Surge overvoltages and surge protection in low-voltage a.c. power systems - General basic information

Presents a general overview on the different kinds of surge overvoltages that can occur on low-voltage installations. Typical surge magnitude and duration as well as frequency of occurrence are described. Information on overvoltages resulting from interactions between power system and communications system is also provided.  Additionally, general guidelines are given concerning surge protection means and systems on the basis of availability and risk considerations, including interactions and the need for coordination and consideration of temporary overvoltages in the selection of surge-protective devices.

Prenapetostna zaščita in zaščita v nizkonapetostnih izmeničnih močnostnih sistemih – Splošne osnovne informacije

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Status
Withdrawn
Publication Date
31-Aug-2006
Withdrawal Date
23-May-2023
Current Stage
9900 - Withdrawal (Adopted Project)
Start Date
23-May-2023
Due Date
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Completion Date
24-May-2023

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SLOVENSKI SIST-TP IEC/TR 62066:2006

STANDARD
september 2006
Prenapetostna zaščita in zaščita v nizkonapetostnih izmeničnih močnostnih
sistemih – Splošne osnovne informacije
Surge overvoltages and surge protection in low-voltage a.c. power systems -
General basic information
ICS 29.020; 91.140.50 Referenčna številka
SIST-TP IEC/TR 62066:2006(en)
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

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TECHNICAL IEC
REPORT
TR 62066
First edition
2002-06
Surge overvoltages and surge protection
in low-voltage a.c. power systems –
General basic information
Surtensions de choc et protection contre la foudre
dans les réseaux à basse tension –
Informations générales fondamentales
 IEC 2002  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch  Web: www.iec.ch
PRICE CODE
Commission Electrotechnique Internationale
XF
International Electrotechnical Commission
Международная Электротехническая Комиссия
For price, see current catalogue

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– 2 – TR 62066  IEC:2002(E)
CONTENTS
FOREWORD.7
1 Scope.9
2 Reference documents.9
3 Definitions .10
4 Overvoltages in low-voltage systems .12
5 Lightning overvoltages.13
5.1 General .13
5.2 Origin of lightning surge overvoltages.18
5.3 Lightning surges transferred from MV systems .21
5.4 Surges caused by direct flash to LV lines .23
5.5 Lightning surges induced into LV systems .23
5.6 Examples of induced overvoltages .25
5.7 Overvoltages caused by flashes to the structures or in close vicinity .27
5.8 Recapitulation on lightning overvoltages.30
6 Switching overvoltages.31
6.1 General .31
6.2 Operation of circuit-breakers and switches .35
6.3 Operation of fuses.37
6.4 Frequency of occurrence .38
6.5 Interactions with surge-protective devices .38
6.6 Recapitulation on switching overvoltages .39
7 Temporary overvoltages .40
7.1 General .40
7.2 Magnitude of temporary overvoltages due to MV and LV faults.40
7.3 Temporary overvoltages due to defects in the LV electrical installation.42
7.4 Probability of occurrence and severity of harm .42
7.5 Recapitulation on temporary overvoltage.44
8 System interaction overvoltages .44
8.1 General .44
8.2 Interaction between power system and communications system .45
8.3 Other interactions.46
8.4 Recapitulation on system interactions.46
9 Observations on surge overvoltages and failure rates.46
9.1 General .46
9.2 Using field failure data.47
9.3 Recapitulation of observations on failure rates .48
10 Considerations on system outage/equipment failure/fires .48
10.1 General .48
10.2 Avoiding interference in system operation .49
10.3 Preventing permanent damage.49
10.4 Costs of surge-related interruptions and failures.50
10.5 Recapitulation on outages and failures .52

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TR 62066  IEC:2002(E) – 3 –
11 Considerations on the use of surge protection .52
11.1 General .52
11.2 Power system configuration.52
11.3 Types of installation .53
11.4 Occurrence of surges .53
11.5 SPD disconnector.54
11.6 Risk assessment .55
11.7 Recapitulation on the need for surge protection.57
12 Surge protection application .57
12.1 General .57
12.2 Surge protective devices in power distribution systems .58
12.3 Basic system characteristics for SPD selection.59
12.4 Considerations for installation of SPDs.64
12.5 Coordination among SPDs and with equipment to be protected .66
12.6 Recapitulation on surge protection application.67
Annex A (informative)  Complementary information on lightning-related overvoltages .68
Annex B (informative)  Switching overvoltages.79
Annex C (informative)  Complementary information on temporary overvoltages .94
Annex D (informative)  Complementary information on system interaction overvoltages
(see clause 8) .97
Annex E (informative)  Complementary information on SPD application .102
Annex F (informative)  Avoiding overvoltages through good practice for earthing and
cabling.124
Bibliography.128
Figure 1 – Examples of lightning flash coupling mechanisms .13
Figure 2 – Examples of lightning flashes to a complex electrical system .15
Figure 3 – Possible waveforms of lightning current striking ground-based objects.16
Figure 4 – Frequency distribution of peak currents for three types of lightning events .16
Figure 5 – Map of annual thunderstorm days [7] .18
Figure 6 – Direct flash to an overhead line.19
Figure 7 – Example of resistive coupling from lightning protection system .21
Figure 8 – Typical earth coupling mechanisms.22
Figure 9 – Typical overvoltages induced on an LV line by a near lightning flash.24
Figure 10 – Example of estimated frequency of occurrence of prospective induced
lightning overvoltages on LV overhead lines .25
Figure 11 – Model of distribution system used in the simulation .26
Figure 12 – Model for computing dispersion of lightning current
among parallel buildings in an example of TN-C system .28
Figure 13 – Generation of overvoltage by switching an RLC circuit .31
Figure 14 – Typical switching overvoltages .33
Figure 15 – Example of a high-frequency switching surge.33
Figure 16 – Distribution of the rate of rise of switching surges at different locations.34
Figure 17 – Distribution of the rise time of switching surges.34
Figure 18 – Rate of rise of the switching surges and their crest values .35
Figure 19 – Distribution of the duration of the switching surges.35

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– 4 – TR 62066  IEC:2002(E)
Figure 20 – Example of distribution of switching surge amplitudes measured
in industrial distribution systems rated 230/400 V .36
Figure 21 – Switching surge during interruption by a miniature fuse [48] .38
Figure 22 – Distribution of the relative frequency of occurrence
of switching surges at different installations .39
Figure 23 – PC/modem connections to the power system
and to the communications system .46
Figure 24 – Example of diversion of lightning current
into the external services (TT system) .61
Figure 25 – Considerations required for the selection of an SPD.63
Figure 26 – Effect of additional connecting lead on the limiting voltage of a varistor .65
Figure 27 – Basic model for energy coordination of SPDs .66
Figure A.1 – Frequency distribution of the lightning peak current I .68
max
Figure A.2 – Frequency distribution of the total lightning charge Q .69
total
Figure A.3 – Frequency distribution of the transient lightning charge Q .69
trans
Figure A.4 – Frequency distribution of the specific lightning energy W/R.70
Figure A.5 – Frequency distribution of the maximum slope of transient current (di/dt) .70
max
Figure A.6 – Frequency distribution of the slope of current (di/dt)
30/90 %
of negative subsequent strokes.71
Figure A.7 – Simplified example with lightning flash to overhead LV line.71
Figure A.8 – Prospective voltages between line and true earth at point of strike (node 1),
at the transformer (node 2) and at the neutral conductor in the consumer installation
(node 3) .72
Figure A.9 – Prospective voltages relative to true earth at node 3 and at node 4 .72
Figure A.10 – Current to earth at the point of strike (node 1), at the transformer (node 2),
and at the consumer installation (node 3) .72
Figure A.11 – Distribution of overvoltage peak magnitudes recorded at the primary
of an MV/LV transformer .73
Figure A.12 – Circuit used for the statistical computation .74
Figure A.13 – Comparison of measured overvoltages [51]
and computed overvoltages (Anastasia).74
Figure A.14 – Model for computing dispersion of lightning current among parallel
buildings (TN-C system) [24].75
Figure A.15 – Dispersion of lightning current among the paths defined in figure A.14.76
Figure A.16 – Model for computing dispersion of lightning current among parallel buildings
(TN-C system, Building 2 with no LPS and no SPDs at the service entrance) [24] . 77
Figure A.17 – Currents and voltage for the example of figure A.16.77
Figure B.1 – Example illustrating transient resonance caused by switching.80
Figure B.2 – Calculated overvoltages at the circuit nodes of figure B.1 .80
Figure B.3 – Typical overvoltage occurring during capacitor bank energizing .81
Figure B.4a – Magnification condition .82
Figure B.4b – Voltage magnification effect .82
Figure B.4 – Magnification of capacitor switching overvoltage at remote bank.82
Figure B.5 – Principle of overvoltage generated by clearing a short-circuit.83
Figure B.6 – Example of survey of switching overvoltages in three types of installations.85
Figure B.7 – Switching surges in an industrial plant measured near the collecting bar .86
Figure B.8 – Frequency of occurrence at selected sites and overall results.88
Figure B.9 – Test circuit and surge during trip of a miniature breaker
due to inrush overload .90
Figure B.10 – Example of overvoltage at the secondary collecting bar
of a 230/400 V transformer substation when blowing 100 A fuses of a feeder .92

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TR 62066  IEC:2002(E) – 5 –
Figure B.11 – Overvoltage factor versus time duration of switching surges
in a distribution system – Short circuit near a feeder fuse .93
Figure B.12 – Overvoltage in a distribution system depending on the cable length
for different fuse ratings – Short circuit at the end of the cable.93
Figure C.1 – Temporary overvoltage resulting from a fault in the primary
of the distribution transformer in a TN system according to North American practice.96
Figure D.1 – PC/modem connections to the power system and communications system .98
Figure D.2 – Voltage difference appearing across PC/modem during surge current flow .98
Figure D.3 – Voltage recorded across reference points for the PC/modem
during a surge.99
Figure D.4 – Insertion of a surge reference equalizer at the PC/modem ports .100
Figure D.5 – Reduction of voltage difference between ports
by a surge reference equalizer.101
Figure E.1 – Example of coordination for two voltage-limiting SPDs (MOV1 and MOV2) .103
Figure E.2 – Comparison of the I/V characteristics of the two MOVs .103
Figure E.3 – Current and voltage versus time characteristics
for the two voltage-limiting SPDs .103
Figure E.4 – Energy distribution among two voltage-limiting SPDs
versus impinging current.104
Figure E.5 – Idealized example for illustrating SPD coordination aspects.104
Figure E.6 – Calculated SPD voltages and current for a 2/20 µs impulse injected in node 1.105
Figure E.7 – Calculated SPD voltages and current for a 10/350 µs impulse injected
in node 2 .106
Figure E.8 – Calculated SPD voltages and current for a 10/350 µs impulse injected
in node 1 .107
Figure E.9 – Example of coordination between a voltage-switching SPD
and a voltage-limiting SPD.107
Figure E.10 – Current and voltage characteristics in the scheme of figure E.9
for no sparkover.108
Figure E.11 – Current and voltage characteristics in the scheme of figure E.9
with sparkover .109
Figure E.12 – Voltage U at spark gap depending on different loads.109
SG
Figure E.13 – Coordination of two SPDs (voltage-switching type) .110
Figure E.14 – Two ZnO varistors with the same nominal discharge current .111
Figure E.15 – Two ZnO varistors with different nominal discharge currents.113
Figure E.16 – Coordination principle for variant I .115
Figure E.17 – Coordination principle for variant II .116
Figure E.18 – Coordination principale for variant III .116
Figure E.19 – Coordination principle for variant IV .117
Figure E.20 – Let-through energy method with standard pulse parameters .117
Figure E.21 – Steepness factor for a surge-current waveform .120
Figure F.1 – EMC cabinet protects electronic equipment
against common-mode currents through cables .125
Figure F.2 – Coupling of common-mode overvoltage caused by switching surges .126
Figure F.3 – Voltages measured in the control room on a cable shorted at the other end,
at the top of the transformer. The common-mode currents are indicated
for the various parallel earth conductors between A and C. .127
Table 1 – Attributes and effects of lightning flashes .14
Table 2 – Statistics of the significant parameters of lightning events.17
Table 3 – Line-to-earth prospective overvoltage levels in the LV installation,
occurrences per year .26

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– 6 – TR 62066  IEC:2002(E)
Table 4 – Current dispersion in available paths in the example
of figure 12 (10/350 µs, 100 kA).29
Table 5 – Time to half-value of the switching surges versus rated current
of miniature fuses .37
Table 6 – Maximum values of overvoltages allowed to occur during MV faults to earth .41
Table 7 – Possible protection modes .64
Table B.1 – Minimum, maximum and mean values of the amplitude and rate
of rise of the recorded switching surges at different locations [48].85
Table B.2 – Distribution of recorded transients.86
Table B.3 – Measurement points and results of the long range measurement
(second part) [1] .88
Table B.4 – Amplitude and rate of rise of switching surges versus rated current
of miniature circuit breakers [48].90
Table C.1 – Maximum values of overvoltages allowed to occur during MV-faults to earth .94
Table C.2 – Maximum possible values for TOVs in LV-installations due to LV-faults .95
Table E.1 – Inductance necessary to ensure gap sparkover.110
Table E.2 – Normalized values .118
Table E.3 – Reference table .118
Table E.4 – Equivalent values.118
Table E.5 – Example of coordination between two SPDs tested according to Class II .122
Table E.6 – Example of coordination between an SPD tested according to Class I
and an SPD tested according to Class II .122
Table E.7 – Parameters for Class I tests (IEC 61643-1) .123

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TR 62066  IEC:2002(E) – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SURGE OVERVOLTAGES AND SURGE PROTECTION
IN LOW-VOLTAGE AC POWER SYSTEMS –
GENERAL BASIC INFORMATION
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. 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. The 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 the 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 National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this technical report may be the subject of
patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However,
a technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard,
for example “state of the art”.
IEC 62066, which is a technical report, has been prepared by Technical Committee 64:
Electrical installations and protection against electric shock.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
64/1125/CDV 64/1163/RVC
Full information on the voting for the approval of this technical report 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 3.

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– 8 – TR 62066  IEC:2002(E)
The committee has decided that the contents of this publication will remain unchanged until 2006.
At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
This document, which is purely informative, is not to be regarded as an International
Standard.
A bilingual version of this document may be issued at a later date.

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TR 62066  IEC:2002(E) – 9 –
SURGE OVERVOLTAGES AND SURGE PROTECTION
IN LOW-VOLTAGE AC POWER SYSTEMS –
GENERAL BASIC INFORMATION
1 Scope
IEC 62066 is a technical report that presents a general overview on the different kinds of
surge overvoltages that can occur on low-voltage installations. Typical surge magnitude and
duration as well as frequency of occurrence are described. Information on overvoltages
resulting from interactions between power system and communications system is also
provided.
Additionally, general guidelines are given concerning surge protection means and systems on
the basis of availability and risk considerations, including interactions and the need for
coordination and consideration of temporary overvoltages in the selection of surge-protective
devices.
2 Reference documents
IEC 60364-4-44:2001, Electrical installations of buildings – Part 4-44: Protection for safety –
Protection against voltage disturbances and electromagnetic disturbances
IEC 60364-5-53:2001, Electrical installations of buildings – Part 5-53: Selection and erection
of electrical equipment – Isolation, switching and control
IEC 60664-1:1992, Insulation coordination for equipment within low-voltage systems – Part 1:
Principles, requirements and tests
Amendment 1 (2000)
IEC/TR 61000-2-5:1995, Electromagnetic compatibility (EMC) – Part 2: Environment –
Section 5: Classification of electromagnetic environments. Basic EMC publication
IEC 61000-4-1:2000, Electromagnetic compatibility (EMC) – Part 4: Testing and measurement
techniques – Overview of IEC 61000-4 series
IEC 61000-4-4:1995, Electromagnetic compatibility (EMC) – Part 4: Testing and measurement
techniques – Section 4: Electrical fast transient/burst immuni
...

TECHNICAL IEC
REPORT
TR 62066
First edition
2002-06
Surge overvoltages and surge protection
in low-voltage a.c. power systems –
General basic information
Surtensions de choc et protection contre la foudre
dans les réseaux à basse tension –
Informations générales fondamentales
 IEC 2002  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch  Web: www.iec.ch
PRICE CODE
Commission Electrotechnique Internationale
XF
International Electrotechnical Commission
Международная Электротехническая Комиссия
For price, see current catalogue

---------------------- Page: 1 ----------------------
– 2 – TR 62066  IEC:2002(E)
CONTENTS
FOREWORD.7
1 Scope.9
2 Reference documents.9
3 Definitions .10
4 Overvoltages in low-voltage systems .12
5 Lightning overvoltages.13
5.1 General .13
5.2 Origin of lightning surge overvoltages.18
5.3 Lightning surges transferred from MV systems .21
5.4 Surges caused by direct flash to LV lines .23
5.5 Lightning surges induced into LV systems .23
5.6 Examples of induced overvoltages .25
5.7 Overvoltages caused by flashes to the structures or in close vicinity .27
5.8 Recapitulation on lightning overvoltages.30
6 Switching overvoltages.31
6.1 General .31
6.2 Operation of circuit-breakers and switches .35
6.3 Operation of fuses.37
6.4 Frequency of occurrence .38
6.5 Interactions with surge-protective devices .38
6.6 Recapitulation on switching overvoltages .39
7 Temporary overvoltages .40
7.1 General .40
7.2 Magnitude of temporary overvoltages due to MV and LV faults.40
7.3 Temporary overvoltages due to defects in the LV electrical installation.42
7.4 Probability of occurrence and severity of harm .42
7.5 Recapitulation on temporary overvoltage.44
8 System interaction overvoltages .44
8.1 General .44
8.2 Interaction between power system and communications system .45
8.3 Other interactions.46
8.4 Recapitulation on system interactions.46
9 Observations on surge overvoltages and failure rates.46
9.1 General .46
9.2 Using field failure data.47
9.3 Recapitulation of observations on failure rates .48
10 Considerations on system outage/equipment failure/fires .48
10.1 General .48
10.2 Avoiding interference in system operation .49
10.3 Preventing permanent damage.49
10.4 Costs of surge-related interruptions and failures.50
10.5 Recapitulation on outages and failures .52

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TR 62066  IEC:2002(E) – 3 –
11 Considerations on the use of surge protection .52
11.1 General .52
11.2 Power system configuration.52
11.3 Types of installation .53
11.4 Occurrence of surges .53
11.5 SPD disconnector.54
11.6 Risk assessment .55
11.7 Recapitulation on the need for surge protection.57
12 Surge protection application .57
12.1 General .57
12.2 Surge protective devices in power distribution systems .58
12.3 Basic system characteristics for SPD selection.59
12.4 Considerations for installation of SPDs.64
12.5 Coordination among SPDs and with equipment to be protected .66
12.6 Recapitulation on surge protection application.67
Annex A (informative)  Complementary information on lightning-related overvoltages .68
Annex B (informative)  Switching overvoltages.79
Annex C (informative)  Complementary information on temporary overvoltages .94
Annex D (informative)  Complementary information on system interaction overvoltages
(see clause 8) .97
Annex E (informative)  Complementary information on SPD application .102
Annex F (informative)  Avoiding overvoltages through good practice for earthing and
cabling.124
Bibliography.128
Figure 1 – Examples of lightning flash coupling mechanisms .13
Figure 2 – Examples of lightning flashes to a complex electrical system .15
Figure 3 – Possible waveforms of lightning current striking ground-based objects.16
Figure 4 – Frequency distribution of peak currents for three types of lightning events .16
Figure 5 – Map of annual thunderstorm days [7] .18
Figure 6 – Direct flash to an overhead line.19
Figure 7 – Example of resistive coupling from lightning protection system .21
Figure 8 – Typical earth coupling mechanisms.22
Figure 9 – Typical overvoltages induced on an LV line by a near lightning flash.24
Figure 10 – Example of estimated frequency of occurrence of prospective induced
lightning overvoltages on LV overhead lines .25
Figure 11 – Model of distribution system used in the simulation .26
Figure 12 – Model for computing dispersion of lightning current
among parallel buildings in an example of TN-C system .28
Figure 13 – Generation of overvoltage by switching an RLC circuit .31
Figure 14 – Typical switching overvoltages .33
Figure 15 – Example of a high-frequency switching surge.33
Figure 16 – Distribution of the rate of rise of switching surges at different locations.34
Figure 17 – Distribution of the rise time of switching surges.34
Figure 18 – Rate of rise of the switching surges and their crest values .35
Figure 19 – Distribution of the duration of the switching surges.35

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– 4 – TR 62066  IEC:2002(E)
Figure 20 – Example of distribution of switching surge amplitudes measured
in industrial distribution systems rated 230/400 V .36
Figure 21 – Switching surge during interruption by a miniature fuse [48] .38
Figure 22 – Distribution of the relative frequency of occurrence
of switching surges at different installations .39
Figure 23 – PC/modem connections to the power system
and to the communications system .46
Figure 24 – Example of diversion of lightning current
into the external services (TT system) .61
Figure 25 – Considerations required for the selection of an SPD.63
Figure 26 – Effect of additional connecting lead on the limiting voltage of a varistor .65
Figure 27 – Basic model for energy coordination of SPDs .66
Figure A.1 – Frequency distribution of the lightning peak current I .68
max
Figure A.2 – Frequency distribution of the total lightning charge Q .69
total
Figure A.3 – Frequency distribution of the transient lightning charge Q .69
trans
Figure A.4 – Frequency distribution of the specific lightning energy W/R.70
Figure A.5 – Frequency distribution of the maximum slope of transient current (di/dt) .70
max
Figure A.6 – Frequency distribution of the slope of current (di/dt)
30/90 %
of negative subsequent strokes.71
Figure A.7 – Simplified example with lightning flash to overhead LV line.71
Figure A.8 – Prospective voltages between line and true earth at point of strike (node 1),
at the transformer (node 2) and at the neutral conductor in the consumer installation
(node 3) .72
Figure A.9 – Prospective voltages relative to true earth at node 3 and at node 4 .72
Figure A.10 – Current to earth at the point of strike (node 1), at the transformer (node 2),
and at the consumer installation (node 3) .72
Figure A.11 – Distribution of overvoltage peak magnitudes recorded at the primary
of an MV/LV transformer .73
Figure A.12 – Circuit used for the statistical computation .74
Figure A.13 – Comparison of measured overvoltages [51]
and computed overvoltages (Anastasia).74
Figure A.14 – Model for computing dispersion of lightning current among parallel
buildings (TN-C system) [24].75
Figure A.15 – Dispersion of lightning current among the paths defined in figure A.14.76
Figure A.16 – Model for computing dispersion of lightning current among parallel buildings
(TN-C system, Building 2 with no LPS and no SPDs at the service entrance) [24] . 77
Figure A.17 – Currents and voltage for the example of figure A.16.77
Figure B.1 – Example illustrating transient resonance caused by switching.80
Figure B.2 – Calculated overvoltages at the circuit nodes of figure B.1 .80
Figure B.3 – Typical overvoltage occurring during capacitor bank energizing .81
Figure B.4a – Magnification condition .82
Figure B.4b – Voltage magnification effect .82
Figure B.4 – Magnification of capacitor switching overvoltage at remote bank.82
Figure B.5 – Principle of overvoltage generated by clearing a short-circuit.83
Figure B.6 – Example of survey of switching overvoltages in three types of installations.85
Figure B.7 – Switching surges in an industrial plant measured near the collecting bar .86
Figure B.8 – Frequency of occurrence at selected sites and overall results.88
Figure B.9 – Test circuit and surge during trip of a miniature breaker
due to inrush overload .90
Figure B.10 – Example of overvoltage at the secondary collecting bar
of a 230/400 V transformer substation when blowing 100 A fuses of a feeder .92

---------------------- Page: 4 ----------------------
TR 62066  IEC:2002(E) – 5 –
Figure B.11 – Overvoltage factor versus time duration of switching surges
in a distribution system – Short circuit near a feeder fuse .93
Figure B.12 – Overvoltage in a distribution system depending on the cable length
for different fuse ratings – Short circuit at the end of the cable.93
Figure C.1 – Temporary overvoltage resulting from a fault in the primary
of the distribution transformer in a TN system according to North American practice.96
Figure D.1 – PC/modem connections to the power system and communications system .98
Figure D.2 – Voltage difference appearing across PC/modem during surge current flow .98
Figure D.3 – Voltage recorded across reference points for the PC/modem
during a surge.99
Figure D.4 – Insertion of a surge reference equalizer at the PC/modem ports .100
Figure D.5 – Reduction of voltage difference between ports
by a surge reference equalizer.101
Figure E.1 – Example of coordination for two voltage-limiting SPDs (MOV1 and MOV2) .103
Figure E.2 – Comparison of the I/V characteristics of the two MOVs .103
Figure E.3 – Current and voltage versus time characteristics
for the two voltage-limiting SPDs .103
Figure E.4 – Energy distribution among two voltage-limiting SPDs
versus impinging current.104
Figure E.5 – Idealized example for illustrating SPD coordination aspects.104
Figure E.6 – Calculated SPD voltages and current for a 2/20 µs impulse injected in node 1.105
Figure E.7 – Calculated SPD voltages and current for a 10/350 µs impulse injected
in node 2 .106
Figure E.8 – Calculated SPD voltages and current for a 10/350 µs impulse injected
in node 1 .107
Figure E.9 – Example of coordination between a voltage-switching SPD
and a voltage-limiting SPD.107
Figure E.10 – Current and voltage characteristics in the scheme of figure E.9
for no sparkover.108
Figure E.11 – Current and voltage characteristics in the scheme of figure E.9
with sparkover .109
Figure E.12 – Voltage U at spark gap depending on different loads.109
SG
Figure E.13 – Coordination of two SPDs (voltage-switching type) .110
Figure E.14 – Two ZnO varistors with the same nominal discharge current .111
Figure E.15 – Two ZnO varistors with different nominal discharge currents.113
Figure E.16 – Coordination principle for variant I .115
Figure E.17 – Coordination principle for variant II .116
Figure E.18 – Coordination principale for variant III .116
Figure E.19 – Coordination principle for variant IV .117
Figure E.20 – Let-through energy method with standard pulse parameters .117
Figure E.21 – Steepness factor for a surge-current waveform .120
Figure F.1 – EMC cabinet protects electronic equipment
against common-mode currents through cables .125
Figure F.2 – Coupling of common-mode overvoltage caused by switching surges .126
Figure F.3 – Voltages measured in the control room on a cable shorted at the other end,
at the top of the transformer. The common-mode currents are indicated
for the various parallel earth conductors between A and C. .127
Table 1 – Attributes and effects of lightning flashes .14
Table 2 – Statistics of the significant parameters of lightning events.17
Table 3 – Line-to-earth prospective overvoltage levels in the LV installation,
occurrences per year .26

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– 6 – TR 62066  IEC:2002(E)
Table 4 – Current dispersion in available paths in the example
of figure 12 (10/350 µs, 100 kA).29
Table 5 – Time to half-value of the switching surges versus rated current
of miniature fuses .37
Table 6 – Maximum values of overvoltages allowed to occur during MV faults to earth .41
Table 7 – Possible protection modes .64
Table B.1 – Minimum, maximum and mean values of the amplitude and rate
of rise of the recorded switching surges at different locations [48].85
Table B.2 – Distribution of recorded transients.86
Table B.3 – Measurement points and results of the long range measurement
(second part) [1] .88
Table B.4 – Amplitude and rate of rise of switching surges versus rated current
of miniature circuit breakers [48].90
Table C.1 – Maximum values of overvoltages allowed to occur during MV-faults to earth .94
Table C.2 – Maximum possible values for TOVs in LV-installations due to LV-faults .95
Table E.1 – Inductance necessary to ensure gap sparkover.110
Table E.2 – Normalized values .118
Table E.3 – Reference table .118
Table E.4 – Equivalent values.118
Table E.5 – Example of coordination between two SPDs tested according to Class II .122
Table E.6 – Example of coordination between an SPD tested according to Class I
and an SPD tested according to Class II .122
Table E.7 – Parameters for Class I tests (IEC 61643-1) .123

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TR 62066  IEC:2002(E) – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SURGE OVERVOLTAGES AND SURGE PROTECTION
IN LOW-VOLTAGE AC POWER SYSTEMS –
GENERAL BASIC INFORMATION
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. 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. The 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 the 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 National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this technical report may be the subject of
patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However,
a technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard,
for example “state of the art”.
IEC 62066, which is a technical report, has been prepared by Technical Committee 64:
Electrical installations and protection against electric shock.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
64/1125/CDV 64/1163/RVC
Full information on the voting for the approval of this technical report 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 3.

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– 8 – TR 62066  IEC:2002(E)
The committee has decided that the contents of this publication will remain unchanged until 2006.
At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
This document, which is purely informative, is not to be regarded as an International
Standard.
A bilingual version of this document may be issued at a later date.

---------------------- Page: 8 ----------------------
TR 62066  IEC:2002(E) – 9 –
SURGE OVERVOLTAGES AND SURGE PROTECTION
IN LOW-VOLTAGE AC POWER SYSTEMS –
GENERAL BASIC INFORMATION
1 Scope
IEC 62066 is a technical report that presents a general overview on the different kinds of
surge overvoltages that can occur on low-voltage installations. Typical surge magnitude and
duration as well as frequency of occurrence are described. Information on overvoltages
resulting from interactions between power system and communications system is also
provided.
Additionally, general guidelines are given concerning surge protection means and systems on
the basis of availability and risk considerations, including interactions and the need for
coordination and consideration of temporary overvoltages in the selection of surge-protective
devices.
2 Reference documents
IEC 60364-4-44:2001, Electrical installations of buildings – Part 4-44: Protection for safety –
Protection against voltage disturbances and electromagnetic disturbances
IEC 60364-5-53:2001, Electrical installations of buildings – Part 5-53: Selection and erection
of electrical equipment – Isolation, switching and control
IEC 60664-1:1992, Insulation coordination for equipment within low-voltage systems – Part 1:
Principles, requirements and tests
Amendment 1 (2000)
IEC/TR 61000-2-5:1995, Electromagnetic compatibility (EMC) – Part 2: Environment –
Section 5: Classification of electromagnetic environments. Basic EMC publication
IEC 61000-4-1:2000, Electromagnetic compatibility (EMC) – Part 4: Testing and measurement
techniques – Overview of IEC 61000-4 series
IEC 61000-4-4:1995, Electromagnetic compatibility (EMC) – Part 4: Testing and measurement
techniques – Section 4: Electrical fast transient/burst immunity test. Basic EMC publication
IEC 61000-4-5:1995, Electromagnetic compatibility (EMC) – Part 4: Testing and measurement
techniques – Section 5: Surge immunity test
Amendment 1 (2000)
IEC/TR 61000-5-2:1997, Electromagnetic compatibility (EMC) – Part 5: Installation and
mitigation guidelines – Section 2: Earthing and cabling
IEC 61024-1:1990, Protection of structures against lightning – Part 1: General principles
IEC 61024-1-1:1993, Protection of structures against lightning – Part 1: General principles –
Section 1: Guide A – Selection of protection levels for lightni
...

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