EN IEC 62793:2020

SLOVENSKI STANDARD
01-januar-2021
Nadomešča:
SIST EN IEC 62793:2018
Zaščita pred delovanjem strele - Sistemi za opozarjanje pred nevihtami
Protection against lightning - Thunderstorm warning systems
Blitzschutz - Gewitterwarnsysteme
Protection contre la foudre - Systèmes d'alerte aux orages
Ta slovenski standard je istoveten z: EN IEC 62793:2020
ICS:
91.120.40 Zaščita pred strelo Lightning protection
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 62793

NORME EUROPÉENNE
EUROPÄISCHE NORM
October 2020
ICS 29.020; 91.120.40 Supersedes EN IEC 62793:2018 and all of its
amendments and corrigenda (if any)
English Version
Thunderstorm warning systems - Protection against lightning
(IEC 62793:2020)
Systèmes d'alerte aux orages - Protection contre la foudre  Gewitterwarnsysteme - Blitzschutz
(IEC 62793:2020) (IEC 62793:2020)
This European Standard was approved by CENELEC on 2020-10-26. 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, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, 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
© 2020 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 62793:2020 E
European foreword
The text of document 81/640/FDIS, future edition 2 of IEC 62793, prepared by IEC/TC 81 "Lightning
protection" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2021-07-26
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2023-10-26
document have to be withdrawn
This document supersedes EN IEC 62793:2018 and all of its amendments and corrigenda (if any).
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 62793:2020 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 62305 (series) NOTE Harmonized as EN 62305 (series)
IEC 62858 NOTE Harmonized as EN IEC 62858
IEC 61400-24 NOTE Harmonized as EN IEC 61400-24

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 62561-4 - Lightning protection system components EN 62561-4 -
(LPSC) - Part 4: Requirements for
conductor fasteners
IEC 62561-1 - Lightning protection system components EN 62561-1 -
(LPSC) - Part 1: Requirements for
connection components
IEC 60068-2-75 2014 Environmental testing - Part 2-75: Tests - EN 60068-2-75 2014
Test Eh: Hammer tests
IEC 60529 - Degrees of protection provided by - -
enclosures (IP Code)
IEC 61180 - High-voltage test techniques for low- EN 61180 -
voltage equipment - Definitions, test and
procedure requirements, test equipment
IEC 61000-6-4 - Electromagnetic compatibility (EMC) - EN IEC 61000-6-4 -
Part 6-4: Generic standards - Emission
standard for industrial environments

IEC 62793 ®
Edition 2.0 2020-09
INTERNATIONAL
STANDARD
colour
inside
Thunderstorm warning systems – Protection against lightning

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 29.020; 91.120.40 ISBN 978-2-8322-8725-5

– 2 – IEC 62793:2020 © IEC 2020
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms, definitions and abbreviated terms . 8
3.1 Terms and definitions . 8
3.2 Abbreviated terms . 11
4 Thunderstorm phases and detectable phenomena for alarming. 12
5 Description of thunderstorm detectors and their properties . 13
6 Alarm method . 14
6.1 General . 14
6.2 Areas . 14
6.2.1 Target (TA) . 14
6.2.2 Surrounding area (SA) . 15
6.2.3 Monitoring area (MA) . 15
6.2.4 Coverage area (CA) . 15
6.3 Alarm triggering and clearing . 16
6.4 Alarm information delivery. 18
7 Installation . 18
8 Maintenance . 19
9 Performance evaluation . 19
9.1 General . 19
9.2 Evaluation of a TWS by cross-correlation with other sources of information . 20
10 TWS application . 21
Annex A (informative) Overview of the lightning phenomena . 22
A.1 Origin of thunderclouds and electrification . 22
A.2 Lightning phenomena . 22
A.3 Electric thunderstorm and lightning characteristics useful for prevention . 24
A.3.1 Electrostatic field . 24
A.3.2 Electromagnetic fields . 24
A.3.3 Other parameters useful in lightning detection . 24
Annex B (informative) Thunderstorm monitoring techniques . 26
B.1 General . 26
B.2 Single sensor detection techniques . 26
B.2.1 Generalities . 26
B.2.2 Detector based on electrostatic field . 26
B.2.3 Detector based on electromagnetic field . 26
B.3 Multi-sensor location techniques . 27
B.3.1 Generalities . 27
B.3.2 Magnetic direction finder (MDF) . 27
B.3.3 Time of arrival (TOA) . 27
B.3.4 Interferometry . 27
Annex C (informative) Recommended preventive actions . 28
Annex D (informative) Example of TWS evaluation . 29

IEC 62793:2020 © IEC 2020 – 3 –
D.1 Example of TWS evaluation on a wind turbine site . 29
D.2 Evaluation of TWS efficiency using LLS . 30
Annex E (normative) How to test thunderstorm detectors . 32
E.1 General . 32
E.2 Laboratory tests . 32
E.2.1 General . 32
E.2.2 Resistance to UV radiation tests (for non-metallic sensor housing) . 32
E.2.3 Resistance tests to corrosion (for metallic parts of sensor) . 33
E.2.4 Mechanical tests . 33
E.2.5 Index of protection confirmation (IP Code) . 33
E.2.6 Electric tests . 34
E.2.7 Marking test . 35
E.2.8 Electromagnetic compatibility (EMC) . 35
E.3 Optional tests on an open air platform under natural lightning conditions . 35
Annex F (informative) Application guide . 38
F.1 General . 38
F.2 Examples of application of a TWS . 39
F.2.1 Golf course . 39
F.2.2 Oil storage facility . 39
F.2.3 Crane . 39
F.3 Selection of parameters of TWS . 40
Bibliography . 43

Figure 1 – Examples of different target and surrounding areas . 15
Figure 2 – Principles of the coverage area (CA), the monitoring area (MA), the

surrounding area (SA) and the target (TA) . 16
Figure 3 – Example of an alarm . 18
Figure A.1 – Standard lightning classifications . 23
Figure D.1 – Lightning activity in the target (TA) in red and surrounding area (SA) in
orange for a period of fifteen years (2000-2014) . 29
Figure E.1 – Difference in electric field measurement during one thunderstorm event . 36
Figure F.1 – Human risk calculated for a crane with LPS at level I . 40
Figure F.2 – Example of the alarms given by a TWS based on an EFS with three
different field thresholds . 41
Figure F.3 – Example of the alarms given by a TWS based on an LLS with three

different radii of the monitoring area . 42

Table 1 – Parameters related to sensor technologies . 13
Table 2 – Local sensor characteristics . 14
Table 3 – Alarms related to LRE . 18
Table D.1 – Performance results of a TWS evaluation based on archived lightning data
for a 15-year period (2000-2014), related to some of the key parameters . 30
Table D.2 – Example of delivered alarms evaluation . 31
Table F.1 – Identification of typical hazardous situations where a TWS improves safety . 38
Table F.2 – Example of effect of settings on alarm performance . 41

– 4 – IEC 62793:2020 © IEC 2020
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
THUNDERSTORM WARNING SYSTEMS –
PROTECTION AGAINST LIGHTNING
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.
International Standard IEC 62793 has been prepared by IEC technical committee 81: Lightning
protection.
This second edition cancels and replaces the first edition, published in 2016. This edition
constitutes a technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
• portable devices are no longer covered by this standard;
• in Clause 5, classes of TWS have been deleted;
• in Clause 6, updated figures and more detailed text are provided to better illustrate the alarm
timeline;
• in Clause 9, the text has been summarized and refers now to the application guide given in
Annex F;
• annexes have been reorganized;
• Annex E is normative.
IEC 62793:2020 © IEC 2020 – 5 –
The text of this International Standard is based on the following documents:
FDIS Report on voting
81/640/FDIS 81/641/RVD
Full information on the voting for the approval of this International Standard can be found in the
report on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document 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 62793:2020 © IEC 2020
INTRODUCTION
Natural atmospheric electric activity and, in particular, cloud-to-ground lightning poses a serious
threat to living beings and properties. Every year severe injuries and deaths of humans are
caused as a result of direct or indirect lightning strikes.
Lightning:
• may affect sport, cultural and political events attracting large concentrations of people, when
in the open field; events may have to be suspended and people evacuated in the case of a
risk of a thunderstorm;
• may affect industrial activities by creating power outages and unplanned interruptions of
production processes;
• may interrupt all kinds of traffic (people, energy, information, etc.);
• has led to a steady increase in the number of accidents and losses per year due to the wider
use of electronic components that are sensitive to the effects of lightning (in industry,
transportation and communication);
• may be a hazard for activities with an environmental risk, for example handling of sensitive,
inflammable, explosive or chemical products;
• may be a cause of fire.
During the last decades, technical systems including systems devoted to real-time monitoring
of natural atmospheric electric activity and lightning, have experienced an extraordinary
development. These systems can provide high quality and valuable information in real-time of
the thunderstorm occurrence, making it possible to achieve information which can be extremely
valuable if coordinated with a detailed plan of action.
Although this information allows the user to adopt anticipated temporary preventive measures,
it should be noted that all the measures to be taken based on monitoring information are the
responsibility of the system user according to the relevant regulations. The effectiveness will
depend to a large extent on the risk involved and the planned decisions to be taken. This
document gives an informative list of possible actions (see Annex C).
Lightning and thunderstorms, as many natural phenomena, are subject to statistical
uncertainties. It is therefore not possible to achieve precise information on when and where an
individual lightning will strike but statistical parameters are defined in this document to help the
user in selecting proper measures.

IEC 62793:2020 © IEC 2020 – 7 –
THUNDERSTORM WARNING SYSTEMS –
PROTECTION AGAINST LIGHTNING
1 Scope
This document describes the characteristics of thunderstorm warning systems (TWSs) in order
to implement lightning hazard preventive measures.
Single sensors and/or a network of sensors (e.g. lightning location system) can be used as a
TWS.
This document provides requirements for sensors and networks collecting accurate data of the
relevant parameters, giving real-time information on lightning and atmospheric electric activity.
It describes the application of the data collected by these sensors and networks in the form of
warnings and historical data.
This document includes:
• a general description of available techniques for TWSs;
• guidelines for alarming methods;
• informative examples of possible preventive actions.
The following aspects are outside the scope of this document:
a) lightning protection systems: such systems are covered by IEC 62305 (all parts) [1] ;
b) other thunderstorm related phenomena such as rain, hail, wind;
c) satellite and radar based thunderstorm detection techniques;
d) portable devices (a device where the sensor is not fixed).
NOTE It is possible that calibration and testing of portable devices will not be sufficient to provide efficient warning.
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 62561-4, Lightning protection system components (LPSC) – Part 4: Requirements for
conductor fasteners
IEC 62561-1, Lightning protection system components (LPSC) – Part 1: Requirements for
connection components
IEC 60068-2-75:2014, Environmental testing – Part 2-75: Tests – Test Eh: Hammer tests
IEC 60529, Degrees of protection provided by enclosures (IP Code)
___________
Numbers in square brackets refer to the bibliography.

– 8 – IEC 62793:2020 © IEC 2020
IEC 61180, High-voltage test techniques for low voltage equipment – Definitions, test and
procedure requirements, test equipment
IEC 61000-6-4, Electromagnetic compatibility (EMC) – Part 6-4: Generic standards – Emission
standard for industrial environments
3 Terms, definitions 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
alarm
information indicating that a defined area is likely to be affected by thunderstorms and the
accompanying lightning related events (LREs)
3.1.2
cloud-to-ground lightning
CG
electric discharge of atmospheric origin that is comprised of one or more cloud-to-ground
lightning strokes that propagate from cloud to ground or vice versa and lead to a net transfer of
charge between cloud and ground
3.1.3
coverage area
CA
area where a given warning equipment has a sufficient detection efficiency (DE) and/or
accuracy to give a warning
3.1.4
detection efficiency
DE
percentage of lightning discharges that is detected by a sensor or a network
3.1.5
effective alarm
EA
alarm where a lightning related event (LRE) occurs in the surrounding area (SA) during the total
alarm duration (TAD)
Note 1 to entry: An effective alarm can only be assessed when LREs are monitored. When LREs are not monitored
the lightning related conditions (LRC) may define a valid alarm, see Figure 3 a).
3.1.6
effective alarm ratio
EAR
number of effective alarms (EAs) with respect to the total number of alarms (TNA)

IEC 62793:2020 © IEC 2020 – 9 –
3.1.7
time to clear
TTC
time between the occurrence of the last lightning related event (LRE) in the monitoring area
(MA) and the time when the alarm is released
3.1.8
failure to warn
FTW
occurrence of a lightning related event (LRE) in the surrounding area (SA) for which no alarm
occurred
3.1.9
failure to warn ratio
FTWR
number of failures to warn with respect to the total number of situations with lightning related
events (LREs) affecting the surrounding area (SA)
3.1.10
false alarm
FA
alarm when there is no thunderstorm activity in the monitoring area (MA)
EXAMPLE An alarm due to TWS equipment malfunction or an alarm triggered by any signal not related to
thunderstorm (snow, sand, electromagnetic disturbances, etc.).
3.1.11
false alarm ratio
FAR
number of false alarms with respect to the total number of alarms (TNA)
3.1.12
electrostatic field sensor
EFS
device for continuous monitoring of the atmospheric electrostatic field, where the sensor is
located, associated with thunderstorms
EXAMPLE An electric field mill.
3.1.13
intra-cloud lightning
IC
electric discharge of atmospheric origin occurring within or among thunderclouds or between
thunderclouds and air and which does not have a ground termination
3.1.14
lead time
LT
time between the start of an alarm and the effective occurrence of the first lightning related
event (LRE) in the surrounding area (SA)
Note 1 to entry: Any efficient preventive action should be completed before the end of the lead time.
Note 2 to entry: A lead time can only be assessed when LREs are monitored. When LREs are not monitored the
lightning related conditions (LRC) may define an estimated lead time, see Figure 3 a).
3.1.15
lightning related event
LRE
event where one or more cloud-to-ground lightning (CG) occurs inside the surrounding area
(SA)
– 10 – IEC 62793:2020 © IEC 2020
3.1.16
lightning related conditions
LRC
static electric field that has reached a level high enough so that lightning is expected to occur
at any time in the surrounding area (SA)
3.1.17
median location accuracy
median value of the distances between real stroke locations and the stroke location given by a
lightning location system
3.1.18
monitoring area
MA
geographic area where the lightning or upcoming lightning (lightning is expected to occur at any
time) activity is monitored in order to provide a valid warning for the surrounding area (SA)
Note 1 to entry: The monitoring area is smaller or equal to the coverage area.
3.1.19
preventive action
action of a temporary nature, that should be completed before the end of the lead time (LT),
taken on the basis of the preventive information and included in the emergency plans
3.1.20
surrounding area
SA
geographic area in which a lightning related event (LRE) causes a potential danger and which
surrounds and includes the target (TA) to be protected
Note 1 to entry: Any lightning related event (LRE) occurring in the surrounding area (SA) is potentially dangerous
for the target. This area is used when evaluating a thunderstorm warning system (TWS) to determine the performance
parameters such as failure to warn ratio (FTWR).
3.1.21
target
TA
object or area for which a thunderstorm warning is needed
3.1.22
thunderstorm detector
equipment capable of evaluating one or more parameters associated with the electrical
characteristics of the thunderstorm
Note 1 to entry: Thunderstorm detectors may consist of a single detector or of a network of connected detectors.
Note 2 to entry: By definition, a thunderstorm only exists when the first lightning strike occurs.
3.1.23
thunderstorm warning system
TWS
system composed of thunderstorm detector(s) able to monitor the lightning or upcoming
lightning activity in the monitoring area (MA) and tools for processing the acquired data to
provide a valid alarm (warning) related to the lightning related events (LREs) or conditions (LRC)
for a defined surrounding area (SA)
Note 1 to entry: Some countries refer to TWS as ‘lightning warning systems’.

IEC 62793:2020 © IEC 2020 – 11 –
3.1.24
total alarm duration
TAD
time between the start and the end of an alarm
3.1.25
probability of detection
POD
number of effective alarms (EAs) with respect to the total number of situations with lightning
related events (LREs) affecting the surrounding area (SA)
Note 1 to entry: POD = 1 – FTWR.
3.1.26
probability of detection with a lead time of x min
POD
x
number of effective alarms (EAs) delivered with a lead time (LT) greater or equal to x min with
respect to the total number of situations with lightning related events (LREs) affecting the
surrounding area (SA)
Note 1 to entry: POD is the percentage of alarms delivered with a lead time (LT) of more than or equal to 10 min.
3.1.27
non-effective alarm
NEA
alarm that occurred when there was no lightning related event (LRE) occurring in the
surrounding area (SA) during the total alarm duration (TAD)
Note 1 to entry: An effective alarm can only be assessed when LREs are monitored. When LREs are not monitored
the lightning related conditions (LRC) may define a valid alarm, see Figure 3 a).
3.1.28
total number of alarms
TNA
sum of the number of false alarms, effective alarms and non-effective alarms
Note 1 to entry: TNA = EA + FA + NEA
3.2 Abbreviated terms
CA coverage area
CG cloud-to-ground lightning
DC direct current
DE detection efficiency
EA effective alarm
EAR effective alarm ratio
EFS electrostatic field sensor
EMC electromagnetic compatibility
FA false alarm
FAR false alarm ratio
FTW failure to warn
FTWR failure to warn ratio
HV high voltage
IC intra-cloud lightning
IP index of protection
– 12 – IEC 62793:2020 © IEC 2020
LA location accuracy
LF low frequency
LLS lightning location system
LPS lightning protection system
LT lead time
LRC lightning related conditions
LRE lightning related event
MA monitoring area
MCS mesoscale convective systems
MDF magnetic direction finder
NEA non-effective alarm
POD probability of detection
POD probability of detection with a lead time of x min
x
SA surrounding area
TA target
TAD total alarm duration
TNA total number of alarms
TOA time of arrival
TTC time to clear
TWS thunderstorm warning system
UV ultraviolet
VHF very high frequency
VLF very low frequency
4 Thunderstorm phases and detectable phenomena for alarming
Four distinct phases regarding detectable phenomena can be identified before the thunderstorm
lifetime cycle (see Annex A):
• Phase 1 or initial phase
This is the phase of cloud electrification by means of electric charge separation within the cloud.
The charges are distributed in regions within the cloud and produce a measurable electrostatic
field at ground level. The electrostatic field or electrostatic field change is considered to be the
first detectable phenomenon of a thunderstorm.
NOTE 1 Electrostatic fields can produce potential dangers such as electrostatic discharges even in the case of no
lightning activity.
• Phase 2 or growth phase
This phase, sometimes also called the development phase, is characterized by the occurrence
of the first lightning discharge (IC or CG). The first IC appears after a partial development of
the charge regions in the cloud. However, in some situations there is no clear time delay
between the first IC and the first CG.
NOTE 2 IC typically represents the majority of the total lightning activity generated by a thunderstorm. Significant
variation in the IC/CG rate is observed for individual storms.
• Phase 3 or mature phase
IEC 62793:2020 © IEC 2020 – 13 –
This phase is characterized by the presence of both CG and IC flashes.
• Phase 4 or dissipation phase
This phase is characterized by the decaying of both IC and CG flash rates and the reduction of
the electrostatic field change to the fair weather level.
5 Description of thunderstorm detectors and their properties
There are several ways to detect thunderstorms. These may be achieved by:
a) a local detector (for example field mill or electrostatic field sensor),
b) a network of detectors (for example field mills or electrostatic field sensors interconnected),
c) a lightning location system (see IEC 62858 [2]).
Table 1 gives the main parameters related to sensor technologies.
Table 1 – Parameters related to sensor technologies
Parameter Electrostatic field Electromagnetic sensor Lightning location
sensor (local detector (local detector) system
or network)
a
CG X
X
EA X X X
NEA X X X
EAR X X X
FTW X X X
FTWR X X X
a
IC X
X
LA  X
LT X X X
LRC X
LRE X X X
POD X X X
POD X X X
x
TAD X X X
TTC X X X
a
The sensor may not be able to differentiate between cloud-to-ground (CG) and intra-cloud (IC).

A local detector detects a thunderstorm in the vicinity of the sensor. By detecting the
electrostatic field, a local detector can provide a warning before the first IC/CG occurs in the
surrounding area. A network of local detectors offers the same information but on a larger scale.
An LLS offers local warnings based on a global view on a large area (uniform performance) with
lightning location capabilities and tracking of thunderstorms allowing to provide a longer LT in
case of thunderstorms approaching the target.
Local sensors are able to measure local conditions (electromagnetic or electrostatic fields).
Their characteristics are described in Table 2.
A network of sensors is able, depending on its performance, to provide the distance and
direction of the thunderstorm and location of single flashes (refer to IEC 62858).

– 14 – IEC 62793:2020 © IEC 2020
Table 2 – Local sensor characteristics
Technology Main Storm phases Range Advantages Drawbacks Maintenance
parameter according to
detected Clause 4
(in km)
Local detector Electromagneti 2,3,4 10's of km Large range Low detection No special
(based on c field efficiency and maintenance
electromagneti accuracy needed, refer
c field) to
No early
manufacturer's
detection
instructions.
when first CG
strikes the SA
Local detector Electrostatic 1,2,3,4 Up to 20 km Detection of Short range No special
(based on field thunderstorms maintenance
No information
electrostatic both needed when
about flash
field) approaching to there are no
location
and forming on moving parts.
the SA
Moving parts
when they
exist may
need to be
replaced due
to
deterioration
and
obstruction.
In both cases,
refer to
manufacturer's
instructions.
6 Alarm method
6.1 General
In order to let the user take all possible preventive actions, a thunderstorm warning system
(TWS) shall provide an alarm for a target where the lightning related event (LRE) represents a
threat. An alarm derives from monitoring the lightning activity, either CG, IC, or the electrostatic
field in the monitoring area (MA) or combination of them. Combinations with additional
meteorological observations may also be employed (e.g. weather radar).
The set-up of an alarm includes three steps:
• areas definition;
• alarm triggering and stopping criteria;
• alarm information delivery.
All three steps should be documented. Guidelines on how to set up an alarm are presented
below.
6.2 Areas
6.2.1 Target (TA)
A precise description of the target should include the physical extension where the warning is
needed. The target can:
• be limited to a single point (Figure 1 a)), for example a tower on which workers are operating,
a limited size factory;
IEC 62793:2020 © IEC 2020 – 15 –
• be of extended size (e.g. large buildings, wind farms, golf courses: Figure 1 b));
• take also into account the services connected to it, for example power line, telecom line or
metal pipes (Figure 1 c)).
NOTE For a system sensitive to overvoltages in a structure connected to a power line, in general the part of the
line that is considered is limited to 1 km from the structure according to IEC 62305-2.
6.2.2 Surrounding area (SA)
The surrounding area defines a zone in the close neighbourhood of the target (see Figure 1),
where the occurrence of an LRE or LRC indicates that the risk is high.

a) Single point b) Arbitrary shape c) Including services

Figure 1 – Examples of different target and surrounding areas
6.2.3 Monitoring area (MA)
The monitoring area is the area where the alarm is triggered if lightning or upcoming lightning
conditions occur. The size and the shape of the monitoring area should be adjusted to the user’s
need (LT, EAR, etc). Use of local detectors may not allow MA adjustment.
6.2.4 Coverage area (CA)
Once the monitoring area (MA) is defined, the detection system should have a coverage area
(CA) that includes the monitoring area (MA). For local detectors, usually CA = MA.
When the CA largely exceeds the MA, the real time data may provide complementary
information (e.g. thunderstorm cell tracking).
Principles of the coverage area (CA), the monitoring area (MA), the surrounding area (SA), and
the target (TA) are shown in Figure 2.

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Key
CA
MA
SA
TA
Figure 2 – Principles of the coverage area (CA), the monitoring area (MA),
the surrounding area (SA) and the target (TA)
6.3 Alarm triggering and clearing
In general, an alarm is triggered as soon as lightning or lightning conditions are detected in the
monitoring area (MA).
NOTE It can be useful for some applications to split the MA in two areas associated with two different procedures
(for example the first procedure can be associated with people evacuation from a dangerous area, when the second
procedure is associated with decoupling from a network and use of a power generator).
The criteria of triggering should be defined and depend on the characteristics of the TWS and
its performance within the monitoring area (MA) (e.g. occurrence of one or several CG flashes,
of one or several IC flashes, of a certain electrostatic field level, of electrostatic field polarity
and combinations of some criteria).
An example of the timing of an alarm is displayed in Figure 3.

IEC 62793:2020 © IEC 2020 – 17 –

a) Alarm based on electric field measurement

b) Alarm based on lightning detection
Key
CA
MA
SA
TA
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NOTE 1 The lightning conditions threshold represents conditions related to a high probability of LRE. When a
lightning conditions threshold is met, an alarm can be considered as a valid alarm.
NOTE 2 The lead time in Figure 3 a) is an estimated lead time for comparison purposes with Figure 3 b) only
because, by definition, the lead time can only be calculated when an LRE occurs and is monitored.
Figure 3 – Example of an alarm
The lead time (LT) is the time available to conduct the preventive actions before the first
lightning related event (LRE) in the surrounding area occurs.
In order to avoid switching the warning state too frequently, the TWS may use a time to clear
(TTC) to sustain the alarm during a minimum period. Systems that use the electrostatic field
level to trigger the alarm may also use this electrostatic field to end the alarm.
The total alarm duration corresponds to the interval between the alarm trigger and the alarm
clearing.
Table 3 summarizes how effective alarms (EAs), non-effective alarms (NEAs), false alarms
(FAs) and failure to warn (FTW) are counted.
Table 3 – Alarms related to LRE
Event LRE did occur in the SA LRE did not occur in the SA
Alarm was delivered EA NEA or FA
No alarm was delivered FTW –
6.4 Alarm information delivery
A clear alarm delivery procedure and protocol shoul
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