IEC 63438:2024

IEC 63438 ®
Edition 1.0 2024-12
INTERNATIONAL
STANDARD
Railway applications – Fixed installations – Protection principles for AC and DC
electric traction power supply systems

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IEC 63438 ®
Edition 1.0 2024-12
INTERNATIONAL
STANDARD
Railway applications – Fixed installations – Protection principles for AC and DC

electric traction power supply systems

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 45.060.01  ISBN 978-2-8327-0063-1

– 2 – IEC 63438:2024 © IEC 2024
CONTENTS
FOREWORD . 4
1 Scope . 6
2 Normative references . 7
3 Terms and definitions . 7
4 System to be protected . 14
4.1 Description . 14
4.2 Interfaces . 15
4.2.1 Infeed . 15
4.2.2 Rolling stock . 15
4.2.3 Electrical installations fed by the electric traction power supply system . 16
5 General principles . 16
5.1 Objectives . 16
5.2 System requirements . 17
5.2.1 General . 17
5.2.2 Protection reliability methods . 18
5.2.3 Load discrimination . 19
5.2.4 Speed of protection . 20
5.2.5 Selectivity of protection . 20
5.2.6 Economic feasibility . 20
5.3 Description of the protection system . 20
5.4 Fault and abnormal conditions . 21
5.5 Protection concept . 22
6 Specific requirements of different systems . 23
6.1 General . 23
6.2 AC systems. 24
6.2.1 Power conversion infeed . 24
6.2.2 Busbar infeed . 24
6.2.3 Line feeder . 25
6.2.4 Switching station feeder. 27
6.2.5 Autotransformer . 28
6.3 DC systems . 28
6.3.1 Power conversion infeed . 28
6.3.2 DC busbar infeed . 29
6.3.3 Line feeder . 30
6.3.4 Switching station feeder. 31
6.3.5 Frame leakage protection . 31
6.4 Overview of protection reliability methods . 31
7 Limitations and residual risks . 33
8 Design verification . 34
Annex A (informative) Examples of protection schemes . 35
A.1 General . 35
A.2 Description of the structure of the protection scheme examples . 35
A.3 Protection scheme examples . 36
Annex B (informative) Example of a protection concept for a 25 kV line section . 41
B.1 Overview. 41
B.2 Protection concept . 41

B.3 Interfaces . 42
B.4 Fault conditions . 42
B.5 Clearance times . 42
B.6 Main protection functions . 42
B.7 Reliability methods . 43
B.8 Selectivity of protection . 43
B.9 Grading time requirements . 43
B.10 Coordination requirements . 43
B.11 Maintenance requirements . 43
B.12 Protection device structure . 43
B.13 Operating sequence . 45
Annex C (informative) Example of a protection scheme for a 25 kV line section with
automatic changeover section . 47
C.1 General . 47
C.2 Function of a changeover section . 47
C.3 Fault condition of neutral section . 48
C.4 Duration of removing fault on neutral section . 49
C.5 Main protection function for changeover section. 49
C.6 Reliability methods for changeover section . 49
Bibliography . 50

Figure 1 – Electric traction power supply system and its interfaces . 15
Figure 2 – Example of a protection system. 21
Figure 3 – Example for single protected line sections. 26
Figure 4 – Example for a grouped protected line section . 26
Figure 5 – Example for an extended protected section of an additional line feeder of a
short section by bridged section insulation . 27
Figure A.1 – Key for protection scheme, example of protected section 'busbar' . 35
Figure A.2 – Example of a protection scheme for AC 50 Hz electric traction power
supply systems without busbar infeed circuit-breaker . 36
Figure A.3 – Example of a protection scheme for AC 50 Hz electric traction power
supply systems with busbar infeed circuit-breaker . 37
Figure A.4 – Example of a protection scheme for AC 16,7 Hz electric traction power

supply systems with busbar infeed circuit-breaker . 38
Figure A.5 – Example of a protection scheme for DC electric traction power supply
systems with busbar infeed circuit-breaker . 39
Figure A.6 – Example of a protection scheme for DC electric traction power supply
systems with regenerative power absorbing equipment . 40
Figure B.1 – System single line diagram . 41
Figure B.2 – Scheme functional diagram of feeder breakers A1 and A2 . 45
Figure B.3 – Typical scheme sequence diagram – Fault on Feeder A. 46
Figure C.1 – Example of protection scheme for AC system with changeover section . 47
Figure C.2 – Example of switching sequence on neutral section passing system with

changeover switchgear . 48

Table 1 – Overview of reliability methods . 32
Table 2 – Limitations of protection systems and generic residual risks . 33

– 4 – IEC 63438:2024 © IEC 2024
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
RAILWAY APPLICATIONS – FIXED INSTALLATIONS –
PROTECTION PRINCIPLES FOR AC AND DC ELECTRIC
TRACTION POWER SUPPLY SYSTEMS
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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IEC 63438 has been prepared by IEC technical committee 9: Electrical equipment and systems
for railways. It is an International Standard.
EN 50633 (2016) has served as a basis for the elaboration of this document.
The text of this International Standard is based on the following documents:
Draft Report on voting
9/3114/FDIS 9/3143/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.

This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
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– 6 – IEC 63438:2024 © IEC 2024
RAILWAY APPLICATIONS – FIXED INSTALLATIONS –
PROTECTION PRINCIPLES FOR AC AND DC ELECTRIC
TRACTION POWER SUPPLY SYSTEMS
1 Scope
This International Standard applies to the electrical protection system, provided for AC and DC
electric traction power supply systems. It:
– establishes railway specific protection principles;
– describes the railway specific protection system functionality;
– specifies minimum functional requirements and informative examples of their application;
– establishes limitations of the protection system and the acceptability of residual risks;
– specifies principles for design verification.
This document is applicable to:
– railways;
– guided mass transport systems, such as tramways, elevated and underground railways,
mountain railways, trolleybus systems, and magnetically levitated systems which use a
contact line system.
This document can also be applied to electrified road traffic with a contact line, such as truck-
trolley systems.
This document applies to new electric traction power supply systems and can be applied to
changes of existing systems.
This document does not apply to:
– underground mine traction systems;
– cranes, transportable platforms and similar transportation equipment on rails, temporary
structures (e.g. exhibition structures) in so far as these are not supplied directly or via
transformers from the contact line system and are not endangered by the traction power
supply system;
– suspended cable cars;
– funicular railways;
– magnetic levitated systems (without a contact line system);
– railways with an inductive power supply without contact system;
– railways with a buried contact system that is required to be energized only below the train
to ensure safety.
This document does not cover:
– technical requirements for products, e.g. protection devices;
– rules for maintenance of protection systems.

2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies.
For undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 61991:2019, Railway applications – Rolling stock – Protective provisions against electrical
hazards
IEC 61992-1:2006, Railway applications – Fixed installations – DC switchgear – Part 1: General
IEC 61992-1:2006/AMD1:2014
IEC 61992-7-1:2006, Railway applications – Fixed installations – DC switchgear – Part 7-1:
Measurement, control and protection devices for specific use in d.c. traction systems –
Application guide
IEC 62128-1:2013, Railway applications – Fixed installations – Electrical safety, earthing and
the return circuit – Part 1: Protective provisions against electric shock
IEC 62128-3:2013, Railway applications – Fixed installations – Electrical safety, earthing and
the return circuit – Part 3: Mutual interaction of a.c. and d.c. traction systems
IEC 62590:2019, Railway applications – Fixed installations – Electronic power converters for
substations
IEC 62313:2009, Railway applications – Power supply and rolling stock – Technical criteria for
the coordination between power supply (substation) and rolling stock
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following
addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
3.1
contact line system
support system and contact line supplying electric energy to vehicles through current-collecting
equipment
Note 1 to entry: The contact line system can comprise
– the contact line;
– masts and foundations;
– supports and any components registering the conductors,
– cross-spans or cables,
– tensioners,
– other along track conductors such as feeders, earth wires and return conductors when supported from the same
masts as the contact line,
– conductors connected permanently to the contact line for supplying other electrical equipment such as lighting,
signal operation, point control and point heating.
[SOURCE: IEC 60050-811:2017, 811-33-59]

– 8 – IEC 63438:2024 © IEC 2024
3.2
electric traction power supply system
railway electrical distribution network used to provide energy for rolling stock
Note 1 to entry: The system includes:
– contact line systems;
– return circuit of electric traction power supply systems;
– electrical installations in power plants and substations, which are utilized solely for distribution of power directly
to the contact line;
– electrical installations of switching stations.
[SOURCE: IEC 60050-811: 2017, 811-36-21, modified – "power supply" added in the term for
enhancing clarity since electric traction is typically used for onboard power supply. Also, running
rails of non-electrified lines in the vicinity of, and conductively connected to the running rails of
an electric traction power supply system, and electrical installations which are supplied from
contact lines either directly or via a transformer have been excluded from Note 1 to entry.]
3.3
traction substation
substation
substation, the main function of which is to supply an electric traction power supply system
Note 1 to entry: The synonym substation is used only when the context is clear
[SOURCE: IEC 60050-811:2017, 811-36-02]
3.4
switching station
traction switching station
installation from which electrical energy can be distributed to different feeding sections or from
which different feeding sections can be switched on and off or can be interconnected
[SOURCE: IEC 60050-811:2017, 811-36-22]
3.5
feeding section
electrical section of the route fed by individual track feeder circuit-breakers within the area
supplied by one or more substations
[SOURCE: IEC 60050-811:2017, 811-36-25]
3.6
electrical safety
freedom from risk that is not tolerable and which is caused by electricity
[SOURCE: IEC 60050-195:2021, 195-01-20]
3.7
electric shock
physiological effect resulting from an electric current passing through a human body or livestock
[SOURCE: IEC 60050-195:2021, 195-01-04]

3.8
return circuit
all conductors which form the intended path for the traction return current and the current under
fault conditions
Note 1 to entry: The conductors can be for example:
– running rails;
– return conductor rails;
– return conductors;
– return cables.
[SOURCE: IEC 60050-811:2017, 811-35-01]
3.9
switchgear
switching devices and their combination with associated control, measuring, protective and
regulating equipment, also assemblies of such devices and equipment with associated
interconnections, accessories, enclosures and supporting structures, intended in principle for
use in connection with generation, transmission, distribution and conversion of electric energy
[SOURCE: IEC 60050-441:1984, 441-11-02]
3.10
protection operating time
interval of time between the fault inception and the instant of initiation of the opening operation
of a switching device, e.g. circuit-breaker
Note 1 to entry: This time includes measurement, communication and protection device operation.
3.11
opening time
interval of time between the specified instant of initiation of the opening operation and the
instant when the arcing contacts have separated in all poles
Note 1 to entry: The instant of initiation of the opening operation, i.e. the application of the opening command (e.g.
energizing the release, etc.), is given in the relevant specifications.
[SOURCE: IEC 60050-441:1984, 441-17-36]
3.12
break-time
interval of time between the beginning of the opening time of a mechanical switching device (or
the pre-arcing time of a fuse) and the end of the arcing time
[SOURCE: IEC 60050-441:1984, 441-17-39]
3.13
fault clearance time
time interval between the fault inception and the fault clearance
Note 1 to entry: This time is the longest fault current interruption time of the associated circuit-breaker(s) for
elimination of fault current on the faulty item of plant.
Note 2 to entry: Fault clearance time is the total of the protection operating time, the (mechanical) opening time
and the arc extinction time. The latter two are included in break-time, IEC 60050-441–17–39.
[SOURCE: IEC 60050-448:1995, 448-13-15, modified – Note 2 to entry has been added.]

– 10 – IEC 63438:2024 © IEC 2024
3.14
touch voltage
voltage between conductive parts when touched simultaneously by a human being or livestock
Note 1 to entry: The value of the touch voltage is influenced by the impedance of the human being or the livestock
in electric contact with these conductive parts.
[SOURCE: IEC 60050-195:2021, 195-05-11]
3.15
fault condition
non intended condition caused by short-circuit, whilst the time duration is terminated by the
correct function of the protection devices and circuit-breakers
Note 1 to entry: For the relevant fault duration the correct operation of protection devices and circuit-breakers is
taken into account.
[SOURCE: IEC 62128-1:2013, 3.4.5, modified – "Whilst" added so as to link the sentence "The
time duration …" with the rest of the definition.]
3.16
low resistance fault
fault condition where the resistance of the fault is sufficiently low that the fault current has a
similar magnitude to that which would flow if the fault resistance were zero
Note 1 to entry: The resistance of the fault is typically dominated by the resistance of the power arc.
Note 2 to entry: In this definition, resistance will be understood as also being impedance for AC fault currents.
3.17
high resistance fault
shunt fault with high resistance at the fault location, where the resistance of the fault is
sufficiently high that the fault current has a substantially different magnitude to that which would
flow with a low resistance fault
Note 1 to entry: In this definition, resistance will be understood as also being impedance for AC fault currents.
[SOURCE: IEC 60050-448:1995, 448-13-08, modified – Definition amended to enhance clarity
for the application in electric traction power supply systems. Note 1 added.]
3.18
abnormal operating condition
condition where the system operates beyond its intended capabilities such that damage or
reduced life expectancy can be anticipated
3.19
short-circuit
accidentdal or intentional conductive path between two or more conductive parts forcing the
electric potential differences between these conductive parts to be equal to or close to zero
[SOURCE: IEC 60050-151:2001, 151-12-04]
3.20
current collector
equipment fitted to a vehicle and intended to collect current from a contact wire or conductor
rail
[SOURCE: IEC 60050-811:2017, 811-32-01]

3.21
protection
provisions for detecting faults or other abnormal operating conditions in a power system, for
enabling fault clearance, for terminating abnormal operating conditions, and for initiating signals
or indications
Note 1 to entry: The term "protection" is a generic term for protection equipment or protection systems.
Note 2 to entry: The term "protection" may be used to describe the protection of a complete power system or the
protection of individual plant items in a power system e.g. transformer protection, line protection, generator
protection.
Note 3 to entry: Protection does not include items of power system plant provided, for example, to limit overvoltages
on the power system. However, it includes items provided to control the power system voltage or frequency deviations
such as automatic reactor switching, load-shedding, etc.
[SOURCE: IEC 60050-448:1995, 448-11-01, modified – "abnormal condition" becomes
"abnormal operating conditions".]
3.22
protection system
arrangement of one or more protection equipments, and other devices intended to perform one
or more specified protection functions
Note 1 to entry: A protection system includes one or more protection equipment, intelligent electronic devices (IED),
instrument transformer(s), wiring, tripping circuit(s), auxiliary supply(s) and, where provided, communication
system(s). Depending upon the principle(s) of the protection system, it may include one end or all ends of the
protected section and, possibly, automatic reclosing equipment.
Note 2 to entry: The circuit-breaker(s) are excluded.
Note 3 to entry: The circuit-breaker protection functions are included, e.g. direct overcurrent or falling voltage
release of dc-circuit-breaker(s).
[SOURCE: IEC 60050-448:1995, 448-11-04, modified – Note 3 to entry added.]
3.23
protection equipment
equipment incorporating one or more protection relays and, if necessary, logic elements
intended to perform one or more specified protection functions
Note 1 to entry: A protection equipment is part of a protection system.
[SOURCE: IEC 60050-448:1995, 448-11-03, modified – Example omitted.]
3.24
protection relay
measuring relay which, either solely or in combination with other relays, is a constituent of a
protection equipment
[SOURCE IEC 60050-448:1995, 448-11-02]
3.25
protected section
part of a power system network, or circuit within a network, to which specified protection has
been applied
Note 1 to entry: The protected section normally originates from a point of automatic disconnection to at least the
next point of automatic disconnection or the end of the circuit.
Note 2 to entry: An electric traction power supply system is a form of power system network.
[SOURCE: IEC 60050-448:1995, 448-11-05, modified – Notes to entry added.]

– 12 – IEC 63438:2024 © IEC 2024
3.26
selectivity of protection
ability of a protection to identify the faulty section and/or phase(s) of a power system
Note 1 to entry: The synonym selectivity is used only when the context is clear.
[SOURCE: IEC 60050-448:1995, 448-11-06, modified – Note 1 to entry added.]
3.27
reliability of protection
probability that a protection can perform a required function under given conditions for a given
time interval
Note 1 to entry: The required function for protection is to operate when required to do so and not to operate when
not required to do so.
[SOURCE: IEC 60050-448:1995, 448-12-05]
3.28
redundancy
in an item, existence of more than one means for performing a required function
[SOURCE: IEC 60050-448:1995, 448-12-08]
3.29
sensitivity
minimum operating level (e.g. current, voltage, frequency, temperature) in a process that can
be detected for the purpose of protection
EXAMPLE Sensitivity of a protection system can be expressed by minimum fault current or maximum fault
impedance coverage.
3.30
main protection
protection expected to have priority in initiating fault clearance or an action to terminate an
abnormal condition in a power system
Note 1 to entry: For a given item of plant, two or more main protections may be provided.
[SOURCE: IEC 60050-448:1995, 448-11-13]
3.31
backup protection
protection which is intended to operate when a system fault is not cleared, or abnormal condition
not detected, in the required time because of failure or inability of other protection to operate
or failure of the appropriate circuit-breaker(s) to trip
[SOURCE: IEC 60050-448:1995, 448-11-14, modified – Note to entry omitted.]
3.32
circuit local backup protection
backup protection where the input is either from those transducers which are used by the main
protection or from transducers associated with the same primary circuit as the main protection
[SOURCE: IEC 60050-448:1995, 448-11-15 modified – "which is energised either from those
instrument transformers which energize"" replaced with "where the input is either from those
transducers which are used by". "instrument transformers" replaced with "a transducer" to make
it more generic. Note to entry omitted.]

3.33
substation local backup protection
backup protection where the input is taken from a transducer located within the same substation
as the corresponding main protection and not associated with the same primary circuit
Note 1 to entry: Substation local backup also extends to switching station local backup where appropriate.
[SOURCE: IEC 60050-448:1995, 448-11-16 modified – 'which is energized" replaced with
"where the input is taken". "instrument transformers" replaced with "a transducer" to make it
more generic. Note 1 to entry added.]
3.34
remote backup protection
backup protection located in a substation remote from that substation in which the
corresponding main protection is located
[SOURCE: IEC 60050-448:1995, 448-11-17]
3.35
circuit-breaker failure protection
protection which is designed to clear a system fault by initiating tripping of other circuit-
breaker(s) in the case of failure to trip of the appropriate circuit-breaker
[SOURCE: IEC 60050-448:1995, 448-11-18]
3.36
tripping
opening of a circuit-breaker by either manual or automatic control or by protective devices
[SOURCE: IEC 60050-448:1995, 448-11-31]
3.37
direct overcurrent release
overcurrent release directly energized by the current in the main circuit of a mechanical
switching device
[SOURCE: IEC 60050-441:1984, 441-16-36]
3.38
indirect overcurrent release
overcurrent release energized by the current in the main circuit of a mechanical switching device
through a current transformer or a shunt
[SOURCE: IEC 60050-441:1984, 441-16-37]

– 14 – IEC 63438:2024 © IEC 2024
4 System to be protected
4.1 Description
The system to be protected within the scope of this document is the electric traction power
supply system, within the limits set out in Figure 1. The electric traction power supply system
comprises:
– infeed to traction power conversion;
– traction power conversion (e.g. converter, transformer);
– infeed to secondary distribution busbar (including bus coupler);
– infeed to power absorbing equipment (e.g. energy storage system or braking resistor unit);
– line feeder, traction power distribution to the contact line system;
– interconnecting feeders between secondary distribution busbars, e.g. between two
substations or switching stations;
– switching station (including switching station feeder and bus coupler);
– autotransformers;
– contact line;
– return circuit.
Not every electric traction power supply system necessarily has all of the above mentioned
parts.
NOTE 1 The operational responsibility of the above mentioned components can be split among different operators
(owners). However, the protection principles described hereafter are valid for all installations.
The electric traction power supply system has interfaces to other parts of the railway system.
These interfaces can include:
– infeed to the primary distribution busbar;
– rolling stock;
– electrical installations fed by the contact line system or busbar (e.g. auxiliary transformers).
Other subsystems or equipment, e.g. signalling and communication can be influenced by the
electric traction power supply system but their protection is not within the scope of this
document.
Transmission and distribution power lines which are in parallel to or in the railway boundary are
not considered to be part of the electric traction power supply system. These are considered to
be covered by the protection principles for general transmission and distribution systems.

Figure 1 – Electric traction power supply system and its interfaces
NOTE 2 For DC systems the infeed to the secondary distribution busbar as shown in figure 1 can either be a circuit-
breaker or a disconnector. See 6.3.2.
Figure 1 shows a traction substation, however it also applies to the relevant parts of a switching
station, for example with a switching station feeder instead of a line feeder.
4.2 Interfaces
4.2.1 Infeed
The interface between the electric traction power supply system and the transmission /
distribution system is the feeder circuit-breaker at the infeed to the traction power conversion.
The upstream installations are considered to be covered by the protection principles for general
transmission and distribution systems, taking into account the following aspects at the interface:
• protection coordination;
• communication;
• automatic reclosure;
• direction of power flow (consumption and regeneration).
4.2.2 Rolling stock
The interface between the electric traction power supply system and the electric rolling stock is
the traction unit circuit-breaker.
For internal faults within a traction unit (i.e. faults occurring downstream of the traction unit
circuit-breaker) the requirements of IEC 62313:2009, Table 5, apply.

– 16 – IEC 63438:2024 © IEC 2024
Protection of electric rolling stock against faults downstream of the traction unit circuit-breaker
is not the primary function of the protection system of the electric traction power supply system,
however it can provide some degree of remote backup protection for such faults.
The protection in the traction substation shall be able to detect faults which include a maximum
vehicle impedance as set out in IEC 61991.
NOTE According to IEC 62313 internal faults on electric rolling stock are preferably cleared by the circuit-breaker
on the vehicle. The vehicle circuit-breaker is not intentionally delayed. The substation circuit-breaker is also tripped
without intentional delay in the main protection, i.e. there is no selectivity between vehicle and substation other than
by current magnitude. Even when considering the outage of one of these circuit-breakers the other provides limited
backup protection. Due to their non-selectivity there is no intentional delay in the clearance time.
In case of vehicles with regenerative braking the requirements of IEC 62313:2009, Clause 12
normally apply. Accordingly compliant vehicles will not continue to regenerate if there is a loss
of supply voltage or a contact line-rail/earth fault condition. In cases where rolling stock is not
IEC 62313 compliant, the arrangements for protection in case of regenerative braking shall be
agreed with the responsible entity.
4.2.3 Electrical installations fed by the electric traction power supply system
Electrical installations not directly related to traction power, for example auxiliary power supply,
are not part of the electric traction power supply system, although they may be fed by the
electric traction power supply system.
The interface between the electric traction power supply system and the electrical installations
which are fed by the contact line is the disconnecting device between the connection to the
contact line, i.e. overhead contact line or conductor rail, and the connection to the return circuit.
The interface of the electric traction power supply system to the electrical installations which
are fed by the substation busbar is the disconnecting device between the substation busbar
and the electrical installation where the downstream protection takes over.
The protection of the electric traction power supply system shall be coordinated with the
protection of the electrical installation. However, detection of internal faults within the electrical
installations fed by the electric traction power supply system is not the primary function of the
electric traction power supply system's protection system.
5 General principles
5.1 Objectives
The function of the protection system is to provide protection in the event of fault conditions
and abnormal operating conditions. This protection is provided by monitoring certain process
values such as current, voltage, frequency and temperature and by the initiation of
interventions, such as tripping of circuit-breakers.
The major objectives for protection systems are:
• continuation of service and performance of the electric traction power supply system and
minimizing the disturbance to operations as far as practicable;
• limitation of the impact and damage to the affected equipment;
• avoidance of cascading effects and expanding to other network areas;
• minimization of arcing effects and energy released during faults;
• contribution to the protection of persons against indirect elect
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