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)

IEC 61643-352:2018 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.

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

General Information

• Status: Published
• Publication Date: 09-Jan-2018
• ICS: 33.040.99 - Other equipment for telecommunication systems
• Technical Committee: SC 37B - Components for low-voltage surge protection
• Drafting Committee: WG 3 - TC 37/SC 37B/WG 3
• Current Stage: PPUB - Publication issued
• Start Date: 10-Jan-2018
• Completion Date: 26-Jan-2018

Standards Content (Sample)

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
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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

– 2 – IEC 61643-352:2018 © IEC 2018
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

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

– 4 – IEC 61643-352:2018 © IEC 2018
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
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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.

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.
– 6 – IEC 61643-352:2018 © IEC 2018
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.
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]

– 8 – IEC 61643-352:2018 © IEC 2018
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.

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.

– 10 – IEC 61643-352:2018 © IEC 2018
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.
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
– 12 – IEC 61643-352:2018 © IEC 2018
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 Ethernet port
and the other in the powering port. In class II powered equipment the Ethernet and powering
port insulation barriers are in series and their surge environment is the differential surge
environment between the signal and powering services. The voltage sharing across two
insulation barriers in series can be difficult to predict due to dynamic and static voltage
distributions. In the worst case, the majority of the surge voltage may occur across one of the
two barriers increasing its rated impulse voltage withstand requirement.
Ports containing SPCs that bridge the port SIT insulation barrier can effectively bridge that
insulation barrier and apply the port surge environment to the other port SIT insulation barrier.
If this happens, then that port insulation barrier should be rated for the total inter-port voltage
surge environment.
Figure 6 shows SIT under common-mode surge conditions. The insulation rated impulse
voltage shall be equal to or greater than the peak common-mode surge voltage for insulation
coordination. Any primary to secondary capacitance (shown as C + C ), that is not
P-SA P-SB
decoupled by the electrostatic screen, ES, provides a capacitive current flow path from the
primary to secondary circuit.
The major parameters for common-mode surges are the rated impulse voltage and the
internal-winding capacitance, plus a post-test insulation resistance check on the insulation
integrity.
5.3 Differential-mode surges
5.3.1 General
Differential-mode surges are typically caused by system asymmetry converting what should
be common-mode surges to differential ones. SIT action occurs on differential-mode surges
and the SIT does little to mitigate them. In some cases SIT bandwidth will result in filtering of
the output surge frequency spectrum.
Signal SITs may suffer core saturation, which truncates the secondary voltage. Some
standards specify testing for differential power faults, requiring the signal SIT to have a
primary winding current rating.
5.3.2 Ethernet transformer differential surge action
Signal transformers with a ferrite magnetic core can truncate differential surges by core
saturation. Figure 1 shows an example of an Ethernet port transformer truncating a primary
differential current surge on its secondary winding output. The green line triangular secondary
winding surge current let-though, I , consists of three phases:
S
a) transformer linear current transfer, which transforms primary current to the secondary;
b) transformer core saturation event, setting the peak secondary current and decoupling the
primary and secondary windings;
c) saturated core secondary winding energy dump set by the transformer saturated core
winding inductance, the peak secondary current and the secondary load impedance.
The peak secondary current depends on the generator front time rate of rise of current. The
longer term generator surge current is of no consequence once the transformer core has
saturated as further surge current transfer is prevented, see Figure 7. The overall surge let
through depends on the surge di/dt, the transformer V , the saturated secondary inductance,
s
the secondary resistance and any shunt secondary voltage limiter. The overall let-though time
period is usually in the 1 µs to 5 µs range.
NOTE V means instantaneous secondary winding peak voltage. See 6.4 of IEC 61643-351:2016.
s
IEC
Figure 7 – Transformer differential surge truncation
6 Selection
6.1 General
SITs application requirements shall comply with IEC 61643-351 and with specifications that
refer to the system to be protected.
6.2 Impulse withstand voltage
The impulse withstand voltage of the SIT should be selected to be higher than the surge
voltage assumed in the install location. The value of the impulse withstand voltage shall
comply with IEC 61643-351.
– 14 – IEC 61643-352:2018 © IEC 2018
6.3 Rated values of SIT
The rated value of SIT should comply with IEC 61643-351. The signal performance of the SIT
shall be selected to be the same as the signal performance of the signal/communication line
to install.
7 Applications
7.1 General
SITs' application requirements shall comply with IEC 61643-351 and with specifications that
refer to the system to be protected. The common-mode of impulse withstand voltage of Ethernet
™
system are required voltage values of 2,5 kV and 6 kV in IEEE Std 802.3 .
7.2 Example of surge protection using SITs with ES for control and terminal
equipment installed in two different buildings respectively
When isolation is required in communication between buildings, SITs for control and terminal
equipment are installed near the communication and control equipment. The electrostatic
screen of the SIT and the cabinet of protected equipment are made equipotential for each
building as shown in Figure 8. The impulse withstand voltage of the SIT shall be selected
higher than the impulse withstand voltage of the communication cables or the surge voltage
assumed in the install location.
Building 1
Building 2
S1 SIT P1 P1 SIT S1
Terminal
Control
equipment
equipment
Communication
line
S2
P2
P2
S2
E E
IEC
Figure 8 – Example of surge protection using SITs in order to
isolate two different buildings
7.3 Example of surge protection using SITs for telecommunication equipment in
substation
For telecommunication lines leading from multiple relays into an SIT substation, SITs for
communication lines are placed on the relay side and on the substation side. The SIT
electrostatic screen and the cabinet of the protected equipment are made equipotential for
each building. Furthermore, high withstand voltage telecommunication cables are used and
the overall system is protected by raising the insulation withstand voltage level. The impulse
withstand voltage of SIT shall be selected higher than the surge voltage assumed in the install
location. In addition, the impulse withstand voltage of SIT shall be selected higher than the
impulse withstand voltage of cables, as shown in Figure 9.

Relay point
Substation
SIT P1
S1 P1 SIT S1
S2 P2 S2
P2
E
SIT SIT S1
P1
S1 P1
S2 P2 S2
P2
E
SIT
P1 SIT S1
S1 P1
High-voltage
S2 P2
insulated cable S2
P2
E
SIT
P1 SIT S1
P1
S1
S2 P2
S2
P2
E
SIT
P1 SIT S1
P1
S1
S2 P2
S2
P2
E
E
E
IEC
Figure 9 – Example of surge protection using SITs in substation

– 16 – IEC 61643-352:2018 © IEC 2018
7.4 Example of surge protection using SITs for transmission and switching
equipment installed in different floors in a communication building
To prevent mutual effects between different systems in a communication building, such as
radio equipment, transmission equipment, and switching equipment, SITs are placed on the
lines that interconnect those systems. When the IBN is configured on the floor level, SITs are
placed on the wiring between floors for isolation. Doing so is effective against switching noise
from the power supply and the air conditioning system as well as lightning surge protection.
The impulse withstand voltage of SITs for communication lines between different floors shall
be selected higher than the voltage between different floors which occurs when lightning hits
a lightning rod.
When assuming the surge protection from common-mode, the measures against surges
(direct lightning effects) are performed in combination with suitable SPD as shown in Figure
10.
Lightning rod
Antenna
SIT SIT
P1 S1
S1 P1
Transmission Radio
equipment
equipment
P2 S2 P2
S2
Equipotential
bonding bar
MDF
SPD
Switching
Telecommunication
or
equipment line
SPCs
Equipotential
bonding bar
Main equipotential bonding bar
Isolator
IEC
Figure 10 – Example of surge protection using SITs in a communication building

7.5 Example of surge protection using SITs for computer network equipment in a data
centre
For computer network devices, and other types of equipment that have low impulse withstand
voltages, SITs are placed on the telecommunication lines for lightning surge protection by
raising the dielectric strength between the external interfaces. For a Power over Ethernet
(PoE) system, however, special SITs for a PoE system should be used as shown in 7.6.
The impulse withstand voltage of SIT for communication shall be selected to be higher than
the impulse withstand voltage of communication cables or surge voltage assumed in the
install location, as shown in Figure 11.
SIT S
P
SIT
S
P
Communication
line ROUTER/HUB
PC
Modem
MDF
SIT
S
P
SIT
S
P
Computer network
IEC
Figure 11 – Example of surge protection using SITs in a data centre
7.6 Example of surge protection using SITs for a Power over Ethernet (PoE) system
In a PoE system, part of the telecommunication line is also the power line, so a special SIT for
each PoE system can be used to isolate and protect the communication ports of the protected
equipment as Figure 12. In the PoE system, SIT can use only signal pair. In the case of power
line of PoE system, SPCs such as an ABD are used. Figure 12 shows an example of the
above protection.
PD
5 5
SIT
SIT
Ethernet PoE
RJ-45 RJ-45
Ethernet
PHY power
PHY
supply
SIT
SIT
Mode A power
IEC IEC
a) PD Solution Schematic b) PSE Solution
Figure 12 – Example of surge protection using SITs for a
Power over Ethernet (PoE) system

– 18 – IEC 61643-352:2018 © IEC 2018
7.7 Example of surge protection using SITs for LAN
In this case, sometimes SITs without electrostatic screen (ES) are used. Therefore earth line
wiring is not required. This type is used in difficult places to connect a good earthing. Figure
13 shows an example of surge protection using SITs without electrostatic screen for LAN.
Surge protector for LAN
RJ45 RJ45
SIT
S
P
1 1
2 2
SIT
S
P
3 3
6 6
SIT
S
4 P 4
5 5
SIT
S
P
7 7
8 8
IEC
Figure 13 – Example of surge protection using SITs for LAN

Annex A
(informative)
Lightning overvoltages of telecommunication line
The surge voltage induced to the telecommunication line has been measured and analysed
for many years. This measurement and analysis are still being conducted now and are used
for the design manual of protection measures of equipment against an induced lightning surge.
There have been many studies on various characteristics of lightning overvoltage and
lightning current that occur to telecommunication lines. Although factors such as the location
of observation, seasons and the configuration of the telecommunication lines were different,
all of the observations show a similar tendency in the occurrence frequency of the peak value.
The majority of lightning overvoltage that occurs to telecommunication lines is considered
induced overvoltage, and the occurrence frequency of the peak value is as shown in Figure
A.1.
-1
-2
0,004
-3
-4
1 2 3 4 5
10 10 10 10 10
Peak of lightning overvoltage (V)

Summer: user side (plain field)

Summer: centre side (plain field)

Winter: user side (mountaintop)
IEC
Figure A.1 – Lightning overvoltages of telecommunication line
As already known, most equipment damage by lightning is caused by induced lightning. The
peak voltage value of induced lightning can be expected from above data. Therefore, effective
surge measures can be taken by installing SIT with a withstand voltage higher than the
expected induced lightning in front of protected equipment.

Cumulative frequency of lightning

overvoltage (times/(IKL•wire))

– 20 – IEC 61643-352:2018 © IEC 2018
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___________
– 22 – IEC 61643-352:2018 © IEC 2018
SOMMAIRE
AVANT-PROPOS . 24
INTRODUCTION . 26
1 Domaine d'application . 27
2 Références normatives . 27
3 Termes, définitions, symboles et termes abrégés . 27
3.1 Termes et définitions .
...