Selection and Application of Lightning Protection Device in the Indoor Information System

Selection and Application of Lightning Protection Device in the Indoor Information System Lightning protection laboratory of signal and communication research institute academy of railway sciences Researcher: QIU Chuan-rui Abstract: This article provides us information about selections and installments of SPD in low voltage power system of standards of International Electro-technical Electro-technical   Commission (IEC), American Standards (AS), Britain standards, Australian Standards and so on and discusses differences between partial standards at present in our country and above-mentioned standards, which arouse aro use colleges‘ interests towards these differences differences research. 1 Preface Indoor information system for lightning protection devices are divided into two parts, lightning protection devices connected with power cable and lightning protection devices connected with signal lines (signal lines‘ is defined as circuits transmitting information, including analog telecommunication lines and data transmitting line and radio antenna and feed lines and so on), that is, lightning protection of Surge Protective Device of electricity and electrical equipments. We We must consider the following factors in selecting SPD for electricity and electrical devices. 1.1 In choosing Surge Protective Device for power equipments, we also consider the following factors except  parameters of nominal nominal discharge current current (In) of SPD, maximum maximum continuous operating voltage (Uc) a)

Installment location of SPD---- different installation location categories should choose different nominal discharge current (In) of SPD, according to coordination principles of SPD.

 b) Level of voltage protection (Up) of SPD----According to coordination principles of SPD and the rated impulse withstand level of protected devices, we should select different voltage protection level (Up) of SPD. c)

The rated impulse withstand withstand voltage level level (Uw) of protected protected equipments ----Selection ----Selection of

different voltage

 protection level of SPD SPD ,according to the rated rated impulse withstand voltage levels of protected devices, devices, can not only reach coordination of SPD, but also reach achieve consummate insulation coordination. 1.2 In selecting SPD for electrical devices, we also have to consider following factors except that we must consider  parameters of SPD for telecommunication and signal web‘s nominal discharge current (In), maximum continuous operating voltage (Uc) and so on (standards at home and abroad called SPD for telecommunication and signal web-net as web-net  as protectors, while scientific terms in the national standards and scientific and technical department call it  protector). a)

The voltage protective level (Up) of protectors ----we select appropriate protectors according to withstand overvoltage capacity of protected electrical devices (the rated impulse withstand voltage level(U w)

 b)

Transmitting frequency f G of protected devices (analog equipments) or data transmitting speed (digital equipments) ---- selected protectors should be within the scope of transmitting frequency f G  or data transferring speed of protected devices (bit/s), inserting losses (a e) of protectors should be not sure to be equal with requests of concerned standards towards system insertion losses.

c) The peculiar impedance of protected equipments of circuit ports ---- peculiar impedances of protectors should  be in accordance with the peculiar impedance of ports of protected devices which avoid producing signal‘s refraction and reflection after protectors involve in circuits. This article only discusses primarily and deletes relevant parts of protectors for telecommunication telecommunication system due to great divergences of selection and application of SPD in low-voltage power supply system at home. 2. Discourses about sources and types of damages to a structure 2.1 Discourses on sources and types of damages to a structure of IEC standards

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Lightning may bring about damages towards constructions and all things within constructions. International electro-technical commission(IEC) 52305-1standards point out that the lightning current is the source of damage(reference: PROTECTION AGAINST LIGHTNING  – Part Part 1: General principles originalities 5.1.2 、 P15).Lightning affecting a structure can cause damage to the structure itself and to its occupants and contents, including failure of internal systems he damages and failures may also extend to the surroundings of the structure and even involve the local environment. The scale of this extension depends on the characteristics of the structure and on the characteristics of the lightning flash. The influence of lightning on constructions may lead to three basic sorts of damage: D1: injuries of living beings due to touch and step voltages---this voltages--- this is the influence on humans. D2 lightning current‘s effect, including physical damages (fire, exploration, mechanical destruction, chemical release) due to lightning current effects including sparking---this is the influence on objects and non-electricity. D3: failure of internal systems due to Lightning Electromagnetic Impulse (LEMP). This is the influence on objects and electricity. Therefore, the influence of lightning on constructions can be divided into influence on humans and on objects. The influence on humans refers to damages on human bodies due to the touch voltage and step voltage that coupling with resistivity and inductivity while influence on objects refers to damages of the construction itself and damages of public facilities connecting with constructions. However, these damages are also divided into influence on electricity and electrical equipments and influence on nonelectrical equipments. Influence on nonelectrical devices includes blazing lightning arc itself or resistance thermal(overheat conductors)produced by lightning current in the conductors and immediate physical damage, fire, and or explosion caused by discharges of erosive ARC (molten mental); coupling resistivity and inductivities and fire and or explosion induced by overvoltage flashes at the partial lightning current channels; the influence on electricity and electrical equipments is the failure of internal systems and abnormal operation due to Lightning Electromagnetic Pulse (LEMP).Electromagnetic compatibility can be defined as capabilities that equipments or systems can work normally in the electromagnetic condition and can‘t  produce too electromagnetic interference towards anything of circumstance. However, only lightning protection of electricity and electrical equipments can be linked with Electromagnetic  Electromagnetic   Comp-abilities. Comp-abilities. Typical modes of Electromagnetic Electromagnetic   Compatibility comprise of source of interference (here it refers to the Lightning Electromagnetic Impulse), coupling mechanism (here it refers to lightning on incoming channels), potentially susceptible equipment (here it refers to the electricity and electrical equipments). Lightning electromagnetic impulse protection for electricity and electrical equipments conforms to definitions and typical modes of the electromagnetic compatibility. compatibility. IEC62305-1 lists four kinds of sources and types of damages to a structure depending on the position of the point of strike relative to the structure considered. S1: flashes to the structure S2: flashes near the structure, S3: flashes to the services connected to the structure, S4: flashes near the services connected to the structure. Flashes of S1and S3 are faced with constructions, so it can be understood as flashes to the structure while S2 and S4 all have implications of‖ flashes near the…‖ and it refers to flashes near the structure. It refers to lightning flash near the structure towards ground construction connecting with services. Lightning flashes between thunderstorm cells in clouds and discharge  between the two charge charge centers in lightning. What‘s meaning meaning of lightning flashes near the structure of IEC? IEC 61312-1: Mr. Hasse, chief editor, has said in the 3.1th chapter‖ Atmosphere Overvoltage ―o f his writing OVERVOLTAGE PROTECTION IN THE LOW VOLT VOLTAGE SYSTERM SYSTERM in 1995 that surges surges of atmospheric atmospheric origin are

basically due to either a direct lightning

strike, close-up lightning strike or a remote lightning strike. In the case of a direct strike, 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, for example, the overhead line is struck.‖Reflected surges‖  (traveling waves) are produced in transmission lines by cloud-to-cloud lightning, and overvoltage is induced by lightning in the surrounding area. He said, in the 3.1.1

2

th

―Direct Lightning Strike and Close-up Lightning Strike‖ Strike‖ ,  , Lightning between thunderstorm cells in clouds generates conducted surge voltages and currents on power lines and on other wide-ranging line system due to interfering electromagnetic radiation. In the two passages, the first passage discusses reflected surges are produced in transmission lines by cloud-to-cloud lightning, the second passage discusses surges are produced in power lines or other wide-ranging circuit by lightning flashes between thunderstorm cells in clouds. 2.2 Discourses about sources and types of damage to a structure in other international standards Lightning flashes in the research of LEMP has also cloud-to-cloud lightning flashes besides lightning flash to earth. The cloud-to-cloud lightning flashes are not called as lighting stroke according to the definition of lighting stroke. As a matter of fact, all standards, whether IEC standards, Britain Standard, France Standard, Australian Standard, Canadian Standard or not,

believes that lighting sources sources and types of damages damages to a structure for

electricity and electrical devices includes flashes to earth, cloud-to-cloud lighting and flashes between thunderstorm cells in

clouds and makes makes specific definitions towards lighting stroke. Lightning stroke refers to single electrical electrical

discharge in a lightning flash to earth. (Reference: IEC 3.1 62305-1 P9; 3.1.1 6651-1999 BS P1; 1.5.31 1768-2005 AS) In describing sources and types of damages to a structure for telecommunication devices, International Telecommunication Union ITU-K K11 Overvoltage and Over-current protection principles recommend as follows: 1.1.1Direct lightning strikes: Such strikes may cause currents of some thousands of amperes to flow along wires or cables for some microseconds. Physical damage may occur and overvoltage surges of many kilovolts may apply stress to the dielectrics of line plant and terminal equipments.1.1.2 Close-up lightning strikes: Lightning currents flowing from cloud to earth or cloud to cloud cause overvoltage in overhead or underground lines near to the strike. The area affected may be large in districts of high earth resistivity. ITU points out lightning sources and types of damages to a structure for telecommunication system has direct lightning and close-up lightning strikes on circuits or terminal devices, however, however, close-up lightning strikes includes lightning flash to earth and cloud-to-cloud lightning. 2.3 Conclusions of sources and types of damages to a structure ITU and IEC don‘t consider these th ese four kinds of categories of S1, S2, S3 and S4 all indicate direct lightning (flashes), not included lightning flashes between thunderstorm cells in clouds and flashes between thunderstorms among clouds. The first picture is from the third chapter ―atmospheric overvoltage‖ of Mr. Hasse‘s writings Low-voltage Overvoltage Protection System, which explains reasons of lighting surge. In the picture illustration of 2b shows that cloud-to-cloud lightning is also one of main reasons of surge due to lightning discharges. In the picture surge inducing from lightning flashes includes electrostatic induce and magnetic induce and disseminate with travelling wave to the two directions, which is a way of devices stricken by thunder and lightning. Nearly all writings on explanations of power line stricken by lightning and telephone line mechanism all refer to influence of cloud-to-cloud lightning on power lines and telecommunication lines. Drawn in the first picture is middle-voltage power line. As a matter of fact, telecommunication lines strike by lighting electromagnetic electromagnetic impulse waves caused by flashes is frequent. Mr. Hasse said in his writing Overvoltage Protection in Low Voltage System that damage distances of lightning flashes towards electrical system devices can reach 1km, even 3km (Reference: P28) while many low thunder and cloud to earth in the summer is not enough 1km, so influences of Lightning electromagnetic Impulse caused by lightning current on electrical devices at the time of cloud-to-cloud lightning are imaginable. Among lighting protection theories of electricity and electrical devices, it is a truth that cloud-to-cloud lightning and lightning between thunderstorm cells in clouds have been regarded as sources and types of damage to a structure.

3

1、Lightning directly stroke or nearby lightning strike:

Lightning strike in the external systems, such as the protection framework (industrial installations.) Cable and waited.

2b

1a In inrush current grounding resistance Rst caused voltage drop.

2a

1b Closed loop sensors have overvoltage 1 L1

20 kV

L2 L3 PEN

2c

Hit the pressure and 2a

1b

overhead power lines Conduction overvoltage

2b

traveling wave - As the cloud of discharge or

1a

nearby overhead lines Rst

2c

Power supply system

generated by lightning sensors. Lightning Road and the surrounding field

Figure 1: 《Overvoltage protection of low voltage system 》 plans 3.1-generated Lightning discharge the reasons for the surge

3. Values of sources and types of damages to a structure 3.1 Lightning in low-voltage power supply system International Electro-technical Commission (IEC) Standard introduces concepts of lightning protection zone (LPZ) when they analysis and deals with influences of lightning electromagnetic impulse on the electricity and electrical equipments within constructions. According to the lightning threatens, they have defined as the following lightning protection zones (LPZ)

External layer zone LPZ0 zone is such zone in which it suffers lightning electromagnetic damages that d on‘t weaken;  meanwhile, it suffers surge damage caused by lightning currents. LPZ0 is also divided into LPZ0A zone: Space of direct lightning strike and total lightning electromagnetic field damage. The circuit suffers surge damage caused by total lightning current LPZ0B: Spaces of protection against direct lightning but suffer damage of total lightning electromagnetic field. Circuit suffers surge and surge damages caused by partial lightning current.

Internal layer zone (direct lightning protection zone) LPZ1: surges in the circuit restrict through sub-current  and SPD at the interface Lightning electromagnetic field energies weaken by space shield. LPZ2….n: surges in the circuit are limited by sub-current  and SPD at the interface forward. Lightning electromagnetic weaken further by space shield. LPZ is realized by LPMS‘s installation (lightning protection measure system). For example, SPD‘s installation coordination and or magnetic shield can stipulate appropriate LPZ, according to area sequences and categories and withstand capacity of protected devices from small partial zone (extending to engine cases with installation of single

4

device) to big whole zone (finally extending to a total constructive space.) 3.1.1 Lightning current values of prospective overload parts at the interface between LPZ0 A and LPZ01 of IEC 3.1.1.1 Lightning current distributions of simple mathematic modes estimations During a variety of lightning protection zones, LPZ0A zone is the 100%

i

unprotected zone, so lightning current in this zone is the biggest. Lightning current values of SPD‘s expecting part at the interface of LPZ0A /LPZ01 zones gain highly concerns. Then, how to consider SPD‘s lightning current values of expecting parts at the interface of

External mine 外部防雷装置 device

ii

With such

Enter building 进入建筑物 ii facilities 的设施

等电位连接带  potential link

LPZ0A/LPZ01 zones？ The 3.4.1.1--- general rules in the first part of lightning Electromagnetic Impulse protection in the IEC 61312-1 has following remarks: external conducting components (that invading in the construction from ground), power line, communication line should calculate partial lightning current of lightning equipotential bonding

Grounding

ii

 points

50%

50%

devices

Picture 2 (IEC 61312-1‘s picture 13) lightning current 接地装置 is

distributions between constructions and indoor facilities (IEC 442/94)

When particular case can‘t carry out calculation, we can suppose 50% of total lightning current flow in the grounding

devices considered LPS of constructions, 50% i, that is, i distributes among various facilities(external conductance components and power line and telecommunication line)(diagram 2). i v flowing in every kind of devices is is/n. Among then, n is quantities of the above facilities. iv in every core strand of unshielded cables is the quotient of cable current i1and cable core strands quantities m, that is, i v = i1/m. The mode of diagram 2 is a simple mode. In this mode, 50% of total lightning current may inflow to earth in the construction earth system and 50% left may inflow out construction through indoor facilities and flow in the ground. ―Indoors facilities ―There are three kinds of indoor facilities in the picture and reasons are following: 1) Ordinary structure can‘t only have power line----a kind of indoors facilities and they should keep in touch with outside, toilet and mental pipes. Therefore, three kinds of indoors facilities are drawn in the picture which are direct to ground or ground by SPD. Every kind of current of facilities distribution is a sixth of total current and it occupies 16% of total \current. Indoor power line has at least two lines: phase line and neutral line, at that time lightning current of every  power line occupies 8.4% of total lightning current. In the worst condition, there are only two indoor lines in the modes of picture and lightning current spared by each power line installing SPD enjoys 25% of whole lightning current. This kind of calculative methods used in power system can be found in Mr. Hasse‘s writing Overvoltage Protection of Low Voltage System (the second edition).It said in the 92th page that lightning current releases not only earth-termination system at that time, but also some parts can flow from external ground into supply system of LPZ. These systems connect shielding layer in the entrance (plurals in the original text----writers note) with shielded layers of lightning protection zone 1.

If planners don‘t make any detailed calculations, it can be based on DIN VDE

0185-103(It is similar with IEC61312-1---writer note)‖Suppose 50% lightning current must release through external supply system. We can suppose further that lightning current evenly distributes in all metals and electrical circuit systems. If electrical circuit system includes multi-core (such as outer conductor of cables and protective conductors,  power supply lines or multi-core communication lines), we also suppose partial lighting current distributes evenly in various conductors and cores in the circuit system. In the picture 3, Dr. Hasse drew four external supply systems (power supply, communication and inlet and outlet mental nipples) and every system share 12.5% of total lightning

5

current. He also drew a cable with four cores, in which every conductor shares 3.1% of total lightning current. But he didn‘t consider situations of shielded cables. Dr. Peter also said that to the worst case, shielding layer is also regarded as conductor. This case must determine distribution of current one by one (Note: it is related to distributed and transfer resistors). The case ―shielding layer is also regarded as conductor‖ is very popular because all outer conductors‘ components into constructions should make lighting equipotential bonding at the interface among LPZ0 A, LPZ0B and LPZ1.He said in 3.4.1.1 that for shield cables, the current will flow along the shield. (Origin in P19), that is, shielding layer of shielding cable also share partial lightning current. This is in accordance with discourses of Dr. Hasse. 3.1.1.2 Situations of partial lightning current expecting methods when circuit is regarded as non-shielded cables Discourses of 3.1.1.1 should regard as cursory qualitative analysis, and whose actual case is relatively complex,  but it can estimate values of lightning distributions with similar method. Appex of IEC 62305-1 should provide a specific and scientific calculative method. When lightning strokes strike constructions, lightning current will conduct directly to earth in the ground terminal system, external conductance components and indoor facilities or through SPD among circuits. If  I f are partial lightning current flowing through every external conductor components or circuit, then

（1）

 I f =   k e I 

k  e is the coefficient related with quantities of parallel routes, equivalent ground impedance of ground components and equivalent ground impedance of earth-termination system. It can get with following calculations Underground equipments

k e

 Z  

 Z 1

Surface devices:

k e

  Z 

( n1



n2

 Z 1  Z 2

(2)

)

 Z  

 Z 2

(n2

  Z 



n1

 Z 2  Z 1

(3)

)

 Z: equivalent ground impedance of ground terminal system  Z 1 equivalent ground impedance of underground external components or circuit (table 1)  Z 2 ground resistors of overload circuit. If grounding resistors of grounding point is unpredicted, we can employ the value of Z 1 of table 1, which is relative to the value of grounding point.  Note: supposed the value of the above formula is the same as every grounding point, otherwise, it need more complex expressions. n1 total quantities of underground external components or circuits n2 total quantities of surface external components or circuits

I: corresponding lighting current values considered LPS ratings

6

 Dia gr am 1 equ ivalent gr ound imp eda nce  Z   and Z 1 calculated by soil resistivity

Equivalent ground impedance values

Z  1

m

concerned with LPS

I

II

III  –  IV

100

8

4

4

4

200

11

6

6

6

500

16

10

10

10

1 000

22

10

15

20

2 000

28

10

15

40

3 000

35

10

15

60

 Note：Listed values are equivalent ground impedances of buried conductors on the impulse condition （10/350μs）

Supposed Z=Z1=Z2 and n2 = 0，n1 = 1, as a kind of appropriately calculations, we also the acknowledge tentative of 2.2.1 k e = 0,5

（4）；

When constructions strike by direct lightning, 50% lightning current will flow in the external components or circuit k e = 0,5 / (n 1 + n2 )

（5）

This is in accordance with hypothesis describing ―particular cases are impossible to count‖ in the 3.4.1.1 of IEC 61312-1. This kind of hypothesis is different from reality. From (2) and (3), k e is concerned with construction  protection rating and earth resistance ratings. Generally speaking, the higher protective ranks, the more lightning current peak values we should consider, meanwhile,

the more current raises, the more the front steepness.

Therefore, inductance of circuit can‘t ignore. At the same time, the more ground resistance rate, the more influence of lighting current peak value on impulse grounding resistor. Take    = 3 000 m as example, constructions of class I  protection, partial lighting current ratio of external components or circuit spared is more smaller than constructions of class III protective 3.1.1.3 Situations of circuit as shielded cables As the above mentioned, shield layers of shielded cable will share partial lightning current. IEC 62305-1 appendix E provides calculative methods of ’ 

sharing current per core. k e calculate based on k e The ratio can be calculated that every line shares lightning current in n conductors calculates according to parallel circuit subcurrent as follows: ’ 

k e = k e   R s / (n’   R s +  Rc )

(6).  RS ohm resistors of per length in the shield

layer  Rc ohm resistors of per length in the internal Figure 4 IEC 61312-3 plans B.1 lightning current distrib ution of the basic model

7

conductors The formula ignores mutual inductances between

cores and shielded layers and may underestimate effect on transfering lightning current of shielded layers. But it can calculate lightning currrent distribution between shielded layers of common low-voltage power cables and core lines. 2

 For example, when power distribution cables employ four armour copper cables with 35mm nominal section , resistance per core is 0.524Ω/km, the tape armoring resistor is 1.9Ω/km. Put it in the (6) formula to calculate, ’ 

k e=0.234 k e. The result is lower than the stipulation of GB50057 stipulated that lightning current per SPD is 30% of  partial lightning current flowing in the cable. 3.1.1.4 Factors that influence lightning current distributions in low-voltage power supply system The third section of Appendix B of Requirements of Surge Protective Devices in Lightning Electromagnetic Impulse Protection of IEC 61312-3 provides information about influences of lightning current distribution in low-voltage power supply system. After we analysis modes of picture 4 and picture 5, we reach conclusions that 1) There is influence of lengths of cables for power distribution on time characteristics of partial lightning current through circuit. Because front of lightning is steep. The longer circuits, the stronger the inherent impedance of circuits on prolonging of fronts 图 2) There is influence of lengths of distributor line cable on current distribution among conductors. The longer circuits, the less effects of impedance of power distribution transformer decrease, in contrary, the main effect is circuit equivalent impedance, Therefore, shared current per phase line and neutral line in the long circuits.

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3) Influences of grounding system. Grounding resistors in the transformer system and grounding resistors in the user system (constructions) are the most key factors of lightning current distribution in the supply circuit. It is the second and third formula that can reckon influence of ground system. It proposes through analysis that it is not determined through grounding in the transformer system and user system, but through lightning current distribution in Figure 6 IEC 61312-3 plans B.5 cable length of 50 m lightning current distribution

the supply circuit in the

IEC62066: 2002 Basic Information of Surge Overvoltage in the Low-voltage Alternating Current System. 10/350µs, 200kA analog direct lightning strike are analyzed with this mode. This example only shows distribution relationships of lightning current in the low-voltage power

supply system. Therefore, it doesn‘t

consider other grounding services systems of external service system, such as signal lines, mental pipes and mineral gas pipes

Lightning buildings of the lightning current, 10/350, 200 kA

Lightning buildings, buildings grounding the lightning current distribution system

Lightning buildings, distribution online distribution of the total EC current mine

Figure 7 IEC 61312-3 plans B.3 lightning current distribution model of the basic circuit diagram

From picture 7, the longer circuits, the less lightning current distributes in the power distribution system. Picture 6 and picture 9 is respectively lightning current distribution sketch when the power distribution cable is 50ml and 500m. In picture 6, current distributed in three phase lines is the same, while current

9

distributed in neutral lines is two ti mes as many as phase lines. When the power distribution cable is 500m, lightning current nearly distributes between neutral lines and phase lines, which represents influences of impedance of transformer for power distribution (that is, grounding impedance of distances) decrease with cable lengths, even no influence. It evenly distributes internal current within cables.

Figure 8 IEC 61312-3 plans B.6 cable length of 100 m, grounding impedance transformer different lightning current distribution diagram

Diagram 8 is a different current distribution diagram of grounding impedance of transformers when cable length is 100m.The lower broken lines is current distribution when impedance of grounding resistance of transformers is 0.3Ωand grounding resistance of constructions is 3Ωwhile the higher broken lines is current distributions when grounding impedance of transformer is 3Ωand grounding impedance of  constructions is 3Ω. From the example, relative relationships between grounding impedance of construction and distance grounding impedance of power lines (transformer) influence current distribution. From the picture, half of all lightning current earths in nearly earthing system of construction and power system when grounding impedance of transformer and construction are 3Ω, that is, R ES=R ET. However, when grounding impedance of transformer is rather lo w, for example, R ES=3Ω，and R ET=0.3Ω，lighting current of earthing system distributes 10% of total lightning current. The above examples are relatively extreme. In reality, divergences of grounding impedance of construction and transformer adopted synthetically earthing system can‘t be so great. There is a point to note, when we analysis influences of analog lightning current of 10/350µs wave-shape on current distribution in the earthing system of construction and earthing system of  power distribution, we find lightning current of earthing system of

10

Figure 9 IEC 61312-3 plans B.4 cable length of 500 m lightning current distribution map

construction is far more than that in the earthing system of power distribution. This is because inductance of supply circuit can‘t be ignored due to steep f ront and big di/dt within front ti me of analog lighting current, current distribution changes with time and wave-shapes will change slowly and resistors only operate and wave-shape changes gently until front end time of analog lightning current. Hence, current distribution is often a constant. 3.1.1.4 Influence of neutral lines grounding. Different countries has different neutral line earthing, so it can be presuppose that lightning current is different from dispersions among  possible paths. Mansoor and Martzloff, two Americans, provide several kinds of earthing  practices in the power distribution system in Dispersion of Lightning Current among Multiple Paths in Low-voltage System. Figure 10 is TN-C-S system mode about grounding of neutral lines of every construction. Due to no SPD among neutral lines loop, pressures of SPD relieve connecting with conductors. Picture 2 shows that secondary transformers for power distribution represent Figure 10: lightning current radiation-shaped structure in the dissipation

radiate configuration towards three users. Suppose

10/350μs waveforms，100kA current strikes a construction, its earthing impedance values are as the following picture, in which it also marks lightning current peak values of three conductors out constructions. The above mentioned, it is relative values of impedance that determine lightning current quantities through power supply system. Although current shared by neutral lines and phases lines is not big, it produces enough plus pressure drops at the entrance of users. In the mode, we suppose earthing resistance of transformers is 5Ω, earthing resistance between constructions is 10Ω. If neutral lines of power supply distribution system have multiple earthing and many earth-terminations, then, relative impedance of neutral lines is lower than those of phase lines, so it reduces SPD‘s pressures of emanative paths. 3.1.1.5 Descriptions and conclusions on expectant partial lightning current of SPD at the interface of LPZ0 A/LPZ01 zones of IEC 62305. As above mentioned, expectant shared partial lightning current at the interface of LPZ0A zone and LPZ01 zone are restricted by various elements, and it can not simply illustrate as that

and external conductance components share

respectively 50%. Therefore, we should escape this kind of description. IEC61312-1especially points out when ―moiety theory‖ is ado pted on the basis that it is impossible to count particular cases. As a matter of fact, it is estimated in most cases. Meanwhile, it is the same as above literature illustrations. Each workgroup of IEC illustrate various elements that influence SPD expectant shared partial lightning current at the interface of LPZ0 A/LPZ01 in the future. Following standards in the future should describe completely towards these considerations of IEC. E.1.2 of appendix E in the IEC 62305-1 FDIS POSTROMA concludes factors which influence lightning current distribution within current lines. We bring forward that partial lightning shared in the detailed computation of SPD at the interface of LPZ0A/LPZ01 zone must attach importance to peak values of this kind of surge and waveforms. (1) Cable lengths may influence current distributions and waveform characteristics due to L/R ratio. (2) Impedance differences of neutral lines and phase lines can influence current of circuits conductors. For example, several points grounding of neutral lines(N),then, impedance of N is lower than L1、L2 and L3, as a result, 50%

11

currents trans-flux N lines and residual 50% distribute on the other three lines( 17% per line). If impedances of N, L1, L2, and L3 are the same, about 25% current distribute per lines. (3) Different transformers impedance influence current distributions (If transformers are protected by SPD, influence can be ignored.) (4) Relationships between grounding resistance of transformers and load side devices influence current distribution. (the lower the impedance of transformers, the more surge current through low-voltage system are ) (5) Parallel users decrease effective impedance in low-voltage system, so lightning current may increase in the system. This is the totally same as above analyses. The E.2 of appendix E of IEC 62305-1 FDIS POSTROMA provides surge connecting constructions with public facilities. When lightning strikes public facilities connecting with constructions, that is, damage sources (S3) ---flashes to the services connected to the structure, public facilities suffer damage greatly. Mr. Hasse said in the page 94 of his writing Overvoltage Protection of Low Voltage System that direct lightning striking public facilities may have more lightning current to invade LPZ1 zone boundary through single supply system. Table 2 is table E3 of appendix 3 of IEC 62305-1 FDIS POSTROMA, so we can select values of  I imp according to table 3 while preferred values of I imp are related to lightning protection levels (LPL). Low voltage system direct lightning stroke and indirect lighting stroke to service

Telecommunication circuits Lightning

Direct lighting stroke and

Lighting

stroke near the

indirect lightning stroke to

stroke near

structure

service

the structure

Damage LPL

Damage source waveform(10/3 50μs) of S3(lightning direct stroke) [kA]

Damage sources waveform( 8/20μs )of S4(indirect lighting stroke [kA]

Damage

sources

sources

waveform

waveform

(10/350μs) of

(8/20s )of

S3

S2(S1induce

( lightning

current):[KA]

direct

S4(indirect lightning stroke) testing with 5/300μs Prediction with

stroke) [kA] III and IV I and II

8/20μs [kA]

Damage sources waveform (8/20μs)of S2 (induce current) 8/20μ [kA]

5

2.5

0.1

1

0.01(0.05)

0.05

10

5

0.2

2

0.02(0.1)

0.1

Supposed shielding layer resistance of shielded cables is equal with resistances of parallel conductors of all public facilities. As for, values of over-current of shield lines, values of table 2 should plus 0.5.Generally speaking, electricity and electrical devices should consider according to protection ranks III and IV, therefore, direct lightning  predicting current of power supply system is 5kA (10/350μs).If it is 4-core power cable, current per core should be 5/4 kA, and expectant current of direct lightning in the telecommunication circuit is 1kA (10/350μs). If telecommunication cable is ten couple twisting lines,then, current of per core is 1/20kA. 3.2 Discources about expectant lightning current of power supply system in the other international standards 3.2.1 Discourses about American standard American standards IEEE Std C62.41.1 TM – 2002 IEEE Guide for Surge Environment

in Low-voltage(1000V and

less) AC Power Circuits, IEEE Std C62.41.2 TM – 2002 IEEE Recommended Practice on Characterization of Surge in Low-voltage (1000V) AC Power Circuits, IEEE Std C62.45 TM -2002 IEEE Recommended Practice on Surge Test of Device in Low-voltage (1000V) AC Power Circuits are called as Lightning protection of Companions. Among them,

12

th

the 4.2 section( Lightning Surge) of the fourth chapter (origins of surge voltage and surge current) in IEEE C62.41.1TM -2002 describes surge in the low-voltage power distribution system. “Lightning surge can be described with two kinds of different scenarios. —  Scenario Ⅰ flashes don’t strike directly on constructions .It has two kinds of coupling mechanisms.

 —  Direct or indirect lightning stroke coupling into electrical power system, and effects on the outer lines entrance of relative constructions.  — Electrical magnetic field through constructions and coupling into constructions.  — Scenario Ⅱ  In the rare situation, flashes directly strike on constructions(or strike on  ground near the construction. There are several coupling mechanisms  —  surges couple directly into a.c electrical power system  —  surges induce couple into a.c electrical power system  —  SPD act due to arises of ground at the entrance of facilities Scenario Ⅰwas proposed by the standard had described and had mature protection measures before 2002. Installation places of SPD for power supply protection are location category C, location category B and location category A. (Note: Many standards, such as American standard and British standard BS6651:1999 Code of Practice for Protection of Structures against Lightning, Australian Standards AS1768-2004(Draft) Lightning Protection adopt same installation location of SPD, that is, concepts of installation location categories select different nominal discharge current of SPD, consequently, lightning current in power supply system is related with installation location. Hence, installation location of SPD will discuss in detail as follows.) The A2.1 Injection of surges [Scenario Ⅰ] of appedix A Detailed Database of IEEE Std C62.41.1 TM – 2002 are as follow: ―Terminals of Overhead conductors of secondary power distribution system strike by lightning, lightning current will look for several grounding points to form grounding pathway. Figure 2(Figure 11 in the article — writers) describes the kind of situation. In the picture, suppose lightning current per first side conductor is 100kA, and first arrester on the electric rods will transfer lightning current into underground through multiple grounding of neutral lines. In the picture, lightning current are divided into several grounding paths and impedances between current and  parallel paths are in inverse proportion. Figures in the picture are designed at random in order to illustrate problems. Values of 100kA are selected according to the following analyses. ‖ Most lightning strike directly on a point near power line or on the power circuit. Frequencies and peak values of direct lightning are from amperes (low values) to 20kA (middle values), even surpass abnormally 100kA. Parameters th

of Lightning Flashes, published in the 41  periodical of ELECTRA in 1975, and Lighting Parameters for th

Engineering Application, published in the 69  periodical of RLEDTRA first describe distribution frequency pictures about current peak values of three typical lightning affairs, such as first negative lighting stroke, subsequent lightning stroke and positive cloud-to- ground. The picture is also adopted by IEC 62305-1(writers note: the picture is picture A.5 Cumulative Frequency Distribution of Lightning Current parameters of Appendix A 81/216/CDV  in IEC 62305. Only 5% negative lightning stroke current can surpass 100kA in the picture. Flashes frequency is correlative to geographical location. According to situation of local constructions, lightning strike points determine by forward streamer. In the most places of America, if there is no high trees or constructions, typical expectant lightning stroke  probabilities is within class k. Therefore, Scenarios in the picture 2, as for a rod, probabilities of lightning strike is once per 1000 years, but there are millions of rods in America.‖Therefore, in these scenarios, lightning current in the

13

grounding conductors may induce surge voltage near its phase lines. Picture B1, current will

sub-current in the

arrestors which is between phases and grounding lines at the entrance constructions. Actually, some rods often suffer lightning strikes and spread electrical wire. Martzloff and Crouch in the report Surge Protection Coordination of Uptown in Low-voltage Circuit in the Canadian power-line technology conference and reports Lightning Protection of Uptown in Low-voltage Circuit towards General Electric Company . According to laboratory simulation, current produce by 8/20µs generators, only 30kA stream to grounding conductors. Data (Picture A.3 to Picture A.6 of the standard---writer note) from A1.1.2 of IEEE Std C62.41.1 TM – 2002 lodge from the above reports. Although current only refer to grounding conductors(neutral lines) of power system grounding, the test is still regarded as Scenario Ⅰ. Results of the test point out that mono-polar  current in the grounding conductors  produce ringing voltage towards neutral lines (grounding lines) in the phase line. Therefore, rated current of secondary arrestor per line at the entrance of construction per line is 10kA, lightning current in the phase lines will conduct ground line of constructions and produce clamping voltage between phase line among construction and grounding lines. On the other hand; lightning strikes directly phase lines at the entrance of constructions, which will produce higher voltage. But this situation happens rarely. The above is Scenario Ⅰ. There are Scenario Ⅱin the statement ―Trilogy‖ of IEEE. Among the standard, Scenario

Ⅰis described as ―the typical surges impinging the building‖ and Scenario Ⅱ as ―the typical surges exiting the  building‖. Writers believe that before ―Trilogy‖ was  proposed , IEEE only consider situations that lightning current flow from external constructions to within constructions and introduce electronic and electrical devices and electromagnetic field through constructions and inductive coupling into constructions. But among three new published lightning protection standards, they also consider lightning flashes directly strike construction and lightning current flow out construction and disperse in the earth through earth electrodes (it not only emphasizes earth devices)within constructions. The situation belongs to Scenario Ⅱ. But the standard illustrates with many words that lightning flashes strike directly constructions in the rare occasions. (There are Picture 11: Picture 2 of Dispersion of lightning current in IEEE Std C62.41.1TM – 2002 among multiple paths

hardly testing data when lightning strikes directly construction, surge current flow in many paths in the earthing system of construction in the recent

 publications and two guarding reports towards lightning current themselves, but guarding reports towards possible lightning current paths)

More importantly, we must note that testing values of these lightning stroke currents are

not testing values of currents or charges in the circuit of low-voltage power system. The section propose especially a idea with in the page 29, that is, when IEEE,ITU and IEC determine lightning th

current parameters, all of them to determine analog lightning waveform with the 41th and 69  information of  bilingual magazines ELECTRA in the CIGRE. At last, lightning parameters adopting IEC differ greatly from IEEE, ITU. There are 46 pages to list many information, such as recording testing and calculation, discussion of database in the Appendix A‖ detailed data‖ of IEEE Std C62.41.1TM – 2002. This standard also expresses reservations that whether every construction must consider situations of Scenario Ⅱ

14

and lay emphasis on repeatedly the fact that lightning is small probability event, while lightning is in a measure. Therefore, civilian constructions and industrial constructions must determine whether it will deal with according to situations of Scenario Ⅱ after risks and investing analysis are carried out. Although it dealt with according to Scenario Ⅱ, SPD for power supply in civilian constructions and industrial constructions is a little bit differences from Scenario Ⅰ. 3.2.2 Discourses about Britain Standard It has following discourses in the 4.2 Lightning Characteristic in the Britain Standard BS6651-1999 Code for  practice of Lightning Protection of Buildings. A range given by various lightning parameters is terser and easier than average values to detail lightning. A significant section of Lightning flashes occurring damages is return stroke. The current range of return strokes is from 2000A to 200000A and lightning frequency distribution probabilities can be represented by so-called log-normal distribution as follows: 1% lighting current surpass 200000A; 10% lightning current surpass 80000A; 50% lightning current surpass 28000A; 90% lightning current surpass 8000A; 99% lightning current surpass 3000A; ―Most ground current emits from negative charges centers of lightning, therefore, flash current from lightning current stream to earth are negative current. Few lightning stroke emit from positive charges centers among lightning. However, the two kinds of polar current are one-way current, arising times of negative flash stroke current is less than 10μs (   But positive flash stroke are a bit longer .)Then, current reduce to lower values. For example, simple single lightning strikes reduce to the lower within 100μs or less time. ―Some flashes include twice or more times lightning strike. These lightning strokes occur like lighting stroke at the interval of 50ms to100ms one by one. Little flash is multiplex lightning beyond 10 times and discharge lasting times reach 1s. ― The following Current peak values （ imax） and lightning current anabatic speed are regarded as the strictest  situation in order to design Lightning Protection System(LPS). “imax=200kA [di/dt]max=200 kA/μs‖ 3.2.3 Requirements of Australian Standards and New Zealand Standards Impulse current waveforms is 8/20μs stipulated in the fifth section Protection of Persons and Equipment Within Buildings of Lightning protection of Australian Standards AS 1w768-1991 and New Zealand Standards NZS 1768-1991 and have detailed illustrations in the valuable appendix D---wave shapes for assessing the susceptibility of equipment to transient overvoltage due to lightning. Now we translate in the following. There are three common waveforms to represent transient phenomenon in the power circuit. They are 1.2/50μs single polar impulse wave, 8/20μs single polar impulse wave and 0.5μs ，100Hz ringing wave. To selection and installation of SPD for power devices, this standard provides suggestions in table D1 of page 85 and table D4 of page 87 (The table D4of this standard is the same as picture 12 of the passage, so it deletes.)

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Table 3

Table 1 of AS 1768-1991/NZS 1768

Installation positions(Reference: Picture 4)

Voltage or current Waveforms

 peak values

Load categories

Categories

Descriptions

A

Long user circuit

0.5μs，100Hz

6kV

High impedance

and outlet

ringing wave

200A

Low impedance

1.2/50μs

6kV

High

8/20μs

3 kA

Low

6kV

High

ringing wave

500A

Low

Overload lines of

1.2/50μs

6kV

High impedance

External facilities

8/20μs

20 kA

Low impedance

into constructions

8/20μs

70 kA

High exposure and high

B

Main power subsystem and short user circuit and user centers

C

0.5μs，100H

dangerous sites, such as telecommunication station of peaks 3.3 Conclusions According to stipulations of IEC 62305-1, expectant values of surge over-current in the public facilities. If considered Class Iand II protective level Iof construction, partial lightning current in the power line are10kA (10/350μs wave-shapes simulation) while high exposure and high dangerous site stipulated by Australia has not been 100kA (10/350μs wave-shapes simulation, which is publicized at home when expectant values of surge over-current caused by lighting of public facilities are in the strictest situation. For example, telecommunication station in the  peak of mountain is 70kA (8/20μs wave-shapes simulation). 4. Differences of setting SPD at the interface of LPZ0 A/LPZ1zone and LPZ0 B/LPZ1 zone IEC have specific stipulation on selection and installation position of SPD for power supply. The fifth chapter Arrangement of SPDs within the Lightning Protection Zones of the third  part Requirements of Surge Protective Devices of Protection against Lightning Electromagnetic Impulse IEC 61312-3:2000 stipulates that SPD install  based on sequences and select based on requirements of through points. The th

6.1 section (Transition from LPZ0 B to LPZ) of the sixth chapter Performance Requirements of SPD believes that circuits through LPZ0 A will share partial Figure 11 (Hasse, and other papers Figure 2) arrester demand (Original arrester is Arrester used the word; the word translated into existing GB "MOA")

lightning current. The 6.2 – Transitions from LPZ0B to LPZ of standards infers

LPZ：Lightning Protection District

to the fact magnetic field caused by

n：Enter the target for protection of the external conductive system

lightning current doesn‘t consider direct

m：Each external conductive system of internal wire

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lightning stroke and has no rein. The situation should imitate induction effect with 8/20μs waveforms surge current (Categories Ⅱ) or appropriate hybrid according to IEC 61643-1 From the above mentioned, SPD are treated variably furnish interfaces of LPZ0 A/LPZ1 and LPZ0B/LPZ1. Dr. Peter Hasse, one of organizers of IEC 61312 standards, together with his colleagues Johanned W Iesinger, Dr. Peter Zahlmann, Dr. Wolfgang Zischank, published Overvoltage Protection even in Case of a Direct Lightning Stroke, According to EMC in the No. SD27/E of DEHN in Dec. 1993. It provided two pictures. The picture 2 of the original  picture is Requirements of Arresters. From the above picture, LPZ0zone in the picture is developed into LPZ0 Azone in the IEC 61313-1 (1995-01) and LPZ0/E is LPZ0Bzone. Illustrations in the literature discourses that partial lightning current in the supply system or partial current of conductors are diverged by appropriate arrestors(surge  protective devices) at the interface of LPZ0 and LPZ1. Lightning current arrester in the a.c power conductors or telecommunication conductors can be accomplished. Disturbance in the system of the Lighting protection zone 0/E results from lightning magnetic field. If there is no analyses, we can suppose disturbance per conductor can be illustrated with 1.2/50µs open impulse voltage (10kV) and 8/20µs short-circuit impulse current (picture 11). While the disturbance can be limited by overvoltage arrester and overvoltage values of lightning protection zone 1 don‘t exceed allowable values. LPZ0/E zone is also marked as the LPZ0 B zone in the page 91 of picture 4.1.3.1.5a (Interface at lightning  protection zone boundaries) of Sir. Hasse‘s writing Overvoltage Protection of Low-voltage System (2000-02) in Michael Faraday House in London. Table 4 the table 4.1.3.2a of Mr. Hasse‘s writing ---Overvoltage protection in low voltage system Interface of lightning zone

0A/1

0B/1

1/2

[1/n·m] ·100kA 10/350µs Arrester test values (per [1/n·m] ·25kA Hybrid Hybrid conductor) 0.25/100µs 10 kV 6kV [1/n·m] ·200A 0.5s  Note: Hybrid, u 1.2/50µs open voltage; i 8/20µs short-circuit current; umax / imax=2Ω, typical testing sequence: 0.1；0.2；0.5；1；2；5；6 or kV n: circuit system numbers of protection targets grounding; m: arrestor numbers of installation per circuit Dr. Hasse believes that partial lightning current at the interface of LPZ0 A and LPZ1 are different from partial lightning current at the interface of LPZ0 B and LPZ1.Therefore, there are several points to refer to selections of SPDs of Class Ⅱtests and Class Ⅲ tests at the interface of LPZ0 B and LPZ1 in the second publication of Overvoltage Protection of Low-voltage System (Mr. Hasse‗s writing). Table 4.1.3.2a (table 4) --- Arrestor typical Testing Values at the entrance of circuit of the lightning protection zone of page 99 illustrates exactly that difference of setting SPD  between at the interface of LPZ0A/ LPZ1 and LPZ0 B/LPZ1. From the above mentioned, selections of SPD at the interface of LPZ0 A/LPZ1 zone and LPZ0 B/LPZ1 have great differences. IEC stipulates that SPD is installed ClassⅠtests at the interface of LPZ0 A/LPZ1in the alternating current  power distribution circuit while SPD is installed ClassⅡtests at the interface of LPZ0 B/LPZ1in the alternating power distribution. It doesn‘t conform to stipulations of IEC standards that SPD settings at the interface of LPZ0A/LPZ1zone are not distinguished while products of Class Ⅰtests employ at the interface of LPZ0 A/LPZ1zone or LPZ0B/LPZ1zone. We will discuss installation positions of SPD in low-voltage power supply system in the IEC 62305-4, in which SPD at the interface of LPZ0 A/LPZ1zone is different from SPD at the interface of LPZ0 B/LPZ1 5. Installation positions of SPD in the low-voltage power supply system

17

Installation positions of SPD in the low-voltage power supply system are very significant. In principle, SPD in the low-voltage power supply system installs at the interface of LPZ0A/LPZ01, LPZ0 B/LPZ01, and LPZ1/LPZ1. But it is not easy, how to determine interfaces of lightning protection zones. Moreover, some cables are truncated in order to install SPD at the interface of lightning protection zones. Therefore, we can‘t understand invariably ―SPD must be installed at the two interface of lightning protection zones. Some standards don‘t easily operate, because original intentions of IEC are not understood fully, some standards are reflected uneasy operation on the spot. In the following, installation positions of SPD in low-voltage power system have no divergences  between IEC and American, British, Australian, Canadian and Southern African Standards.

5.1 Stipulations in the American Standards American standards adopt principles of location Figure 12 low-voltage distribution system SPD installation locations

categories. Installation positions of SPD in low-voltage power distribution system are defined

as three installation positions, that is, three location categories Category A、Category B、Category C and sketch of th

Figure 12 (Figure 9 in originality )and text illustrations in the 7.7 sections ―Location Categories‖ of IEEE TM

C62.41.1

 – 2002.

Category C---- entrances of external constructions and devices, overhead lines from rods to constructions, electricity meters and frontals of distribution boards and cable tunnels into constructions. Category B-----feeding and short brand circuit, the distribution board, factory feeding lines, illumination system for construction. Category A----- long brand circuit, power socket, power sockets that are away from 10m with Categories B, and  power sockets that are 20m far away from Categories C. As for low-voltage devices, the shed of location categories B and location categories C may be electricity th

meter or main circuit-breakers (reference: the 230-70  in the National Electric Code ANSI/NFPA 70-1990). When we provide current for users transformers with high voltage, we can employ secondary side transformer. 5.2 Stipulations in the British Standards There are some following remarks in the C.13.1.3‖ Categories Location‖ of  Appendix C lightning Protection Recommendation against Construction with Electric Device in the British Standard BS6651-1999 Code of Practice for Protection of Structures against Lightning SPD installing the following positions are classified into Category C: The C.13.2 also provides peak values of testing waveforms of SPD for power supply about various installation categories: As for tested SPDs, different installation categories and testing of system level can select appropriate testing values between C.8 and C.10.

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―Surge Protective Device installing the following positions can Table 5， table C.8 — Category A BS6651

 be classified into Category C:

（ power supply）

―a) Supply distribution board for input power source, switchgear 

Systematic exposure

Peak

Peak current

categories

voltage

Low

2kV

500A

middle

4kV

333.3A

―b) Load distribution board for output power source, switchgear

high

6kV

166.7A

(Power supply transfers from constructions into other

(Power supply introduces from power supply bureaus, high-voltage or low-voltage transformers or other constructions into power distribution devices within the construction)

constructions, external illumination devices or water pump). Table 6: table C.9---Category B in BS6651

（ power supply） Systematic

Peak voltage

c) Outer lines constructions ―SPD installing the following positions are classified into

Peak current

Categories B‖ a)

exposure

Load power distribution lines system, distribution boards for input power supply or switchgear and supply sockets or

categories low

2kV

1kA

middle

4kV

2kA

high

6kV

3kA

fuses.  b) Internal electrical apparatus that no pass through power sockets or disconnectors. c)

Load power sockets or fuses that are far away from less

20m power cables lengths among Location Categories C. ― Load power sockets or disconnectors and load protectors of power sockets or disconnectors that are far away from 20m power cables among location categories C.  Note: It should be no Location Categories A when construction that in power lines distances between power Tablesmall 7, BS6651 C.10-leader the installation sockets and Location Categories C is less thancategory 20m C (Power) The C.13.2 also provides testing waveform peak values of SPD for power supply of various location Grading system

categories:

exposed

The peak

Peak current

voltage

As for tested SPD, different location categories and different testing of system exposure level can select 6kV 3kA appropriate testing electrical level from table C.8 toLow C.10. In B are combinative 10kV 5kA generators, which can ―Generators of installation categories C and categories waveform High waveforms 20kV 10kA As for Category A, a  produce 1.2/50μs voltage waveforms and 8/20μs current (Reference C.13.7).

non-inductance output resistor should be added to have appropriate values. Waveforms of short-circuit current should be less than 8/20μs. The standard not only stipulates installation positions of SPD in low-voltage power supply system, but also  provides voltage values of various installation points.（Reference: table 5, 6, 7 ） 5.3 Stipulations of Australian and New Zealand standards Location categories of SPD in the picture D4 are provided in the of the Appendix D Wave-shapes for Assessing the Susceptibility of Equipment to Transient Overvoltage due to Lightning in the Australian and New Zealand AS 1768-1991/NZS 1768-1991. Picture 4 is the same as picture 12 of the passage, because both are from Picture 4 Location Categories of IEEE C62.41-1980. But there is a passage to illustrate in the following of D4, we translate as follows now: ―Categories A----Power sockets and long user‘s circuit; power sockets that are 10m far away from Categories B;  power sockets that are 20m far away from Categories C ―Categories B----Main power brand system, short users circuits and users centers; power brand system of factories,  power sockets connecting with devices, illumination system of commercial buildings ―Categories C----external constructions and entrances of facilities; overhead lines from electric rod into entrances of

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constructions, cables between AS 1768-1992 and NZS1768-1991 were revised in 2004. There is no any modification in the DR 02359 revised documents published in 2003. We found there is no change about table D1 and picture 4 in Page 139and 140 between the DR 02359 document and documents in 1991. 5.4 Requirements of selections and location positions of SPD in low-voltage power distribution system in the IEC 5.4.1 Requirements of relative standards of the 81th technological committee in IEC Recently, the 81th technological committee (TC 81) of IEC will employ past lightning protection standards instead of IEC 62305 to ration past lightning protection standards. Principles of location categories are also adopted in Part 4: Protection against Lightning ---Electrical and Electronic Systems within Structures in IEC 62305-4. But there are some discourses in Appendix D.1.2 Selection with Regard to Location and to of Discharge Current Appendix D Selection and Installation of a Coordinated SPD Protection of Landers (62305-4-v24-lnd FDIS) of IEC in June 31th, 2004 The appendix of IEC 62305-1 stipulates SPD should share expectant discharge current in the installation points. Selections of SPD depend upon withstand capacities. SPD for power supply is classified by IEC 61643 -1while SPD for telecommunication system is classified by IEC 61643-21. Installation positions of SPD are as follows: ●Entrance of construction (at the interface of LPZ1, that is, on main board of power circuit) . External lines ●As for SPD for I imp,(  10/350 typical waveforms, that is, SPD of class I  tests),impulse current I i mp of SPD should be recommended expectant (partial)lightning current (typical 10/350 surge)of installing points after LPL is  selected according to appendix E.1 or item E. ●SPD tested  with I n( 8/20 typical waveforms, that is, SPD of class II test) When failure risks that external lines caused by LPZ0 B or S1 and S3 can be ignored, it can adopt the categories.  It should be required expectant surge of installing points of nominal discharge current I n of SPD according to the appendix E.1 and E.2 of IEC 62305-1. b) Near the protected devices (at the LPZ or higher interface, that is, at the SB or SA) ●SPD tested by I n (8/20 typical waveform , that is SPD tested by Class II tests) should be required that nominal discharge current I n of SPD should select expectant surge(Typical 8/20 current waveforms) of installing points determined by LPL(lightning protection level) according to Appendix E.3 of IEC 62305-1. ●SPD tested by combinative waves (8/20 typical current waveforms, that is, SPD tested by Class III tests When open circuit voltage U oc is selected  by combinative operators, corresponding short-circuit current include expectant surge of installing points of LPL (lightning protection level) determined by appendix E.3 of IEC 62305-1 Appendix D.2.1‖Location Position of SPD‖ of IEC 62305-4 also stipulates that it must be in accordance with D.1.2, which influences in the following factors: 1) Protections should have effect on given damage sources, such as 2) Protections should be close to entrances of the external line into constructions, thus, it can conduct to ground through surge over-current. In the first place, the more SPD should be near to the entrance of constructions, the more SPD can protect devices (economic benefits). In the second place, tests must be carried out. The more SPD is close to protected devices, the better the protective effect is (technological benefits). Two criterions are not sometimes sufficed. D.1.2. selects the second criterions, that is, installs on MB, SB, SA. It differs from 6.4.7 that SPD should install near the ends of shielded circuits in the GB 50057-94(2000).

20

Stipulations of IEC easily operate while it is not too definite for installing specific location of SPD near the ends of shielded circuits. The seventh chapter ―SPD system‖ of the 81/212/CD in IEC 62305 -4 explains location categories as follows: If you are interested, you can find the originality in the 89 page of the document: ―SPD should withstand discharge current that their installation points may happen. There are some following installation points in the SPD systems. ―Main Board (MB) The location is at the interface of LPZ1orLPZ0A/LPZ1 or LPZ0B/LPZ1 ―Sub Board (SB) (or llll). The location is at the interface of LPZ1/LPZ2 or higher levels. ―SA: The position is electrical devices or terminals of electrical devices. Although there are no specific explanations in the following 62305-4-v24-lnd FDIS, basic ideas of IEC is specific and uniform. ―Installation position categories of IEC are as follows 1) Main distribution board (MB): It is si milar to Categories C of British, American and Australian standards. When external lines at the entrance of MB may introduce by overhead lines, it should be near the interface of LPZ0A and LPZ1 with lightning protection zones; When it may not introduce by overhead lines, it should  be near the interfaces of LPZ0B and LPZ1 Sub-branch distribution board (SB): It is similar to Categories B of British, American and Australian standard. Lighting protection zone is used to explain near LPZ 1 and LPZ 2 or internal LPZ1. 2) Sub-branch distribution board (SB): It should be near the interface of LPZ1and LPZ2 zone or within LPZ1 zone. 3) SA: It should be near the interface of LPZ1and LPZ2 or within LPZ2 zone with the concepts of lightning  protection zones, which is similar to Categories A of British Standard, American Standard and Australian Standard. We reach the conclusion that to describe installation locations and selections of SPD with location categories is easier to operate than installation on interface of lightning protection zones. Conclusion: SPD of class Ⅰtests is installed at the interface of LPZ0 A/LPZ01in the alternating power distribution circuit while SPD of class Ⅱtests is installed at the interface of LPZ0B/LPZ01LPZ0B/LPZ01zones in the alternating power distribution circuit. There are two kinds of cases about MB pos itions, one is circuit introduces in LPZ1 zone from LPZ0A, other is circuit introduces in LPZ1 zone from LPZ0  B. The following description illustrates selections of SPD from LPZ0 A into LPZ1in the Appendix C SPD Coordination, page 73, of 81/238/CDV and translates as follows: Lines incoming from LPZ0A (where direct strike are possible) carry partial lightning currents. At the interface LPZ0 A to LPZ1, therefore, SPD (class I test) are needed to divert these current. Lines incoming from LPZ0B (where direct strikes are excluded, whereas full electromagnetic field exist) carry only induced surge. In this case at the interface LPZ0 B to LPZ1 the induced effects should be simulated  by means of either a surge current with a wave-shape 8/20 (class test) or an adequate combination wave test (class

test) according to IEC61643-1.

From the above remark, we have expounded in detail about selection principles and installment position of SPD in low-voltage power distribution system. 5.4.2 Related standards requests of the 37A sub-technology commission (SC37A) in IEC IEC 61643-1(2002-01) and IEC w61643-12(2002-02) is a couple of standards. IEC 61643-1 is about performance requirements and testing methods of SPD for power voltage. Therefore, it stipulates testing methods of various specifications of SPD, including tests of the strictest categories (SPD of class Ⅰtests) and tests of common categories(SPD of class Ⅲtests ). However, IEC 61643-12 Low-voltage Surge protective devices - part 12 ：Surge

21

 protective devices connected to low-voltage power distribution system- Selection and application principles are a kind of selection principles of SPD in low-voltage power distribution system. The 6.1.5 Choice of the Location of the SPD Depending on the classes of Test of the sixth chapter Application of SPDs in Low-voltage Power Distribution Systems in IEC 61643-12（2002-02） points out that we can select SPD for class Ⅰtests, class Ⅱtests and class Ⅲ tests according to lightning intensities incoming from constructions. The consideration of surge intensities is one of key factors of selecting SPD. Class Ⅱ tests and class Ⅲ tests are appropriate to install near protected devices. From the above, we find that SPD at the entrance of constructions can select class Ⅰtests, classⅡ tests and class Ⅲ tests, which represents SPD tested by class Ⅰtests is not an exclusive selection. It is in accordance with that Lines incoming from LPZ0 B (where direct strikes are excluded, whereas full electromagnetic field exists) carry only induced surge. Hence, between LPZ0 A and LPZ1 should install with SPD tested by class Ⅰ tests. Lines incoming from LPZ0 A (where direct strike are possible) carry partial lightning currents. At the interface LPZ0 A to LPZ1, therefore, SPD (class I test) are needed to divert these current. However, Lines incoming from LPZ0B (where direct strikes are excluded, whereas full electromagnetic field exist) carry only induced surge. In this case at the interface LPZ0 B to LPZ1 the induced effects should be simulated by means of either a surge current with a wave-shape 8/20 (class Ⅱtest) or an adequate combination wave test (class Ⅲtest) according to IEC61643-1. That is to say, when overhead lines introduces from constructions, SPD tested by class w tests installs at the MB, while ground cables introduces from constructions, SPD is installed at the MB tested by Class Ⅱtests, even class Ⅲ tests. Three instances are wholly given in Referent Appendix G Application Example to understand the stipulation. One is  power protection for civil buildings, the other is protection for power supply of industrial buildings, wand another is  power protection of wireless mountainous base station. Original tests is introduced in the test due to long original tests, readers can be found in the 175-183 of IEC 61643-12

Figure 13 (Original plans G.1)

（2002-02）. The civil construction instance G1 of Appendix G. MV‘s transmitting electrics is 10km high-voltage overhead lines, while LV‘s is that after high voltage transmit into low voltage (230/440), low-voltage overhead lines transmit electric 1km, then introduce constructions with 200m ground cables. Ng =2 2

time/km /year in the. Constructions are located in plain areas and have protective measures. Over-current  protectors install at the entrance of power lines, MB in the ground floor, and SB in the first floor. Grounding resistors of constructions is 50Ω, grounding modes in the supply system is TT and there are washing machines, computers, alarms, video cassette recorders and TV

22

Figure 14 (Original plans G.3)

indoors. SPD should be selected through risk analyses when the construction is in the areas of high lightning flash frequency; there are high-voltage and low-voltage overhead lines both side of transformers; there is susceptibility of electric devices, therefore, it should select SPD. At last, SPD of the example (Graphic G.1 in the original test) are as follows: SPD at the MB, I n≥5kA  per line, 8/20 wave-shape  (class Ⅱ tests) and U  p≤1.5kV

while other SPDs, I n≥2kA per line, 8/20

wave-shape (class Ⅱtests) and U p≤0.8kV。 The civil construction instance G1 of Appendix G2: Installed graphics of SPD were only provided in original text, but selection methods were not provided (selection methods were in the consideration in the original texts). Mountainous wireless base station examples G.3 of Appendix G: There is direct lightning protection system (LPS) in the tower; MV‘s transmission conditions is 10km high-voltage overhead line; LV‘s transmitting conditions is 500m low-voltage overhead line into constructions. The area is located in the peak of mountain and is Ng =6 2

time/km /year. Neutral line grounds at the foot of mountains; while devices grounds PE on the spot; resistance of  protected constructions is 10Ω; grounding resistance of transformers is 10Ω; And grounding mode in the power supply system is TT. We believe after risks analysis that SPD tested by class Ⅰtests should be selected between phase lines and ground lines, phase lines and neutral lines and neutral lines and ground lines. Because most lightning current strike on antenna tower during lightning direct strike, withstand current capacity of SPD should be more than 20kA of class Ⅰtests. Protection levels of line devices sides SPD should be 1.5kV while protection levels of line transformers sides should be the same or higher a little (the most is 4kV). 5.5 Discourse on selection and location position of SPD in low-voltage power distribution system From three illustrations listed by Appendix G of IEC 61643-12, if power supply lines incomes from cable into constructions, industrial and civil constructions introduce LPZ1 from LPZ0B zone while protectors installed at the MB select SPD tested by class Ⅱtests, whose nominal current are selected according to preferred values of 5.2 in IEC 61 643-1 after risks analysis. As for mountainous wireless base stations with high exposure circumstance and employments of high-voltage and low-voltage overhead transmission line, SPD installed at the MB select SPD tested  by class Ⅰtests and values of nominal current should be selected according to preferred values of 5.1 in IEC 61643-1. At last, SPD installs in the example, such as , SPD ：at the MB per line nominal discharge current I n≥5kA8/20 wave-shape（class Ⅱtests）There are some discourses in 5.5.2.2 Iimp and Imax for SPDs according to class Ⅰand class

Ⅱtests（Iimp and Imax of SPD tested by class Ⅰand Ⅱtests）of IEC as follows. Iimp and Imax for SPD according to class Ⅰand Ⅱtests. Iimp and Imax and their submultiples are test parameters use in the operating duty test for class Ⅰand class Ⅱtests respectively. They are related to the maximum values of discharge current, which are expected to occur only very rarely at the location of the SPD in the system. I max is associated with classⅡtests and Iimp is associated with classⅠtests. Imax is used for class Ⅱtests and Iimp is used for classⅠtests. There are two points to note about the  passage. Firstly, discharge current occurs at the location of the SPD, the expression ―very rarely at the location of the SPD in the system‖ is in the original test. Secondly, I max is 20 kA while the amount of charge is 10 coulomb. The

23

amount of charge of single lightning discharge are several coulombs, therefore, it is strictest for SPD. As a matter of fact, IEC 62305-4, that is, 81/238/CDV is in accordance with IEC 61643-12. Discourses of the C.1General of Appendix C, in page 73, of IEC 62305-4 are as follows: Lines incoming from LPZ0 A (where direct strikes are possible) carry partial lightning currents. At the interface LPZ0A to LPZ1 therefore SPD (class Ⅰtest) are needed to divert these current. Lines incoming from LPZ0 B (where direct strikes are excluded, whereas full electromagnetic field exist), carry only induced surge. In this case at the interface LPZ0 B to LPZ1the induced effects should be simulated by means of either a surge current with a wave-shape 8/20 (class Ⅱtest) or an adequate combination wave test (class Ⅱ test) according to IEC w61643-1.It also represents that overhead lines incoming from constructions can be selected SPD tested by class Ⅰtests. 5.6 Conclusion SPD should be installed in MB, SB and SA, these three positions, in low-power system. The three-grade lightning  protection may also install on the three different positions in the past. But some people misunderstands the three grades lighting protection and didn‘t install three grade lightning protection on the installment position stipulated by IEC, American standards, Britain standards and Australian standards discussed in our paper. 6. Coordination in low-voltage power system 6.1 Aims and installation graphics of SPD coordination. SPD‘s different installation positions must coordinate energy, whose aims to energy coordination are to avoid concatenation installation of overload SPD within a system. Therefore, we should select appropriate SPD. Energies coordination of SPD firstly coordinate with protected devices, that is, Energies coordination of SPD should coordinate with protected devices, that is, SPD can not protect protected devices, but to damage themselves. Secondly, multi-accordance of parallel installment SPD will share their stresses according to energies absorption capacities. If partial energies dispersed in each SPD of total surge current is lower or equal to its energy withstand capacities, then, energies coordination can reach. Lightning current shared by SPD depend upon its installation positions and characteristics. Main lightning threatens have three parts lightning current. Lightning threatens are mainly composed of three parts lightning current ●First short stroke ●Sequent long stroke ●Long-time stroke An effective coordination should be considered:1) various characteristics published by manufacturers 2) threatens suffered of installation location 3)withstand overvoltage(including insulation density) and over-current capacity of protected devices First short stroke is a decisive element of coordination among SPD concatenation. If inductance is used as decoupling components, high current gradient decouples easily. Single SPD only shares partial lightning current which need determine expectant partial lightning current of SPD according to methods. IEC recommends that first short lightning stroke current can be imitated by 10 ／350 wave-shapes. But, partial lighting current or induce current in the system have different waveforms due to multi-reactions between lightning current and low-voltage devices. Hence, IEC will consider the following impulse testing current (surge) in order to aims of coordination. I10/350 testing current with 10／350 waveforms, especially energies coordination for SPD tests. As for power lines, it is a kind of similar current defined by peak value current and charges used for Class Ⅰtests （IEC 61643-1. I8/20 testing current of 8 ／20 waveforms. As for the power line, its waveform is used in Class Ⅱtest(IEC 61643-1). ICWG Current(IEC 61000-4-5) waveforms from hybrid generators depend upon overload (1.2 ／50open circuit voltage and 8／20short circuit current) and used as Class Ⅲ  test（IEC 61643-1）

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IRAMP testing current of 0.1kA／μs current gradient. It imitates partial lightning stroke current due to interactions  between lightning current and low-voltage devices, which is especially used for decoupling effects of parallel connections. Picture 15 shows demonstrations of SPD applications in the power distribution according to concepts of lightning  protection zones. SPD should be selected installations according to given installation positions. To select SPD and install in the total electricity system within constructions should guarantee that most of lightning current release to the grounding system at the interface of LPZ 0 A and LPZ 1. Power lines introduce overhead through LPZ0A zones. SPDⅠis Class Ⅰof SPD , which installs in MB . SPD Ⅱinstalls in SB which is Class Ⅱ. SPD Ⅲ is Class Ⅲ of SPD, which installs in SA. Once most energies of partial lightning current transfer through the first SPD, secondary SPD only design to deal with residual threatens of interfaces between LPZ 0 A and LPZ1 and influences of internal electromagnetic induces of LPZ1 (in particular, in the nonelectric shield). Circuit from LPZ 0A (It may suffer direct lightning stroke here.) carries partial lightning current. Therefore, SPD (for example, SPD of ClassⅠtests) with I imp tests transfers these current at the interface of LPZ 0 Aand LPZ 1. Circuit from LPZ 0 B (It excludes direct lightning stroke, but it exits total electrical magnetic field) only carries induce surge. In such condition, induction effects at the interface of LPZ 0 B and LPZ 1 can not only imitate surge current (for example, SPD of Class Ⅱ test)of 8／20 waveforms, but also imitate hybrid waveforms(SPD of Class Ⅲ  test). Plus threaten from transitions of LPZ 0 to LPZ 1 and induction effect of electromagnetic field within LPZ 1 depends upon requirements of SPD at the interface of LPZ 1and LPZ 2. If threatening values are not possible towards detailed analysis , it can imitate main stresses according to 8／20 surge current (for example, SPD of Class Ⅱtest) and hybrid waveforms (for example, SPD of Class

25

Ⅲ tests) according to IEC 61643-1.

LPZ 0A

LPZ 0B

LPZ 1 LPZ 2

SPD II

LPZ 3

SPD III

Power 

SPD I

SPD II

SPD III

line

Figure 15 IEC 62305-4 plans C.1 - Power Distribution

6.2 Coordination principles Coordination principles among SPDs adopt one of the following principles:

◎Coordination of V-I characteristics(no decoupling elements) This method is appropriate with voltage limiting t ype SPD (such as MOV or transient suppressors) based on static V-I characteristic. The method is not sensitive to current waveforms.

Although impedance of circuit

has certain intrinsic decoupling, the method needs not decoupling.

◎Coordination of the triggering type SPD (with no decoupling elements) In order to the triggered type SPDs coordination, impedance of enough surge withstand capacity is regard as decoupling elements. Resistors mainly employ in the telecommunication while inductance in the power system. To coordination effect of inductance, climbing steepness of current dI/dt is also crucial parameter. Decoupling elements can be achieved not only by independent devices, but also by natural impedance of circuit among SPD concatenation. Inductance in the circuit is inductance of two parallel conductors. If two conductors phase and ground line) are in the same cables, inductance is about from 0.5 to 1μH ／m(it is correlated with wire size); If two conductors separate, inductance will be higher (it is related to spacing distances of two conductors.)

◎Coordination of SPD( no decoupling elements) We can achieve coordination through

. Their electrical flip flop circuit must insure that energies withstand

capacities of secondary, SPD don‘t surpass. Although circuit impedance has some intrinsic decoupling effects, the method doesn‘t need decoupling. From practices, because electrical flip flop circuit always damages in advance

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 before lightning stroke and can‘t achieve trigger in advance, so they are not appropriate to popularize at present. In the actual, there are two kinds of coordination as follows: 1) Coordination of two voltage limiting t ype SPDs 2) Coordination between voltage switching type SPD and voltage limiting type SPD The two kinds of coordination should consider influence of waveforms with high steepness of current (for example, 8 ／20μs or 10／350μs, steepness of these two kinds of impulse waves are near to each other, time arising to peak values is 8μs(8 ／20μs), 10μs (10／350μs) )and waveforms with low steepness of current. According to analog testing data provided by appendix C of IEC 62305-4, coordination between voltage switching type SPD and voltage limiting t ype SPD, we request decoupling inductance between two SPD in the power circuit be 8μH or 10μH with waveforms of 8 ／20μs or 10／350μs while 10μH or 12μH with waveforms of 0.1kA ／μs. Conditions of successful coordination is that SG must fire before MOV reach values of withstand energies. Supposed we are strict in selecting values in the project, decoupling inductance adopts 12μH ，0.5μH 0.5 to 1μH per m. We need cables of 12 m to 24m to reach 12μH. Therefore, when cable diameters are not enough 12m to 24m, it should add decoupling inductance in addition. In some standards, such as American standard, British standard, Australian standard and New Zealand standard, they stipulate distances between Categories A and Categories B should be more than 10m, and Categories A and Categories C should be more than 20m. Mr. Hasse said Overvoltage Protection of Low-voltage System, in the page 180, that inductance of power cable depends upon cabling routes of PE. If cable of protective lines are the same cables as L1、L2、L3 and N line, decoupling cables of lightning current arrester of class B and surge arrester of class C are cables with at least 15m. If protective lines are not the same as L1 、L2、L3 and N line and the length between  protective lines and cable is 1m, then, the length of decoupling cable is at least 5m. Two cables situations here is which is in accordance with discourses‖ cable inductance is correlated to gap distances between two conductors.‖ Hence, it is not scientific that circuit lengths between voltage switching type SPD and voltage limiting type SPD should not be less than 10m while circuit lengths between the voltage limiting type SPD should not be less than 5m in the 6.4.11 items of GB 50057-94（2000. Recently, 5m-principle, 10m-principle among some installation principles of SPD in some articles, whose writers also introduce 30m-principle.What is the basis? Generally speaking, two voltage limiting type SPD is easier to achieve coordination, therefore, coordination  principles of SPD mainly discuss coordination between voltage switching type SPD and voltage limiting type SPD in IEC. Graphic 16 is an elementary circuit diagram of coordination scene that spark gaps and MOV are regarded as spark gaps and MOV. Graphic 17 explains the basic principle of energies coordination of the voltage switching type SPD1 with the voltage limiting type SPD2. These information, the latest is from 2002, represent accuracies of standard testing waveforms of IEEE selecting 1.2/50μs voltage wave, 8/20μs current wave, 100 kHz ringing wave as standard surge-testing waveforms , 10/1000 μs long waveforms as additional waveform. Fire of SG (SPD1) depends upon the sum of residual voltage U 2 of MOV (SPD2) and dynamic voltage drop. Once surpasses

Decoupling components

Sur e

Protected Side

voltage,

coordination,

U DE, I DE SG SPD1

U 1, I 1

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dynamic fire SG will fire

and reach which

voltage U1

SPD2 MOV U 2, I 2

Figure 16 Combinative circuits  between SG and MOV

depends on:

●Characteristics of MOV ●Steepness and peak value of surge ●We should consider surge current arising time and peak values( R eference:10／350 or 8／20). When

W  [kJ]

inductance

1,0

is used for decoupling

最大电流 SG

0,8

elements, we should

未达到配合

surge

MO

0,6

consider

MOV 承受的能量 W max

current anabatic

0,4

times and

达到配合

 peak values

SG 未放电

(such as 10

SG

0,2

／350 or 8

SG 已 放

／20).The MOV

more the

0,0

steepness

1,0

2,0

3,0

4,0

5,0

 I SURGE [kA]

di/dt is, the less the

17  – 

SG

MOV

inductance of

decoupling. In particular, coordination between SPD( class Ⅰtest) tested by I imp with SPD tested by I n should consider 0.1kA／μs minimum current steepness of lightning current (reference: Appendix C.1 of IEC 62305-1).(These SPD coordinate when it can coordinate 10 ／350 lightning current with 0.1kA ／μs minimum steepness. We should consider the following two kinds of basic complexions.  Non ignitable spark gap If spark gap (SG) doesn‘t fire, all surges current will flow MOV. If energies of surge consumption are higher than energies withstand capacities of MOV, coordination doesn‘t achieve. If we use inductance as decoupling elements, the situation is in the worst conditions at the time of 0,1 kA/µ minimum current steepness. Ignitable spark gap If spark gap fire, lasting times of current from MOV reduce greatly. Before MOV reaches withstand energies values, SG fire, thus, it will reach accurate energies coordination. Ignitable spark gaps don‘t often discharge due to unstable discharge voltage. Because it appears scotoma, MOV withstands over-voltage to damage. Before it is successful that SG must fire, MOV must achieve withstand energies values. Decoupling elements (inductance or resistance) (reference IEC 61643-1) 6.3 Protection distances l po due to vibration Protection distances l po refer to circuit maximum lengths between SPD and devices. Within the limitation, SPD  protected effectively devices (it has been considered oscillation phenomenon and capacitance overload.). Because SPD is in the operation, lines of installation positions of SPD---ground voltage is limited within U P. If circuit

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distances between SPD and protected devices are so long that transmit of surge will produce oscillation. When  protected terminal devices are in open modes, Overvoltage of device ends will arise to 2UP. Although UP ≤Uw is selected, it can still damage protected devices. These data depend upon technology of SPD, installation rules and overload capacitance. If maximum circuit length is more than 10m or UP> Uw /2, protective distances should estimate by following formulas: l  po  = [U w  – U  p]/ k  

(m)

k  = 25 V/m 6.4 Protection distances due to induce When lightning strikes constructions or earth near constructions, it will induce overvoltage in the loop forming  by SPD and protected devices, and it decreases protection of SPD due to it is added U P. Dimensions Induce overvoltage raise with loop (circuit routes include circuit lengths, protective grounding PE and distances of phase lines, and loop acreages decreases with attenuation of electromagnetic field density (space shield and/or circuit shield). Protection distances l pi are maximum circuit lengths among protected devices. Considered induce  phenomenon, SPD is effective towards protection against protected devices within distances; Generally speaking, when lightning produces strong magnetic fields, it will endure loop between SPD and devices, or it can be reduced magnetic field intensity with following ways. Space shielding of constructions (LPZ1) or rooms (LPZ2 or higher areas) Circuit shielding (employments of shield cables or cable channels) If enough shielding are provided, we can ignore protection distances l pi. When long, no circuit shielding, big loop become problems of installation of SPD, we can estimate protection distances (l pi) with following formulas: l  pi  = [U w  – U  p]/ h  h = 30000× K S1 × K S2 × K S3  

(m) (V/m)

While K S1, K S2, K S3 are coefficients of the B.3th items of IEC 62305-2.  K S1: Space shielding provided by LPS or other LPZ 0/1 boundary shielding measures  K S2: Space shielding provided by LPZ 1/2 or higher areas boundary shielding measures  K S3: Characteristics of internal circuit 6.5 Procedures of installation coordination of SPD Coordination of SPD installs based on following procedures: 1.

SPD1 is installed in the entrance of constructions.( LPZ1 boundary, for example, MB---installation points) (The D.1.2 item)

2.

Determination of impulse withstand voltage Uw of internal protected systems

3.

Selecting the protective level U p1 of SPD 1 and effective protective level is U p1  Uw..

4.

Examinations protection distances of l po/1 and l pi/1. (The D.2.3and D.2.4 item).

If it meets requirements of 3) and 4), then SPD 1 protects effectively protected devices. Otherwise, it need set SPD2. 5.

SPD2 is installed near protected devices (in the boundary of LPZ2, for example, SB — installation points).

6.

Selection of the protective level

Up2 of

SPD2 makes effective protection level U p2  Uw Same SPDs are ready

to coordinate effectively. 7.

Checking protection distances l po//2 and l pi/2 If it meets 6) and 7) requirements, SPD1and SPD2 with energy coordination protected effectively protected

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