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The following cases are outside the scope of this standard:

• railway systems;

• vehicles, ships, aircraft, offshore installations;

• underground high pressure pipelines;

• pipe, power and telecommunication lines placed outside the structure.

NOTE These systems usually fall under special regulations produced by various specialized authorities.

2. Normative references

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

IEC 62305-2:2010, Protection against lightning - Part 2: Risk management

IEC 62305-3:2010, Protection against lightning - Part 3: Physical damage to structures and life hazard

IEC 62305-4:2010, Protection against lightning - Part 4: Electrical and electronic systems within structures

3. Terms and definitions

For the purposes of this document, the following terms and definitions apply.

lightning flash to earth

electrical discharge of atmospheric origin between cloud and earth consisting of one or more strokes

downward flash

lightning flash initiated by a downward leader from cloud to earth

NOTE A downward flash consists of a first impulse, which can be followed by subsequent impulses. One or more impulses may be followed by a long stroke.

upward flash

lightning flash initiated by an upward leader from an earthed structure to cloudNOTE An upward flash consists of a first long stroke with or without multiple superimposed impulses. One or more impulses may be followed by a long stroke.

lightning stroke

single electrical discharge in a lightning flash to earth

short stroke

part of the lightning flash which corresponds to an impulse current

NOTE This current has a time T₂ to the half peak value on the tail typically less than 2 ms (see Figure A.1).

long stroke

part of the lightning flash which corresponds to a continuing current

NOTE The duration time T. _n._lr (time from the 10 % value on the front to the 10 % value on the tail) of this continuing current is typically more than 2 ms and less than 1 s (see Figure A.2).

multiple strokes

lightning flash consisting on average of 3-4 strokes, with typical time interval between them of about 50 ms

NOTE Events having up to a few dozen strokes with intervals between them ranging from 10 ms to 250 ms have been reported.

point of strike

point where a lightning flash strikes the earth, or protruding structure (e.g. structure, LPS, line, tree, etc.)

NOTE A lightning flash may have more than one point of strike.

lightning current

і

current flowing at the point of strike

3.10

current peak value

I

maximum value of the lightning current

3.11

average steepness of the front of impulse current

average rate of change of current within a time interval At = t₂ - t₁

NOTE It is expressed by the difference At = r(t₂) - i(t^) of the values of the current at the start and at the end of this interval, divided by the time interval At = t₂ - f₁ (see Figure A.1).

3.12

front time of impulse current

^T1

virtual parameter defined as 1,25 times the time interval between the instants when the 10 % and 90 % of the peak value are reached (see Figure A.1)

3.13

virtual origin of impulse current

O,

point of intersection with time axis of a straight line drawn through the 10 % and the 90 % reference points on the stroke current front (see Figure A.1); it precedes by 0,1 that instant at which the current attains 10 % of its peak value

3.14

time to half value on the tail of impulse current

T₂

virtual parameter defined as the time interval between the virtual origin O₁ and the instant at which the current has decreased to half the peak value on the tail (see Figure A.1)

3.15

flash duration

T

time for which the lightning current flows at the point of strike

3.16

duration of long stroke current

Л-ONG

time duration during which the current in a long stroke is between 10 % of the peak value during the increase of the continuing current and 10 % of the peak value during the decrease of the continuing current (see Figure A.2)

3.17

flash charge

$FLASH

value resulting from the time integral of the lightning current for the entire lightning flash duration

3.18

impulse charge

Qshort

value resulting from the time integral of the lightning current in an impulse

3.19

long stroke charge

Qlong

value resulting from the time integral of the lightning current in a long stroke

3.20

specific energy

W/R

value resulting from the time integral of the square of the lightning current for the entire flash duration

NOTE It represents the energy dissipated by the lightning current in a unit resistance.

3.21

specific energy of impulse current

value resulting from the time integral of the square of the lightning current for the duration of the impulse

NOTE The specific energy in a long stroke current is negligible.

3.22

structure to be protected

structure for which protection is required against the effects of lightning in accordance with this standard

NOTE A structure to be protected may be part of a larger structure.

3.23

line

power line or telecommunication line connected to the structure to be protected

3.24

telecommunication lines

lines intended for communication between equipment that may be located in separate structures, such as a phone line and a data line

3.25

power lines

distribution lines feeding electrical energy into a structure to power electrical and electronic equipment located there, such as low voltage (LV) or high voltage (HV) electric mains

3.26

lightning flash to a structure

lightning flash striking a structure to be protected

3.27

lightning flash near a structure

lightning flash striking close enough to a structure to be protected that it may cause dangerous overvoltages

3.28

electrical system

system incorporating low voltage power supply components

3.29

electronic system

system incorporating sensitive electronic components such as telecommunication equipment, computer, control and instrumentation systems, radio systems, power electronic installations

3.30

internal systems

electrical and electronic systems within a structure

3.31

physical damage

damage to a structure (or to its contents) due to mechanical, thermal, chemical and explosive effects of lightning

3.32

injury of living beings

permanent injuries, including loss of life, to people or to animals by electric shock due to touch and step voltages caused by lightning

NOTE Although living beings may be injured in other ways, in this standard the term 'injury to living beings' is limited to the threat due to electrical shock (type of damage D1)

.3.33

failure of electrical and electronic systems

permanent damage of electrical and electronic systems due to LEMP

3.34

lightning electromagnetic impulse

LEMP

all electromagnetic effects of lightning current via resistive, inductive and capacitive coupling that create surges and radiated electromagnetic fields

3.35 surge

transient created by LEMP that appears as an overvoltage and/or an overcurrent

3.36

lightning protection zone

LPZ

zone where the lightning electromagnetic environment is defined

NOTE The zone boundaries of an LPZ are not necessarily physical boundaries (e.g. walls, floor and ceiling).

3.37 risk R

value of probable average annual loss (humans or goods) due to lightning, relative to the total value (humans or goods) of the structure to be protected

3.38 tolerable risk

«Т

maximum value of the risk which can be tolerated for the structure to be protected

3.39

lightning protection level

LPL

number related to a set of lightning current parameters values relevant to the probability that the associated maximum and minimum design values will not be exceeded in naturally occurring lightning

NOTE Lightning protection level is used to design protection measures according to the relevant set of lightning current parameters.

3.40

protection measures

measures to be adopted for the structure to be protected in order to reduce the risk

3.41

lightning protection

LP

complete system for protection of structures against lightning, including their internal systems and contents, as well as persons, in general consisting of an LPS and SPM

3.42

lightning protection system

LPS

complete system used to reduce physical damage due to lightning flashes to a structure

NOTE It consists of both external and internal lightning protection systems.

3.43

external lightning protection system

part of the LPS consisting of an air-termination system, a down-conductor system and an earth-termination system

3.44

internal lightning protection system

part of the LPS consisting of lightning equipotential bonding and/or electrical insulation of external LPS

3.45

air-termination system

part of an external LPS using metallic elements such as rods, mesh conductors or catenary wires intended to intercept lightning flashes

3.46

down-conductor system

part of an external LPS intended to conduct lightning current from the air-termination system to the earth-termination system

3.47

earth-termination system

part of an external LPS which is intended to conduct and disperse lightning current into the earth

3.48

external conductive parts

extended metal items entering or leaving the structure to be protected such as pipe works, cable metallic elements, metal ducts, etc. which may carry a part of the lightning current

3.49

lightning equipotential bonding

EB

bonding to LPS of separated metallic parts, by direct conductive connections or via surge protective devices, to reduce potential differences caused by lightning current

3.50

conventional earthing impedance

ratio of the peak values of the earth-termination voltage and the earth-termination current which, in general, do not occur simultaneously

3.51

LEMP protection measures

SPM

measures taken to protect internal systems against the effects of LEMP

NOTE This is part of overall lightning protection.

3.52

magnetic shield

closed, metallic, grid-like or continuous screen enveloping the structure to be protected, or part of it, used to reduce failures of electrical and electronic systems

3.53

surge protective device

SPD

device intended to limit transient overvoltages and divert surge currents; contains at least one non linear component

3.54

coordinated SPD system

SPDs properly selected, coordinated and installed to form a system intended to reduce failures of electrical and electronic systems

3.55

rated impulse withstand voltage

impulse withstand voltage assigned by the manufacturer to the equipment or to a part of it, characterizing the specified withstand capability of its insulation against overvoltages

NOTE For the purposes of this standard, only withstand voltage between live conductors and earth is considered.

[IEC 60664-1:2007, definition 3.9.2]'¹¹ 1

3.56

isolating interfaces

devices which are capable of reducing conducted surges on lines entering the LPZ

NOTE 1 These include isolation transformers with earthed screen between windings, metal free fibre optic cables and opto-isolators.

NOTE 2 Insulation withstand characteristics of these devices are suitable for this application intrinsically or via SPD.

4. Lightning current parameters

The lightning current parameters used in the IEC 62305 series are given in Annex A.

The time function of the lightning current to be used for analysis purposes is given in Annex B.

Information for simulation of lightning current for test purposes is given in Annex C.

The basic parameters to be used in laboratories to simulate the effects of lightning on LPS components are given in Annex D.

Information on surges due to lightning at different installation points is given in Annex E.

5. Damage due to lightning

   1. Damage to a structure

Lightning affecting a structure can cause damage to the structure itself and to its occupants and contents, including failure of internal systems. The damages and failures may also extend to the surroundings of the structure and even involve the local environment. The scale of this extension depends on the characteristics of the structure and on the characteristics of the lightning flash.

The main characteristics of structures relevant to lightning effects include:

- construction (e.g. wood, brick, concrete, reinforced concrete, steel frame construction);

References in square brackets refer to the bibliography

• .function (dwelling house, office, farm, theatre, hotel, school, hospital, museum, church, prison, department store, bank, factory, industry plant, sports area);

• occupants and contents (persons and animals, presence of combustible or non­combustible materials, explosive or non-explosive materials, electrical and electronic systems with low or high withstand voltage);

• connected lines (power lines, telecommunication lines, pipelines);

• existing or provided protection measures (protection measures to reduce physical damage and life hazard, protection measures to reduce failure of internal systems);

• scale of the extension of danger (structure with difficulty of evacuation or structure where panic may be created, structure dangerous to the surroundings, structure dangerous to the environment).

Table 1 reports the effects of lightning on various types of structures.

Table 1 - Effects of lightning on typical structures

5.1.2 Sources and types of damage to a structure

The lightning current is the source of damage. The following situations shall be taken into account, depending on the position of the point of strike relative to the structure considered:

1. S1: flashes to the structure;

2. S2: flashes near the structure;

3. S3: flashes to the lines connected to the structure;

4. S4: flashes near the lines connected to the structure.

1. Flashes to the structure can cause:

• immediate mechanical damage, fire and/or explosion due to the hot lightning plasma arc itself, due to the current resulting in ohmic heating of conductors (over-heated conductors), or due to the charge resulting in arc erosion (melted metal);

• fire and/or explosion triggered by sparks caused by overvoltages resulting from resistive and inductive coupling and to passage of part of the lightning currents;

• injury to living beings by electric shock due to step and touch voltages resulting from resistive and inductive coupling;

• failure or malfunction of internal systems due to LEMP.

2. Flashes near the structure can cause:

- failure or malfunction of internal systems due to LEMP.

3. Flashes to a line connected to the structure can cause:

• fire and/or explosion triggered by sparks due to overvoltages and lightning currents transmitted through the connected line;

injury to living beings by electric shock due to touch voltages inside the structure caused by lightning currents transmitted through the connected line;

• failure or malfunction of internal systems due to overvoltages appearing on connected lines and transmitted to the structure.

4. Flashes near a line connected to the structure can cause:

• failure or malfunction of internal systems due to overvoltages induced on connected lines and transmitted to the structure.

NOTE 1 Malfunctioning of internal systems is not covered by the IEC 62305 series. Reference should be made to IEC 61000-4-5 ^[2] .

NOTE 2 Only the sparks carrying lightning current (total or partial) are regarded as able to trigger fire.

NOTE 3 Lightning flashes, direct to or near the incoming pipelines, do not cause damages to the structure, provided that they are bonded to the equipotential bar of the structure (see IEC 62305-3).

As a result, the lightning can cause three basic type of damage:

• D1: injury to living beings by electric shock;

• D2: physical damage (fire, explosion, mechanical destruction, chemical release) due to lightning current effects, including sparking;

• D3: failure of internal systems due to LEMP.

5.2 Types of loss

Each type of damage relevant to structure to be protected, alone or in combination with others, may produce different consequential loss. The type of loss that may appear depends on the characteristics of the structure itself.

For the purposes of IEC 62305, the following types of loss, which may appear as consequence of damages relevant to structure, are considered:

• L1: loss of human life (including permanent injury);

• L2: loss of service to the public;

• L3: loss of cultural heritage;

• L4: loss of economic value (structure, its content, and loss of activity).

NOTE For the purposes of IEC 62305, only utilities such as gas,water,TV, TLC and power supply are considered service to the public.

Losses of type L1, L2 and L3 may be considered as loss of social values, whereas a loss of type L4 may be considered as purely an economic loss.

The relationship between source of damage, type of damage and loss is reported in Table 2.

Table 2 - Damage and loss relevant to a structure according to
different points of strike of lightning

Types of loss resulting from types of damage and the corresponding risks are reported in Figure 2.