EN 50124-1:2017

SLOVENSKI STANDARD
01-maj-2017
1DGRPHãþD
SIST EN 50124-1:2002
SIST EN 50124-1:2002/A1:2004
SIST EN 50124-1:2002/A2:2005
äHOH]QLãNHQDSUDYH8VNODGLWHYL]RODFLMHGHO2VQRYQH]DKWHYH,]RODFLMVNHLQ
SOD]LOQHUD]GDOMH]DYVRHOHNWULþQRLQHOHNWURQVNRRSUHPR
Railway applications - Insulation coordination - Part 1: Basic requirements - Clearances
and creepage distances for all electrical and electronic equipment
Bahnanwendungen - Isolationskoordination - Teil 1: Grundlegende Anforderungen - Luft-
und Kriechstrecken für alle elektrischen und elektronischen Betriebsmittel
Applications ferroviaires - Coordination de l'isolement - Partie 1: Prescriptions
fondamentales - Distances d'isolement dans l'air et lignes de fuite pour tout matériel
électrique et électronique
Ta slovenski standard je istoveten z: EN 50124-1:2017
ICS:
29.080.01 (OHNWULþQDL]RODFLMDQD Electrical insulation in
VSORãQR general
29.280 (OHNWULþQDYOHþQDRSUHPD Electric traction equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN 50124-1
NORME EUROPÉENNE
EUROPÄISCHE NORM
March 2017
ICS 29.080.01; 29.280 Supersedes EN 50124-1:2001
English Version
Railway applications - Insulation coordination - Part 1: Basic
requirements - Clearances and creepage distances for all
electrical and electronic equipment
Applications ferroviaires - Coordination de l'isolement - Bahnanwendungen - Isolationskoordination - Teil 1:
Partie 1: Prescriptions fondamentales - Distances Grundlegende Anforderungen - Luft- und Kriechstrecken für
d'isolement dans l'air et lignes de fuite pour tout matériel alle elektrischen und elektronischen Betriebsmittel
électrique et électronique
This European Standard was approved by CENELEC on 2017-02-06. 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, Serbia, 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
© 2017 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN 50124-1:2017 E
Contents Page
European foreword . 5
Introduction . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 Basis for insulation coordination . 11
4.1 Basic principles . 11
4.1.1 General . 11
4.1.2 Insulation coordination with regard to voltage . 11
4.1.3 Insulation coordination with regard to environmental conditions . 12
4.2 Voltages and voltage ratings . 13
4.2.1 General . 13
4.2.2 Rated insulation voltage U . 13
Nm
4.2.3 Rated impulse voltage U . 13
Ni
4.3 Time under voltage stress. 14
4.4 Pollution . 14
4.5 Insulating material . 15
4.5.1 General . 15
4.5.2 Comparative tracking index (CTI) . 15
5 Requirements and dimensioning rules for clearances . 16
5.1 General . 16
5.2 Minimum clearances . 16
5.2.1 Functional insulation. 16
5.2.2 Basic and supplementary insulation . 16
5.2.3 Reinforced insulation . 16
5.3 Contingency . 16
5.4 Clearances for altitudes higher than 2 000 m . 17
6 Dimensioning rules for creepage distances . 17
6.1 General . 17
6.2 Minimum creepage distances . 17
6.2.1 Functional, basic and supplementary insulations . 17
6.2.2 Reinforced insulation . 17
7 Tests and measurements . 18
7.1 General . 18
7.2 Measurement of creepage distances and clearances . 18
7.2.1 Method and values . 18
7.2.2 Acceptance criteria . 18
7.3 Verification of clearances by impulse test . 18
7.3.1 Method and values . 18
7.3.2 Test acceptance criteria . 19
7.4 Verification of clearances by power-frequency test . 19
7.4.1 Method and values . 19
7.4.2 Test acceptance criteria . 19
7.5 Verification of clearances by d.c. voltage test . 19
7.5.1 Method and values . 19
7.5.2 Test acceptance criteria . 19
8 Specific requirements for applications in the railway field . 20
8.1 General . 20
8.2 Specific requirements for signalling . 20
8.2.1 Overvoltage categories . 20
8.2.2 Rated impulse voltages . 21
8.2.3 Induced voltages . 21
8.2.4 Installation instructions . 21
8.2.5 Pollution degrees . 21
8.3 Specific requirements for rolling stock . 21
8.3.1 Determination of the rated impulse voltage U by method 1 . 21
Ni
8.3.2 Creepage distances . 22
8.3.3 Roof installations . 22
8.4 Specific requirements for fixed installations . 22
8.4.1 Determination of the rated impulse voltage U by method 1 . 22
Ni
8.4.2 Distances of outdoor insulators . 23
Annex A (normative) Tables . 24
Annex B (normative) Provisions for type and routine dielectric tests for
equipment . 31
B.1 General . 31
B.2 Tests . 31
Annex C (normative) Methods of measuring creepage distances and clearances . 33
Annex D (normative) Correlation between U and U . 40
n Nm
Annex E (informative) Macro-environmental conditions . 41
Annex F (informative) Application guide . 42
F.1 Introduction . 42
F.2 Determination of minimum clearances and creepage distances . 42
F.3 Examples . 48
F.4 Tests . 50
Annex ZZ (informative) Relationship between this European Standard and the
Essential Requirements of EU Directive 2008/57/EC . 52
Bibliography . 53
Tables
Table A.1 — Rated impulse voltage U for low voltage circuits not powered
Ni
directly by the contact line . 24
Table A.2 — Rated impulse voltages (U ) for circuits powered by the contact line
Ni
and for traction power circuits in thermo-electric driven vehicles . 25
Table A.3 — Minimum clearances in air for the standard altitude ranges based on
the rated impulse voltage U . 26
Ni
Table A.4 — Definition of pollution degrees . 27
Table A.5 — Minimum creepage distances based on rated insulation voltage U
Nm
up to 1 000 V for printed wiring material and associated components . 27
Table A.6 — Minimum creepage distances for low values of rated insulation
voltage U for materials other than printed wiring material . 28
Nm
Table A.7 — Minimum creepage distances (in mm/kV) for high values of rated
insulation voltage U . 28
Nm
Table A.8 — Test voltages for verifying clearances at atmospheric and altitude
reference conditions, not to be used for routine dielectric tests . 29
Table A.9 — Altitude correction factors for clearances in circuits with U up to
Ni
and including 60 kV when equipment is intended to be used above 2 000 m . 30
Table A.10 — Altitude correction factors for clearances in circuits with U higher
Ni
than 60 kV when equipment is intended to be used above 2 000 m . 30
Table B.1 — Dielectric test for equipment - Short-duration power-frequency (a.c.)
test levels U (kV) based on the rated impulse voltage U (kV) . 32
a Ni
Table C.1 — Minimum dimensions of grooves . 33
Table D.1 — Correlation between nominal voltages of the railway power
distribution system and the required insulation voltages for circuits of
equipment which are intended to be connected to these systems . 40
Table E.1 — Correlation between pollution degrees and macro-environmental
conditions . 41
Table F.1 — Example for the determination of clearances and creepage distances . 50
Table ZZ.1 — Correspondence between this European Standard, the TSI
“Locomotives and Passenger Rolling Stock” (REGULATION (EU) No 1302/2014 of
18 November 2014 . 52
) and Directive 2008/57/EC
Table ZZ.2 — Correspondence between this European Standard, the TSI “Energy”
(REGULATION (EU) No 1301/2014 of 18 November 2014) and Directive 2008/57/EC . 52
European foreword
This document (EN 50124-1:2017) has been prepared by CLC/TC 9X, “Electrical and electronic
applications for railways.”
The following dates are fixed:
• latest date by which this document has to be (dop) 2018–02–06
implemented at national level by publication
of an identical national standard or by
endorsement
• latest date by which the national standards (dow) 2020–02–06
conflicting with this document have to

be withdrawn
This document supersedes EN 50124-1:2001, EN 50124-1:2001/A1:2003 and
EN 50124-1:2001/A1:2005.
1:2001:
• the scope has been enlarged to include altitudes higher than 2 000 m above sea level;
• related requirements have been included, especially new subclause 5.4, Table A.9 and
Table A.10.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
This document has been prepared under a mandate given to CENELEC by the European Commission
and the European Free Trade Association, and supports essential requirements of EU Directive(s).
For the relationship with EU Directive(s) see informative Annex ZZ, which is an integral part of this
document.
Introduction
Special conditions occurring in railway applications and the fact that the equipment here concerned
falls into the scope of both the EN 60071 series (prepared by CLC/SR 28) and EN 60664-1 (prepared
by CLC/SR 109), led to the decision to draw from these documents and from EN 60077-1 (prepared
by CLC/TC 9), a single document of reference for all standards applicable to the whole railway field.
EN 50124 consists of two parts:
— EN 50124-1, Railway applications - Insulation coordination - Part 1: Basic requirements -
Clearances and creepage distances for all electrical and electronic equipment;
— EN 50124-2, Railway applications - Insulation coordination - Part 2: Overvoltages and related
protection.
This Part 1 allows, in conjunction with EN 50124-2, to take into account advantages resulting from the
presence of overvoltage protection when dimensioning clearances.
1 Scope
This European Standard deals with insulation coordination in railways. It applies to equipment for use
in signalling, rolling stock and fixed installations.
Insulation coordination is concerned with the selection, dimensioning and correlation of insulation both
within and between items of equipment. In dimensioning insulation, electrical stresses and
environmental conditions are taken into account. For the same conditions and stresses, these
dimensions are the same.
An objective of insulation coordination is to avoid unnecessary over dimensioning of insulation.
This standard specifies:
— requirements for clearances and creepage distances for equipment;
— general requirements for tests pertaining to insulation coordination.
The term equipment relates to a section as defined in 3.3 it may apply to a system, a sub-system, an
apparatus, a part of an apparatus, or a physical realization of an equipotential line.
This standard does not deal with:
— distances through solid or liquid insulation;
— distances through gases other than air;
— distances through air not at atmospheric pressure;
— equipment used under extreme conditions.
Product standards should align with this generic standard.
However, they may require, with justification, different requirements due to safety and/or reliability
reasons, e.g. for signalling, and/or particular operating conditions of the equipment itself, e.g.
overhead contact lines which should comply with EN 50119.
This standard also gives provisions for dielectric tests (type tests or routine tests) on equipment (see
Annex B).
NOTE For safety critical systems, specific requirements are needed. These requirements are given in the
product specific signalling standard EN 50129.
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 50123 (all parts), Railway applications - Fixed installations - D.C. switchgear
EN 50163, Railway applications - Supply voltages of traction systems
EN 60060-1, High-voltage test techniques - Part 1: General definitions and test requirements (IEC
60060-1)
EN 60071-1, Insulation co-ordination - Part 1: Definitions, principles and rules (IEC 60071-1)
EN 60112, Method for the determination of the proof and the comparative tracking indices of solid
insulating materials (IEC 60112)
EN 60587, Electrical insulating materials used under severe ambient conditions - Test methods for
evaluating resistance to tracking and erosion (IEC 60587)
EN 60664-1:2007, Insulation coordination for equipment within low-voltage systems - Part 1:
Principles, requirements and tests (IEC 60664-1:2007)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE The definitions apply according to the following order of priority:
— the definition given here-under;
— the definition given in EN 60664–1;
— the definition given in the documents mentioned in Clause 2 other than EN 60664–1.
3.1
clearance
shortest distance in air between two conductive parts
3.2
creepage distance
shortest distance along the surface of the insulating material between two conductive parts
3.3 Sections
3.3.1
section
part of an electrical circuit having its own voltage ratings for insulation coordination
Note 1 to entry: Sections fall into two categories: earthed section and floating section.
3.3.2
earthed section
section connected to earth or to the vehicle body through a circuit for which interruption is not
expected
3.3.3
floating section
section isolated from earth or from the vehicle body
Note 1 to entry: A section can be under electrical influence from adjacent sections.
Note 2 to entry: A particular point of a circuit can be considered as a section.
3.4 Voltages
3.4.1
nominal voltage
U
n
suitable approximate voltage value used to designate or identify a given supply system
3.4.2
working voltage
highest r.m.s. value of the a.c or d.c voltage which can occur between two points across any
insulation, each circuit likely to influence the said r.m.s. value being supplied at its maximum
permanent voltage
Note 1 to entry: Permanent means that the voltage lasts more than 5 min, as Umax 1 in EN 50163.
3.4.3
rated voltage
value of voltage assigned by the manufacturer to a component, device or equipment and to which
operation and performance characteristics are referred
Note 1 to entry: Equipment may have more than one rated voltage value or may have a rated voltage range.
3.4.4
rated insulation voltage
U
Nm
r.m.s. withstand voltage value assigned by the manufacturer to the equipment or a part of it,
characterising the specified permanent (over 5 min) withstand capability of its insulation
Note 1 to entry: UNm is a voltage between a live part of equipment and earth or another live part. For rolling
stock, earth refers to the vehicle body.
Note 2 to entry: For circuits, systems and sub-systems in railway applications this definition is preferred to
“highest voltage for equipment” which is widely used in international standards
Note 3 to entry: U is higher than or equal to the working voltage. As a consequence, for circuits directly
Nm
connected to the contact line, UNm is equal to or higher than Umax1 as specified in EN 50163.
Note 4 to entry: UNm is not necessarily equal to the rated voltage which is primarily related to functional
performance.
3.4.5
working peak voltage
highest value of voltage which can occur in service across any particular insulation
3.4.6
recurring peak voltage
maximum peak value of periodic excursions of the voltage waveform resulting from distortions of an
a.c. voltage or from a.c. components superimposed on a d.c. voltage
Note 1 to entry: Random overvoltages, for example due to occasional switching, are not considered to be
recurring peak voltages.
3.4.7
rated impulse 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
Note 1 to entry: UNi is higher than or equal to the working peak voltage.
3.5
overvoltage
voltage having a peak value exceeding the corresponding peak value (including recurrent
overvoltages) of maximum steady-state voltage at normal operating conditions
3.5.1
temporary overvoltage
overvoltage of relatively long duration due to voltage variations
Note 1 to entry: A temporary overvoltage is independent of the network load. It is characterized by a
voltage/time curve.
3.5.2
transient overvoltage
short duration overvoltage of a few milliseconds or less due to current transfers
Note 1 to entry: A transient overvoltage depends on the network load. It cannot be characterized by a
voltage/time curve. Basically, a transient overvoltage is the result of a current transfer from a source to the load
(network).
Note 2 to entry: Two particular transient overvoltages are defined in 3.5.3 and 3.5.4.
3.5.3
switching overvoltage
transient overvoltage at any point of the system due to specific switching operation or fault
3.5.4
lightning overvoltage
transient overvoltage at any point of the system due to a specific lightning discharge
Note 1 to entry: The definitions of 3.5 are in accordance with those of EN 60664–1 and EN 50163. However, the
prevalence of the nature of the cause (voltage variations or current transfer) upon time, for segregating transient
overvoltages from temporary ones, is clearly stated here (whereas the nature of the cause is not considered in
EN 60664–1). Long-term (typically 20 ms to typically 1 s) overvoltages defined in EN 50163, dedicated to contact
line networks, are equivalent to temporary overvoltages.
3.6 Insulations
3.6.1
functional insulation
insulation between conductive parts which is necessary only for the proper functioning
3.6.2
basic insulation
insulation applied to live parts to provide basic protection against electric shock
3.6.3
supplementary insulation
independent insulation applied in addition to basic insulation, in order to provide protection against
electric shock in the event of failure of basic insulation
3.6.4
double insulation
insulation comprising both basic insulation and supplementary insulation
3.6.5
reinforced insulation
single insulation system applied to live parts, which provides a degree of protection against electric
shock equivalent to double insulation
Note 1 to entry: The term “single insulation system” does not imply that the insulation involves one
homogeneous piece. It may involve several layers which cannot be tested singly as basic and supplementary
insulation.
3.7 Contact lines
3.7.1
contact line
conductor system for supplying electric energy to vehicles through current-collecting equipment
[SOURCE: IEC 60050-811:1991, 811-33-01]
3.7.2
overhead contact line
catenary (deprecated)
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, 811-33-02]
4 Basis for insulation coordination
4.1 Basic principles
4.1.1 General
Insulation coordination implies the selection of the electric insulation characteristic of the equipment
with regard to its application and in relation to its surroundings.
Insulation coordination can only be achieved if the design of the equipment is based on the stresses to
which it is likely to be subjected during its anticipated lifetime.
4.1.2 Insulation coordination with regard to voltage
4.1.2.1 General
Consideration shall be given to:
— the voltages which can appear in the system;
— the voltages generated by the equipment (which could adversely affect other equipment in the
system);
— the degree of the expected availability of the equipment;
— the safety of persons and property, so that the probability of undesired incidents due to voltage
stresses do not lead to an unacceptable risk of harm;
— the safety of functions for control and protection systems;
— voltages induced in track-side cables;
— the shape of insulating surfaces;
— the orientation and the location of creepage distances;
— if necessary: the altitude that applies.
4.1.2.2 Insulation coordination with regard to permanent a.c. or d.c. voltages
Insulation coordination with regard to permanent voltages is based on:
— rated voltage;
— rated insulation voltage;
— working voltage.
Unless otherwise specified in product standards, permanent voltages last more than five minutes.
4.1.2.3 Insulation coordination with regard to transient overvoltage
Insulation coordination with regard to transient overvoltage is based on controlled overvoltage
conditions. There are two kinds of control:
— inherent control: the condition within an electrical system wherein the characteristics of the
system can be expected to limit the prospective transient overvoltages to a defined level;
— protective control: the condition within an electrical system wherein specific overvoltage
attenuating means can be expected to limit the prospective transient overvoltages to a defined
level.
NOTE 1 Overvoltages in large and complex systems such as overhead contact lines subjected to multiple and
variable influences can only be assessed on a statistical basis. This is particularly true for overvoltages of
atmospheric origin and applies whether the controlled condition is achieved as a consequence of inherent control
or by means of protective control.
A probabilistic analysis is recommended to assess whether inherent control exists or whether
protective control is needed.
NOTE 2 The specific overvoltage attenuating means can be a device having means for storage or dissipation
of energy and, under defined conditions, capable of harmlessly dissipating the energy of overvoltages expected at
the location.
EXAMPLE of inherent control: Control ensured by flash-over across insulators or spark gap horns on overhead
contact lines.
EXAMPLE of protective control: Control ensured by the filter of a locomotive on the downstream circuit, provided
that no switching overvoltage source is likely to perturb the said circuit.
Insulation coordination uses a preferred series of values of rated impulse voltage: it consists of the
values listed in the first column of Table A.3.
4.1.2.4 Insulation coordination with regard to recurring peak voltage
Consideration shall be given to the extent partial discharges can occur in solid insulation or along
surfaces of insulation.
4.1.3 Insulation coordination with regard to environmental conditions
The micro-environmental conditions for the insulation shall be taken into account as classified by the
pollution degree.
The micro-environmental conditions depend primarily on the macro-environmental conditions in which
the equipment is located and in many cases the environments are identical. However, the micro-
environment can be better or worse than the macro-environment where, for example, enclosures,
heating, ventilation or dust influence the micro-environment.
NOTE Protection by enclosures provided according to classes specified in EN 60529 does not necessarily
improve the micro-environment with regard to pollution.
4.2 Voltages and voltage ratings
4.2.1 General
For determining the working voltage of a floating section, it is considered that a connection is made to
earth or to another section, so as to produce the worst case.
It is recommended to avoid floating sections in high voltage systems.
The voltages in 4.2 are “required voltages” that would be specified for a particular application. These
are different from rated voltages that are stated by a manufacturer for a product.
Rated voltages are defined for each section of a circuit.
4.2.2 Rated insulation voltage U
Nm
The minimum value of the rated insulation voltage of a section shall be higher or equal to the highest
working voltage appearing within the section, or produced by adjacent sections.
Stresses shorter than 5 min (e.g U as defined in EN 50163) may be taken into account case by
max2
case, considering in particular the interval between such stresses.
4.2.3 Rated impulse voltage U
Ni
4.2.3.1 General
The minimum value of rated impulse voltage of a section shall be determined either by method 1 or by
method 2.
In inherent control, method 1 should be used.
In protective control, method 1 and method 2 may be used.
4.2.3.2 Method 1
Method 1 is based on rated insulation voltages and overvoltage categories.
The relation between rated insulation voltages and nominal voltages commonly used in railway
applications is given in Table D.1 of Annex D.
Method 1 uses four overvoltage categories to characterize the exposure of the equipment to
overvoltages.
— OV1: Circuits which are protected against external and internal overvoltages and in which only
very low overvoltages can occur because:
— they are not directly connected to the contact line;
— they are being operated indoor;
— they are within an equipment or device;
— OV2: The same as OV1, but with harsher overvoltage conditions and/or higher requirements
concerning safety and reliability;
— OV3: The same as OV4, but with less harsh overvoltage conditions and/or lower requirements
concerning safety and reliability;
— OV4: Circuits which are not protected against external or internal overvoltages (e.g. directly
connected to the contact or outside lines) and which can be endangered by lightning or switching
overvoltages.
Further details for specific applications are given in Clause 8.
In method 1, the minimum value of rated impulse voltage of a section shall be determined as follows:
— For low voltage circuits not powered directly by the contact line, the rated impulse voltage is given
by Table A.1;
— For circuits powered by the contact line and for traction power circuits in thermo-electric driven
vehicles the rated impulse voltage is given by Table A.2.
When a specific protection against overvoltages is involved, the choice of the overvoltage category is
linked to the characteristics of this protective device.
4.2.3.3 Method 2
In method 2, the minimum value of rated impulse voltage of a section shall be higher or equal to the
working peak voltage appearing within the section, or produced by adjacent sections.
4.2.3.4 Contingency
Contingency need not be applied to the rated impulse voltage, whatever the method.
4.3 Time under voltage stress
With regard to creepage distances, the time under voltage stress influences the number of drying-out
incidents capable of causing surface electrical discharge with energy high enough to entail tracking.
The number of drying-out incidents is considered to be sufficiently large to cause tracking:
— in equipment intended for continuous use and not generating in its interior sufficient heat for
drying-out;
— in equipment on the input side of a switch and between the line and load (input and output)
terminals of a switch supplied directly from the low-voltage mains;
— in equipment subject to condensation for long periods and frequently switched on and off.
The creepage distances shown in Tables A.5, A.6 and A.7 have been determined for insulation
intended to be under continuous voltage stress for a long time.
4.4 Pollution
The micro-environment determines the effect of pollution on the insulation. The macro-environment,
however, shall be taken into account when considering the micro-environment.
Means may be provided to reduce pollution at the insulation under consideration by effective use of
enclosures, encapsulation or hermetic sealing. Such means to reduce pollution may not be effective
when the equipment is subject to condensation or if, in normal operation, it generates pollutants itself.
Small clearances can be bridged completely by solid particles, dust and water and therefore minimum
clearances are specified where pollution can be present in the micro-environment.
NOTE 1 Pollution will become conductive in the presence of humidity. Pollution caused by contaminated
water, soot, metal or carbon dust is inherently conductive.
NOTE 2 Conductive pollution by ionized gases and metallic deposits occurs only on specific instances, for
example in arc chambers of switchgear or controlgear, and is not covered by this standard.
For the purpose of evaluating creepage distances and clearances, seven degrees of pollution PD1,
PD2.PD4B are established according to Table A.4.
NOTE 3 The seven pollution degrees were derived from EN 60664–1, IEC/TR 60815:1986 and EN 60077–1,
but some definitions are not identical. The main reason is that PD4 of EN 60664–1 and EN 60077–1 had to be
broken down into PD3A, PD4, PD4A and PD4B of this standard to cover railway applications and experience.
Nevertheless, the definitions given in this standard are consistent with those of EN 60077–1 when the pollution
degree is strictly identical.
The classification considers micro-environmental conditions only. However, macro-environmental
conditions should not be ignored. Annex E gives some guidance when trying to define the relevant PD
to be applied to a practical case.
4.5 Insulating material
4.5.1 General
External high voltage insulators shall comply with their relevant product standards. Additional
compliance to this standard is not required.
4.5.2 Comparative tracking index (CTI)
4.5.2.1 Insulating materials can be roughly characterized according to the damage they suffer
from concentrated release of energy during electrical discharge when a surface leakage current is
interrupted due to drying of the contaminated surface. The following behaviour of insulating materials
in the presence of electrical discharge can occur:
— decomposition of the insulating material;
— the wearing away of the insulating material by action of electrical discharges (electrical erosion);
— the progressive formation of conductive paths which are produced on the surface of solid
insulating material due to the combined effects of electric stress and electrolytic contamination on
the surface (tracking).
NOTE Tracking or erosion will occur when:
— a liquid film carrying the surface leakage current breaks, and
— the applied voltage is sufficient to break down the small gap formed when the film breaks, and
— the current is above a limiting value which is necessary to provide sufficient energy locally to
thermally decompose the insulating material beneath the film.
Deterioration increases with the time for which the current flows.
4.5.2.2 A method of classification for insulating materials according to 4.5.2.1 does not exist. The
behaviour of the insulating material under various contaminants and voltages is extremely complex.
Under these conditions many of the materials can exhibit two, or even three of the characteristics
stated. A direct correlation with the material groups of 4.5.2.3 is not practical. However, it has been
found by experience and tests that insulating materials having a higher relative performance also have
approximately the same relative ranking according to the comparative tracking index (CTI). Therefore,
this standard uses the CTI values to categorize insulation materials.
4.5.2.3 Materials are separated into four groups according to either their CTI values as defined in
EN 60112 or their class as determined by EN 60587 tests.
Material Group I 600 ≤ CTI or class 1A4.5
Material Group II 400 ≤ CTI < 600 or class 1A3.5
Material Group IIIa 175 ≤ CTI < 400 or class 1A2.5
Material Group IIIb 100 ≤ CTI < 175 or class 1A0
The CTI values above refer to values obtained, in accordance with EN 60112, on samples specifically
made for the purpose and tested with solution A.
NOTE 1 The proof-tracking index (PTI) is also used to identify the tracking characteristics of materials. A
material may be included in one of the four groups given above on the basis that its PTI, established by the
method of EN 60112 using solution A, is equal to or greater than the lower value specified for the group.
NOTE 2 Equivalence between CTI and classes has not been demonstrated.
5 Requirements and dimensioning rules for clearances
5.1 General
Clearances shall be dimensioned to withstand the voltages referred to in 5.2, taking into account all
the parameters affecting breakdown of insulation during the whole life of the equipment.
For correct measurement of clearances, the requirements of Clause 7 apply.
The clearances given in Table A.3 apply to altitudes up to 2 000 m above sea level. For higher
altitudes, correction methods are given in 5.4.
5.2 Minimum clearances
5.2.1 Functional insulation
Minimum clearances for functional insulation are based on the rated impulse voltage, according to
Table A.3, for altitudes higher than 2 000 m clearances shall be increased in accordance with 5.4.
A smaller value may be adopted, in particular in case of homogeneous fields. The decreased distance
shall withstand the required rated impulse voltage U . Its compliance shall be verified by test. The test
Ni
voltage is the value of U , U or U of Table A.8 for a distance equal to the minimum clearance
i ac dc
according to Table A.3.
5.2.2 Basic and supplementary insulation
Minimum clearances for basic and supplementary insulation are based on the rated impulse voltage,
according to Table A.3, for altitudes higher than 2 000 m clearances shall be increased in accordance
with 5.4.
Smaller values are not allowed.
5.2.3 Reinforced insulation
When dimensioning reinforced insulation, 5.2.2 applies with the following modification: the rated
impulse voltage shall be 160 % of the rated impulse voltage required for basic insulation.
Smaller values are not allowed.
5.3 Contingency
Attention is drawn to the fact that a higher value of U may be determined by electromagnetic
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compatibility test requirements as those given in the EN 50121 series.
In addition, applications may require larger clearances in order to take account of the following:
— atmospheric conditions, special pollution risks, high humidity;
— ionized environment;
— installation conditions;
— connections;
— human safety;
— variations in production, in maintenance;
— ageing in service;
— failure situations and other exceptional cases;
— kinematic conditions, electromechanical forces;
— bacteria, biological and chemical substances;
— whiskers (hair shaped metal bodies growing from the metal surface);
— etc.
5.4 Clearances for altitudes higher than 2 000 m
The clearances given in Table A.3 apply for use up to 2 000 m above sea level. For altitudes higher
than 2 000 m the clearances given in Table A.3 shall be increased.
For circuits with rated impulse voltage U up to and
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