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Contents

1 Introduction 1

2 Damage due to lightning and surges 5

2.1 Damage statistics 5 2.2 Examples 10 2.2.1 Damage in hazardous areas 10 2.2.2 Damage to industrial plants 15 2.2.3 Damage to power supply systems 24 2.2.4 Damage to a house 27 2.2.5 Damage to aircraft and airports 36 2.2.6 Damage to wind power stations 38 2.2.7 Catastrophic damage 39

3 Origin and effect of surges 43

3.1 Atmospheric overvoltages 45 3.1.1 Direct and close-up strikes 45 3.1.1.1 Voltage drop at the impulse earthing resistance 48 3.1.1.2 Induced voltages in metal loops 49 3.1.2 Remote strikes 56 3.1.3 Coupling of surge currents on signal lines 57 3.1.3.1 Ohmic coupling 58 3.1.3.2 Inductive coupling 58 3.1.3.3 Capacitive coupling 59 3.1.4 Magnitude of atmospheric overvoltages 60 3.2 Switching overvoltages 61

4 Protective measures, standards 67

4.1 Lightning protection 69 4.1.1 Risk analysis, protection levels 74 4.1.2 External and internal lightning protection, DIN VDE

0185 Part 1, DIN V ENV 61024-1 (VDE V 0185 Part 100) 78

4.1.3 Concept of lightning protection zones, DIN VDE

0185-103 (VDE 0185 Part 103) 79 4.1.3.1 LEMP-protection planning 83 4.1.3.1.1 Definition of lightning protection levels 83 4.1.3.1.2 Definition of lightning protection zones 83 4.1.3.1.3 Room shielding measures 84 4.1.3.1.4 Equipotential bonding networks 90 4.1.3.1.5 Equipotential bonding measures for supply

lines and electric lines at the boundaries of

the lightning protection zones 92 4.1.3.1.6 Cable routing and shielding 94 4.1.3.2 Realization of LEMP protection 97 4.1.3.3 Installation and supervision of LEMP

protection 99 4.1.3.4 Acceptance inspection of LEMP protection 100 4.1.3.5 Periodic inspection 101 4.1.3.6 Costs 101 4.2 Surge protection for electrical systems of buildings, IEC

60364, DIN VDE 0100 103 4.2.1 IEC 60364-4-443/DIN VDE 0100 Part 443 104 4.2.2 IEC 60664-1/DIN VDE 0110 Part 1 105 4.2.3 IEC 60364-5-534/DIN VDE 0100 Part 534 109 4.3 Surge protection for telecommunications systems, DIN

VDE 0800, DIN VDE 0845 110 4.4 Electromagnetic compatibility including protection

against electromagnetic impulses and lightning,

VG 95 372 112 4.5 Standards for components and protective devices 112

4.5.1 Connection components, E DIN EN 50164-1

(VDE 0185 Part 201) 113 4.5.2 Arresters for lightning currents and surges 113

4.5.2.1 Arresters for power engineering, IEC

61643-1/E DIN VDE 0675 Part 6 113 4.5.2.1.1 Important data for arrester selection 119 4.5.2.1.2 Coordination of the arresters according to

requirements and locations 120 4.5.2.1.3 N-PE arrester, E DIN VDE 0675 Part

6/A2 121 4.5.2.2 Arresters for information technology,

IEC SC 37A/E DIN VDE 0845 Part 2 122 4.5.2.2.1 Important data for arrester selection 124 4.5.2.2.2 Arrester coordination according to

requirements and locations 125 4.5.2.3 Arrester coordination 125

5 Components and protective devices: construction, effect and

application 127

5.1 Air terminations 127 5.2 Building and room shields 129 5.3 Shields for lines between screened buildings 138 5.4 Shields for cables in buildings 141 5.5 Optoelectronic connections 143 5.5.1 Optical fibre transmission system 144 5.5.2 Optocoupler 145 5.6 Equipotential bonding 145 5.7 Isolating spark gaps 150 5.8 Arresters 153 5.8.1 Arresters for power engineering 155

5.8.1.1 Surge arresters for low-voltage overhead lines,

class A 155 5.8.1.2 Lightning current arresters for lightning

protection equipotential bonding, class B 157 5.8.1.3 Surge arresters for protection of permanent

installation, class C 167 5.8.1.4 Surge arresters for application at socket outlets,

class D 174 5.8.1.5 Surge arresters for application at equipment

inputs 175 5.8.1.6 Application of lightning current arresters and

surge arresters 175 5.8.1.6.1 Graded application of arresters, energetic

coordination between surge arresters and

equipment to protect 178 5.8.1.6.2 Application of arresters in different system

configurations 182 5.8.1.6.3 Selection of arrester backup fuses 196 5.8.2 Arresters for information technology 206 5.8.2.1 Arresters for measuring and control systems 209

5.8.2.1.1 Blitzductor®_{CT: Construction and mode of}

functioning 210 5.8.2.1.2 Blitzductor®_{CT: Selection criteria 223}

5.8.2.1.3 Blitzductor®_{CT: Examples of application 228}

5.8.2.1.4 Arresters for intrinsically safe measuring

and control circuits and their application 238 5.8.2.1.5 Arresters for cathodic protection systems 246 5.8.2.1.6 Arresters in Euro-card format 248 5.8.2.1.7 Arresters in LSA-Plus technology 248 5.8.2.2 Combined protective devices for power supply

inputs and information technology inputs 253

5.8.2.3 Protective devices for data networks/systems 255 5.8.2.3.1 Protective devices for application-neutral

cabling 255 5.8.2.3.2 Protective devices for token ring-cabling 262 5.8.2.3.3 Protective devices for Ethernet twisted

pair-cabling 265 5.8.2.3.4 Protective devices for Ethernet coax-cabling 267 5.8.2.3.5 Protective devices for standard cabling 271 5.8.2.3.6 Protective devices for data telecontrol

transmission by ISDN base terminal 277 5.8.2.3.7 Protective devices for data telecontrol

transmission by ISDN primary multiplex

terminal 284 5.8.2.3.8 Protective devices for data telecontrol

transmission by analogous a/b-wire

terminal 286

6 Application in practice: Some examples 293

6.1 Industrial plants 295 6.1.1 Fabrication hall 295 6.1.2 Store and dispatch building 296 6.1.3 Factory central heating 302 6.1.4 Central computer 307 6.1.5 European installation bus (EIB) 309 6.1.6 Other bus systems 313 6.1.7 Fire and burglar alarm system 313 6.1.8 Video control system 316 6.1.9 Radio paging system 318 6.1.10 Electronic vehicle weighbridge 320 6.2 Peak-load power station 323 6.3 Mobile radio systems 328 6.4 Television transmitter 334 6.5 Mobile telecommunication facility 339 6.6 Airport control tower 343

7 Prospects 351

Index 353

Chapter 1

Introduction

Business, industry and public institutions depend on electronic data engineering. Electronic data processing (EDP) systems, measuring and control systems, instrumentation and control as well as secondary tech-nology are all part of a modern industrial plant. Data recording devices at the production facilities are connected to office terminals and com-puters by information networks ranging between buildings—together making CIM (computer integrated manufacturing). Open networks, where different types of computers and different operating systems communicate, are often the basis for CIM. This rapidly expanding business process is now approaching the CIE (computer integrated enterprise) or CIB (computer integrated business); in other words, the complete integration of all ranges of administration into a multi-EDP system. The future lies in the computer-integrated factory or in computer-integrated business and administration.

Everywhere, computers in local banks are connected to the computing centre of the main bank. This ‘networked’ world, with its growing flow of information, is, however, severely hindered by interference or damage to the essential transmission systems in the telephone and data networks, as well as at terminals (Figure 1 a). Dependence on electronic data processing can quickly lead to catastrophe if the system fails.

An American study in 1987 highlighted the seriousness of the situ-ation. According to this, banks will only be able to manage without EDP for 2 days, sales-oriented enterprises will be able to manage for 3.3 days, manufacturers for 4.9 days, and insurance companies for 5.6 days. An investigation by IBM Germany disclosed that enterprises without functioning EDP would be on the verge of ruin after about 4.8 days. In many business sectors within the European Market this risk will certainly continue to increase in the future.

Computer safety experts point out that nine out of ten enterprises will close if the computer fails for two weeks. The most frequent reason for

the failure of such electronic systems is transient electromagnetic interfer-ences that disturb the flow of data and destroy electronic equipment.

Risk can be controlled by electromagnetic compatibility (EMC) meas-ures. This specifies conditions under which any kinds of electric equipment do not disturb each other and also where electromagnetic phenomena, for example, lightning discharges, will not disturb their function.

The European Community has declared EMC as a protection goal by issuing the ‘Richtlinie des Rats vom 3. Mai 1989 zur Angleichung der Rechtsvorschriften der Mitgliedstaaten über die Elektromagnetische Verträglichkeit’ (Council Directive of 3 May 1989 to Harmonise Laws of the Member Nations concerning Electromagnetic Compatibility). All apparatus, facilities and systems that include electric or electronic components must demonstrate sufficient ‘withstand’ levels against elec-tromagnetic disturbances to guarantee proper operation of equipment.

The instructions of the Council especially mention the following facil-ities: industrial equipment, telecommunication networks and equipment, mobile radio sets, information technology equipment, private sound and TV-radio-receivers, commercial mobile radio and radio-telephones, med-ical and scientific apparatus and equipment, household appliances and electronic household equipment, radio sets for navigation, electronic edu-cation gear, transmitters for radio and television, and luminaires and fluorescent lamps. These instructions were transferred into German law on 9 November 1992 as the ‘Gesetz über die Electromagnetische Verträg-lichkeit von Geräten (EMVG)’ (Law on the Electromagnetic Compatibility of Devices (EMCD)) and was fully valid as from 1 January 1996. A change to the EMVG was made on 30 August 1995. Violation of the EMC law, and thus of the EMC general instructions, is deemed a summary offence.

Among the threats from the electromagnetic environment, lightning discharge (Figure 1 b) is the most important and therefore this

deter-Figure 1 a Partial lightning currents propagate on lines and mains

mines to a great extent the protective measures that must be undertaken in the framework of EMC. Therefore, modern lightning protection does not only mean protection of buildings but especially the protection of those devices covered by Section 2, item 4 of EMVG, meaning that a lightning protection system also must be erected, even if it is not neces-sary for the building, for the equipment it contains, in the sense of Section 2, item 4 of EMVG.

This book presents proven lightning and surge protection measures, taking into account the latest standards and engineering. The com-ponents and devices that are used to achieve these protective measures are explained in terms of their function and application by means of practical examples.

Sources

SACHSE, CH.: ‘Computersicherheit – Tanz auf dem Vulkan’ (Management-Wissen, 1987) No. 6, pp. 68–72

PIGLER, F.: ‘EMV und Blitzschutz leittechnischer Anlagen’ (Siemens AG, Berlin u. München, 1990)

SCHWAB, A. J.: ‘Elektromagnetische Verträglichkeit’ (Springer Verlag, Berlin, Heidelberg, New York, 1990)

BEIERL, O.: ‘Elektromagnetische Verträglichkeit beim Blitzeinschlag in ein Gebäude’ (Fortschrittsberichte VDI, 1991) Reihe 21, Nr. 93 (VDI-Verlag GmbH, Düsseldorf)

KOHLING, A.: ‘EG-Rahmenrichtlinie und Europäische Normen zur EMV’, etz Elektrotech. Z., 1991, 12, (9), pp. 438–441

Figure 1 b Lightning discharge – a special electromagnetic source of interference

GONSCHOREK, K.-H. and SINGER, H.: ‘Elektromagnetische Verträg-lichkeit’ (B. G. Teubner, Stuttgart–Leipzig, 1992)

HABIGER, E.: ‘Elektromagnetische Verträglichkeit. Grundzüge ihrer Sicherstellung in der Geräte- und Anlagentechnik’ (Hüthig Buchverlag GmbH, Heidelberg, 1992)

HABIGER, E.: ‘Handbuch Elektromagnetische Verträglichkeit’ (Verlag Technik GmbH, Berlin–München, 1992)

MEYER, H. (Ed.): ‘Elektromagnetische Verträglichkeit von Automatisie-rungssystemen’ (VDE-Verlag, GmbH, Berlin/Offenbach, 1992)

DIN VDE 0870 Teil 1: ‘Elektromagnetische Beeinflussung (EMB)’ Begriffe. (VDE-Verlag, GmbH, Berlin/Offenbach, July 1984)

Richtlinien des Rats vom 3 May 1989 zur Angleichung der Rechtsvorschriften der Mitgliedstaaten über die Elektromagnetische Verträglichkeit (89/336/ EWG). Brüssel: Amtsblatt der Gemeinschaft L 139/19 (23 May 1989)

Gesetz über die Elektromagnetische Verträglichkeit von Geräten (EMVG), 9 Nov. 1992. Bundesgesetzblatt Teil 1, Nr. 52 (12 Nov. 1992)

Erstes Gesetz zur Änderung des EMVG vom 30 August 1995 (1. EMVG ÄndG). Bundesgesetzblatt Teil 1. Nr. 47 (8 Sept. 1995).

‘Guidelines on the Application of Council Directive 89/336/EEC of 3 May 1989 on the Approximation of the Laws of the Member States Relating to Electro-magnetic Compatibility’ (Directive 89/336/EEC Amended by Directives 91/263/ EEC, 92/31/EEC, 93/68/EEC, 93/97/EEC)

SCHNITZLER, J.: ‘Rechtliche Aspekte für Planer, Errichter und Prüfer von Blitzschutzanlagen’. 2. VDE/ABB-Fachtagung (6–7 Nov. 1997) Neu-Ulm: Neue Blitzschutznormen in der Praxis

Chapter 2

Damage due to lightning and surges

Damage to electronic installations is increasing due to the following factors: (i) the increasing use of electronic equipment and systems, (ii) the lower signal levels, which means higher sensitivity, and (iii) the increasing use of networks that cover large areas. Although the con-comitant destruction of electronic components is not often spectacular, interruptions to operations in most cases are rather long. Thus, the

con-sequential damage is often considerably higher than the damage to the hardware (Figure 2 a).

2.1 Damage statistics

One important electronic insurance company in Germany reported that the costs of compensation for surge damage due to electromagnetic

disturbances on electronic systems and equipment, such as communica-tion systems, computers, measuring devices and medical appliances, have quadrupled within a period of ten years (Figure 2.1 a). In 1984 8.5% of all damage adjustments were caused by surges. In 1993 34.6%, in 1994 35.5%, in 1995 33% out of 11 000 cases of damage and in 1996 26.6% and in 1997 31.68% out of 8722 cases of damage were caused by surges (Figure 2.1 b).

Figure 2.1 a Development of the percentage of damage due to surges compared

with the total damage sum

(Source: Württembergische Feuerversicherung AG, Stuttgart)

Figure 2.1 b Electronics sector: damage in 1997 (analysis of more than 9600

cases of damage)

In the former Federal Republic of Germany (FRG) in 1990, damage costs to electronic equipment and systems caused by surges may have exceeded one billion DM. Surge damage analysis has shown that light-ning discharges are the dominant disturbances, followed by those due to switching operations in power technical systems. There are also dangers caused by electrostatic discharge.

A statistic concerning lightning damage published for many years by the Upper Austrian fire prevention authority (Table 2.1 a) shows (additionally to the damage due to direct lightning strikes), indirect damage caused by electromagnetic lightning disturbances. Such indirect

Table 2.1 a Damage statistics of the Fire Prevention Authority, Upper Austria

damage costs are far higher than those due to direct lightning. For example, in 1993 there were 23 646 indirect damage incidents amounting to 86.2 million ÖS (Austrian schillings), compared to 64 direct damage incidents for which 27.4 million ÖS had to be compensated.

There is now worldwide agreement that the danger radius around a point struck by lightning is about 2 km (Figure 2.1 c, a). Within this domain electronic systems are affected by conducted and radiated disturbances that may cause destruction (Figure 2.1 c, b). In the case of an

electro-Figure 2.1 c (a) Lightning discharge hazard 2 km around the strike point

Figure 2.1 c (b) Electronic systems are interfered with or damaged by conducted

and radiated interference

magnetic disturbance by lightning, the hardware damage is only a small part of the total impact. Consequential damage, such as factory standstill due to the breakdown of computer systems or pollution due to the failure of measuring and control systems in chemical plants, causes the greatest proportion of the total loss, to say nothing of the possible liabilities.

Insurers only compensate for hardware damage, and today they usu-ally pay for the damage only if it is a first event. Thereafter, they will demand installation of protective measures according to the level of standardization and engineering technology, otherwise they will cancel the insurance contract (Figure 2.1 d). It is a usual condition for the

Figure 2.1 d Text of a letter from the Liability Insurance Association of the

German Industry concerning ‘surge damage’

conclusion of new contracts that proof of existing relevant protective measures be supplied.

2.2 Examples

Some examples of damage due to lightning discharge, switching operations or electrostatic discharge now follow.

2.2.1 Damage in hazardous areas

The disastrous consequences of lightning strikes in hazardous areas will be illustrated by the following five examples.

In 1965 a 1500 m3 _{solid-roof petrol tank in the DEA-Scholven refinery}

in Karlsruhe was struck by lightning. The tank exploded and burnt out completely (Figure 2.2.1 a). Figure 2.2.1 b shows the measuring equip-ment inside the tank. The ohmic resistance of a nickel spiral with float serves for measuring the temperature in the tank. As lightning struck the tank there was a flashover from the tank to the wires of the measuring cable which had the potential of the ‘remote’ earth. The explosive mixture was struck and the tank burnt out.

A similar remarkable case happened ten years later in the Nether-lands. A 5000 m3 _{kerosene tank exploded due to a lightning strike (Figure}

2.2.1 c). The inner tank temperature was controlled by a thermoelement

connected to the control room by a 200 m long measuring cable which also had, as in the above-mentioned case, the ‘remote’ earth potential. As

Figure 2.2.1 a Burned out tank due to a lightning strike, Karlsruhe, 1965

(Source: DEA-Scholven, Karlsruhe)

one of the surrounding willow trees was struck by lightning, there was a discharge from the roots of the tree to the earthing system of the tank. The potential of the tank system increased in accordance with its impulse earthing resistance. As a consequence, there was a sparkover to the measuring line and due to this open sparkover, the kerosene-air– mixture caught fire. An amateur photographer shot pictures of this lightning strike and the following explosion (Figure 2.2.1 d).

A lightning strike with severe consequences also happened in a chem-ical plant in Herne in August 1984 where an alcohol tank burnt out (Figure 2.2.1 e). Here, TÜV experts managed to find out the reason for

Figure 2.2.1 b Measuring equipment to determine the temperature inside the tank

Figure 2.2.1 c Lightning strike to a kerosene tank, Netherlands, 1975

Figure 2.2.1 d (a)

Figure 2.2.1 d (b)

Figure 2.2.1 d (a, b) 250 m high

explosion cloud after the lightning strike to a kerosene tank

(Source: Brood, T.G.P.)

Figure 2.2.1 e Burning alcohol tank

due to a lightning strike, Herne, 1984

(Source: Kartenberg, H. J.)

the damage. Once again it was a measuring cable entering the tank with the potential of the ‘remote’ earth that led to the burn out.

In October 1995 lightning struck the Indonesian oil refinery Pertamina in Cilacap on the south coast of Java. The tank exploded and the burning oil set fire to six neighbouring tanks (Figures 2.2.1 f and g). Again the reason was incomplete equipotential bonding. Thousands of Cilacap inhabitants and 400 Pertamina employees had to be evacuated for their safety. There was a standstill for about 18 months for this refinery which supplied 34% of Indonesia’s inland need. This meant that oil, petrol, kerosene and diesel, worth about DM 600 000, had to be imported daily for the supply of Java. Only in Spring 1997 was the company able to restart its own production.

In June 1996 a lightning strike in New Jersey, USA, set fire to petrol tanks containing 300 000 gallons of petrol. About 200 people had to be evacuated (Figure 2.1 h).

The reasons for these cases of damage are indicated as shown in Figure

2.2.1 i. Lightning hits an almost closed Faraday cage which has a hole. A

line coming from a distant building and which is earthed there enters this hole. Between the lightning-struck Faraday cage and this ‘remote’ earth a voltage drop develops that is caused by the lightning current at the impulse earth resistance (e.g. in Figure 2.2.1 i, 100 kV). Conventional measuring line insulations, however, can only withstand impulse voltages of some 100 V; higher values will cause punctures with arcing.

Sources

v. THADEN, H.-W.: ‘Tankbrand durch Blitzeinschlag’ (Erdöl u. Kohle-Erdgas-Petro-chemie, 1966), pp. 422–424

BROOD, T. G. P.: ‘Bericht über infolge Blitzeinschlag verursachte Brände in zwei geschützten Tanks für die Lagerung von brennbaren Flüssigkeiten’. 13. Intern. Blitzschutzkonf., Venedig (1976), Referat R-4.5

WESTDEUTSCHE ALLGEMEINE ZEITUNG: ‘Herner Tank-Unglück – Blitzschlag trotz einer Schutzanlage’ (4 Dec. 1984)

THE JAKARTA POST: ‘Cilacap fire won’t affect domestic fuel oil supplies’ (26 Oct. 1995)

THE NEW YORK TIMES: ‘Lightning starts fuel tank fire in New Jersey’ (12 June 1996)

SIRAITI, K. T., PAKPAHAN, P., ANGGORO, B., SOEWONO, S, ISKANTO, E., GARNIWA, I., and RAHARDJO, A., ‘An analysis of origin of internal sparks in kerosene tank due to lightning strikes’. Lightning and Mountains ’97, June 1997, Chamonix Mont Blanc/France

ZORO, R., SUDIRHAM, S., and SASONGKO, D. (ITB Bandung, Indonesia): ‘Kerosene tank explosions due to lightning strikes in an Indonesian refinery plant’. Lightning and Mountains ’97, June 1997, Chamonix Mont Blanc/ France

Figure 2.2.1 f, g Oil refinery Pertamina, Cilacap/Java, 1995. Seven tanks burned out due to a lightning strike

2.2.2 Damage to industrial plants

Repeated and extensive surge damage was caused to Europe’s largest computer-controlled lorry factory, Daimler–Benz AG, at Wörth, near Karlsruhe. Often the production came to a standstill and, correspond-ingly, extended production losses resulted from both direct and remote lightning strikes. The factory halls are on a site with a length of 1.5 km and a width of 1 km. In two shifts, 10 000 workers produce 400 lorries per shift. The material stock computers are connected with those in produc-tion control by a DC data transmission system; this digital symmetric transmission system works at ±350mV. At the beginning of the 1980s, surges repeatedly damaged the linked equipment, each time bringing with it a complete production standstill.

Figure 2.2.1 h Lightning strike sets petrol tank on fire, New Jersey, USA, 1996

In a textile mill in the former GDR the fire alarm system was activated by the ionization detector following a lightning strike on the roof of a high-bay warehouse. This activated the automatic sprinkler system. Con-sequential water damage was about 1 million DM. The warehouse was only equipped with an ‘external lightning protection system’.

A lightning strike to the roof was also the reason for a production standstill in the cutting department of a ready-made clothes manu-facturer in Dresden, in 1989. Here the central computer and machine control were disturbed by the 80 m long data cable. The so-called ‘external lightning protection system’ could not prevent this damage; ‘internal lightning protection’ measures were absent.

Systems with cables and lines crossing several buildings are especially endangered. In the Leuna works, in 1989, thunderstorms caused a failure of electronic control and supervision equipment causing a standstill in production. Distributed sensors in the process system were connected with the control room by cables the shields of which were bonded with the equipotential bonding bar of the control room. Complete lightning protection equipotential bonding, however, had been neglected and only a few special cables were connected with protective diodes. The damage loss exceeded 1 million DM.

A lightning occurrence in 1983 will now be described due to its particular characteristics. The conclusions that are drawn are valid even today. The case entails the administration tower of Klöckner– Humboldt–Deutz in Cologne (Figures 2.2.2 a and b). This was struck by lightning that was diverted to earth by the ‘external lightning protec-tion system’. Because of the absence of an ‘internal lightning protecprotec-tion

Figure 2.2.1 i Lightning strike to the Faraday cage causes flashover to the line at

the ‘Faraday hole’

system’, about 100 terminals (Figure 2.2.2 c) and numerous computer processors (Figure 2.2.2 d) in the computer centre (about 120 m away) were disturbed by this strike (Figure 2.2.2 e). Hardware damage alone amounted to 2 million DM; the consequential loss due to the non-availability of the computer systems was about 4 million DM. During this particular thunderstorm other neighbouring industrial plants had surge damage to their computers, telephone and telex systems. The reasons for these types of damage can be explained by considering Figure

2.2.2 f. If lightning strikes building

䊊

1 , a partial lightning current will flow into building

䊊

2 only because of the resistive coupling (Section 3.1.3 (a)) and thus cause damage there. Microelectronic components and circuits can also be destroyed by electrostatic discharge (Figures 2.2.2 g). False tripping of common ‘residual current circuit breakers’ (RCCB) due to electromagnetic interference at lightning discharge in close sur-roundings can occur. Reports such as: ‘Numerous animals killed because of an indirect lightning strike. In an intensive animal breeding farm 14 000 chickens suffocated as the ventilators failed because of false tripping of a residual current circuit breaker, after an indirect lightning strike’ are not unusual. It must be explained that in intensive chicken breeding farms about 15 000 chickens are reared within six weeks on a surface area of about 1000 m2 _{(Figure 2.2.2 h). During this period,}

the birds are fed automatically. But, besides food and water, the continu-ity of air supply (Figure 2.2.2 i) is of obvious vital importance. If, for example, the ventilation system is shut down by false tripping of the

Figure 2.2.2 a Lightning strike into the administration building of Messrs KHD,

Cologne, 1983

Figure 2.2.2 b Administration building behind the computing centre (Messrs KHD)

Figure 2.2.2 c Computer terminals in the administration building (Messrs

KHD)

Figure 2.2.2 d Computing centre (Messrs KHD)

Figure 2.2.2 e Computer PCB damaged by lightning surge

Figure 2.2.2 f At a lightning strike to building

䊊

1 : Surge damage in buildings

䊊

1 and

䊊

2

Figure 2.2.2 g (a, b) MOS module damaged by electrostatic discharge.

(Source: 3M Deutschland GmbH, Neuss) Figure 2.2.2 g (a)

Figure 2.2.2 g (b)

Figure 2.2.2 h Automatic feeding

Figure 2.2.2 i Ventilator in an intensive animal breeding building

corresponding residual current circuit breaker, the chickens will suffocate within 20 minutes.

In 1987 a defect was to occur in the 20 kV cable network of the town Neumarkt while several switching operations were made. This gave rise to switching surges in the 220/380 V system, leading to flashover with damaging arcs in the reactive-current compensation system of the local abattoir (Figures 2.2.2 j).

There were several instances of damage of up to 70 000 DM each in a combined building services and access control system with about 300 interconnected individual components. In the parts of the building affected, the automatic access control only functioned after several days of repair. In each of these cases the reason was a surge ‘incoupling’ into external components, like code card scanners, due to lightning. All external components of the control system are connected to a central computer by station computers and bus connections. The printed boards of the station computers and bus couplers were thus damaged by the incoupling of the surges (Figures 2.2.2 k, a and b).

A loss of about 100 000 DM occurred as surges damaged the printed boards of a printing press (Figure 2.2.2 l, a), (Figure 2.2.2 l, b). For this production phase this was the only machine available (maximum capacity machine). A longer standstill of production, due to some dif-ficulties in obtaining spare parts for this machine, caused problems in delivery and a great loss of income. The reason for the defective machine

Figure 2.2.2 j (a, b) Reactive current compensation system in a slaughter house

damaged due to switching surges, Neumarkt, 1987

Figure 2.2.2 j (a)

Figure 2.2.2 j (b)

was a cable fault in the 20 kV power supply system, causing surges in the low-voltage system.

Sources

HASSE, P., and PRADE, G.: ‘Das Auslöseverhalten von FI-Schutzschaltern bei Gewittern. de/der elektromeister+ deutsches elektrohandwerk’, 4 (1980), pp. 203–207

Figure 2.2.2 k (a) and (b) Surge damage in a building services control system

Figure 2.2.2 k (a) Figure 2.2.2 k (b)

Damaged interface card Damaged bus coupler

Figure 2.2.2 l (a) Surge damage at a printing press

GUGENBAUER, A.: Blitze–Feuerzauber der Natur. die österreichische feuerwehr (1983) H. 7

HASSE, P.: ‘Überspannungsschutz von Niederspannungsanlagen – Einsatz elektronischer Geräte auch bei direkten Blitzeinschlägen. 3. aktualisierte Auflage’ (Verlag TÜV Rheinland, Köln, 1993)

DAUSEND, A.: ‘Überspannungsschutz als Teil des betrieblichen Risk-Managements’ Teil II: Schadenfälle aus der Praxis. In: HASSE, P. (Ed.): 5. Forum für Versicherer ‘Blitz- und Überspannungsschutz – Massnahmen der EMV’ (Dehn + Söhne, Neumarkt, 1994)

2.2.3 Damage to power supply systems

The public is alarmed sometimes by reports of lightning strikes to power supply systems or even nuclear power stations. In 1983 lightning struck the 110/20 kV transformer substation of the town Neumarkt (Figures

2.2.3 a and b). There was considerable damage to the switching station

and a failure of the 220 V direct voltage control. The 20 kV surge arresters were already damaged by the initial partial lightning strikes (Figure 2.2.3

c) and, thus, the subsequent lightning strikes could no longer be

dis-charged. Sparkover arcs occurred in one switchbay (Figure 2.2.3 d) which ran along the bus bar and damaged other switchbays. Further short-circuit arcs were generated on the 20 kV overhead lines. Heavy conductor rope vibrations made the ropes glow and tear. To add further to the problems, the supplying 110 kV transformer exploded during this thun-derstorm (Figure 2.2.3 e) with the consequence that the whole town of Neumarkt (about 30 000 inhabitants) lost power for about six hours.

Figure 2.2.2.l (b) Damaged module of the printing press control

Figure 2.2.3 a Transformer substation 110/20 kV, OBAG, Neumarkt

Figure 2.2.3 b Site plan of the transformer substation 110/20 kV, OBAG,

Neumarkt

Figure 2.2.3 c Surge arresters destroyed by lightning strike

Figure 2.2.3 d Damage in 20 kV switching bays due to lightning surge

Sources

DER SPIEGEL: ‘Blitz im Atommeiler’ (1983) No. 36, p. 15

NEUMARKTER TAGBLATT: ‘Kurzschluss in Kernkraftwerk’ (22 May 1985)

2.2.4 Damage to a house

Lightning strikes into unearthed aerials of houses (without lightning pro-tection systems), such as the family house in Figure 2.2.4 a, occur fre-quently. Figures 2.2.4 b to h show the damage caused by lightning current

Figure 2.2.3 e Exploded 110 kV transformer due to lightning strike, Neumarkt, 1983

on its path of sparkovers and punctures through the electrical wiring of the house. The lightning current flows over the aerial standpipe (Figure 2.2.4 b), feeding partial lightning currents into the power system, aerial line, telephone line and water pipe. So, usually, all connected electrical appliances and the telephone system will be damaged. In the case men-tioned, the fuel oil pipe was also damaged, and oil leaked into the cellar. In a circle of radius more than 1 km, telephone systems failed due to this lightning strike; the traffic-light systems of the town were also disturbed and RC circuit breakers were tripped within a radius of about 3 km.

Figure 2.2.4 a Site plan of a house damaged by lightning, Neumarkt, 1986

Figure 2.2.4 b Damage near the antenna-pole in the loft, Neumarkt, 1986

In 1994, during a thunderstorm burst, the radio aerial of a central taxi station in Neumarkt was struck by lightning (Figure 2.2.4 i). The whole radio system was destroyed (Figure 2.2.4 j). The electrical cables and socket outlets were torn out of the walls and the entire electrical equip-ment (TV and household appliances) was damaged so heavily that it could no longer be used.

Figure 2.2.4 d Antenna line damaged by lightning strike

(a) Neumarkt 1986 (b) Similar case

Figure 2.2.4 c Punctures to concealed cables due to lightning strike

(a) Neumarkt 1986 (b) Similar case

Figure 2.2.4 e Distribution cabinets damaged by lightning strike (b) Similar case (c) Similar case (a) Neumarkt 1986

Figure 2.2.4 f Boiler damaged by lightning strike, Neumarkt, 1986

Figure 2.2.4 h Puncture from the

power line to the metal oil pipe due to lightning strike, Neumarkt, 1986

Figure 2.2.4 i (a, b) Lightning strike to the Lutter taxi central office, Neumarkt,

1994

Figure 2.2.4 g Telephone

system damaged by lightning strike, Neumarkt, 1986

Figure 2.2.4 i (a)

Figure 2.2.4 i (b)

A pressure wave smashed windows and window frames. Tiles were torn off the wall and there were cracks in the ceilings and the walls. Socket outlets were torn out of the wall (Figure 2.2.4 k). Partial lightning cur-rents were conducted along the telephone system and the power supply system, thus causing other damage in the neighbourhood (Figure 2.2.4 l). In the vicinity and wider surroundings this lightning strike caused considerably more damage than listed here. In the office of the District President, the district hospital, the inferior court, the municipal works and the abattoir, as well as in industrial and commercial enterprises, the computer systems and telephones were damaged. In the district hospital, a church, an elementary school and a museum, the safety and fire alarm systems were damaged (Table 2.2.4 a). In Figure 2.2.4 m, circles are drawn, at a separation of 1 km, around the lightning striking point (marked by an arrow). The locations of the damage are marked by bullets. Damage occurred, even at a distance of 3 km from the point of strike, for example, in the traffic-light system at the southern perimeter road of the town. The Neumarkter Nachrichten duly reported on the damage caused to telephone and cable television connections in 40 households and numerous individual TV sets.

Repeatedly, there are extended disturbances in telecommunication sectors due to solitary lightning strikes. The Hamburger Abendblatt of 12 July 1995 reported on a thunderstorm two days previously when 25 000 Telecom customers in the suburbs of Hamburg were concerned by failures of cable TV. Some 50 microchip amplifiers had to be repaired in Pinneberg, Wedel, Quickborn and Norderstedt. Underground cables damaged by lightning currents reveal high interference energies.

Figure 2.2.4 j Damaged radio system Figure 2.2.4 k Damaged

electrical lines

The reason for the above examples of damage is that electrical light-ning interferences are conducted through power and data lines from the point of strike over distances of several kilometres directly to the inputs of electronic systems and equipment (Figures 2.1 c and 2.2.4 n). Tele-phone systems, for example, are used in data processing and alarm systems, making them susceptible.

Sources

NEUMARKTER NACHRICHTEN: ‘Blitzschlag zerfetzte Leitungen und hob den Dachstuhl’ (2–3 Aug.1986)

NEUMARKTER NACHRICHTEN: ‘Unheil mit einzigem Blitzschlag’ (3 May 1994)

HAMBURGER ABENDBLATT: ‘Kabelfernsehen: Vom Blitz getroffen’ No. 160 (12 July 1995)

Figure 2.2.4 l Lightning damage (at Telekom systems) in the surroundings of

the point of strike

Table 2.2.4 a Consequences of a lightning strike to the Lutter Taxi Company Neumarkt, 1994

Table 2.2.4 a continued –

Figure 2.2.4 m Lightning damage in a radius of 3 km around the point of strike

2.2.5 Damage to aircraft and airports

The following report from the Kölnischen Rundschau of 12 November, 1987, for example, describes the damage due to a lightning strike to an airliner:

“Immediately after take-off, the Boeing 747 flying to Newark (New Jersey) entered a thunderstorm zone. Within a few minutes, four lightning discharges struck the plane with 225 passengers and 18 crew members on board. Autopilot, weather radar and the radio connection to the tower were knocked out. Also the manual control of the elevator was damaged so strongly that the pilot and copilot had to use their whole strength to keep the Jumbo flying. A British Airways jet flying in the same space followed the distress call of the struck Boeing and piloted it on the correct glide path to the emergency landing. After touchdown, Captain Richards – a former Phantom fighter pilot and Vietnam veteran – stated that the braking thrust reversal of the four engines had also failed. Only the landing gear brakes still worked. The plane was brought to a standstill a few metres before the end of the runway. Later, in the Continental repair hangar, more than a hundred instances of fire damage to the shell and wings of the Jumbo were counted. Parts of the tail fin were missing. Chief pilot Fred Abbott told: ‘I never saw a plane that was damaged so heavily by lightning.’ ”

There are reports from the Public Information section of the German Federal Ministry of Defence in January 1986 of an electrostatic accident involving a rocket:

“The fire accident with a Pershing II motor stage happened on 11 January 1985 on the Waldheide near Heilbronn. During this accident, three members of the US Army were killed, nine were injured. The accident investigation was finished by the American investigation committee in December 1985. It confirms the

Figure 2.2.4 n Dangerous surges in neighbouring buildings

Figure 2.2.5 a Newspaper reports concerning lightning strikes to planes, the control tower of the Frankfort/Main airport, the Changi airport (Singapore) and the Düsseldorf airport

statement of the first accident report of 15 April 1985, that a discharge of static electricity was the reason for the accident . . .” [The results are then elaborated] From the evidence supplied, the report of 15 April 1985 concludes that a dis-charge of static electricity caused a spark disdis-charge in the propelling dis-charge of the motor stage, which was the cause for the fire accident.

On 14 November 1964 the space ship Apollo 12 and then the Saturn V rocket were struck by lightning 36 seconds after lift-off from Cape Canav-eral. The space ship was about 2 000 m above ground when a lightning strike between the rocket and the launching platform on the ground was noticed. The crew registered disturbances of the energy supply, a number of other electrical disturbances and the response of some safety switches. On 26 March 1987, a 78 million dollar Atlas Centaur rocket went out of control 51 seconds after its launch from Cape Canaveral and had to be destroyed over the Atlantic together with its freight, an 83 million dollar Pentagon satellite. The reason for the loss of control was a lightning strike to the nose of the rocket. A piece of fibreglass from the wreck revealed a carbonized hole, having a diameter of about 5 cm, which was very similar to the holes registered after lightning strikes to airplanes. Owing to the strike, the main computer gave false commands to the driving engines so that the rocket’s trajectory failed and it had to be destroyed.

A lightning strike tripped the ignition mechanisms of three small research rockets on 10 June 1987 which were ready for launch at the NASA base on Wallops island, offshore Virginia. On board the rockets were measuring devices for thunderstorm research. The rockets had a common earthing system. According to eyewitness reports, they lifted off ‘simultaneously’ as lightning struck. After a short flight, they fell into the Atlantic without causing any damage.

Newpaper reports about lightning strikes to passenger planes and con-trol towers at airports (Figure 2.2.5 a) show that the hazard can extend beyond the immediate system that is damaged.

Sources

DOLOMITEN: ‘Blitzeinschläge in Flugzeuge’ No. 230 (2–3 Oct. 1993) SONNTAG AKTUELL, STUTTGART: ‘Ein Blitz zerschlug die Radarnase des Airbus – Passagiere wohlauf’ (3 Oct. 1993)

BLITZSCHLAG IN CHANGI AIRPORT/SINGAPUR (summer 1995)

2.2.6 Damage to wind power stations

The lightning protection of wind power stations is of current and future importance in Britain, Germany and other European countries. Light-ning damage, especially to rotor blades (Figure 2.2.6 a), greatly exceeds

what is expected, both in frequency and height. Cases are known where insurance companies see no possibility of further insurance after a single lightning strike, that is, until the operator or the producer provides an adequate lightning protection system (Figure 2.2.6 b).

2.2.7 Catastrophic damage

At the 21st International Conference on Lightning Protection (ICLP), S. Lundquist described an especially intense lightning storm in Skane, Southern Sweden, on 1 July 1988. The fire brigade in the town of Lund recorded 1400 alarms. There was a breakdown of the telephone exchange and the mobile police radio was damaged. As an example of many similar life-endangering cases, the situation in the municipal hospital was described. As the 130 kV system failed due to the lightning strike, the hospital was deprived of power for 80 minutes. The lights went out, elevators stopped and the appliances in the intensive care unit could not work. The emergency power generator refused to start because the con-trol computer was damaged; because of the failure of the telephone and the central fire alarm, the technical staff could not be called. When they had managed to start the emergency power generator by hand after half an hour, it failed shortly afterwards due to overheating as the ventilator was supplied by the unfused system. There was serious damage also to the low-voltage mains distribution, the control room and the computer terminals. This episode was particularly horrendous.

The consequences of lightning strikes into tall or extended buildings become apparent from events reported from all over the world. Light-ning strikes into large-scale buildings, such as office buildings and department stores, cause current failures resulting in: stoppage of full elevators, breakdown of the lighting, tripping of sprinkler systems, flooding of rooms by protective gas, blocking of electronically secured

Figure 2.2.6 a Lightning damage to the rotor blade of a wind power generator

doors and garage doors, failure of air-conditioning systems as well as breakdown of the telephone network (Figure 2.2.7 a) and the control systems. Failures of this kind can lead to life-endangering situations and, not least, panic.

What characterizes disturbances and failures due to a lightning strike in a building is that safety-relevant systems may be involved at the same time, as well as the infrastructure over a wide area that may also be dis-turbed. During a thunderstorm with spatial and temporal distribution of lightning, vast damage to vital infrastructure is possible. Catastrophic events, as described by some examples, should not be tolerated. There-fore, precautions must be taken to avoid personal danger. Safety must be

Figure 2.2.6 b Report from the Stuttgarter Zeitung, 25 March 1995

guaranteed for the power and information technology systems that are absolutely necessary for vital infrastructure in special situations. These include: airports, public transport, traffic guide and signal systems, hospitals, power stations, above all nuclear power stations and switching plants, high-power transmitters, signal and alarm systems for civil pro-tection, meeting places, schools, kindergardens and mass sports facilities, office and computing centres, buildings with extended safety systems, systems for large-scale supervision of pollutants (including radioactivity) in the air, water and ground, control and alarm systems for defence purposes, telephone exchanges and satellite and relay stations.

Sources

LUNDQUIST St.: ‘Effects on the society of an intense lightning storm’, Tagungsband 21. Internationale Blitzschutzkonferenz (ICLP), Berlin (22–25 Sept. 1992)

THÜRINGER ALLGEMEINE: ‘Ein Blitz legte Telefone “tot” ’ (29 June 1994) HASSE, P., and WIESINGER, J.: ‘Can you avoid disasters caused by light-ning?’ DEHN Publication No. SD 261E, reprint from etz, 1993, 2, pp. 154–156

Figure 2.2.7 a Lightning strike causes collapse of the telephone network

(Source: Thüringer Allgemeine, 29 June 1994)

Chapter 3

Origin and e

ffect of surges

Electromagnetic compatibility (EMC) engineering usually proceeds from an interference model consisting of a source of interference (trans-mitter), a coupling mechanism (path) and a potentially susceptible equipment (receiver) (Figure 3 a).

Electrical systems with electronic devices as potentially susceptible equipment are endangered by conducted interferences and interfering radiation (Figure 3 b) from the following six sources of interference:

(i) Direct and close-up lightning discharges

Lightning electromagnetic impulse (LEMP): predominantly conducted interference such as lightning currents and partial lightning currents, potential increase of the struck system as well as interfering radiation. (ii) Power technical switching operations

Switching electromagnetic impulse (SEMP): predominantly conducted interference as well as magnetic interfering radiation.

(iii) Power technical system perturbation

Predominantly conducted interference with voltage distortions. (iv) Electrostatic discharges

(ESD): predominantly conducted interference by spark discharge. (v) Low and high frequency transmitters

Resulting in continuous interfering radiation.

(vi) Nuclear explosions

Nuclear electromagnetic impulse (NEMP): with a resulting impulse-shaped interfering radiation.

The coupling between the source of interference and potentially suscep-tible equipment can be realized by either conduction and/or radiation (electric field, magnetic field or electromagnetic field). The coupling path can be described in the equivalent circuit diagram by combinations of resistances and/or capacitances and/or inductances.

Potentially susceptible equipment includes telecommunications engin-eering systems (i.e. electrical systems with electronic equipment and facili-ties). In lightning protection engineering, structural facilities, such as meeting places and areas with fire and explosion hazards, are considered to contain potentially susceptible equipment in the sense of EMC. Such potentially susceptible equipment is found in (i) commercial areas (e.g., industry, trade, commerce, agriculture, banks and insurance buildings), (ii) public areas (e.g., hospitals, meeting places, air traffic control facili-ties, museums, churches and sports facilities), and (iii) private areas.

In the following Sections, lightning discharges and switching opera-tions as sources of interference are described according to their priority.

Sources

DIN EN 61000 series. ‘Electromagnetic compatibility (EMC)’.

Figure 3 b Electronic system endangered by radiation and conducted

interference

3.1 Atmospheric overvoltages

Lightning, as a source of interference, affects buildings and indoor elec-trical equipment and systems.

Surges of atmospheric origin (Figure 3.1 a) are basically due to either a direct-/close-up strike or a remote strike. In the case of a direct strike (Figure 3.1 a, case

䊊

1 ), lightning strikes the protected building; but in the case of a close-up strike, lightning strikes an extended system or a line (e.g., a pipeline, data or power transmission line) leading directly into the protected system. However, in the case of a remote strike (Figure 3.1 a, case

䊊

2 ), for example, the overhead line is struck. ‘Reflected surges’ (travelling waves) are produced in transmission lines by cloud-to-cloud lightning, and overvoltages are induced by lightning in the surrounding area.

3.1.1 Direct and close-up strikes

Lightning current in a lightning channel and in the lines of the lightning protection system (a) causes a voltage drop at the impulse earth resist-ance of the earthing system (

䊊

1a in Figure 3.1 a) and (b) induces surge voltages and currents in loops formed by installation lines inside the structure (

䊊

1b in Figure 3.1 a). Owing to the voltage drop at the impulse earth resistance, partial lightning currents also will be discharged by the supply lines that have been connected as a measure of lightning pro-tection equipotential bonding.

A lightning strike in the surrounding area causes induced surge vol-tages and thus surge currents in installation loops especially due to its magnetic interfering radiation. If lightning strikes a feeding overhead

Figure 3.1 a Reasons for surges at lightning discharges

line, there will be conducted surge voltages and currents on the incoming power line. Lightning between thunderstorm cells in clouds generates conducted surge voltages and currents on power lines and on other wide-ranging line systems due to interfering electromagnetic radiation.

The parameters of lightning current components (first partial light-ning surge current, subsequent lightlight-ning surge current and lightlight-ning long duration current) are specified in the following standards: VG 95371 in accordance with IEC 61024-1, DIN V ENV 61024-1 (VDE 0185 Part 100), IEC 61312-1 and DIN VDE 0185 Part 103 (Figure 3.1.1 a). Here three protection levels are specified in accordance with IEC, or two degrees of danger in accordance with VG (Table 3.1.1 a).

If an exact analysis is not possible or justified because of the expense, the partial lightning currents on supply lines coming from a struck building can be estimated in accordance with IEC 61312-1 and DIN

Figure 3.1.1 a Lightning current components (protection level I acc. to IEC

61024-1/ENV 61024-1 or degree of danger ‘high’ acc. to VG 96901

Table 3.1.1 a Lightning current parameters

VDE 0185 Part 103. As shown in Figure 3.1.1 b, it is assumed that 50% of the lightning current flows into the earthing system of the structure and 50% is distributed equally to the outgoing remote-earthed supply systems (e.g., piping, power and communication lines). To make things less complicated one assumes that the partial lightning currents in every supply system will be distributed equally to the different conductors (e.g., L1, L2, L3, and PEN of a power technical cable or four wires of a data line).

In DIN V ENV 61024-1 (VDE V 0185 Part 100) annex C there is a method to estimate the lightning partial currents discharged by the incoming lines (for the case when lightning strikes the protected system). Hence, the lightning current will be distributed to the earthing system, the external conductive parts and the incoming lines (which are con-nected directly or by arresters) now as follows:

The share It of lightning current on every external conductive part and

every line depends on their number, their equivalent earth resistance and the equivalent earth resistance of the earthing system:

It=

Z× I

nt× Z + Zt

where Z is the equivalent earth resistance of the earthing system, Zt is

the earth resistance of the external conductive parts or lines, nt is the

total number of the external conductive parts or lines and I is the light-ning current according to the protection level.

If electrical or information technology (IT) lines are not shielded or laid in metal conduits, every conductor carries a partial current accord-ing to It/n′ where n′ is the total number of conductors in these lines (Table

3.1.1 b).

Figure 3.1.1 b Estimation of the partial lightning currents on supply systems

(acc. to IEC 61312-1; VDE 0185 Part 103)

Sources

VG 95 371-2: ‘Elektromagnetische Verträglichkeit (EMV) einschliesslich Schutz gegen den elektromagnetischen Impuls (EMP) und Blitz’; Allgemeine Grundlagen; Begriffe (Beuth Verlag, GmbH, Berlin), March 1994

IEC 61024-1: ‘Protection of structures against lightning. Part 1: General prin-ciples’. International Electrotechnical Commission, Geneva CH-1211, March 1990

DIN V ENV 61024-1 (VDE V 0185 Teil 100): ‘Blitzschutz baulicher Anlagen. Teil 1: Allgemeine Grundsätze’ (VDE Verlag, GmbH, Berlin/Offenbach), Aug. 1996

IEC 61312-1: 1995-02: ‘Protection against lightning electromagnetic impulse. Part 1: General principles’. Central de la Commission Electrotech-nique Internationale. Geneva CH-1211, Feb.1995

DIN VDE 0185 Teil 103: ‘Schutz gegen elektromagnetischen Blitzimpuls. Teil 1: Allgemeine Grundsätze’. (IEC 1312-1: 1995, modifiziert,) (VDE Verlag, GmbH, Berlin/Offenbach) Sept. 1997

3.1.1.1 Voltage drop at the impulse earthing resistance

The maximum voltage drop û_E arising at the impulse earthing resistance

Rst of the affected building is calculated in terms of the maximum value î

of lightning current (Figure 3.1.1.1 a):

ûE= îRst

This voltage drop ûE, however, is not dangerous for the protected system,

if the lightning protection equipotential bonding has been installed effectively. National as well as international lightning protection stand-ards presently call for a comprehensive lightning protection

equipoten-Table 3.1.1 b Equivalent earthing resistances Z and Z1 depending on the earth

resistivity

tial bonding, where all lines (incoming or outgoing) are connected dir-ectly or by spark gaps or surge protective devices to the earthing system. In the event of a lightning strike, the potential of the whole system will rise by ûE , but, within the system, there will be no dangerous differences.

3.1.1.2 Induced voltages in metal loops

The maximum rate of lightning current rise, Δi/Δt, effective during the period Δt, determines the peak values of electromagnetically induced voltages in all open or closed installation loops which are in the vicinity of conductors carrying lightning current.

The magnetically induced square-wave voltage, U, in a metal loop during a period of Δt is given by (Figure 3.1.1.2 a):

U= M

冢

Δi

Δt

冣

where U is in V, M is the mutual inductance of the loop in H and Δi/Δt the current rate of rise in A/s.

For the sizing of lightning protection systems, the maximum values of the average front current rate of rise I/T1, effective during the front time

T1 , of Table 3.1.1 a can be used.

To estimate what maximum induced square-wave voltages, U, have to be taken into account in installation loops (e.g., in a building) it is assumed that the loops are in the vicinity of infinitely extended, lightning current-carrying down conductors.

For the square-wave voltage of a square loop formed by an infinitely wide lightning current-conducting line and an installation line (e.g., the protective conductor of the electrical installation, which is connected to

Figure 3.1.1.1 a Potential increase compared with the distant earth by the peak

value of the lightning current

the down conductor of the lightning protection system at the equipoten-tial bonding bar), the following is applicable:

U= M1

冢

Δi Δt

冣

where U is in kV, M1 is the mutual inductance of the loop in μH and Δi/

Δt the current change in the lightning current conducting line in kA/μs.

M1 depends on the side length a of the loop and the cross section q of

the lightning current conducting line. This can be taken from Figure

3.1.1.2 b. According to the requirements, Δi/Δt = I/T1 can be taken from

Table 3.1.1 a (Figure 3.1.1.2 c).

For a square loop, formed by an installation line which is insulated from an infinitely wide lightning current conducting line, the following is applicable for the square-wave voltage:

U= M2

冢

Δi Δt

冣

where U is in kV, M2 is the mutual inductance of the loop in μH and Δi/

Δt the current change in the lightning current conducting line in kA/μs.

M2 depends on the side length of the loop a and the distance s between

the loop and the lightning current conducting line. This can be taken from Figure 3.1.1.2 d. Δi/Δt = I/T1 is taken from Table 3.1.1 a, according

to the requirements (Figure 3.1.1.2 e).

Apart from the induced effects in wide loops, which are due to installa-tion configurainstalla-tions, the induced effects in very small elongated loops formed by parallel wires of unshielded, layer-wise stranded, cables in the surroundings of lightning current conducting lines are also of interest. Induced voltages arising between the wires are called ‘transverse

volt-Figure 3.1.1.2 a Induced square-wave voltages in loops by the rate of rise Δi/Δt

of the lightning current

ages’. They can be harmful especially to electronic equipment. For a small elongated loop formed by the wires of an installation line and run in parallel to an infinitely wide lightning current conducting line, the following is applicable for the square-wave voltage:

U= M′3 l

冢

Δi Δt

冣

where U is in V, M′3 is the wire length-related mutual inductance of the

loop in nH/m, l is the length of the installation line in m and Δi/Δt the current change in the lightning current conducting line in kA/μs. M′3

depends on the distance of the wires b, and on the distance s between the installation line and the lightning current conducting line. This can be

Figure 3.1.1.2 b Mutual inductance M1 to calculate the square-wave voltages in

square loops, formed by lightning current-carrying conductor and installation line

Figure 3.1.1.2 c Example

taken from Figure 3.1.1 2 f. Δi/Δt = I/T1 is to be taken from Table 3.1.1 a,

according to the requirements (Figure 3.1.1.2 g).

For a small elongated loop, formed by the wires of an installation line and run in a distance vertically to an infinitely wide lightning current conducting line, the square-wave voltage is given by:

U= M′4 b

冢

Δi Δt

冣

where U is in V, M′4 is the wire-distance-related mutual inductance of

the loop in nH/mm, b is the wire distance in mm and Δi/Δt the current change in the lightning current conducting line in kA/μs. M′4 depends on

the line length l and the distance s between the installation line and the lightning current conducting line. This can be taken from Figure 3.1.1. 2

h. Δi/Δt = I/T1 is to be taken from Table 3.1.1 a, according to the

requirements (Figure 3.1.1.2 i).

In contrast to the high voltage values in the case of wide loops, there are only induced voltages up to about 100 V in small, elongated loops. But, keep in mind that these are transverse voltages on information technology lines, which are operated by nominal voltages in the range 1–10 V and which are connected to surge-sensitive electronic equipment. In the case of lines with twisted wires and especially in the case of electromagnetically shielded lines, the induced square-wave voltages will be very much reduced compared to the values calculated according to the above equations and the transverse voltage values are usually not dangerous.

Figure 3.1.1.2 d Mutual inductance M2 to calculate the square-wave voltages in

square loops, formed by installation line (an equipotential bonding line, between the loop and the lightning

current-carrying conductor, does not have any influence on M2).

Figure 3.1.1.2 e Example

Figure 3.1.1.2 f Mutual inductance M′₃ to calculate the square-wave voltages in

two-wire lines (an equipotential bonding line, between the loop and the lightning current-carrying conductor, does not have any

influence on M′3).

Figure 3.1.1.2 g Example

If a metal loop is short-circuited or its insulating distance punctured due to the induced square-wave voltage U, an induced current iiflows in

the loop for which the following equation is applicable:

dii dt+ 1 πii= M L

冢

di dt

冣

with τ = L R

where t is the time in s, τ is the time constant of the loop in s, R is the ohmic resistance of the loop in Ω, L is the self-inductance of the loop in

Figure 3.1.1.2 h Mutual inductance M′4 to calculate the square-wave voltages in

two-wire lines (an equipotential bonding line, between the loop and the lightning current-carrying conductor, does not have any

influence on M′4).

Figure 3.1.1.2 i Example

H, M is the mutual inductance of the loop in H and i the lightning current in the lightning current conducting line in A.

Formulas and examples to calculate the self-inductance L are indi-cated in the ‘Handbuch für Blitzschutz und Erdung’.

In the vicinity of the lightning channel or the lightning current conducting lines, rapidly changing magnetic fields will arise due to the extreme rate of increase of the lightning current. Surges of up to 100 000 V are generated by these fields within the building in wide ‘induc-tion loops’ formed by the effects of installa‘induc-tion lines, such as power and information technology lines, water and gas pipings.

Figure 3.1.1.2 j, for example, shows a computer connected to the power

and the data system. The data cable is duly connected to the equipoten-tial bonding bar after entering the building; then the cable goes through the data socket outlet into the computer. The power cable is also con-nected to the equipotential bonding bar by lightning current arresters and supplies the computer through the power socket outlet. As the power and the data cable are independently installed lines, they can form an induction loop including a surface of 100 m2_{. The open ends of this loop}

are in the computer; here the surge, magnetically induced into the loop, becomes effective. Not only in the case of direct lightning strikes, but also in the case of strikes in closer proximity, surges of such intensity can be induced into the loop, causing punctures in the equipment or sometimes even fire.

The computer must be protected from these lightning surges ‘on the scene’, meaning at the equipment itself or directly at its power and data socket outlets (Section 5.8.2.3).

Figure 3.1.1.2 j Electronic equipment endangered by induced lightning

overvoltages

Sources

HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’ (Pflaum Verlag München; VDE Verlag, Berlin; 4th edn, 1993)

3.1.2 Remote strikes

In the case of remote strikes, travelling surges either propagate along the lines (

䊊

2a and

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2b in Figure 3.1 a), or lightning strikes (

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2c in Figure 3.1 a) in the vicinity of the protected systems, thereby generating electro-magnetic fields which affect the system.

In particular, damage due to surges of atmospheric origin in the 1990s has shown that electronic installations, up to a distance of about 2 km from the lightning point of strike, are susceptible to induced or conducted surges and surge currents (Section 2.1). This wide area of danger is due to the increasing sensitivity of high-technology equipment to cables extending beyond the building and the growth in the use of sensitive networks.

The maximum permissible length of data transmission lines connect-ing equipment has increased dramatically with advances in technol-ogy. For example, the interface V.24/V.28 (which was introduced during the advent of electronic data processing techniques) specifies the elec-trical characteristics of line drivers permitting a direct bonding up to about 15 m cable length. Today, however, there are line drivers and inter-faces available on the market which allow a direct bonding over twisted twin-core cables up to a length of about 1000 m!

When lightning partial currents flow in cables they generate longi-tudinal and transverse voltages (Figure 3.1.2 a).The longilongi-tudinal voltage

Figure 3.1.2 a Surges in a cable

ul generated between the wire and the metal cable shield creates stress

on the insulation of the connected device between its input terminals and the earthed enclosure. The transverse voltage uq is established between

the wires and this exerts pressure on the input circuit of the connected device. If the lightning partial current î2 is known, the longitudinal

voltage ûl can be calculated from the cable coupling resistance Rk (Table

3.1.2 a).

3.1.3 Coupling of surge currents on signal lines

The following examples will demonstrate how surge currents can be coupled ohmically, inductively and capacitively onto the signal lines of extended systems. Consider the arrangement with device 1 in building 1 and device 2 in building 2. The devices are interconnected by a signal line. Furthermore, we will assume that both devices are connected to the

Table 3.1.2 a Coupling resistances at lightning currents