltage.

• Testing Procedures
  IEC 60871-4:2014 mandates rigorous routine and type tests, including:

  • Discharge tests simulating capacitor element faults.
  • Disconnecting tests to verify fuse operation under fault conditions.
  • Measurement of capacitance before and after tests to ensure minimal degradation.
  • Voltage withstand tests post-fuse operation.

• Coordination Guidance
  The standard provides guidance on coordinating fuse protection with the overall capacitor bank protection scheme, emphasizing proper sequence and response times to optimize reliability and minimize damage.

Applications

• High Voltage Shunt Capacitors
  Used in electrical utilities and industrial facilities, these capacitors require reliable fault isolation to maintain power quality, improve power factor, and protect equipment.

• Capacitor Banks in AC Power Systems
  Internal fuses per IEC 60871-4 help prevent cascading failures in capacitor banks by isolating defective elements, ensuring uninterruptible operation of the bank, and facilitating safer maintenance.

• Power System Equipment Protection
  This standard supports design and maintenance practices that enhance the safety and longevity of high-voltage capacitor installations through well-defined fuse characteristics and testing criteria.

Related Standards

• IEC 60871-1:2005 – Shunt Capacitors for AC Power Systems Above 1000 V: General Requirements
  Provides foundational definitions, ratings, and general requirements underpinning IEC 60871-4.

• Other Parts of IEC 60871 Series
  The series covers various aspects of shunt capacitors including performance, testing, and application guidelines for different voltage levels and capacitor types.

Summary

IEC 60871-4:2014 is a critical standard ensuring the performance and safety of internal fuses for high-voltage shunt capacitors. By defining strict testing protocols and performance requirements, it promotes safe isolation of faulty capacitor elements, enabling continued operation of capacitor banks and enhancing system reliability. Electrical engineers, designers, and maintenance personnel benefit from adherence to this standard to optimize fuse coordination and enhance protection in AC power systems above 1,000 V.

Keywords: internal fuses, shunt capacitors, AC power systems, high voltage capacitors, capacitor protection, fuse coordination, capacitor element isolation, IEC 60871-4, capacitor bank safety, electrical standards.

Standards Content (Sample)

IEC 60871-4 ®
Edition 2.0 2014-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Shunt capacitors for AC power systems having a rated voltage above 1 000 V –
Part 4: Internal fuses
Condensateurs shunt pour réseaux à courant alternatif de tension assignée
supérieure à 1 000 V –
Partie 4: Fusibles internes
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IEC 60871-4 ®
Edition 2.0 2014-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Shunt capacitors for AC power systems having a rated voltage above 1 000 V –

Part 4: Internal fuses
Condensateurs shunt pour réseaux à courant alternatif de tension assignée

supérieure à 1 000 V –
Partie 4: Fusibles internes
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX L
ICS 29.240.99; 31.060.70 ISBN 978-2-8322-1495-4

– 2 – IEC 60871-4:2014 © IEC 2014
CONTENTS
FOREWORD . 3
1 Scope and object . 5
2 Normative references . 5
3 Terms and definitions . 5
4 Performance requirements. 5
4.1 General . 5
4.2 Disconnecting requirements . 6
4.3 Withstand requirements . 6
5 Tests . 6
5.1 Routine tests. 6
5.1.1 General . 6
5.1.2 Discharge test . 7
5.2 Type tests . 7
5.3 Disconnecting test on fuses . 7
5.3.1 Test procedures . 7
5.3.2 Capacitance measurement . 8
5.3.3 Inspection of the unit . 8
5.3.4 Voltage test after opening the container . 8
Annex A (normative) Test procedures for the disconnecting test on internal fuses . 9
A.1 General . 9
A.2 Test procedures . 9
Annex B (informative) Guide for coordination of fuse protection . 11
B.1 General . 11
B.2 Protection sequence . 11

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SHUNT CAPACITORS FOR AC POWER SYSTEMS
HAVING A RATED VOLTAGE ABOVE 1 000 V –

Part 4: Internal fuses
FOREWORD
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60871-4 has been prepared by IEC technical committee 33: Power
capacitors and their applications.
This second edition cancels and replaces the first edition published in 1996. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– The disconnecting requirements have been modified.

– 4 – IEC 60871-4:2014 © IEC 2014
The text of this standard is based on the following documents:
FDIS Report on voting
33/548/FDIS 33/561/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 parts in the IEC 60871 series, published under the general title Shunt capacitors
for AC power systems having a rated voltage above 1 000 V, 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.
SHUNT CAPACITORS FOR AC POWER SYSTEMS
HAVING A RATED VOLTAGE ABOVE 1 000 V –

Part 4: Internal fuses
1 Scope and object
This part of IEC 60871 applies to internal fuses which are designed to isolate faulty capacitor
elements, in order to allow operation of the remaining parts of that capacitor unit and the bank
in which the capacitor unit is connected. Such fuses are not a substitute for a switching device
such as a circuit-breaker, or for external protection of the capacitor bank or any part thereof.
The object of this part of IEC 60871 is to formulate requirements regarding performance and
testing and to provide a guide for coordination of fuse protection.
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 60871-1:2005, Shunt capacitors for a.c. power systems having a rated voltage above
1000 V – Part 1: General
3 Terms and definitions
For the purpose of this part of IEC 60871, the terms and definitions in IEC 60871-1, as well as
the following, apply.
3.1
rated voltage of a capacitor element
U
Ne
r.m.s. value of the alternating voltage for which the capacitor element has been designed
4 Performance requirements
4.1 General
The fuse is connected in series to the element(s) which the fuse is intended to isolate if the
element(s) becomes faulty. The range of currents and voltages for the fuse is therefore
dependent on the capacitor design, and in some cases also on the bank in which the fuse is
connected.
The requirements are valid for a bank or a capacitor switched by restrike-free circuit-breakers.
If the circuit-breakers are not restrike-free, other requirements shall be agreed between
manufacturer and purchaser.
The operation of an internal fuse is in general determined by one or both of the two following
factors:
– 6 – IEC 60871-4:2014 © IEC 2014
– the discharge energy from elements or units connected in parallel with the faulty element
or unit;
– the power-frequency fault current.
The additional current and voltage resulting from the blowing of some fuses should be taken
into account in the design.
4.2 Disconnecting requirements
The fuse shall enable the faulty element to be disconnected when electrical breakdown of
elements occurs in a voltage range, in which u = 0,9× 2U is the lowest, and
1 Ne
u = 2,5× 2U is the highest (instantaneous) value of the element voltage at the instant of
2 Ne
fault.
The range u to u is based on the voltage that might occur across the capacitor element at
1 2
the instant of electrical breakdown.
The u value is of a transient nature, mostly related to switching operations, and some
allowance has been made for the extra voltage increase that might occur (before activation of
protection) due to earlier disconnection of parallel elements in a series group of elements
(See B.1).
If the application of capacitors leads to u and u value, other than those indicated, for
1 2
example for filter capacitors or when the protection settings limit the value of overvoltage, the
lower and upper test voltage limits shall be changed according to an agreement between
manufacturer and purchaser.
4.3 Withstand requirements
After operation, the fuse assembly shall withstand full element voltage, plus any unbalance
voltage due to fuse action, and any short-time transient overvoltages normally experienced
during the life of the capacitor.
Throughout the life of the capacitor, the fuses shall be capable of carrying continuously a
current equal to or greater than the maximum permissible unit current divided by the number
of parallel fused paths.
The fuses shall be capable of withstanding the inrush-currents due to the switching operations
expected during the life of the capacitor.
The fuses connected to the undamaged elements shall be able to carry the discharge currents
due to the breakdown of elements.
The fuses shall be able to carry the currents due to short-circuit faults on the bank external to

the unit(s) occurring at a peak voltage of 2,5 × U
N .
5 Tests
5.1 Routine tests
5.1.1 General
The fuses shall be able to withstand all routine tests of the capacitor unit in accordance with
IEC 60871-1.
5.1.2 Discharge test
Capacitors having internal fuses shall be subjected to one short-circuit discharge test, from a
d.c. voltage of 1,7 U through a gap situated as closely as possible to the capacitor, without
N
any additional impedance in the circuit (see note).
The capacitance shall be measured before and after the discharge test. The difference
between the two measurements shall be less than an amount corresponding to one internal
fuse operation.
The discharge test may be made before or after the voltage test between terminals (see
IEC 60871-1:2005, Clause 9). However, if it is made after the voltage test between terminals,
a capacitance measurement at rated voltage shall be made afterwards to detect fuse
operation.
If, by agreement with the purchaser, capacitors are accepted with operated fuses, the voltage
test between terminals (IEC 60871-1:2005, Clause 9) shall be made after the discharge test.
It is permitted that d.c. charging voltage be generated by initially energizing with an a.c.
voltage of 1,7 U peak value and disconnecting at a current zero. The capacitor is then
N
immediately discharged from this peak value.
Alternatively, if the capacitor is disconnected at a slightly higher voltage than 1,7 U , the
N
discharge may be delayed until the discharge resistor reduces the voltage to 1,7 U .
N
5.2 Type tests
The fuses shall be able to withstand all type tests of the capacitor units in accordance with
IEC 60871-1.
The unit(s) shall have passed all routine tests stated in IEC 60871-1.
A disconnecting test on fuses (see 5.3) shall be performed either on one complete capacitor
unit or, at the choice of the manufacturer, on two units, one unit being tested at the lower
voltage limit, and one unit at the upper voltage limit, in accordance with 5.3.1.
Due to testing, measuring and safety circumstances, it may be necessary to make some
modifications to the unit(s) under test; for example those indicated in annex A. See also the
different test methods given in Annex A.
Type tests are considered valid if they are performed on capacitor(s) of a design identical with
that of the capacitor offered, or on a capacitor(s) of a design that does not differ from it in any
way that might affect the properties to be checked by the type tests.
5.3 Disconnecting test on fuses
5.3.1 Test procedures
The disconnecting test on fuses shall be performed at the lower a.c. element voltage limit of
0,9 × U and at the upper voltage limit of 2,5 × U or other values according to an
Ne Ne
agreement between manufacturer and purchaser
If the test is carried out with d.c., the test voltage shall be 2 times the corresponding a.c.
test voltage.
NOTE Normally the dielectric would only withstand an a.c. voltage of 2.5 U for a very limited period of time.
N
Therefore a test with d.c. is in most cases to be preferred.

– 8 – IEC 60871-4:2014 © IEC 2014
If the test is carried out with a.c., the triggering of the element failure with a voltage peak shall
not be necessary for the test at the lower voltage limit.
Certain test methods are indicated in Annex A.
5.3.2 Capacitance measurement
After the test, the capacitance shall be measured to prove that the fuses have blown. A
measuring method shall be used that is sufficiently sensitive to detect the capacitance change
caused by one blown fuse.
5.3.3 Inspection of the unit
Before opening, no significant deformation of the container shall be apparent.
After opening the container, a check shall be made to ensure that:
a) no severe deformation of sound fuses is apparent;
b) no more than one additional fuse (or one-tenth of fused elements directly in parallel) has
been damaged (see note 1 to Clause A.1). If method b) given in Annex A is used, note 1
to Clause A.1 shall be observed.
NOTE A small amount of blackening of the impregnant will not affect the quality of the capacitor.
It should be noted that dangerous trapped charges may be present on elements disconnected
either by operated fuses or by damage to their connections. All elements should be
discharged with great care.
5.3.4 Voltage test after opening the container
A voltage test shall be carried out by applying a d.c. voltage of 3,5 × U (U element
Ne Ne
voltage) for 10 s across the broken down element and the gap in its blown fuse. The element
and the fuse should not be removed from the unit for this test. During the test, the gap shall
be in the impregnant. No breakdown over the fuse gap or between any part of the fuse and
any other part of the unit is allowed.
NOTE For units with all elements in parallel, or in all other cases if test procedure b), c), d), or e) indicated in
Annex A is used, this test can be replaced by an a.c. test before the opening of the unit. The test voltage between
the terminals is calculated using the capacitance ratio such that the voltage across the breakdown element and the
gap in its blown fuse is 3,5×U 2 .
Ne
Annex A
(normative)
Test procedures for the disconnecting test on internal fuses

A.1 General
One of the test procedures a), b), c), d), e) or an alternative method, shall be used.
The capacitor voltage and current shall be recorded during the test to verify that the fuse has
disconnected correctly.
To verify the current-limiting behavior of the fuses when tested at the upper voltage limit, the
voltage drop, excluding transient, across the blown fuse shall not exceed 30 %.
If the voltage drop exceeds 30 %, precaution shall be taken to make certain that the parallel
stored energy and the power-frequency fault current available from the test system are
representative of service conditions. A test shall then be made under these conditions to
demonstrate satisfactory operation of the fuse.
Precautions should be taken when performing this test against the possible explosion of a
capacitor unit and the explosive projection of the nail.
NOTE At the upper voltage limit, one additional fuse (or one-tenth of the fused elements directly in parallel)
connected to a sound element(s) is allowed to be damaged.
A.2 Test procedures
a) Capacitor preheating
The capacitor unit is preheated in a chamber before applying the a.c. test voltage at the
lower voltage limit. Preheating temperature (100 °C to 150 °C) is chosen by the
manufacturer to achieve a practical short time (some minutes to some hours) to the first
breakdown.
To prevent excessive internal liquid pressure due to high temperature, the unit may be
equipped with a relief tube including a valve which is closed at the instant of applying the
test voltage.
A lower preheating temperature may be used when applying the test voltage at the upper
voltage limit, in order to avoid breakdowns before reaching the test voltage.
b) Mechanical puncture of the element
Mechanical puncture of the element is made by a nail, which is forced into the element
through a pre-drilled hole in the container. The test voltage may be d.c. or a.c., the choice
being left to the manufacturer.
If a.c. voltage is used, the timing of the puncture shall be made so that breakdown occurs
close to the instant of peak voltage.
Puncture of only one element cannot be guaranteed. In order to limit the possibility of a
flashover to the container along the nail, or through the hole caused by the nail, the
punctures may be performed in the elements connected, permanently or during the test, to
the container.
NOTE DC voltage is especially suitable for capacitors having all elements in parallel.
c) Electrical breakdown of the element (first method)
Some elements in the test unit are each provided with, for example, a tab inserted
between the dielectric layers. Each tab is connected to a separate terminal.

– 10 – IEC 60871-4:2014 © IEC 2014
The test voltage may be a.c. or d.c. the choice being left to the manufacturer.
To obtain breakdown of an element thus equipped, a surge voltage of sufficient amplitude
is applied between this tab and one of the foils of the modified element.
In the case of a.c. voltage, the surge shall be triggered close to the instant of peak
voltage.
d) Electrical breakdown of the element (second method)
Certain elements in the test unit are each provided with a short fusible wire connected to
two extra tabs and inserted between the dielectric layers. Each tab is connected to a
separate insulated terminal.
The test voltage may be d.c. or a.c., the choice being left to the manufacturer.
To obtain breakdown of an element equipped with this fusible wire, a separate capacitor
charged to a sufficient voltage is discharged into the wire in order to blow it.
In the case of a.c. voltage, the discharge of the charged capacitor causing the wire to blow
shall be triggered off close to the instant of the peak voltage.
e) Electrical breakdown of the element (third method)
A small part of an element (or of several elements) in a unit is removed at the time of
manufacture and replaced with a weaker dielectric.
2 2
For example: 10 cm to 20 cm of a film-paper-film dielectric is cut out and replaced with
two thin papers.
Annex B
...