Protection Voltage Surges

8/22/2019 Protection Voltage Surges

1/25Schneider Electric - Electrical installation guide 2008

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SchneiderElectric-allrightsreserved

Chapter J

Protection against voltage surgesin LV

Contents

General J2

1.1 What is a voltage surge? J2

1.2 The four voltage surge types J2

1.3 Main characteristics of voltage surges J4

1.4 Different propagation modes J5

Overvoltage protection devices J6

2.1 Primary protection devices (protection of installations J6against lightning)

2.2 Secondary protection devices (protection of internal J8installations against lightning)

Protection against voltage surges in LV J

3.1 Surge protective device description J11

3.2 Surge protective device standards J11

3.3 Surge protective device data according to IEC 61643-1 standard J11

3.4 Lightning protection standards J13

3.5 Surge arrester installation standards J13

Choosing a protection device J4

4.1 Protection devices according to the earthing system J14

4.2 Internal architecture of surge arresters J15

4.3 Coordination of surge arresters J16

4.4 Selection guide J17

4.5 Choice of disconnector J22

4.6 End-of-life indication of the surge arrester J23

4.7 Application example: supermarket J24

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J - Protection against voltage surges in LV

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General

. What is a voltage surge?

A voltage surge is a voltage impulse or wave which is superposed on the rated

network voltage (see Fig. J).

VoltageLightning type impulse(duration = 100 s)

"Operating impulse"type dumped ring wave(F = 100 kHz to 1 MHz)

Irms

Fig. J1 : Voltage surge examples

This type o voltage surge is characterised by ( see Fig. J2):

b The rise time (t) measured in s

b The gradient S measured in kV/s

A voltage surge disturbs equipment and causes electromagnetic radiation.Furthermore, the duration o the voltage surge (T) causes a surge o energy in theelectrical circuits which is likely to destroy the equipment.

Voltage (V or kV)

U max

50 %

tRise time (tf)

Voltage surge duration (T)

Fig. J2: Main overvoltage characteristics

.2 The our voltage surge types

There are our types o voltage surges which may disturb electrical installations and

loads:

b Atmospheric voltage surges

b Operating voltage surges

b Transient overvoltage at industrial requency

b Voltage surges caused by electrostatic discharge

Atmospheric voltage surges

Lightning risk a ew fguresBetween 2,000 and 5,000 storms are constantly orming around the earth. These

storms are accompanied by lightning which constitutes a serious risk or both peopleand equipment. Strokes o lightning hit the ground at a rate o 30 to 100 strokes per

second. Every year, the earth is struck by about 3 billion strokes o lightning.




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General

Lightning comes rom the discharge o electricalcharges accumulated in the cumulo-nimbusclouds which orm a capacitor with the ground.Storm phenomena cause serious damage.Lightning is a high requency electricalphenomenon which produces voltage surgeson all conductive elements, and especially onelectrical loads and wires.

b Throughout the world, every year, thousands o people are struck by lightning andcountless animals are killed

b Lightning also causes a large number o res, most o which break out on arms

(destroying buildings or putting them out o use)b Lightning also aects transormers, electricity meters, household appliances, andall electrical and electronic installations in the residential sector and in industry.

b Tall buildings are the ones most oten struck by lightning

b The cost o repairing damage caused by lightning is very high

b It is dicult to evaluate the consequences o disturbance caused to computer ortelecommunications networks, aults in PLC cycles and aults in regulation systems.

Furthermore, the losses caused by a machine being put out o use can have fnancialconsequences rising above the cost o the equipment destroyed by the lightning.

Characteristics o lightning discharge

Figure J3 shows the values given by the lighting protection committee (TechnicalCommittee 81) o the I.E.C. As can be seen, 50 % o lightning strokes are o a orcegreater than 33 kA and 5 % are greater than 85 kA. The energy orces involved arethus very high.

It is important to dene the probability o adequate protection when protecting a site.Furthermore, a lightning current is a high requency (HF) impulse current reachingroughly a megahertz.

The eects o lightning

A lightning current is thereore a high requency electrical current. As well asconsiderable induction and voltage surge eects, it causes the same eects as anyother low requency current on a conductor:b Thermal eects: usion at the lightning impact points and joule eect, due to thecirculation o the current, causing res

b Electrodynamic eects: when the lightning currents circulate in parallel conductors,they provoke attraction or repulsion orces between the wires, causing breaks ormechanical deormations (crushed or fattened wires)

b Combustion eects: lightning can cause the air to expand and create overpressurewhich stretches over a distance o a dozen metres or so. A blast eect breaks windowsor partitions and can project animals or people several metres away rom their origina lposition. This shock wave is at the same time transormed into a sound wave: thunder

b Voltage surges conducted ater an impact on overhead electrical or telephone lines

b Voltage surges induced by the electromagnetic radiation eect o the lightningchannel which acts as an antenna over several kilometres and is crossed by aconsiderable impulse current

b The elevation o the earth potential by the circulation o the lightning current in theground. This explains indirect strokes o lightning by step voltage and the breakdowno equipment

Operating voltage surges

A sudden change in the established operating conditions in an electrical networkcauses transient phenomena to occur. These are generally high requency ordamped oscillation voltage surge waves (see Fig. J1).They are said to have a slow gradient: their requency varies rom several ten toseveral hundred kilohertz.

Operating voltage surges may be created by:b The opening o protection devices (use, circuit-breaker), and the opening orclosing o control devices (relays, contactors, etc.)b Inductive circuits due to motors starting and stopping, or the opening otransormers such as MV/LV substationsb Capacitive circuits due to the connection o capacitor banks to the networkb All devices that contain a coil, a capacitor or a transormer at the power supplyinlet: relays, contactors, television sets, printers, computers, electric ovens, flters, etc.

Fig. J3: Lightning discharge values given by the IEC lightning protection committee

Beyond peak Current Gradient Total Number o

probability peak duration discharges

P% I (kA) S (kA/s) T (s) n

95 7 9.1 0.001 1

50 33 24 0.01 2

5 85 65 1.1 6




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Transient overvoltages at industrial requency(see Fig. J4)

These overvoltages have the same requency as the network (50, 60 or 400 Hz); andcan be caused by:

b Phase/rame or phase/earth insulating aults on a network with an insulated orimpedant neutral, or by the breakdown o the neutral conductor. When this happens,single phase devices will be supplied in 400 V instead o 230 V.

b A cable breakdown. For example, a medium voltage cable which alls on a lowvoltage line.

b The arcing o a high or medium voltage protective spark-gap causing a rise in earthpotential during the action o the protection devices. These protection devices ollowautomatic switching cycles which will recreate a ault i it persists.

Voltage surges caused by electrical discharge

In a dry environment, electrical charges accumulate and create a very strongelectrostatic eld. For example, a person walking on carpet with insulating soles

will become electrically charged to a voltage o several kilovolts. I the person walksclose to a conductive structure, he will give o an electrical discharge o severalamperes in a very short rise time o a ew nanoseconds. I the structure containssensitive electronics, a computer or example, its components or circuit boards maybe damaged.

.3 Main characteristics o voltage surges

Figure J5 below sums up the main characteristics o voltage surges.

Three points must be kept in mind:

b A direct or indirect lightning stroke mayhave destructive consequences on electricalinstallations several kilometres away romwhere it alls

b Industrial or operating voltage surges also

cause considerable damageb The act that a site installation is undergroundin no way protects it although it does limit therisk o a direct strike

Type o voltage surge Voltage surge Duration Front gradientcoefcient or requency

Industrial requency y 1.7 Long Industrial requency(insulation ault) 30 to 1,000 ms (50-60-400 Hz)

Operation 2 to 4 Short Average

1 to 100 ms 1 to 200 kHz

Atmospheric > 4 Very short Very high

1 to 100 s 1 to 1,000 kV/s

Fig. J5: Main characteristics o voltage surges

Fig. J4: Transient overvoltage at industrial requency

Normal voltage230/400 V

Normal voltage230/400 V

t

Transient overvoltage

General




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General

.4 Dierent propagation modes

Common mode

Common mode voltage surges occur between the live parts and the earth:phase/earth or neutral/earth (see Fig. J6).

They are especially dangerous or devices whose rame is earthed due to the risk odielectric breakdown.

Fig. J6: Common mode

Fig. J7: Dierential mode

Ph Imd

N

Imd

U voltage surge

differential modeEquipment

Ph

Imc

Imc

N

Voltage surge

common mode

Equipment

Dierential mode

Dierential mode voltage surges circulate between live conductors: Phase to phaseor phase to neutral (see Fig. J7). They are especially dangerous or electronicequipment, sensitive computer equipment, etc.




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2 Overvoltage protection devices

Two major types o protection devices are used to suppress or limit voltage surges:they are reerred to as primary protection devices and secondary protection devices.

2. Primary protection devices (protection oinstallations against lightning)

The purpose o primary protection devices is to protect installations against direct

strokes o lightning. They catch and run the lightning current into the ground. Theprinciple is based on a protection area determined by a structure which is higher

than the rest.

The same applies to any peak eect produced by a pole, building or very highmetallic structure.

There are three types o primary protection:

b Lightning conductors, which are the oldest and best known lightning protectiondevice

b Overhead earth wires

b The meshed cage or Faraday cage

The lightning conductor

The lightning conductor is a tapered rod placed on top o the building. It is earthed byone or more conductors (oten copper strips) (see Fig. J8).

Fig. J8: Example o protection using a lightning conductor

Copper stripdown conductor

Test clamp

Crow-foot earthing




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The design and installation o a lightning conductor is the job o a specialist.

Attention must be paid to the copper strip paths, the test clamps, the crow-ootearthing to help high requency lightning currents run to the ground, and the

distances in relation to the wiring system (gas, water, etc.).Furthermore, the fow o the lightning current to the ground will induce voltagesurges, by electromagnetic radiation, in the electrical circuits and buildings to beprotected. These may reach several dozen kilovolts. It is thereore necessary tosymmetrically split the down conductor currents in two, our or more, in order tominimise electromagnetic eects.

Overhead earth wires

These wires are stretched over the structure to be protected (seeFig. J9). They areused or special structures: rocket launch pads, military applications and lightningprotection cables or overhead high voltage power lines (see Fig. J0).

Fig. J9: Example o lightning protection using overhead earth wires

Fig. J10: Lightning protection wires

Tin plated copper 25 mm2

Frame grounded earth belt

h

d > 0.1 h

Metal post

i/2i/2

i

Lightning

protection

cables





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The meshed cage (Faraday cage)

This principle is used or very sensitive buildings housing computer or integratedcircuit production equipment. It consists in symmetrically multiplying the number o

down strips outside the building. Horizontal links are added i the building is high; orexample every two foors (see Fig. J). The down conductors are earthed by rogsoot earthing connections. The result is a series o interconnected 15 x 15 m or10 x 10 m meshes. This produces better equipotential bonding o the building andsplits lightning currents, thus greatly reducing electromagnetic elds and induction.

Primary lightning conductor protection devicessuch as a meshed cage or overhead earthwires are used to protect against direct strokeso lighting.These protection devices do notprevent destructive secondary eects onequipment rom occurring. For example, risesin earth potential and electromagnetic inductionwhich are due to currents owing to the earth.To reduce secondary eects, LV surge arrestersmust be added on telephone and electricalpower networks.

Fig. J11: Example o protection using the meshed cage (Faraday cage) principle

2.2 Secondary protection devices (protection ointernal installations against lightning)

These handle the eects o atmospheric, operating or industrial requency voltage

surges. They can be classied according to the way they are connected in aninstallation: serial or parallel protection.

Serial protection device

This is connected in series to the power supply wires o the system to be protected

(see Fig. J2).

Secondary protection devices are classed intwo categories: Serial protection and parallelprotection devices.

Serial protection devices are specifc to asystem or application.Parallel protection devices are used or: Powersupply network, telephone network, switchingnetwork (bus).

Installation to be protectedPower supply

Up

Serial

protection

Fig. J12: Serial protection principle

Transormers

They reduce voltage surges by inductor eect and make certain harmonicsdisappear by coupling. This protection is not very eective.

FiltersBased on components such as resistors, inductance coils and capacitors theyare suitable or voltage surges caused by industrial and operation disturbancecorresponding to a clearly dened requency band. This protection device is notsuitable or atmospheric disturbance.





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Wave absorbersThey are essentially made up o air inductance coils which limit the voltage surges,and surge arresters which absorb the currents. They are extremely suitable or

protecting sensitive electronic and computing equipment. They only act againstvoltage surges. They are nonetheless extremely cumbersome and expensive.

Network conditioners and static uninterrupted power supplies (UPS)These devices are essentially used to protect highly sensitive equipment, such ascomputer equipment, which requires a high quality electrical power supply. Theycan be used to regulate the voltage and requency, stop intererence and ensure acontinuous electrical power supply even in the event o a mains power ailure (orthe UPS). On the other hand, they are not protected against large, atmospheric typevoltage surges against which it is still necessary to use surge arresters.

Parallel protection device

The principleThe parallel protection is adapted to any installation power level (see Fig. J3).

This type o overvoltage protection is the most commonly used.

Main characteristicsb The rated voltage o the protection device must correspond to the network voltageat the installation terminals

b When there is no voltage surge, a leakage current should not go through theprotection device which is on standby

b When a voltage surge above the allowable voltage threshold o the installationto be protected occurs, the protection device abruptly conducts the voltage surgecurrent to the earth by limiting the voltage to the desired protection level Up(see Fig. J4).


Installation to

be protected

Power supply

UpParallel

protection

Fig. J13: Parallel protection principle

Fig. J14: Typical U/Icurve o the ideal protection device

0 I(A)

U (V)

Up

When the voltage surge disappears, the protection device stops conducting andreturns to standby without a holding current. This is the ideal U/I characteristic curve:

b The protection device response time (tr) must be as short as possible to protect theinstallation as quickly as possible

b The protection device must have the capacity to be able to conduct the energycaused by the oreseeable voltage surge on the site to be protected

b The surge arrester protection device must be able to withstand the rated current In.




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The products used

b Voltage limitersThey are used in MV/LV substations at the transormer output, in IT earthing scheme.

They can run voltage surges to the earth, especially industrial requency surges(see Fig. J5)

Fig. J15: Voltage limiter

b LV surge arrestersThis term designates very dierent devices as ar as technology and use areconcerned. Low voltage surge arresters come in the orm o modules to be installedinside LV switchboard. There are also plug-in types and those that protect poweroutlets. They ensure secondary protection o nearby elements but have a small fowcapacity. Some are even built into loads although they cannot protect against strongvoltage surges

b Low current surge arresters or overvoltage protectors

These protect telephone or switching networks against voltage surges rom theoutside (lightning), as well as rom the inside (polluting equipment, switchgear

switching, etc.)Low current voltage surge arresters are also installed in distribution boxes or

built into loads.

MV/LV

Overvoltagelimiter

Permanentinsulationmonitor

PIM




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J - Protection against voltage surges in LV 3 Protection against voltage

surges in LV

3. Surge protective device description

A surge protective device (SDP) is a device that limits transient voltage surges and

runs current waves to ground to limit the amplitude o the voltage surge to a saelevel or electrical installations and equipment.

The surge protective device includes one or several non linear components.

The surge protective device eliminates voltage surges:

b In common mode: Phase to earth or neutral to earth

b In dierential mode: Phase to phase or phase to neutral

When a voltage surge exceeds the Uc threshold, the surge protective device (SDP)conducts the energy to earth in common mode. In dierential mode the divertedenergy is directed to another active conductor.

The surge protective device has an internal thermal protection device which protectsagainst burnout at its end o lie. Gradually, over normal use ater withstandingseveral voltage surges, the Surge Protective Device degrades into a conductivedevice. An indicator inorms the user when end-o-lie is close.

Some surge protective devices have a remote indication.

In addition, protection against short-circuits is ensured by an external circuit-breaker.

3.2 Surge protective device standards

International standard IEC 6643- ed. 02/2005

Surge protective devices connected to low-voltage power distribution systems.

Three test classes are dened:

b Class I tests: They are conducted using nominal discharge current (In), voltageimpulse with 1.2/50 s waveshape and impulse current Iimp.The class I tests is intended to simulate partial conducted lightning current impulses.SPDs subjected to class I test methods are generally recommended or locationsat points o high exposure, e.g., line entrances to buildings protected by lightning

protection systems.b Class II tests: They are conducted using nominal discharge current (In), voltageimpulse with 1.2/50 s waveshape

b Class III tests: They are conducted using the combination waveorm (1.2/50 and8/20 s).

SPDs tested to class II or III test methods are subjected to impulses o shorterduration. These SPDs are generally recommended or locations with lesser exposure.

These 3 test classes cannot be compared, since each originates in a country andeach has its own specicities. Moreover, each builder can reer to one o the 3 testclasses.

European standard EN 6643- 2002

Some requirements as per IEC 61643-1. Moreover SPDs are classied in threecategories:

Type 1: SPD tested to Class I

Type 2: SPD tested to Class IIType 3: SPD tested to Class III

3.3 Surge protective device data according toIEC 6643- standard

bSurge protective device (SPD): A device that is intended to limit transientovervoltages and divert surge currents. It contains at least one nonlinear component.

bTest classes: Surge arrester test classication.

bIn: Nominal discharge current; the crest value o the current through the SPDhaving a current waveshape o 8/20. This is used or the classication o the SPD orthe class II test and also or preconditioning o the SPD or class I and II tests.

bImax: Maximum discharge current or class II test; crest value o a current throughthe SPD having an 8/20waveshape and magnitude according to the test sequenceo the class II operating duty test. Imax is greater than In.

bIc: Continuous operating current; current that fows in an SPD when supplied atits permament ull withstand operating voltage (Uc) or each mode. Ic correspondsto the sum o the currents that fow in the SPDs protection component and in all theinternal circuits connected in parallel.



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bIimp: Impulse current, it is dened by a current peak value Ipeak and the chargeQ. Tested according to the test sequence o the operating duty test. This is used orthe classication o the SPD or class I test.

bUn: Rated network voltage.

bUc: Maximum continuous operating voltage; the maximum r.m.s. or d.c. voltagewhich may be continuously applied to the SPDs mode o protection. This is equal tothe rated voltage.

bUp: Voltage protection level; a parameter that characterizes the perormance othe SPD in limiting the voltage across its terminals, which is selected rom a list opreerred values. This value shall be greater than the highest value o the measuredlimiting voltages.

The most common values or a 230/400 V network are: kV - .2 kV - .5 kV - .8 kV - 2 kV - 2.5 kV .

bUres: Residual voltage, the peak value o the voltage that appears between theterminals o an SPD due to the passage o discharge current.

The SPD is characterised by Uc, Up, In and Imax (see Fig. J6)

b To test the surge arrester, standardized voltage and current waves have been

dened that are specic to each country:v Voltage wavee.g. 1.2/50 s (see Fig. J7)

v Current waveExample 8/20 s (see Fig. J8)

20

8

Maxi

100 %

I

50 %

t

Fig. J18: 8/20s wave

In Imax< 1 mA

I

U

Up

Uc

Fig. J16: Voltage/current characteristics

Maxi

100 %

50 %

1,2

50

t

V

Fig. J17: 1.2/50s wave

v Other possible wave characteristics:4/10 s, 10/1000 s, 30/60 s, 10/350 s...Comparison between dierent surge protective devices must be carried out using thesame wave characteristics, in order to get relevant results.

3 Protection against voltage

surges in LV



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3.4 Lightning protection standards

The IEC 62305 series (part 1 to 5) restructures and updates the publications o

IEC 61024 series, IEC 61312 series and IEC 61663 series.The need or protection, the economic benets o installing protection measures andthe selection o adequate protection measures should be determined in terms o riskmanagement. Risk management is the subject o IEC 62305-2.

The criteria or design, installation and maintenance o lightning protection measuresare considered in three separate groups:b The rst group concerning protection measures to reduce physical damage and liehazard in a structure is given in IEC 62305-3.b The second group concerning protection measures to reduce ailures o electricaland electronic systems in a structure is given in IEC 62305-4.b The third group concerning protection measures to reduce physical damage andailures o services connected to a structure (mainly electrical and telecommunicationlines) is given in IEC 62305-5.

3.5 Surge arrester installation standards

bInternational: IEC 61643-12 selection and application principles

bInternational:IEC 60364 Electrical installations o buildings

v IEC 60364-4-443: protection or saetyWhen an installation is supplied by, or includes, an overhead line, a protection deviceagainst atmospheric overvoltages must be oreseen i the keraunic level o the sitebeing considered corresponds to the external infuences condition AQ 1 (more than25 days per year with thunderstorms).

v IEC 60364-4-443-4: selection o equipment in the installation.This section helps with the choice o the protection level Up or the surge arrester inunction o the loads to be protected.

Rated residual voltage o protection devices must not be higher than the value in thevoltage impulse withstand category II (see Fig. J9):

(1) According to IEC 60038

(2) In Canada and USA or voltages to earth higher than 300 V,

the impulse withstand voltage corresponding to thenext higher voltage in column one applies.

Category I is addressed to particular equipment engineering.

Category II is addressed to product committees or equipment

or connection to the mains.

Category III is addressed to product committees o installation

material and some special product committees.

Category IV is addressed to supply authorities and systemengineers (see also 443.2.2).

Nominal voltage o Required impulse withstand voltage or

the installation() V kV

Three-phase Single-phase Equipment at Equipment o Appliances Specially

systems(2) systems with the origin o distribution and protectedmiddle point the installation nal circuits equipment

(impulse (impulse (impulse (impulsewithstand withstand withstand withstand

category IV) category III) category II) category I)

120-240 4 2.5 1.5 0.8

230/400(2) - 6 4 2.5 1.5277/480(2)

400/690 - 8 6 4 2.5

1,000 - Values subject to system engineers

Fig. J19: Choosing equipment or the installation according to IEC 60364


surges in LV



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v IEC 60364-5-534: choosing and implementing electrical equipmentThis section describes surge arrester installation conditions:

- According to earthing systems: The maximum continuous operating voltage Uc

o SPDs shall be equal to or higher than shown in Fig. J20.

- At the origin o the installation: i the surge arrester is installed at the source oan electrical installation supplied by the utility distribution network, its rated dischargecurrent may be lower than 5 kA.I a surge arrester is installed downstream rom an earth leakage protection device,an RCD o the s type, with immunity to impulse currents o less than 3 kA (8/20 s),must be used.

- Protection against overcurrent at 50 Hz and consequences o a SPD ailure:protection against SPDs short-circuits is provided by the overcurrent protectivedevices F2 which are to be selected according to the maximum recommended ratingor the overcurrent protective device given in the manuacturer's SPD instructions.

- In the presence o lightning conductors: a surge arrester must be installed,additional specications or surge arresters must be applied (see IEC 62305 part 4).

SPDs connected

between

System confguration o distribution network

TT TN-C TN-S IT with

distributedneutral

IT without

distributedneutral

Line conductor and

neutral conductor

1.1 Uo NA 1.1 Uo 1.1 Uo NA

Each line conductor and

PE conductor

1.1 Uo NA 1.1 Uo 3Uo(1) Line-to-linevoltage (1)

Neutral conductor and PE

conductor

Uo(1) NA Uo(1) Uo(1) NA

Each line conductor and

PEN conductor

NA 1.1 Uo NA NA NA

NA: not applicable

NOTE 1: Uo is the line-to-neutral voltage o the low-voltage system.

NOTE 2: This table is based on IEC 61643-1 amendment 1.

Fig. J20: Minimum required Uc o the SPD dependent on supply system confguration


surges in LV

(1) These values are related to worst case ault conditions,thereore the tolerance o 10 % is not taken into account




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4 Choosing a protection device

When installing surge arresters, several elements must be considered, such as:

b Cascading

b Positioning with respect to residual current devices

b The choice o disconnection circuit breakersThe earthing system must also be taken into account.

4. Protection devices according to the earthingsystem

b Common mode overvoltage: basic protection involves the installation o a commonmode surge arrester between phase and PE or phase and PEN, whatever type oearthing system is used.

b Dierential mode overvoltage: in the TT and TN-S earthing systems, earthing theneutral leads to dissymmetry due to earthing impedances, which causes dierentialmode voltages to appear, whereas the overvoltage induced by a lightning strike is acommon mode voltage.For example, let us consider a TT earthing system. A two-pole surge arrester isinstalled in common mode to protect the installation (see Fig. J2).

Fig. J21 : Common mode protection only

I

I

II

The neutral earthing resistor R1 used or the pylons has a lower resistance than theearthing resistor R2 used or the installation. The lightning current will fow throughcircuit ABCD to earth via the easiest path. It will pass through varistors V1 and V2 inseries, causing a dierential voltage equal to twice the residual voltage o the surgearrester (Up1 + Up2) to appear at the terminals o A and C at the entrance to theinstallation in extreme cases.

To protect the loads between Ph and N eectively, the dierential mode voltage(between A and C) must be reduced.

Another earthing system is thereore used (see Fig. J22).The lightning current fows through circuit ABH which has a lower impedance thancircuit ABCD, as the impedance o the component used between B and H is null (gaslled spark gap).In this case, the dierential voltage is equal to the residual voltage o the surgearrester (Up2).

Fig. J22: Common + dierentiel mode protection

I

I

I




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Mode Between TT TN-S TN-C IT

Dierential phase and neutral yes yes - -

Common phase and earth yes yes yes yes

phase and earth yes yes - yes (i distributed

neutral)

Fig. J23: Connections to be made according to the earthing systems used, in the case o

atmospheric overvoltages

4.2 Internal architecture o surge arresters

b 2P, 3P, 4P surge arresters (see Fig. J24):v They provide protection against common-mode overvoltages only

v They are appropriate or TN-C and IT earthing systems.

Fig. J24: 2P, 3P, 4P surge arresters

b 1P+N, 3P+N surge arresters (see Fig. J25):v They provide protection against common-mode and dierential-mode overvoltagesv They are appropriate or TT, TN-S, and IT earthing systems.

Fig. J25: 1P+N, 3P+N surge arresters

b Single-pole (1P) surge arresters (see Fig. J26):v They are used to satisy the demand o dierent assemblies (according to themanuacturers instructions) by supplying only one product.However, special dimensioning will be required or N - PE protection

(or example 1+N and 3P+N)v The assembly must be validated by means o the tests specied in EN 61643-11.

Fig. J26: Connection example

PE

Earthing conductor

Main earth terminal





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4.3 Coordination o surge arresters

The overvoltage protection study o an installation may show that the site is highly

exposed and that the equipment to be protected is sensitive. The surge arrestermust be able to discharge high currents and have a low level o protection. This dualconstraint cannot always be handled by a single surge arrester. A second one willthereore be required (see Fig. J27).

The rst device, P1 (incoming protection) will be placed at the incoming end o theinstallation.Its purpose will be to discharge the maximum amount o energy to earth with alevel o protection y 2000 V that can be withstood by the electrotechnical equipment(contactors, motors, etc.).The second device (ne protection) will be placed in a distribution enclosure, asclose as possible to the sensitive loads. It will have a low discharge capacity and alow level o protection that will limit overvoltages signicantly and thereore protectsensitive loads (y 1500 V).

Cascading protection requires a minimumdistance o at least 10 m between the twoprotection devices.

This is valid, whatever the feld o application:domestic, tertiary or industrial.

Fig. J27: Cascading o surge arresters

The ne-protection device P2 is installed in parallel with the incoming protectiondevice P1.

I the distance L is too small, at the incoming overvoltage, P2 with a protectionlevel o U2 = 1500 V will operate beore P1 with a level o U1 = 2000 V. P2 will notwithstand an excessively high current. The protection devices must thereore becoordinated to ensure that P1 activates beore P2. To do this, we shall experimentwith the length L o the cable, i.e. the value o the sel-inductance between the twoprotection devices. This sel-inductance will block the current fow to P2 and cause acertain delay, which will orce P1 to operate beore P2. A metre o cable gives a sel-inductance o approximately 1H.

The rule U=Ldi

dtcauses a voltage drop o approximately 100 V/m/kA, 8/20 s

wave.

For L = 10 m, we get UL1 = UL2 1000 V.

To ensure that P2 operates with a level o protection o 1500 V requires

U1 = UL1 + UL2 + U2 = 1000 + 1000 + 1500 V = 3500 V.Consequently, P1 operates beore 2000 V and thereore protects P2.

Note: i the distance between the surge arrester at the incoming end o theinstallation and the equipment to be protected exceeds 30 m, cascading the surgearresters is recommended, as the residual voltage o the surge arrester may riseto double the residual voltage at the terminals o the incoming surge arrester; as inthe above example, the ne protection surge arrester must be placed as close aspossible to the loads to be protected.

Installation rules (see page Q2).

I

I

I

Fig. J28: Coordination o surge arresters





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4.4 Selection guide

Estimate the value o the equipment to be protectedTo estimate its value, consider:

b The cost o the equipment in nancial termsb The economic impact i the equipment goes down.

bDomestic equipment:

vaudio-video, computers

vhousehold appliances

vburglar alarm.

bSensitive equipment:

vburglar alarm

vre alarm

vaccess controlvvideo surveillance.

bBuilding equipment:

vautomated heating orair-conditioning

vlit.

bProessional equipment:

vprogrammable machine

vcomputer server

vsound or light control system.

bHeavy equipment:

vmedical inrastructure

vproduction inrastructure

vheavy computer processing.

Determine the electrical architecture o buildings

Lightning protection can be calculated or an entire building or or part o a

building that is electrically independent

Depending on the size o the building and the extent o its electrical system, one or

more surge arresters must be used in the various switchboards in the installation.b Detached house.b Apartment, small semi-detached house.b Communal part o a building.b Proessional premises.b Tertiary and industrial buildings:

v single switchboard, main switchboardv distribution board

v sensitive equipment more than 30 m rom the switchboard.

Understand the risk o the impact o lightning on the site

Lightning is attracted by high points that conduct electricity. They can be:

b Natural: tall trees, mountain crest, wet areas, errous soilb

Articial: chimney, aerial, pylon, lightning conductor.Indirect eects can be incurred within a ty metre radius around the point o impact.

Location o the building

In an urban, peri-urban,

grouped housing area.

In an area where there is a

particular hazard (pylon, tree,

mountainous region, mountaincrest, wet area or pond).

In fat open country. In an exceptionally exposed area

(lightning conductor on a buildingless than 50 metres away).

2

3





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Domestic equipment

Audio-video, computers,

household appliances,

burglar alarm, etc.

Type 2

10 kA

Type 2

40 kA

Type 1

25 kA

+

Type 2

40 kA

Type 1

25 kA

+

Type 2

40 kA

Type 2

10 kA

Equipment to beprotected

Determine thearchitecture o thebuilding

Risk level othe impact o alightning strike

Choice o type osurge arrester

Detached house,

Proessional

premises

Apartment, smallsemi-detachedhouse

Communal part o a

building

3

2

Type 2

40 kA

Type 2

65 kA

Type 1

25 kA

+

Type 2

40 kA

Type 1

25 kA

+

Type 2

40 kA

Note:

Type 1: very high discharge capacity surge arrester used with a lightning conductor with an impact level o and .

Type 2: surge arrester used in cascade behind a type 1 surge arrester or alone in zone and .

Lightning also propagates through

telecommunications networks.It can damage all the equipment connected tothese networks.

Protection o telecommunications equipment

Choice o surge arresters PRC

Analogue telephone networks < 200 V b

Fig. J32: Domestic equipment





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Sensitive equipment: Building equipment:

Burglar alarm,

re alarm,

access control,

video-surveillance, etc.

Automated heating or

air-conditioning,

lit, etc.

Single

switchboard,main

switchboard

Type 2

20 kA

Type 2

8 kA

Type 2

20 kA

Type 2

40 kA

Type 2

40 kA

Type 1

25 kA

or

35 kA

+

Type 2

40 kA

Dedicated

protection,more than

30 m rom a

switchboard

Distribution

board





3

2

Note:



Fig. J33: Sensitive equipment, Building equipment





J2






3

2

Note:



Fig. J34: Proessional equipment

Proessional equipment

Programmable machine,

server,

sound or light control system,

etc.

Type 2

20 kA

Type 2

8 kA

Type 2

40 kA

Type 2

65 kA

Type 2

65 kA

Type 1

25 kA

or

35 kA

+

Type 2

40 kA

Single

switchboard,

mainswitchboard

Dedicated

protection,

more than30 m rom a

switchboard

Distribution

board





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Heavy equipment

Medical, production,

or heavy computer

processing inrastructure,

etc.

Type 2

20 KA

Type 2

8 kA

Type 2

65 kA

Type 1

25 kA

+

Type 2

40 kA

Type 1

25 kA

or

35 kA

+

Type 2

40 kA

Type 1

25 kA

or

35 kA

+

Type 2

40 kA

Single

switchboard,

mainswitchboard

Dedicated

protection,

more than30 m rom a

switchboard

Distribution

board





3

2

Note:



Lightning can also propagate through

telecommunications and computer networks.It can damage all the equipment connectedto these networks: telephones, modems,computers, servers, etc.

Protection o telecommunications and computer equipment

Choice o surge arresters PRC PRI

Analogue telephone networks < 200 V b

Digital networks, analogue lines < 48 V b

Digital networks, analogue lines < 6 V

VLV load supply < 48 Vb

Fig. J35: Heavy equipment





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4.5 Choice o disconnector

The disconnector is necessary to ensure the saety o the installation

b One o the surge arrester parameters is the maximum current (Imax 8/20 swave) that it can withstand without degradation. I this current is exceeded, the surgearrester will be destroyed; it will be permanently short circuited and it is essential toreplace it.

The ault current must thereore be eliminated by an external disconnector installedupstream.

The disconnector provides the complete protection required by a surge arresterinstallation, i.e.:

v It must be able to withstand standard test waves:

- it must not trip at 20 impulses at In

- it can trip at Imax without being destroyed

v the surge arrester disconnects i it short-circuits.

b The ready-to-cable surge arresters with an integrated disconnection circuit breakerare:

v Combi PRF1

v Quick PF

v Quick PRD.

Surge arrester / disconnection circuit breaker correspondencetable

Fig. J36: Coordination table between SPD and its disconnector


Types Surge arrester

namesIsc

Imax or Iimp

6 kA 0 kA 5 kA 25 kA 36 kA 50 kA 70 kA 00 kA

Type

PRF1 Master 35 kA() Compact NSX160B 160A Compact

NSX160F

160A

Compact

NSX160N

160A

PRD1 Master 25 kA() NG 125 N C 80A NG 125L C 80A

PRD1 25r NG 125 N C 80A NG 125L C 80A

PRF1 D125 Dcurve

Combi PRF1 Integrated

PRF1 12,5 r 2,5 kA() NG 125 N C 80A NG 125L C 80A

Type 2

PF 65/ PRD 65r 65 kA(2) C60N 50A C curve C60H 50AC curve

NG125L50A C

curve

Fuse NH 50A gL/gG

PF 40 / PRD 40r 40 kA(2) C60N 40A C curve C60H 40AC curve

NG125L40A C

curve

Fuse 22x58 40A gL/gG

Quick PRD 40r Integrated Contact us


NG125L25A C

curve

Fuse 22x58 25A gL/gG

Quick PRD 20r Integrated Contact us

Quick PF 10 0 kA(2) Integrated


NG125L 20A C curve

Quick PRD 8 r Integrated Contact us

Isc: prospective short-circuit current at the point o installation.

(1)Iimp.

(2) Imax.




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4.6 End-o-lie indication o the surge arrester

Various indication devices are provided to warn the user that the loads are no longer

protected against atmospheric overvoltages.

Type surge arresters (with gas flled spark gap)

PRF P 260 V, Combi P+N and 3P+N and PRF Master

These surge arresters have a light indicating that the module is in good workingorder. This indicator light requires a minimum operating voltage o 120 V AC.b The light does not come on:

v i the operating voltage is y 120 V ACv i there is no network voltagev i the spark-over electronics are deective.

Type 2 surge arresters (varistor, varistor + gas flled spark gap)

PF, PRD

At end o lie, the surge arrester or the cartridge are destroyed.

b This can occur in two ways:v internal end-o-lie disconnection: the accumulated electric shocks cause thevaristors to age, resulting in an increase in leakage current.Above 1 mA, a thermal runaway occurs and the surge arrester disconnects.

v external end-o-lie disconnection: this occurs in the event o an excessiveovervoltage (direct lightning strike on the line); above the discharge capacity o thesurge arrester, the varistor(s) are dead short-circuited to ear th (or possibly betweenphase and neutral). This short-circuit is eliminated when the mandatory associateddisconnection circuit breaker opens.

Quick PRD and Quick PF

Whatever the hazards o the power supply network, Quick PRD and Quick PFincorporate a perectly coordinated disconnector.b In the event o lightning strikes < Imax: like all surge arresters, they have internalanti-ageing protection.b In the event o a lightning strike > Imax: Quick PRD and Quick PF are sel-protected by their integrated disconnector.b In the event o neutral disconnection or phase-neutral reversal occurring on thepower supply:

Quick PRD and Quick PF are sel-protected by their integrated disconnector.To simpliy maintenance work, Quick PRD is tted with local indicators and draw-outcartridges that are mechanically combined with the disconnector.

Quick PRD has indicator lights on the car tridges and on the integrated disconnector,so that the work to be carried out can quickly be located.

For saety reasons, the disconnector opens automatically when a cartridge isremoved. It cannot be set until the cartridge is plugged in.When changing the cartridge, a phase/neutral ailsae system ensures that it can beplugged in saely.

Operating state continuous display

Quick PRD has an integrated reporting contact to send inormation about the

operating state o the surge arrester rom a remote location.Monitoring the surge arresters installed throughout the installation makes it possibleto be continuously aware o their operating state and to ensure that the protectiondevices are always in good working order.b A reporting contact gives the alert:v at end o lie o a cartridge

v i a cartridge is missing, as soon as it has been removedv i a ault occurs on the line (short-circuit, neutral disconnection, phase-neutralreversal)

v in the event o local manual operation (handle down).

Quick PF has an optional indication reporting auxiliary (SR) that sends inormationabout the operating state o the surge arrester rom a remote location.

Fig. J37: Example o indication or PRD

Fig. J39: Example o indication or Quick PRD



25/25


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Electric-allrightsreserved

C60

40 A

PRD

40 kA

C60

20 A

PRD

8 kA

C60

20 A

PRD

8 kA

ID

"si"

ID

"si"

160 kVA

MV/LV transormer

Main

switchboard

Switchboard 1 Switchboard2

Heating Lighting Freezer Rerigerator

Storeroom lighting Power outlets

Fire-fghting system Alarm

IT system Checkout

4.7 Application example: supermarket

Solutions and schematic diagram

b The surge arrester selection guide has made it possible to determine the precisevalue o the surge arrester at the incoming end o the installation and that o theassociated disconnection circuit breaker.

bAs the sensitive devices (Uimp < 1.5 kV) are located more than 30 m rom theincoming protection device, the ne protection surge arresters must be installed as

close as possible to the loads.b To ensure better continuity o service or cold room areas:v"si" type residual current circuit breakers will be used to avoid nuisance trippingcaused by the rise in earth potential as the lightning wave passes through.b For protection against atmospheric overvoltages:

v install a surge arrester in the main switchboardv install a ne protection surge arrester in each switchboard (1 and 2) supplying thesensitive devices situated more than 30 m rom the incoming surge arresterv install a surge arrester on the telecommunications network to protect the devicessupplied, or example re alarms, modems, telephones, axes.

Cabling recommendations

b Ensure the equipotentiality o the earth terminations o the building.

b Reduce the looped power supply cable areas.

Installation recommendations

b Install a surge arrester, Imax = 40 kA (8/20 s) and a C60 disconnection circuitbreaker rated at 20 A

Fig. J39: Application example : supermarket


Documents

Protection Voltage Surges