SIST EN 60664-4:2007

SLOVENSKI STANDARD
01-januar-2007
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Insulation coordination for equipment within low-voltage systems -- Part 4: Consideration
of high-frequency voltage stress
Isolationskoordination für elektrische Betriebsmittel in Niederspannungsanlagen -- Teil 4:
Berücksichtigung von hochfrequenten Spannungsbeanspruchungen
Coordination de l'isolement des matériels dans les systèmes (réseaux) à basse tension -
- Partie 4: Considérations sur les contraintes de tension à haute fréquence
Ta slovenski standard je istoveten z: EN 60664-4:2006
ICS:
29.080.30 Izolacijski sistemi Insulation systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 60664-4
NORME EUROPÉENNE
January 2006
EUROPÄISCHE NORM
ICS 29.080.30 Incorporates Corrigendum October 2006

English version
Insulation coordination for equipment within low-voltage systems
Part 4: Consideration of high-frequency voltage stress
(IEC 60664-4:2005)
Coordination de l'isolement des matériels Isolationskoordination für elektrische
dans les systèmes (réseaux) Betriebsmittel in Niederspannungsanlagen
à basse tension Teil 4: Berücksichtigung von
Partie 4: Considérations hochfrequenten
sur les contraintes de tension Spannungsbeanspruchungen
à haute fréquence (IEC 60664-4:2005)
(CEI 60664-4:2005)
This European Standard was approved by CENELEC on 2005-10-01. 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 Central Secretariat 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 Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, Switzerland
and United Kingdom.
CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2006 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60664-4:2006 E
Foreword
The text of document 109/51/FDIS, future edition 2 of IEC 60664-4, prepared by IEC TC 109, Insulation
co-ordination for low-voltage equipment, was submitted to the IEC-CENELEC parallel vote and was
approved by CENELEC as EN 60664-4 on 2005-10-01.
This European Standard is to be used in conjunction with EN 60664-1 or EN 60664-5.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2006-08-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2008-10-01
Annex ZA has been added by CENELEC.
The contents of the corrigendum of October 2006 have been included in this copy.
__________
Endorsement notice
The text of the International Standard IEC 60664-4:2005 was approved by CENELEC as a European
Standard without any modification.
__________
- 3 - EN 60664-4:2006
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following referenced documents are indispensable for the application 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.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.
Publication Year Title EN/HD Year

IEC 60112 2003 Method for the determination of the proof and EN 60112 2003
the comparative tracking indices of solid
insulating materials
IEC 60664-1 (mod) 1992 Insulation coordination for equipment within
+ A1 2000 low-voltage systems
+ A2 2002 Part 1: Principles, requirements and tests EN 60664-1 2003

IEC 60664-5 2003 Insulation coordination for equipment within EN 60664-5 2003
low-voltage systems
Part 5: A comprehensive method for
determining clearances and creepage
distances equal to or less than 2 mm

IEC Guide 104 1997 The preparation of safety publications and the - -
use of basic safety publications and group
safety publications
NORME CEI
INTERNATIONALE
IEC
60664-4
INTERNATIONAL
Deuxième édition
STANDARD
Second edition
2005-09
PUBLICATION FONDAMENTALE DE SÉCURITÉ
BASIC SAFETY PUBLICATION
Coordination de l'isolement des matériels
dans les systèmes (réseaux) à basse tension –
Partie 4:
Considérations sur les contraintes
de tension à haute fréquence
Insulation coordination for equipment
within low-voltage systems –
Part 4:
Consideration of high-frequency voltage stress
 IEC 2005 Droits de reproduction réservés  Copyright - all rights reserved
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électronique ou mécanique, y compris la photocopie et les photocopying and microfilm, without permission in writing from
microfilms, sans l'accord écrit de l'éditeur. the publisher.
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Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
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МеждународнаяЭлектротехническаяКомиссия
Pour prix, voir catalogue en vigueur
For price, see current catalogue

60664-4  IEC:2005 – 3 –
CONTENTS
FOREWORD.9
INTRODUCTION.13
1 Scope and object.15
2 Normative references .17
3 Terms and definitions .17
4 Clearances .19
4.1 General conditions .19
4.2 Basic information.19
4.3 Homogeneous and approximately homogeneous fields.19
4.4 Inhomogeneous fields .21
5 Creepage distances.27
5.1 Experimental data .27
5.2 Dimensioning of creepage distances .27
6 Solid insulation.33
6.1 General consideration .33
6.2 Influencing factors .33
6.3 Dimensioning of solid insulation .35
7 High-frequency testing.37
7.1 Basic requirements.37
7.2 Test voltage source .39
7.3 Conditioning .39
7.4 High-frequency breakdown test .39
7.5 High-frequency partial discharge test .39
7.6 Examples of test results .45
8 Non sinusoidal voltages.45
8.1 General considerations.45
8.2 Periodic impulse voltage.47
8.3 Harmonic analysis .47
8.4 Dimensioning procedure and testing.47

Annex A (informative) Insulation characteristics of clearances at high-frequency
voltages.51
Annex B (informative) Insulation characteristics of creepage distances at high-
frequency voltages.65
Annex C (informative) Insulation characteristics of solid insulation at high-frequency
voltages.71
Annex D (normative) Testing of insulation at high-frequency voltages.91
Annex E (informative) Insulation stressed with non-sinusoidal high-frequency voltages .119
Annex F (informative) Dimensioning diagrams .129

Bibliography.133

60664-4  IEC:2005 – 5 –
Figure 1 – Dimensioning of inhomogeneous clearances in air at atmospheric pressure
(point-plane-electrodes, 5 µm radius) to avoid PD (clearance ≥ 1 mm) or breakdown
(clearance < 1 mm) .25
Figure 2 – Dimensioning of creepage distances to avoid partial discharge (creepage
distance ≥ 1 mm) or breakdown (creepage distance < 1 mm) .31
Figure 3 – Permissible field strength for dimensioning of solid insulation according to
Equation (3).37
Figure 4 – Periodic impulse voltage (see Part 1) .47
Figure A.1 – Breakdown at high frequency in air at atmospheric pressure,
homogeneous field, frequency range 50 Hz – 25 MHz [3].53
Figure A.2 – Breakdown at high frequency in air at atmospheric pressure,
homogeneous field, frequency range 50 Hz – 2,5 MHz [4].55
Figure A.3 – Needle tip after (upper) and before (lower) breakdown.57
Figure A.4 – PD inception voltages in air at atmospheric pressure for f = 100 kHz,
point-plane electrodes with different point radius [6] .59
Figure A.5 – PD extinction voltages and breakdown voltages in air at atmospheric
pressure for f = 460 kHz, point-plane electrodes with BB-needles [6] .61
Figure A.6 – PD extinction voltages and breakdown voltages in air at atmospheric
pressure for f = 1 MHz, point-plane electrodes with BB-needles [6].63
Figure B.1 – Test specimen for measuring the PD voltages and the withstand voltages
of creepage distances up to 6,3 mm .65
Figure B.2 – Test results of the PD extinction voltage U of creepage distances up to
e
6,3 mm [6] .69
Figure B.3 – Test results of the breakdown voltage U of creepage distances up to
b
6,3 mm [6] .69
Figure C.1 – PD withstand capability of coatings; constant test voltage U (f = 50 Hz)
t
[12] 73
Figure C.2 – PD withstand capability of coatings; linearly increasing test voltage U (f =
t
50 Hz) [12].73
Figure C.3 – Breakdown at high frequency, solid insulation; d = 0,75 mm [15] .79
Figure C.4 – Breakdown at high frequency, solid insulation, influence of humidity;
conditioning at 50 °C; #1: mica-filled phenolic, d = 0,75 mm; #2: glass-silicone
laminate, d = 1,5 mm [19] .81
Figure C.5 – Breakdown at high frequency, insulating films; #1: Cellulose-
Acetobutyrate, #2: Polycarbonate; #3: Cellulose-Triacetate [20] .85
Figure C.6 – Breakdown at high frequency, insulating films; #1: Polystyrene, d =
80 µm, #2: Polyethylene, d = 50 µm [20] .89
Figure D.1 – High-frequency resonance transformer; influence of the number of turns
of the secondary coil N on the output voltage U ; N = 20; N = 210/280/350/420/560
2 1 2
[22] 91
Figure D.2 – High-frequency high power oscillator [5] and [6] .93
Figure D.3 – PD test circuit for high-frequency voltage tests [22] .97
Figure D.4 – Diagram of the test circuit [5] and [6] .99
Figure D.5 – PD impulse response for an assumed PD impulse frequency of 2 MHz for
rd
different upper cut-off frequencies f of the test circuit; this includes a 3 order band-
c
stop filter with f = 1 MHz [5] and [6].101
centre
Figure D.6 – Equivalent circuit of a PD test circuit with lumped elements [5] .105
Figure D.7 – Transfer characteristics of PD test circuits when using a PD-impulse
voltage source versus a PD impulse current source [5] .107

60664-4  IEC:2005 – 7 –
Figure D.8 – Input signal U and measuring signal U depending upon the
in m
capacitance of the coupling capacitor C (capacitance of the test specimen C =
k 3
10 pF) [5].111
Figure D.9 – PD testing of optocouplers at high-frequency voltage [30].113
Figure D.10 – PD testing of impulse transformers; influence of the frequency of the
voltage [30].115
Figure D.11 – PD testing of coated printed circuit boards; U , d = 0,2 mm [30] .115
i
Figure D.12 – Lifetime t of enamelled wires (twisted pair) at high-frequency voltage;
stress is 10 % above the PD inception voltage [31] .117
Figure E.1 – Periodic impulse voltage, rectangular waveshape .121
Figure E.2 – Periodic impulse voltage, rectangular waveshape, spectrum.121
Figure E.3 – Periodic impulse voltage, rectangular waveshape with overshoot (see
Figure 4).123
Figure E.4 – Periodic impulse voltage, rectangular waveshape with overshoot,
spectrum.123
Figure E.5 – Periodic impulse voltage, rectangular waveshape with ringing (1 MHz) .125
Figure E.6 – Periodic impulse voltage, rectangular waveshape with ringing (1 MHz),
spectrum.125
Figure E.7 – Periodic impulse voltage, rectangular waveshape with high overshoot .127
Figure E.8 – Periodic impulse voltage, rectangular waveshape with high overshoot,
spectrum.127
Figure F.1 – Diagram for dimensioning of clearances.129
Figure F.2 – Diagram for dimensioning of creepage distances .131

Table 1 – Minimum values of clearances in air at atmospheric pressure for
inhomogeneous field conditions .27
Table 2 – Minimum values of creepage distances d for different frequency ranges.33
Table B.1 – Materials included in the investigations .67
Table D.1 – Data of the test voltage source [5] and [6].93

60664-4  IEC:2005 – 9 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
INSULATION COORDINATION FOR EQUIPMENT
WITHIN LOW-VOLTAGE SYSTEMS –
Part 4: Consideration of high-frequency voltage stress

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60664-4 has been prepared by IEC technical committee 109:
Insulation co-ordination for low-voltage equipment.
This second edition cancels and replaces the first edition which was issued as a technical
report in 1997. It constitutes a technical revision and now has the status of an International
Standard.
The major changes made during the revision of IEC 60664-4 were the following:
– inclusion of more recent information about the withstand characteristics of insulation at
high-frequency voltage stress (see Annexes A, B and C);

60664-4  IEC:2005 – 11 –
– inclusion of requirements for the dimensioning of clearances at high-frequency voltage
stress (see Clause 4);
– inclusion of requirements for the dimensioning of creepage distances at high-frequency
voltage stress (see Clause 5);
– inclusion of requirements for the dimensioning of solid insulation at high-frequency voltage
stress (see Clause 6);
– inclusion of diagrams to provide guidance on dimensioning with respect to high-frequency
voltage stress (see Annex F);
– specification of tests with respect to high-frequency voltage stress (see Clause 7).
– inclusion of test circuits for high-frequency voltage withstand testing and partial discharge
testing (see Annex D.1 and D.2.1);
– inclusion of design criteria for partial discharge test circuits at high-frequency voltage (see
Annex D.2.2);
– Inclusion of criteria for dealing with non sinusoidal voltage stress (see Clause 8 and
Annex E).
It has the status of a basic safety publication in accordance with IEC Guide 104.
This International Standard is to be used in conjunction with IEC 60664-1 or IEC 60664-5.
The text of this standard is based on the following documents:
FDIS Report on voting
109/51/FDIS 109/53/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
IEC 60664 consists of the following parts under the general title Insulation coordination for
equipment within low-voltage systems:
Part 1: Principles, requirements and tests
Part 2: Application guide
Part 3: Use of coating, potting or moulding for protection against pollution
Part 4: Consideration of high-frequency voltage stress
Part 5: A comprehensive method for determining clearances and creepage distances equal
to or less than 2 mm
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
60664-4  IEC:2005 – 13 –
INTRODUCTION
High electrical stress also occurs in low-voltage equipment. The frequency is usually
50/60 Hz, but in some applications a higher frequency (400 Hz) or a lower frequency
(16 2/3 Hz) or d.c. can occur. A particular situation exists in high-power RF transmitters. The
development of such equipment had motivated earlier research on the withstand capability of
insulation at radio frequencies. Since that time, the aspect of high-frequency voltage stress
had not been pursued with much effort.
At present, high-frequency working voltages exceeding 30 kHz are often used in low-voltage
equipment, and the use of frequencies in the MHz range is likely in the future. Many of the
voltage shapes are non sinusoidal. Small dimensions are necessary for miniaturization and
for high efficiency, for instance in high-frequency transformers. Consequently, very high
stresses are common in solid insulation.
By increasing the frequency the deteriorating effect of partial discharges is also increased
roughly proportionally to the frequency, so that the impact of partial discharges on
dimensioning is much higher compared to power frequency.
As dimensions are likely to decrease further and frequencies increase, this situation will be
aggravated in the future. Therefore, with respect to safety of personnel and reliability of
equipment, the stress due to high frequencies up to 100 MHz has to be considered for
insulation coordination of low-voltage equipment, (see note 2 in the Scope of Part 1).
This standard summarizes the most important available data concerning high-frequency
stress of insulation, and identifies how materials and their dimensioning are influenced. Data
for dimensioning of clearances, creepage distances and solid insulation are specified. This
standard also describes how tests can be performed with respect to this stress.

60664-4  IEC:2005 – 15 –
INSULATION COORDINATION FOR EQUIPMENT
WITHIN LOW-VOLTAGE SYSTEMS –
Part 4: Consideration of high-frequency voltage stress

1 Scope and object
This part of IEC 60664 deals with basic, supplementary and reinforced insulation subjected to
high-frequency voltage stress within low-voltage equipment. The dimensioning values directly
apply for basic insulation; for reinforced insulation additional requirements apply according to
Part 1. It is applicable for the dimensioning of clearances, creepage distances and solid
insulation stressed by any type of periodic voltages with a fundamental frequency above
30 kHz and up to 10 MHz.
This part of IEC 60664 can only be used together with IEC 60664-1 or with IEC 60664-5 (in
this standard called Part 1 or Part 5). By using Part 1 or Part 5 together with this part the
frequency limit of Part 1 or Part 5 is extended to frequencies higher than 30 kHz.
This part also applies to Part 3 for frequencies greater than 30 kHz and protection of type 1.
For type 2 protection this question is under consideration.
NOTE 1 Dimensioning values for frequencies above 10 MHz are under consideration.
NOTE 2 This standard does not consider the high-frequency emission to the mains. In normal use of equipment, it
is assumed that the interference of high-frequency voltages emitted to the mains is negligible with respect to
insulation stress. Therefore it is not necessary to take it into account.
It applies to equipment for use up to 2 000 m above sea level having a rated voltage up to a.c.
1 000 V.
It specifies the requirements for clearances, creepage distances and solid insulation for
equipment based upon their performance criteria. lt includes methods of electric testing with
respect to insulation coordination.
The minimum clearances specified in this part do not apply where ionized gases occur.
Special requirements for such situations may be specified at the discretion of the relevant
technical committee.
This part does not deal with distances
− through liquid insulation,
− through gases other than air,
− through compressed air.
NOTE 3 Higher voltages may exist in internal circuits of the equipment.
NOTE 4 Requirements for altitudes exceeding 2 000 m can be derived from Table A.2 of Annex A of Part 1.

60664-4  IEC:2005 – 17 –
The object of this standard is to guide technical committees responsible for different
equipment in order to rationalise their requirements so that insulation coordination is achieved
when specifying clearances in air, creepage distances and solid insulation for equipment.
2 Normative references
The following referenced documents are indispensable for the application 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 60112:2003, Method for determining the comparative and the proof tracking indices of
solid insulating materials under moist conditions
IEC 60664-1:1992, Insulation coordination for equipment within low-voltage systems: Part 1:
Principles, requirements and tests
Amendment 1 (2000)
Amendment 2 (2002)
IEC 60664-5:2003, Insulation coordination for equipment within low-voltage systems: A
comprehensive method for determining clearances and creepage distances equal to or less
than 2 mm
IEC Guide 104:1997, The preparation of safety publications and the use of basic safety
publications and group safety publications
3 Terms and definitions
For the purposes of this document, the terms and definitions given in Part 1, as well as the
following terms and definitions, apply.
3.1
approximately homogeneous field
for frequencies exceeding 30 kHz, the field is considered to be approximately homogeneous
when the radius of curvature of the conductive parts is equal or greater than 20 % of the
clearance
3.2
inhomogeneous field
for frequencies exceeding 30 kHz the field is considered to be inhomogeneous when the
radius of curvature of the conductive parts is less than 20 % of the clearance
3.3
U
peak
peak value of any type of periodic peak voltage across the insulation
3.4
f
crit
critical frequency at which the reduction of the breakdown voltage of a clearance occurs
3.5
f
min
frequency at which the maximum reduction of the breakdown voltage of a clearance occurs

60664-4  IEC:2005 – 19 –
3.6
PD-voltage
generic term for both partial discharge inception voltage U and partial discharge extinction
i
voltage U
e
3.7
electrical field strength E
voltage gradient per unit length usually expressed in kV/mm
4 Clearances
4.1 General conditions
This clause is applicable to clearances in air. The dimensioning data are valid for a maximum
altitude of 2 000 m above sea level. For higher altitudes, the altitude correction factors of
Table A.2 of Part 1 are applicable.
4.2 Basic information
According to the basic information given in Clause A.1 the withstand capability of clearances
can only be influenced by the frequency of the voltage if periodic voltages are relevant (see
3.1.1.2 of Part 1 or Part 5). For transient overvoltages dimensioning according to 3.1.1.1 of
Part 1 or Part 5 is sufficient.
4.3 Homogeneous and approximately homogeneous fields
4.3.1 Conditions for approximately homogeneous field
For frequencies exceeding 30 kHz, an approximately homogeneous field is considered to exist
when the radius of curvature of the conductive parts is equal or greater than 20 % of the
clearance.
4.3.2 Experimental data of breakdown characteristics
, at which the reduction of the
As a conclusion from A.2.1, the critical frequency f
crit
breakdown voltage occurs, depends upon the value of the clearance as follows:
0,2
f ≈ MHz (1)
crit
d / mm
where
d is the clearance.
The experimental data, presented in A.2.1 for homogeneous field conditions, shows a
maximum reduction of the breakdown voltage with frequency of 20 % compared to the 50/60
Hz-values. The frequency, at which the maximum reduction occurs, is called f .
min
NOTE For the purposes of this standard, f as illustrated in Figure A.1 is accepted as 3 MHz.
min
4.3.3 Dimensioning of clearances for homogeneous and approximately
homogeneous field conditions
The insulating characteristics of homogeneous field clearances in air at atmospheric pressure
with respect to frequency can be summarized by the following statements.

60664-4  IEC:2005 – 21 –
– Above f the breakdown voltage is reduced with increasing frequency. The maximum
crit
reduction of the breakdown voltage is about 20 %.
– The breakdown voltage reaches a minimum at a frequency f . For higher frequencies,
min
the breakdown voltage is increased and can exceed the value at power frequency.
It is assumed that these characteristics are also applicable for approximately homogeneous
field conditions.
Dimensioning for homogeneous fields is based upon Case B values of Table 7 of Part 1 or
Table 3 of Part 5. The use of these values requires a withstand test according to 4.1.1 of
Part 1 or Part 5.
Dimensioning for approximately homogeneous fields is based on Case A values of Table 7 of
Part 1 or Table 3 of Part 5. No withstand test is required. However the radius of curvature of
the conductive parts shall be equal or greater than 20 % of the clearance.
There are two methods for dimensioning:
1. If no detailed evaluation is intended, the clearance shall be designed within the frequency-
scope of this standard for 125 % of the required withstand voltage according to Table 7 of
Part 1 or Table 3 of Part 5.
2. If a detailed evaluation is intended, the following applies:
a) For frequencies below f (see Equation (1)) the clearance shall be designed for
crit
100 % of the required withstand voltage according to Table 7 of Part 1 or Table 3 of
Part 5.
b) For frequencies above f the clearance shall be designed for 125 % of the required
min
withstand voltage according to Table 7 of Part 1 or Table 3 of Part 5.
c) For frequencies between f and f the clearance shall be designed for
crit min
f − f
crit
100 % + × 25 % (2)
f − f
min crit
of the required withstand voltage according to Table 7 of Part 1 or Table 3 of Part 5.
In order to obtain the critical frequency, in a first step the clearance is assumed for 100 % of
the required withstand voltage according to Table 7 of Part 1 or Table 3 of Part 5. Then it has
to be decided, if condition 2a, 2b or 2c is applicable. As this evaluation can be influenced by
the result obtained (clearance), a second iteration can be required.
NOTE Further information about dimensioning is given in Annex F.
4.4 Inhomogeneous fields
4.4.1 Conditions for inhomogeneous field
For frequencies exceeding 30 kHz, an inhomogeneous field is considered to exist when the
radius of curvature of the conductive parts is less than 20 % of the clearance.

60664-4  IEC:2005 – 23 –
4.4.2 Experimental data of partial discharge and breakdown characteristics
For inhomogeneous field conditions, f can still be approximated from Equation (1). Above
crit
f , the influence of frequency on the breakdown voltage is much more significant compared
crit
to homogeneous field conditions. The reduction of the breakdown voltage with respect to that
at power frequency can be more than 50 %.
For inhomogeneous field conditions partial discharges (corona) must be expected at voltages
below the breakdown voltage. Due to the high risk of deterioration caused by these
discharges with high repetition frequency dimensioning shall be sufficient to avoid the
occurrence of partial discharges (PD).
The experimental data are presented in A.2.2.
4.4.3 Dimensioning of clearances for inhomogeneous field conditions
For frequencies below f (see Equation (1)) the clearance shall be designed for 100 % of the
crit
required withstand voltage according to Table 7 of Part 1 or Table 3 of Part 5.
The frequency of the voltage shall be taken into account for dimensioning for frequencies
equal to or greater than f . As PD can be started by transient overvoltages and shall not be
crit
maintained by any steady state voltage (see 4.1.2.4 of Part 1), the PD-extinction voltage shall
be used for dimensioning. The relevant data (see the note) is shown in Figure 1
(measurement) together with a limiting curve (dimensioning).
NOTE 1 For dimensioning, data from A.2.2 are applicable, obtained for clearances up to 0,75 mm from the
breakdown voltages and above from the PD-extinction voltages at 1 MHz.
The dimensioning data for inhomogeneous fields are summarized in Table 1. These values
are applicable if a small radius of curvature of the conductive parts occurs. In practice this
condition is fulfilled if the radius of curvature of the conductive parts is smaller than 20 % of
the clearance.
NOTE 2 Further information about dimensioning is given in Annex F.

60664-4  IEC:2005 – 25 –
IEC 1345/05
Key
d clearance
Figure 1 – Dimensioning of inhomogeneous clearances in air at atmospheric pressure
(point-plane-electrodes, 5 µm radius) to avoid PD (clearance ≥ 1 mm)
or breakdown (clearance < 1 mm)

60664-4  IEC:2005 – 27 –
Table 1 – Minimum values of clearances in air at atmospheric pressure for
inhomogeneous field conditions
Voltage Clearance
U
peak
kV mm
a) b)
Up to 0,6  0,065
a)
0,8 0,18
a)
1,0 0,5
a)
1,2 1,4
a)
1,4 2,35
a)
1,6 4,0
a)
1,8 6,7
a)
2,0 11,0
a)
For voltages between the values stated in this table, interpolation
is permitted.
b)
No data is available for voltages U of less than 0,6 kV.
peak
5 Creepage distances
5.1 Experimental data
The influence of frequency on the breakdown voltages of creepage distances is taken into
account according to the data given in Annex B.
The experimental conditions for the investigations being performed and the materials being
included in the experiments are described in Clause B.2.
The experimental data are shown in Clause B.3. Both the PD-voltages and the breakdown
voltages are significantly influenced by the frequency of the voltage.
5.2 Dimensioning of creepage distances
Measuring data for three different frequency ranges up to 100 kHz, up to 1 MHz and up to
3 MHz are shown in Figure 2 (measurement) together with limiting curves (dimensioning). The
dimensioning data for creepage distances are summarized in Table 2. The data for the
additional frequency ranges have been obtained by linear interpolation. These data are valid
for pollution degree 1.
NOTE 1 For dimensioning of creepage distances the data from Clause B.3 for the PD-extinction voltage are
applicable as PD at high-frequency voltage will have a destructive effect on the base material, if it occurs during a
longer period of time.
Experiments [5] have shown that creepage distances for pollution degree 2 and 3 can be
derived from the distances determined for pollution degree 1 by application of a multiplication
factor. For pollution degree 2, the multiplication factor 1,2 and for pollution degree 3 the
multiplication factor 1,4 are applicable.
———————
Figures in square brackets refer to the bibliography.

60664-4  IEC:2005 – 29 –
The data given in Table 2 do not take into account the influence of tracking phenomena. For
that purpose Part 1 or Part 5 of IEC 60664 have to be taken into account. Therefore if the
values from Table 2 of this standard are smaller than the relevant values from Table 4 of
Part 1 or Part 5, the latter are applicable.
These dimensioning data are applicable for all materials that can be deteriorated by thermal
effects. For materials where such deterioration is not likely to occur (for example ceramics)
dimensioning for clearances according to Clause 4 of this standard is sufficient.
NOTE 2 Further information about dimensioning is given in Annex F.

60664-4  IEC:2005 – 31 –
IEC 1346/05
Key
d creepage distance
Figure 2 – Dimensioning of creepage distances to avoid partial discharge
(creepage distance ≥ 1 mm)
or breakdown (creepage distance < 1 mm)

60664-4  IEC:2005 – 33 –
Table 2 – Minimum values of creepage distances for different frequency ranges
a)
Voltage Creepage distance
mm
for for for for for for for
U b) b) b) b) b) b)
peak 30 kHz < f ≤ f ≤ 0,2 MHz f ≤ 0,4 MHz f ≤ 0,7 MHz f ≤ 1 MHz f ≤ 2 MHz f ≤ 3 MHz
kV
100 kHz
0,1 0,0167   0,3
0,2 0,042   0,15 2,8
0,3 0,083 0,09 0,09 0,09 0,09 0,8 20
0,4 0,125 0,13 0,15 0,19 0,35 4,5
0,5 0,183 0,19 0,25 0,4 1,5 20
0,6 0,267 0,27 0,4 0,85 5
0,7 0,358 0,38 0,68 1,9 20
0,8 0,45 0,55 1,1 3,8
0,9 0,525 0,82 1,9 8,7
1 0,6 1,15 3 18
1,1 0,683 1,7 5
1,2 0,85 2,4 8,2
1,3 1,2 3,5
1,4 1,65 5
1,5 2,3 7,3
1,6 3,15
1,7 4,4
1,8 6,1
a)
The values for the creepage distances in the table apply for pollution degree 1. For pollution degree 2 a

multiplication factor of 1,2 and for pollution degree 3 a multiplication factor 1,4 shall be used.
b)
Interpolation between columns is allowed.

6 Solid insulation
6.1 General consideration
Compared to clearances in air, solid insulation can provide a breakdown field strength that is
at least one order of magnitude higher. However in practical use the high breakdown field
strength of solid insulation is of little use.
NOTE The mechanisms that are responsible for degradation and finally breakdown at much lower field strengths
than expected are described in detail in Clause C.1.
6.2 Influencing factors
For a frequency of 1 MHz, the short-time breakdown field strength can be as low as 10 % of
the power-frequency value. The breakdown field strength does not seem to reach a lower limit
even at frequencies as high as 100 MHz.
NOTE High-frequency breakdown characteristics are shown in Clause C.2.
...