SIST EN 50526-3:2016
(Main)Railway applications - Fixed installations - D.C. surge arresters and voltage limiting devices - Part 3 Application guide
Railway applications - Fixed installations - D.C. surge arresters and voltage limiting devices - Part 3 Application guide
This Application Guide supports the European Standards EN 50526 1 and EN 50526 2. Guidance is offered on the following subjects. – The selection and installation of surge arresters – The selection and installation of voltage limiting devices as VLD-O and VLD-F. – The arrangement of the surge arresters and VLDs Because of differences in the established, proven methods, electric traction systems of nominal voltage 600 V – 750 V are treated separately from the systems at higher nominal voltages. This application guide does not treat systems different from the d.c. electrified traction systems
Bahnanwendungen - Ortsfeste Anlagen - Überspannungsableiter und Spannungsbegrenzungseinrichtungen für Gleichspannungsnetze - Teil 3: Anwendungsleitfaden
Dieser Anwendungsleitfaden unterstützt die Europäischen Normen EN 50526 1 und EN 50526 2.
Der Leitfaden ist auf folgende Themen ausgerichtet:
– die Auswahl und Installation von Überspannungsableitern;
– die Auswahl und Installation von Spannungsbegrenzungseinrichtungen als VLD-O und VLD-F;
– die Anordnung von Überspannungsableitern und VLDs.
Aufgrund der Unterschiede in den eingeführten und bewährten Methoden werden Bahnstromversorgungen mit einer Nennspannung von DC 600 V bis DC 750 V getrennt von Systemen mit höheren Nennspannungen behandelt.
Dieser Anwendungsleitfaden gilt ausschließlich für Gleichstrom-Bahnenergieversorgungssysteme.
Applications ferroviaires - Installations fixes - Parafoudres et limiteurs de tension pour systèmes à courant continu - Partie 3: Guide d'application
Le présent guide d’application prend en charge les Normes européennes EN 50526-1 et EN 50526-2. Des lignes directrices sont données sur les points suivants: – Le choix et l’installation des parafoudres – Le choix et l’installation des limiteurs de tension tels que VLD-O et VLD-F. – Le montage des parafoudres et des limiteurs de tension Du fait des différences dans les méthodes établies et éprouvées, les réseaux de traction électrique de tension nominale de 600 V à 750 V sont traités séparément des réseaux à tensions nominales plus élevées. Le présent guide d’application ne traite pas des réseaux différents des réseaux de traction électrique à courant continu.
Železniške naprave - Stabilne naprave električne vleke - Enosmerni prenapetostni odvodniki in omejilniki napetosti - 3. del: Navodilo za uporabo
To navodilo za uporabo podpira evropska standarda EN 50526 1 in EN 50526 2.
Navodila so na voljo za naslednja področja:
– izbira in namestitev prenapetostnih odvodnikov,
– izbira in namestitev omejilnikov napetosti kot VLD-O in VLD-F,
– razvrstitev prenapetostnih odvodnikov in omejilnikov napetosti.
Zaradi razlik v uveljavljenih in dokazanih metodah se električni vlečni sistemi z nazivno napetostjo 600 V do 750 V obravnavajo ločeno od sistemov z višjo nazivno napetostjo.
To navodilo za uporabo ne obravnava sistemov drugače od enosmernih elektrificiranih vlečnih sistemov.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-junij-2016
äHOH]QLãNHQDSUDYH6WDELOQHQDSUDYHHOHNWULþQHYOHNH(QRVPHUQLSUHQDSHWRVWQL
RGYRGQLNLLQRPHMLOQLNLQDSHWRVWLGHO 1DYRGLOR]DXSRUDER
Railway applications - Fixed installations - D.C. surge arresters and voltage limiting
devices - Part 3 Application guide
Ta slovenski standard je istoveten z: EN 50526-3:2016
ICS:
29.120.50 9DURYDONHLQGUXJD Fuses and other overcurrent
PHGWRNRYQD]DãþLWD protection devices
29.280 (OHNWULþQDYOHþQDRSUHPD Electric traction equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EUROPEAN STANDARD EN 50526-3
NORME EUROPÉENNE
EUROPÄISCHE NORM
January 2016
ICS 29.120.50; 29.280
English Version
Railway application - Fixed installations - D.C. surge arresters
and voltage limiting devices - Part 3: Application Guide
Applications ferroviaires - Installations fixes - Parafoudres et Bahnanwendungen - Ortsfeste Anlagen -
limiteurs de tension pour systèmes à courant continu - Überspannungsableiter und
Partie 3: Guide d'application Spannungsbegrenzungseinrichtung für
Gleichspannungsnetze - Teil 3: Anwendungsleitfaden
This European Standard was approved by CENELEC on 2015-12-07. CENELEC members are bound to comply with the CEN/CENELEC
Internal Regulations which stipulate the conditions for giving this European Standard the status of a national standard without any alteration.
Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the CEN-CENELEC
Management Centre or to any CENELEC member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CENELEC member into its own language and notified to the CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 50526-3:2016 E
Content Page
European foreword . 4
Introduction . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions. 7
4 General considerations . 13
4.1 General . 13
4.2 Application of surge arresters . 14
4.2.1 General . 14
4.2.2 Insulation level of equipment to be protected . 14
4.2.3 Internal overvoltages . 14
4.2.4 Lightning Overvoltages . 15
4.3 Application of VLDs . 16
4.3.1 General . 16
4.3.2 Short term protection . 16
4.3.3 Long term protection . 17
4.3.4 Selection of VLD-F or VLD-O . 17
5 Symbols for surge arresters and VLDs . 17
6 Guideline for Surge Arresters . 18
6.1 General . 18
6.1.1 Electrical characteristics . 18
6.1.2 Housing . 19
6.1.3 Porcelain-housed surge arresters . 19
6.1.4 Polymer-housed surge arresters . 19
6.2 Systems and equipment to be protected by surge arresters . 20
6.3 Nominal discharge current I . 23
n
6.4 Selection of Continuous Operating Voltage . 23
6.4.1 Continuous operating voltage U for arresters A1 . 23
c
6.4.2 Continuous operating voltage U for arresters A2 . 24
c
6.5 Protective level of A1 and A2 arresters. . 24
6.6 Charge transfer capability . 27
6.6.1 General . 27
6.6.2 Typical overvoltages during clearing a line fault . 27
6.6.3 Arrester A1 . 33
6.6.4 Arrester A2 . 34
6.7 Procedure to select an A1 arrester . 34
6.8 Procedure to select an A2 arrester . 38
6.9 Connecting leads of arresters . 38
6.10 Earthing requirements. 38
7 Guideline for VLDs . 39
7.1 Introduction . 39
7.2 General . 40
7.3 Mass transit railways and trams (U up to d.c. 750 V) . 40
n
7.3.1 General . 40
7.3.2 Trams with OCL . 40
7.3.3 Metros with a conductor rail . 42
7.3.4 Light-rail metros with OCLs . 43
7.4 Railways (d.c. 1 500V … d.c. 3 000 V) . 43
7.4.1 General . 43
7.4.2 Application of VLDs along the lines or at the substations and in the sectioning posts . 43
7.4.3 Recommended characteristics of VLDs . 45
7.5 Workshops . 46
7.5.1 Application of VLD-O . 46
7.5.2 Application of VLD-F . 46
8 Further considerations . 46
8.1 Installation recommendations . 46
8.1.1 Mounting aspect . 46
8.1.2 Periodicity of inspection and management of alarms . 48
8.1.3 Colours of the cables . 49
8.2 Interaction between arresters and VLDs . 49
8.3 Interaction with other systems . 49
8.3.1 Interaction with signalling systems . 49
8.3.2 Interaction with earthing systems . 50
8.3.3 Interaction with tunnel earthing systems . 50
8.3.4 Separation of a.c. cable screens . 50
Bibliography . 51
European foreword
This document (EN 50526-3:2016) has been prepared by CLC/SC 9XC, "Electric supply and earthing
systems for public transport equipment and ancillary apparatus (Fixed installations)", of CLC/TC 9X,
"Electrical and electronic applications for railways".
The following dates are fixed:
• latest date by which this document has to be (dop) 2016-12-07
implemented at national level by publication of
an identical national standard or by
endorsement
• latest date by which the national standards (dow) 2018-12-07
conflicting with this document have to
be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent
rights.
Introduction
This European Standard is divided into three parts.
Part 1 deals with metal oxide arresters without gaps for d.c. railway traction systems (fixed installations)
and is based on EN 60099-4.
Part 2 deals with voltage limiting devices for specific use in d.c. railway traction systems (fixed
installations).
Part 3 is a Guide of application of metal-oxide arresters and of voltage limiting devices.
1 Scope
This Application Guide supports the European Standards EN 50526-1 and EN 50526-2.
Guidance is offered on the following subjects:
– the selection and installation of surge arresters;
– the selection and installation of voltage limiting devices as VLD-O and VLD-F;
– the arrangement of the surge arresters and VLDs.
Because of differences in the established, proven methods, electric traction systems of nominal voltage
d.c. 600 V – d.c. 750 V are treated separately from the systems at higher nominal voltages.
This Application Guide only applies to d.c. electrified traction systems
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.
EN 50122-1:2011, Railway applications - Fixed installations - Electrical safety, earthing and the return
circuit - Part 1: Protective provisions against electric shock
EN 50122-2:2010, Railway applications - Fixed installations - Electrical safety, earthing and the return
circuit - Part 2: Provisions against the effects of stray currents caused by d.c. traction systems
EN 50123-2:2003, Railway applications - Fixed installations - D.C. switchgear - Part 2: D.C. circuit
breakers
EN 50123-7-1:2003, Railway applications - Fixed installations - D.C. switchgear - Part 7-1:
Measurement, control and protection devices for specific use in d.c. traction systems - Application guide
EN 50124-1:2001, Railway applications - Insulation coordination - Part 1: Basic requirements -
Clearances and creepage distances for all electrical and electronic equipment
EN 50163: 2004 , Railway applications - Supply voltages of traction systems
EN 50526-1:2012, Railway applications - Fixed installations - D.C. surge arresters and voltage limiting
devices - Part 1: Surge arresters
EN 50526-2:2014, Railway applications - Fixed installations - D.C. surge arresters and voltage limiting
devices - Part 2: Voltage limiting devices
EN 62305-2, Protection against lightning - Part 2: Risk management.
IEC 60050-195:1998, International Electrotechnical Vocabulary - Chapter 195: Earthing and protection
against electric shock
IEC 60050-441:1984, International Electrotechnical Vocabulary - Chapter 441: Switchgear, controlgear
and fuses
IEC 60050-604:1987, International Electrotechnical Vocabulary. Chapter 604: Generation, transmission
and distribution of electricity - Operation
IEC 60050-811:1991, International Electrotechnical Vocabulary - Chapter 811: Electric traction
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
nominal voltage
U
n
designated value for a system
[SOURCE: EN 50163:2004, 3.3]
3.2
highest permanent voltage
U
max1
maximum value of the voltage likely to be present indefinitely
[SOURCE: EN 50163:2004, 3.4]
3.3
highest non-permanent voltage
U
max2
maximum value of the voltage likely to be present for a limited period of time
[SOURCE: Adapted from EN 50163:2004, 3.5]
3.4
rated insulation voltage
U
Nm
d.c withstand voltage value assigned by the manufacturer to the equipment or a part of it, characterising
the specified permanent (over five minutes) withstand capability of its insulation
[SOURCE: EN 50526-1:2012, 3.4]
3.5
rated impulse withstand voltage
U
Ni
impulse voltage value assigned by the manufacturer to the equipment or a part of it, characterising the
specified withstand capability of its insulation against transient overvoltages
[SOURCE: EN 50526-1:2012, 3.5]
3.6
overvoltage
voltage having a peak value exceeding the corresponding peak value of the highest non-permanent
voltage U
max2
[SOURCE: EN 50526-1:2012, 3.6]
3.7
transient overvoltage
short duration overvoltage of a few (up to 20 ms) milliseconds or less associated with a transient regime
Note 1 to entry: Two particular transient overvoltages are defined: switching overvoltage and lightning overvoltage.
[SOURCE: EN 50526-1:2012, 3.7]
3.8
switching overvoltage
U
so
transient overvoltage at any point of the system due to specific switching operation or fault
[SOURCE: EN 50526-1:2012, 3.8]
3.9
lightning overvoltage
transient overvoltage at any point of the system due to a lightning discharge
[SOURCE: EN 50124-1:2001,1.3.3.2.2]
3.10
surge arrester
device intended to limit the transient overvoltages to a specified level
[SOURCE: EN 50526-1:2012, 3.10]
3.11
metal-oxide surge arrester
arrester having non-linear metal-oxide resistors connected in series and/or in parallel without any
integrated series or parallel spark gaps
[SOURCE: EN 50526-1:2012, 3.11]
3.12
continuous operating voltage of an arrester
U
c
designated permissible d.c. voltage value that may be applied continuously between the arrester
terminals
[SOURCE: EN 50526-1:2012, 3.12]
3.13
rated voltage of an arrester
U
r
voltage by which the arrester is designated
Note 1 to entry: Because of the particular nature of the d.c. electrical installation dealt with, the rated voltage of a
d.c. arrester coincides with the continuous operating voltage.
[SOURCE: EN 50526-1:2012, 3.13]
3.14
lightning impulse protection level
U
pl
the maximum residual voltage for the nominal discharge current
[SOURCE: EN 50526-1:2012, 3.15]
3.15
switching impulse protection level
U
ps
maximum residual voltage at the specified switching impulse current
[SOURCE: EN 50526-1:2012, 3.16]
3.16
charge transfer capability
Q
T
maximum charge per impulse that can be transferred during the charge transfer test and during the
operating duty test
[SOURCE: EN 50526-1:2012, 3.17]
3.17
discharge current of an arrester
impulse current which flows through the arrester
[SOURCE: EN 50526-1:2012, 3.18]
3.18
nominal discharge current of an arrester
I
n
peak value of lightning current impulse which is used to classify an arrester
[SOURCE: EN 50526-1:2012, 3.19]
3.19
high current impulse of an arrester
peak value of discharge current having a 4/10 µs impulse shape which is used to test the stability of the
arrester on direct lightning strikes
[SOURCE: EN 50526-1:2012, 3.20]
3.20
steep current impulse
current impulse with a virtual front time of 1 µs with limits in the adjustment of equipment such that the
measured values are from 0,9 µs to 1,1 µs and the virtual time to half-value on the tail is not longer than
20 µs
[SOURCE: EN 50526-1:2012, 3.21]
3.21
lightning current impulse
8/20 µs current impulse with limits on the adjustment of equipment such that the measured values are
from 7 µs to 9 µs for the virtual front time and from 18 µs to 22 µs for the time to half-value on the tail
[SOURCE: EN 50526-1:2012, 3.22]
3.22
direct lightning current impulse
impulse defined by the charge Q and the peak value of the current impulse I
imp
[SOURCE: EN 50526-1:2012, 3.23]
3.23
switching current impulse of an arrester
I
sw
peak value of discharge current having a virtual front time greater than 30 µs but less than 100 µs and a
virtual time to half value on the tail of roughly twice the virtual front time
[SOURCE: EN 50526-1:2012, 3.24]
3.24
porcelain-housed arrester
arrester using porcelain as housing material, with fittings and sealing systems
[SOURCE: EN 50526-1:2012, 3.30]
3.25
polymer-housed arrester
arrester using polymeric and/or composite materials for housing
[SOURCE: EN 50526-1:2012, 3.31]
3.26
flashover
disruptive discharge over a solid surface
[SOURCE: EN 50526-1:2012, 3.44]
3.27
impulse
unidirectional wave of voltage or current which without appreciable oscillations rises rapidly to a
maximum value and falls – usually less rapidly – to zero with small, if any, excursions of opposite
polarity
Note 1 to entry: The parameters which define a voltage or current impulse are polarity, peak value, front time and
time to half value on the tail.
[SOURCE: EN 50526-1:2012, 3.45]
3.28
voltage-limiting device
VLD
protective device whose function is to prevent existence of an impermissible high touch voltage
[SOURCE: EN 50122-1:2011, 3.1.20]
3.29
recoverable VLD
VLD that recovers after triggering
[SOURCE: EN 50526-2:2014, 3.2]
3.30
non-recoverable VLD
VLD remaining in its low resistance state permanently after triggering
[SOURCE: EN 50526-2:2014, 3.3]
3.31
welding-shut spark gap
voltage fuse
VLD which triggers by electrical discharge across a gap causing a permanent short-circuit by melting of
metallic parts
[SOURCE: EN 50526-2:2014, 3.4]
3.32
rated current
I
r
maximum value of the direct current that may flow permanently through the VLD in specified
environmental conditions
[SOURCE:EN 50526-2:2014, 3.5]
3.33
short time withstand current
I
W
current that a VLD can carry in closed status, during a specified short time under prescribed conditions
of use and behaviour
[SOURCE: EN 50526-2:2014, 3.6]
3.34
breaking capacity
maximum current that a recoverable VLD can interrupt at a stated voltage
[SOURCE: IEC 60050-441:1984, 17-08]
3.35
residual voltage
U
res
a) peak value of voltage that appears between the terminals of an arrester during the passage of
discharge current
b) value of voltage that appears between the terminals of the VLD during the passage of a specified
current
[SOURCE: EN 50526-1:2012, 3.27] and [SOURCE: EN 50526-2:2014, 3.17]
3.36
structure earth
construction made of metallic parts or construction including interconnected metallic structural parts,
which can be used as an earth electrode
[SOURCE: EN 50122-1:2011, 3.2.4]
3.37
open connection
connection of conductive parts to the return circuit by a voltage-limiting device which makes a
conductive connection either temporarily or permanently if the limited value of the voltage is exceeded
[SOURCE: EN 50122-1:2011, 3.2.12]
3.38
return circuit
all conductors which form the intended path for the traction return current
EXAMPLE Conductors may be:
– running rails,
– return conductor rails,
– return conductors,
– return cables.
[SOURCE: EN 50122-1:2011, 3.3.1]
3.39
rail potential
U
RE
voltage occurring between running rails and earth
[SOURCE: EN 50122-1:2011, 3.3.7]
3.40
(traction) substation
installation to supply a contact line system and at which the voltage of a primary supply system, and in
certain cases the frequency, is transformed to the voltage and the frequency of the contact line
[SOURCE: EN 50122-1:2011, 3.4.2]
3.41
(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: EN 50122-1:2011, 3.4.3]
3.42
normal operation
operation without fault condition on the line
Note 1 to entry: In this standard normal operation includes also degraded mode (loss of one or several substations)
3.43
fault (or fault condition)
non intended condition caused by short-circuit. 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: Adapted from EN 50122-1:2011, 3.4.5]
3.44
internal overvoltage
an overvoltage in the system resulting from switching or from a fault in the system itself
[SOURCE: IEC 60050-604:1987, 03-31]
3.45
short-circuit
accidental 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 60050-195:1998, 04-11]
3.46
stray current
part of the current caused by a d.c.-traction system which follows paths other than the return circuit
[SOURCE: Adapted from EN 50122-1:2011, 3.6.3]
3.47
overhead contact line
OCL
contact line placed above (or beside) the upper limit of the vehicle gauge and supplying vehicles with
electric energy through roof-mounted current collection equipment
[SOURCE: IEC 60050-811:1991, 33-02]
3.48
conductor rail
contact line made of a rigid metallic section or rail, mounted on insulators located near the running rails
[SOURCE: EN 50119:2009, 3.1.7]
3.49
overhead contact line zone
OCLZ
zone whose limits are in general not exceeded by a broken overhead contact line
[SOURCE: EN 50122-1:2011, 3.5.9]
3.50
current collector zone
CCZ
zone whose limits are in general not exceeded by an energised collector no longer in contact with the
contact line or broken collector and its fragments
[SOURCE: EN 50122-1:2011, 3.5.10]
4 General considerations
4.1 General
Surge arresters are intended to protect power equipment from the lightning overvoltages. A surge
arrester can be used also in order to protect electronic equipment against high transient voltages in the
circuits to which the equipment is connected. See EN 50526-1 for the product specification.
VLDs are intended to protect persons from impermissible touch voltages between conductive parts
caused by train operating currents or faults. When selecting a VLD, it should be considered whether the
required function is VLD-F, or VLD-O or both as described in EN 50122-1. This is a question for the
system design. See EN 50526-2 for the product specification.
4.2 Application of surge arresters
4.2.1 General
The contact lines of electric railways are exposed to direct and to indirect lightning overvoltages. These
overvoltages may cause flashover of the line insulation and, travelling along the lines, may enter the
supply substations and stress or even damage the insulation of the equipment inside. Overvoltages may
also appear on the track and, travelling along it, stress the insulation of the electronic equipment
connected to it.
The insulation of the substation equipment is critical, as flashover of such insulation in most cases
causes a permanent outage of the substation. Also the insulation of the equipment connected to the
track is critical as it is not self-restoring. Such equipment should be protected by surge arresters of such
characteristics as to reduce the overvoltages below its insulation level.
Flashover of the line insulation is in general non critical. The flash over initiates a short circuit of the
power supply system which is then cleared by the protective circuit breaker. In most cases the insulation
is self-restoring and the line can be re-energized after a short time (a few seconds) following the tripping
Therefore, line insulation does not require to be protected by surge arresters except in special cases:
e.g. cable terminations connected to the line, discontinuities along the line in regions with a very high
flash density, very high short circuit follow-through currents able to damage the insulators, etc.
In order to protect the insulation it is necessary to coordinate properly the characteristics of the
protecting surge arresters with those of the protected insulation. For this purpose the following
information is necessary as a minimum:
– Lightning impulse withstand level of the equipment to be protected (see 4.2.2);
– Characteristics of the lightning overvoltages (see 4.2.4);
– Protection level of the arrester (see 6.5);
– Charge transfer capability of the arrester (see 6.6).
The protection is effective if the protection level provided by the arrester is lower with enough margin
than the lightning impulse withstanding level of the equipment to be protected.
In choosing the arrester, knowledge is necessary also of the maximum internal overvoltages (see 4.2.3)
as it is necessary to make sure that the charge transfer capability of the arrester is not exceeded.
4.2.2 Insulation level of equipment to be protected
For the equipment powered by the contact line, Table A.2 in EN 50124-1:2001 gives information on
). In general, for equipment connected to the return
minimum values of the rated impulse voltage (U
Ni
circuit inside the substations, the insulation level is assumed to be the same as for circuits directly
connected to the contact line. For bonding cables and related items no standard impulse withstand
voltage is available.
4.2.3 Internal overvoltages
For equipment powered by the contact line:
– Annex A in EN 50163:2004 gives information on the amplitude and duration of the voltage that may
appear on the contact line and stress the connected equipment.
– the highest switching overvoltage may be assumed to be 3 - 4 times the nominal voltage as the arc
voltage in the circuit breaker is limited to four times U (see 5.7 of EN 50123-2:2003).
n
For equipment connected to the track a voltage as a function of the time as indicated in Table 6 in
EN 50122-1:2011 may be assumed.
4.2.4 Lightning Overvoltages
Traction systems can be treated in the same way as medium voltage distribution systems with respect to
overvoltages and insulation co-ordination.
Lightning parameters are derived from statistical analysis of worldwide lightning measurements. The
most frequently occurring negative cloud-to-ground flashes have current peak values between 14 kA
(95 % probability) and 80 kA (5 % probability). With a probability of 50 %, the following values are
reached or exceeded (see for instance Cigré TB 287):
– Current peak value: 30 kA
– Rise time: 5,5 µs
– Time to half value: 75 µs
Extreme lightning surges can reach peak values up to 200 kA, with half-time values of 2 000 µs. A peak
value of 20 kA with a probability of 80 % is often used in the standardisation work, and for test and co-
ordination purposes for surge arresters. This standardized nominal lightning current has a rise time of 8
µs and a half time of 20 µs (wave shape 8/20). Other standardized currents are the high current impulse
with the wave shape 4/10 µs and peak values up to 200 kA, and the switching current impulse with
30/60 µs wave shape and peak values up to 2 kA.
A specific wave shape 10/350 µs for direct lightning is also defined (see EN 50526-1). Normally, there is
a flashover at each pole (see below) leading after a few spans to an 8/20 µs wave shape, so that this
wave shape is finally used for classifying surge arresters.
In case of a direct lightning strike into the contact line, the charge flows in the form of two equal current
waves in both directions, starting from the point of strike. A voltage wave is accompanied by the current
wave due to the surge impedance of the line.
Typical values for the surge impedances of overhead lines in d.c. traction systems are 460 Ω for non-
catenary overhead contact lines and 380 Ω for catenary overhead contact lines. For conductor rails a
value of 160 Ω can be used.
NOTE For other specific cases calculation methods are available in the literature.
Considering the peak value of 30 kA, as mentioned above, and a surge impedance of 460 Ω, a very high
transient overvoltage occurs, with a steepness of about 1 250 kV/µs. None of the equipment in d.c.
railway systems up to 3 000 V is insulated for such voltage stresses. Therefore, surge arresters have to
be used to limit the transient overvoltages from lightning according to the rules of insulation co-
ordination.
Besides the regional exposure to lightning, the frequency of lightning strikes depends on the topography
and the structural design of the line (see EN 62305-2). In particular, the frequency of lightning strikes is
relatively high if there are big crossing areas, bridges, viaducts and spacious operating areas. It is to be
noted that lightning protection can always only cover a certain percentage of all possible lightning strikes
and mainly depends on operational and economic aspects (see EN 62305-2).
4.3 Application of VLDs
4.3.1 General
As stipulated by EN 50122-1, a VLD operates in such a way as to bond the return circuit of d.c. railway
systems to the earthing system or the exposed conductive parts, in order to suppress impermissible
touch voltages in normal operation or in fault condition. The voltages admissible in the track as defined
by EN 50122-1 are indicated in Figure1.
For general requirements for the application of VLDs refer to EN 50122-1:2011, Annex F.
U
V
A B
0,02 0,7 s 300
t
Key
A short-term protection
B long-term protection
t time duration (s)
Figure 1 – Permissible touch voltages in d.c. traction systems according to EN 50122-1
4.3.2 Short term protection
The short term protection aims at protecting people and equipment against dangerous accessible
voltages that can arise in fault condition, such as the fall of a broken contact wire. VLDs type F ensure
this function: the VLD-F function is required when the source of the impermissible voltage is the voltage
on the contact line, when a fault occurs, and the risks are of electric shock by indirect contact as
described in EN 50122-1.
The VLD-F need a short-time current capability to carry the expected short time current, especially when
the fault location is close to the substation. A VLD-F needs not interrupt the part of the fault current
which flows through it, as line circuit breakers are employed to limit the risks from that current.
An A2 arrester may be put in parallel to a VLD. In this case the A2 arrester provides the protection of the
VLD against the lightning overvoltages while the VLD protects against impermissible touch voltages.
Additionally, the VLD may reduce the required charge transfer capability of the A2 arrester.
4.3.3 Long term protection
The long term protection provided by a VLD-O corresponds to protection against impermissible touch
voltages that may arise in normal operation due to the train traffic and to the fact that permanent
equipotential bonding should not be provided because of the risks from damage to assets by stray
current, as described in EN 50122-2. A VLD-O should be able to interrupt the current that flows in it, in
order to minimise the risks from stray current. VLD-Os require a long term current capability.
4.3.4 Selection of VLD-F or VLD-O
A single VLD can fulfil both functions; VLD-F and VLD-O, if attention is paid to the relevant
characteristics when the device is selected.
To limit the risks from stray current, all of these devices (VLD-F and VLD-O) offer better performance if
they are recoverable (Classes 2, 3 and 4) than if they are non-recoverable (Class 1).
Definite selection and application of appropriate Class is subject to specific requirements depending on
several factors like: location, type of system, object to be protected, etc.
NOTE Classes of VLDs are defined in EN 50526-2:2014.
5 Symbols for surge arresters and VLDs
The following symbols should be used to designate the arresters and voltage limiting devices, whatever
the technology used for the device is:
5.1
A1 arrester
5.2
A2 arrester
5.3
Voltage Limiting Device
5.4
Combination of VLD and A2
arrester
NOTE This symbol of arrester A1 also refers to a varistor, but is used to keep consistency with the symbols
used in EN 50526-1.
6 Guideline for Surge Arresters
6.1 General
6.1.1 Electrical characteristics
Figure 2 shows the typical U-I characteristic of a metal oxide arrester measured by applying d.c.
currents and current impulses of different wave shapes.
Key
U Residual voltage;
res
U Lightning impulse protective level;
pl
U Reference voltage,
ref
I Reference current;
ref
I Nominal discharge current.
n
Figure 2 – Typical residual voltage of a metal oxide arrester as a function of the current
Typical values of the lightning protective levels (U ) and of the switching protective levels (U )
pl ps
depending on the discharge current and on the wave form are indicated in Table 1 as ratio to the
continuous operating voltage, 0,29 kV ≤ U ≤ 5 kV.
c
Table 1 – Typical lightning and switching protective levels of d.c. metal oxide arresters.
Class U /U U /U
pl c ps c
typical values at typical values At
DC-A 2,5 to 3,1 10 kA - 8/20 μs 2,0 to 2,5 500 A - 30/60 μs
DC-B 2,3 to 2,5 10 kA - 8/20 μs 2,0 to 2,2 1 000 A -
30/60 μs
DC-C 2,4 to 2,5 20kA - 8/20 μs 2,0 to 2,2 2 000 A -
30/60 μs
6.1.2 Housing
The active part of d.c. surge arrester is made of MO resistor elements enclosed in a housing.
The main requirements of the housing are:
– sealing against moisture ingress;
– mechanical strength;
– voltage withstand at lightning or switching transients, to prevent flashovers;
– creepage distance, to prevent flashovers;
– performance under polluted conditions;
– pressure relief under overload conditions;
– conduct heat from the metal oxide resistor elements to the environment.
6.1.3 Porcelain-housed surge arresters
The active part of the arrester is placed in a porcelain insulator with terminations on both ends. The gap
between active part and inner wall of the housing may be completely or partly filled with gas or by other
material. The gas in these arresters typically is nitrogen or (synthetic) air. Usually pressure relief devices
are provided which ensure that the housing will not break violently after puncture or flashover of the
active part due to energetic overload. Special care about safety considerations shall be taken for
designs without pressure relief devices.
Surge arresters with a housing from epoxy-resin behave mechanically like porcelain-housed arresters,
because epoxy resin is a brittle material, and shall be treated and tested as porcelain-housed surge
arresters.
6.1.4 Polymer-housed surge arresters
A variety of different designs has been developed, the main types of which are according to the following
basic design principles:
a) "Tube design": The composite housing is formed from a tube of fibre glass reinforced plastic (FRP)
covered by outer weather sheds from polymeric material with terminations on both ends. The outer
weather sheds are either directly moulded to the tube or drawn as individual parts. This design has
a sealing system and a pressure relief device which ensures that the housing will not break violently
after puncture or flashover of the active part due to energetic overload. The internal design is similar
to porcelain-housed arresters with an inner gas volume.
b) "Wrapped design": The housing is directly applied to the stack of metal oxide resistor elements
without an intended gas volume inside. The mechanical supporting part of the housing is formed by
a wrapped FRP structure with terminations on both sides and outer weather sheds from polymeric
material.
c) "Cage design": The stack of metal oxide resistor elements is clamped by FRP loops or rods or bands
at high mechanical tension forces. The metal oxide resistor elements act as part of the mechanically
supporting structure and the FRP elements form an open cage. The outer weather sheds are
directly moulded to the modules. The housing is without intended gas volume inside.
The outer part of a polymeric housing, which is exposed to the environment, may be made from different
kinds of materials, such as EPDM (ethylene-propylene-diene-monomer), EVA (ethylene-vinyl-acetate) or
SIR (silicone rubber). In most cases, these polymeric materials are doped by chemicals or filled by fillers
in order to provide sufficient resistance to environmental impact. Most important characteristics are
hydrophobicity (the ability to repel water) and tracking and erosion resistance.
Table 2 – Some characteristics of porcelain-housed and polymer-housed arresters
porcelain-housed surge arrester polymer-housed surge arrester
high weight low weight
brittle material, sensitive to mechanical shocks flexible outer sheds, tolerant to mechanical shocks
cleaning of polluted housings necessary no cleaning of polluted housing necessary
medium behaviour at polluted environment excellent behaviour at polluted environment,
hydrophobic behaviour
6.2 Systems and equipment to be protected by surge arresters
It is recommended to apply surge arresters in substations, at sectioning posts and at specific points
along the contact line system to protect the connected equipment from transient overvoltages (see
Figures 3 and 4).
The terminations of the insulated cables connected to the contact line system and the electronic
apparatus connected to the return pole of the rectifier in the substations should be protected by surge
arresters.
Surge arresters may also be installed between the OCL system and earth where discontinuities in the
line are present and reflections of the overvoltage waves may occur, for example:
– at each feeding switch-disconnector or disconnector;
– along the line, at both sides of a normally open switch-disconnector or disconnector (bridging a
section-insulator);
– along the line, at a normally closed switch-disconnector or disconnector (bridging a section-
insulator);
– at the ends of a section;
– at power demand points (e.g. for switch heating).
For track sections with frequen
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.
Loading comments...