SIST EN IEC 61643-352:2018

Components for low-voltage surge protection - Part 352: Selection and application principles for telecommunications and signalling network surge isolation transformers (SIT)

This part of IEC 61643 covers the application of surge isolation transformers (SITs) that are
used in telecommunication transformer applications with signal levels up to 400 V peak to
peak. These transformers have a high rated impulse voltage with or without screen between
the input and output windings. SITs are components for surge protection and are used to
mitigate the onward propagation of common-mode voltage surges. This document describes
SITs' selection, application principles and related information. This document does not cover
power line communication transformers.

Bauelemente für Überspannungsschutzgeräte für Niederspannung – Teil 352: Auswahl- und Anwendungsprinzipien für Überspannungstrenntransformatoren (SIT) für den Einsatz in Telekommunikations- und signalverarbeitenden Netzwerken

Composants pour protection par parafoudres basse tension - Partie 352: Principes de choix et d'application pour les transformateurs d'isolement contre les surtensions (SIT) dans les réseaux de signalisation et de télécommunications

IEC 61643-352:2018 trait à l'application des transformateurs d'isolement contre les surtensions (SIT) utilisés dans des applications de transformateur de télécommunication dont les niveaux de signal atteignent 400 V de crête à crête. Ces transformateurs ont une tension assignée de tenue aux chocs élevée, avec ou sans blindage entre les enroulements d'entrée et de sortie. Les SIT sont des composants de protection contre les surtensions; ils sont utilisés pour atténuer la propagation de surtensions en mode commun. Le présent document traite du choix des SIT, de leurs principes d'application et des informations les concernant. Le présent document ne couvre pas les transformateurs de communication sur ligne d'alimentation.
Mots clés: transformateurs d'isolement contre les surtensions (SIT), applications de transformateur de télécommunication

Sestavni deli za nizkonapetostne naprave za zaščito pred prenapetostnimi udari - 352. del: Izbira in načini uporabe izolacijskih transformatorjev (SIT) v telekomunikacijskih in signalnih omrežjih

V tem delu standarda IEC 61643 je obravnavana uporaba izolacijskih transformatorjev (SIT), ki se uporabljajo pri telekomunikacijskih transformatorjih z ravnmi signala do 400 V od vršne vrednosti do vršne vrednosti. Ti transformatorji imajo visoko nazivno udarno napetost z zaslonom med vhodnim in izhodnim navitjem ali brez njega. Izolacijski transformatorji (SIT) so komponente za zaščito pred prenapetostnimi udari in se uporabljajo za širjenje običajnega načina napetostnih udarov. V tem dokumentu so opisani izbor izolacijskih transformatorjev, načela uporabe in povezane informacije. Ta dokument ne obsega komunikacijskih transformatorjev elektroenergetskih vodov.

General Information

• Status: Published
• Publication Date: 18-Apr-2018
• ICS: 29.240.10 - Substations. Surge arresters
• ICS: 33.040.99 - Other equipment for telecommunication systems
• Technical Committee: POD - Surge aresters
• Current Stage: 6060 - National Implementation/Publication (Adopted Project)
• Start Date: 05-Apr-2018
• Due Date: 10-Jun-2018
• Completion Date: 19-Apr-2018
• Ref Project: EN IEC 61643-352:2018 - Components for low-voltage surge protection - Part 352: Selection and application principles for telecommunications and signalling network surge isolation transformers (SITs)

Standards Content (Sample)

SLOVENSKI STANDARD
SIST EN IEC 61643-352:2018
01-maj-2018
6HVWDYQLGHOL]DQL]NRQDSHWRVWQHQDSUDYH]D]DãþLWRSUHGSUHQDSHWRVWQLPLXGDUL
GHO,]ELUDLQQDþLQLXSRUDEHL]RODFLMVNLKWUDQVIRUPDWRUMHY6,7Y
WHOHNRPXQLNDFLMVNLKLQVLJQDOQLKRPUHåMLK
Components for low-voltage surge protection - Part 352: Selection and application
principles for telecommunications and signalling network surge isolation transformers
(SIT)
Ta slovenski standard je istoveten z: EN IEC 61643-352:2018
ICS:
29.240.10 Transformatorske postaje. Substations. Surge arresters
Prenapetostni odvodniki
33.040.99 Druga oprema za Other equipment for
telekomunikacijske sisteme telecommunication systems
SIST EN IEC 61643-352:2018 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN IEC 61643-352:2018

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SIST EN IEC 61643-352:2018


EUROPEAN STANDARD EN IEC 61643-352

NORME EUROPÉENNE

EUROPÄISCHE NORM
March 2018
ICS 33.040.99

English Version
Components for low-voltage surge protection - Part 352:
Selection and application principles for telecommunications and
signalling network surge isolation transformers (SITs)
(IEC 61643-352:2018)
Composants pour protection par parafoudres basse tension Bauelemente für Überspannungsschutzgeräte für
- Partie 352: Principes de choix et d'application pour les Niederspannung - Teil 352: Auswahl- und
transformateurs d'isolement contre les surtensions (SIT) Anwendungsprinzipien für
dans les réseaux de signalisation et de télécommunications Überspannungstrenntransformatoren (SIT) für den Einsatz
(IEC 61643-352:2018) in Telekommunikations- und signalverarbeitenden
Netzwerken
(IEC 61643-352:2018)
This European Standard was approved by CENELEC on 2018-02-14. 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: Rue de la Science 23, B-1040 Brussels
© 2018 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
 Ref. No. EN IEC 61643-352:2018 E

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SIST EN IEC 61643-352:2018
EN IEC 61643-352:2018 (E)

European foreword
The text of document 37B/161/FDIS, future edition 1 of IEC 61643-352, prepared by IEC/SC 37B,
"Components for low-voltage surge protection" of IEC/TC 37 "Surge arresters" was submitted to the
IEC-CENELEC parallel vote and approved by CENELEC as EN IEC 61643-352:2018.

The following dates are fixed:
• latest date by which the document has to be (dop) 2018-11-14
implemented at national level by
publication of an identical national
standard or by endorsement
(dow) 2021-02-14
• latest date by which the national
standards conflicting with the
document have to be withdrawn

Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.

Endorsement notice
The text of the International Standard IEC 61643-352:2018 was approved by CENELEC as a
European Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:

IEC 60065:2001 NOTE Harmonized as EN 60065:2002 (modified).
IEC 60068-2-1:2007 NOTE Harmonized as EN 60068-2-1:2007 (not modified).
IEC 60068-2-2:2007 NOTE Harmonized as EN 60068-2-2:2007 (not modified).
IEC 60076-1:2011 NOTE Harmonized as EN 60076-1:2011 (not modified).
IEC 60064-1 NOTE Harmonized as EN 60064-1.
IEC 60721-3-9:1993 NOTE Harmonized as EN 60721-3-9:1993 (not modified).
IEC 61340-4-8:2014 NOTE Harmonized as EN 61340-4-8:2015 (not modified).
IEC 61558-1 NOTE Harmonized as EN 61558-1.
IEC 61558-2-4:2009 NOTE Harmonized as EN 61558-2-4:2009 (not modified).
IEC 61558-2-6:2009 NOTE Harmonized as EN 61558-2-6:2009 (not modified).
IEC 61643-21 NOTE Harmonized as EN 61643-21.

2

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SIST EN IEC 61643-352:2018
EN IEC 61643-352:2018 (E)

Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications

The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.

NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.

NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu.

Publication Year Title EN/HD Year
IEC 61643-351 -  Components for low-voltage surge EN 61643-351 -
protective devices - Part 351: Performance
requirements and test methods for
telecommunications and signalling network
surge isolation transformers (SIT)


3

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SIST EN IEC 61643-352:2018




IEC 61643-352

®


Edition 1.0 2018-01




INTERNATIONAL



STANDARD




NORME



INTERNATIONALE
colour

inside










Components for low-voltage surge protection –

Part 352: Selection and application principles for telecommunications and

signalling network surge isolation transformers (SITs)




Composants pour protection par parafoudres basse tension –

Partie 352: Principes de choix et d'application pour les transformateurs


d'isolement contre les surtensions (SIT) dans les réseaux de signalisation et de

télécommunications











INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE


INTERNATIONALE




ICS 33.040.99 ISBN 978-2-8322-5225-3



Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, symbols and abbreviated terms . 7
3.1 Terms and definitions . 7
3.2 Symbols . 8
3.3 Abbreviated terms . 9
4 Service conditions . 10
4.1 Temperature range . 10
4.2 Humidity . 10
4.3 Altitude . 10
4.4 Microclimate . 10
5 SIT surge conditions . 11
5.1 SIT surge mitigation . 11
5.2 Common-mode surges . 12
5.3 Differential-mode surges . 13
5.3.1 General . 13
5.3.2 Ethernet transformer differential surge action . 13
6 Selection . 13
6.1 General . 13
6.2 Impulse withstand voltage . 13
6.3 Rated values of SIT . 14
7 Applications . 14
7.1 General . 14
7.2 Example of surge protection using SITs with ES for control and terminal
equipment installed in two different buildings respectively . 14
7.3 Example of surge protection using SITs for telecommunication equipment in
substation . 14
7.4 Example of surge protection using SITs for transmission and switching
equipment installed in different floors in a communication building . 16
7.5 Example of surge protection using SITs for computer network equipment in a
data centre . 17
7.6 Example of surge protection using SITs for a Power over Ethernet (PoE)
system . 17
7.7 Example of surge protection using SITs for LAN . 18
Annex A (informative) Lightning overvoltages of telecommunication line . 19
Bibliography . 20

Figure 1 – Symbol for a two-winding SIT . 8
Figure 2 – Symbol for a two-winding SIT with polarity indication . 9
Figure 3 – Symbol for a two-winding SIT with electric screen . 9
Figure 4 – SIT with centre tapped windings . 9
Figure 5 – Common-mode surge conditions for SIT . 11
Figure 6 – Common-mode surge conditions for SIT with an electric screen . 12
Figure 7 – Transformer differential surge truncation . 13

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Figure 8 – Example of surge protection using SITs in order to isolate two different
buildings . 14
Figure 9 – Example of surge protection using SITs in substation . 15
Figure 10 – Example of surge protection using SITs in a communication building . 16
Figure 11 – Example of surge protection using SITs in a data centre . 17
Figure 12 – Example of surge protection using SITs for a Power over Ethernet (PoE)
system . 17
Figure 13 – Example of surge protection using SITs for LAN . 18
Figure A.1 – Lightning overvoltages of telecommunication line. 19

Table 1 – List of abbreviated terms used in this document . 10
Table 2 – Classification of microclimate condition . 10

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INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

COMPONENTS FOR LOW-VOLTAGE SURGE PROTECTION –

Part 352: Selection and application principles for telecommunications and
signalling network surge isolation transformers (SITs)

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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
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.
IEC 61643-352 has been prepared by subcommittee 37B: Components for low-voltage surge
protection, of IEC technical committee 37: Surge arresters.
The text of this standard is based on the following documents:
FDIS Report on voting
37B/161/FDIS 37B/167/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.
A list of all parts in the IEC 61643 series, published under the general title Low-voltage surge
protection, can be found on the IEC website.

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SIST EN IEC 61643-352:2018
IEC 61643-352:2018 © IEC 2018 – 5 –
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website 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.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.

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INTRODUCTION
This document covers surge isolation transformers whose rated impulse withstand voltage
coordinates with the expected surge environment of the installation.
This type of surge protective component, SPC, isolates and attenuates transient voltages and
is often used in conjunction with current diverting components (e.g. GDT, MOV, etc.) or in
SPDs.

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IEC 61643-352:2018 © IEC 2018 – 7 –
COMPONENTS FOR LOW-VOLTAGE SURGE PROTECTION –

Part 352: Selection and application principles for telecommunications and
signalling network surge isolation transformers (SITs)


1 Scope
This part of IEC 61643 covers the application of surge isolation transformers (SITs) that are
used in telecommunication transformer applications with signal levels up to 400 V peak to
peak. These transformers have a high rated impulse voltage with or without screen between
the input and output windings. SITs are components for surge protection and are used to
mitigate the onward propagation of common-mode voltage surges. This document describes
SITs' selection, application principles and related information. This document does not cover
power line communication transformers.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 61643-351, Components for low-voltage surge protective devices – Part 351: Performance
requirements and test methods for telecommunications and signalling network surge isolation
transformers (SIT)
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1.1
surge isolating transformer
SIT
isolation transformer which has high impulse withstand voltage with/without electrostatic
screen between input and output windings
3.1.2
electric screen
ES
barrier or enclosure that limits the penetration of an electrostatic field
3.1.3
clearance
shortest distance in air between two conductive parts
[SOURCE: IEC TR 60664-2-1:2011, 3.4]
3.1.4
creepage distance
shortest distance along the surface of a solid insulating material between two conductive
parts
[SOURCE: IEC TR 60664-2-1:2011, 3.7]

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3.1.5
impulse withstand voltage
highest peak value of impulse voltage of prescribed form and polarity which does not cause
breakdown of insulation under specified conditions
[SOURCE: IEC TR 60664-2-1:2011, 3.15]
3.1.6
isolation transformer
transformer with protective separation between the input and output windings
[SOURCE: IEC 60065:2001, 2.7.1, modified – The original definition referred to isolating
transformers.]
3.1.7
insulation
that part of an electrotechnical product which separates the conducting parts at different
electrical potentials
[SOURCE: IEC TR 60664-2-1:2011, 3.17]
3.1.8
overvoltage
any voltage having a peak value exceeding the corresponding peak value of maximum
steady-state voltage at normal operating conditions
[SOURCE: IEC TR 60664-2-1:2011, 3.21]
3.1.9
microclimate
climatic condition at the place where a component is installed in the product
Note 1 to entry: Only the inside product maximum air temperature (classes X1 to X7) and, optionally, the
maximum air humidity class (classes Y1 to Y4) are taken into account.
[SOURCE: IEC 60721-3-9:1993, 3.1, modified – Note 1 to entry has been added.]
3.1.10
Power over Ethernet
PoE
equipment powering via Ethernet twisted-pair cabling
3.2 Symbols
For the purposes of this document, the symbols shown in Figures 1 to 4 apply.
P1 S1
S2
P2
IEC

Key
P1: primary winding terminal 1 S1: secondary winding terminal 1
P2: primary winding terminal 2 S2: secondary winding terminal 2
Figure 1 – Symbol for a two-winding SIT
Figure 2 shows the symbol for a two-winding SIT with instantaneous voltage polarity
indicators, similar to symbol IEC 60617-S00843:2006-09 made with terminal connections.

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IEC 61643-352:2018 © IEC 2018 – 9 –
P1 S1
P2 S2
IEC

Key

P1: primary winding terminal 1 S1: secondary winding terminal 1
P2: primary winding terminal 2 S2: secondary winding terminal 2
Figure 2 – Symbol for a two-winding SIT with polarity indication
Figure 3 shows the symbol for a two-winding SIT with an electrostatic screen between the
windings, similar to symbol IEC 60617-S00853:2006-10 made with terminal connections.
P1 S1
P2 S2
E
IEC

Key
P1: primary winding terminal 1 S1: secondary winding terminal 1
P2: primary winding terminal 2 S2: secondary winding terminal 2
E: earth terminal (electrostatic screen terminal)
Figure 3 – Symbol for a two-winding SIT with electric screen
Figure 4 shows the symbol for SIT centre tapped windings, similar to symbol
IEC 60617-S00855:2006-10 made with two centre tapped windings and terminal connections.
When testing is done with shorted windings, the centre tap is also connected to the short.
Other testing is done without any connection to the centre tap terminal.
P1 S1
CT CT
P2 S2
IEC

Key
P1: primary winding terminal 1 S1: secondary winding terminal 1
P2: primary winding terminal 2 S2: secondary winding terminal 2
CT: centre tap terminal
Figure 4 – SIT with centre tapped windings
3.3 Abbreviated terms
For the purposes of this document, the abbreviated terms given in Table 1 apply.

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Table 1 – List of abbreviated terms used in this document
ABD Avalanche Breakdown Diode
ES Electrostatic Screen
IBN Isolated Bonding Network
ICT Information and Communications Technology
IR Insulation Resistance
LAN Local Area Network
SIT Surge Isolation Transformer
SPD Surge Protective Device
SPC Surge Protective Components
PoE Power over Ethernet

4 Service conditions
4.1 Temperature range
Normal range: −20 °C to 40 °C
Extended range: This range is decided based on agreement between manufacturer and user.
4.2 Humidity
Not exceeding 90 %.
4.3 Altitude
Normal range: Not exceeding 1 000 m.
Extended range: This range is decided based on agreement between manufacturer and user.
4.4 Microclimate
When microclimate condition applies, use the classes of Table 2.
Table 2 – Classification of microclimate condition
High air temperature severity Class Typical component Product application
temperature range
(°C) (°C)
55 X1
70 X2 0 to 70 Commercial
85 X3 −40 to 85 Industrial
100 X4
125 X5 −55 to 125 Military
a
155 X6 −65 to 150
Storage
200 X7
a
Storage temperature rating verification is outside the scope of this document. See IEC 60068-2-1:2007 and
IEC 60068-2-2:2007.

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5 SIT surge conditions
5.1 SIT surge mitigation
An SIT couples a service across the transformer insulation by magnetic induction. When
common-mode surges occur on the incoming service the insulation is voltage stressed. The
insulation has three physical paths:
a) solid insulation – insulation material interposed between the two-windings;
b) creepage distance;
c) clearance.
Clearance distances should be set so that the maximum expected voltage difference does not
breakdown the clearance. Creepage distances should be set so that the maximum expected
voltage difference and pollution degree do not cause surface flashover or breakdown
(tracking). Solid insulation thickness should be set so that the maximum expected voltage
difference does not cause breakdown.
The higher frequency components of a surge impulse will be electrostatic coupled by SIT
internal-winding capacitance (shown as C + C ) from one winding to the other,
P-SA P-SB
see Figure 5.
C
P-SA
Z W W Z

S P S T
R
C
P-SB
IEC

Key
W : primary winding C , C : primary to secondary capacitance, paths A and B

P P-SA P-SB
W : secondary winding
R: reference plane or point
S
Z : terminating or load impedance

T
Z : service source impedance

S
Figure 5 – Common-mode surge conditions for SIT
To reduce internal-winding capacitance a conducting electrostatic screen can be used
between the windings, see Figure 6. The electrostatic screen decouples most of the winding
capacitance (shown as CP-Screen A, CP-Screen B, CS-Screen A and CS-Screen B) leaving a
much smaller value of internal-winding capacitance (shown as C + C ).
P-SA P-SB

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C
P-SA
C C
P-Screen A S-Screen A
Z
S
W W Z
P S
T
ES
C C
P-Screen B S-Screen B
R
C
P-SB
IEC

Key
W : primary winding C C
,
P P-Screen A P-Screen B: primary to screen capacitance, paths A and B
W : secondary winding C , C
: secondary to screen capacitance, paths A
S S-Screen A P-Screen B
and B
ES: electrostatic screen C , C : primary to secondary unscreened capacitance, paths A
P-SA P-SB
and B
Z : service source impedance
S
R: reference plane or point Z : terminating or load impedance
T
Figure 6 – Common-mode surge conditions for SIT with an electric screen
5.2 Common-mode surges
Lightning surges are likely introduced by induction, local protective earthing potential rise and
via breakdown or bypassing of a series insulation barrier. These surges will inherently be
longitudinal/common-mode in nature.
Equipment may have two or more SIT insulation barriers, for example one in an Ethern
...