mechanism of lightning and the latest lightning protection

Mechanism of lightning

and the latest lightning protection

1

LIGITNING PROTEC TAKETANI Co., Ltd.

and the latest lightning protection


Inside of water droplets in the air, polarization continues to occur at all the time due to

the electrical field 0.0001[V/m] which exists on the surface of the ground. When this

droplets is mechanically divided, the charge should also be divided into + and .

If many droplets with same polarity gather and move at the same time due to the

turbulence in the air, a part of cloud comes to have opposite polarity. The charge in the

bottom part of cloud induces opposite charge on the surface of the ground.

2LIGITNING PROTEC TAKETANI Co., Ltd.

Figure 1. Charge which affects thundercloud and the ground

― ― ― ―― ― ――

+ + + + +

E : electric field

ground

As the water droplets with same polarity gather at once, a part of the electrical

field comes to exceed the dielectric strength of the air.

Afterward a discharge path is formed and the so-called stepped leader moves

toward the ground step by step.


the edge of the stepped leader


Figure 2. Gradual growth of stepped leader and occurrence of trapped discharge

+ + + + + + ground

trapped

discharge

the edge of the stepped leader


An enough charge for ionizing air is supplied from the cloud to the lightning discharge

path. It is said that the radius of space column influenced by the lightning is 500m.

It is known that the standard wave form is 10µs in crest length and 350µs in wave tail.

If this value is analyzed in Fourier series, you will find that this value is the sum of the

direct current and high frequency current with several kHz to hundreds of kHz.

rCharge with high frequency returns up to the


Figure 3. Return of the charge flowing to the cloud through the capacitance

― ― ――

Charge with high frequency returns up to the

cloud through the capacitance

⇒Subsequent stroke occurs due to the

returning charge

―ground

① LPL Ⅰ nuclear power plant / chemical plant /

installation with risk of explosion / large-scale computer center

② LPL Ⅱ industry plant / hospital / big banks / corporate headquarters

③ LPL Ⅲ and Ⅳ general office / administrative department

Lightning protection level

Protection efficiency of Lightning protection

Selected range of lightning current peak value


Protection efficiency of

LPS

Lightning protection

levelmax. current min. current

0.98 Ⅰ 200 kA 2.9 kA

0.95 Ⅱ 150 kA 5.4 kA

0.90 Ⅲ 100 kA 10.1 kA

0.80 Ⅳ 100 kA 15.7 kA

source: IEC61024-1-1

Lightning current components

Figure 4. Definition of impulse current

which has crest length T and wave tail T

crest

length wave tail


which has crest length T1 and wave tail T2

Lightning protection level

Ⅰ Ⅱ Ⅲ Ⅳ

Possibility of lightning

current peak value is below

the specified value99% 98% 97% 97%

Possibility of lightning

current peak value exceeding

the specified value1% 2% 3% 3%

See specified value in table on page 7. source: IEC62305-1

Occurrence probability of the lightning current

occurrence

probability


Figure 5. Distribution for occurrence probability of

lightning current peak value indicated by CIGRE

(CIGRE: Conference Internationale des Grands Reseaux Electriques a haute tension)

1 : first negative downward flash

2 : second negative downward flash

3 : positive lightning stroke

Distribution of lightning current

100kV

electrical device

power supply

structureair termination rod

lightning current path

electrical device

conductor

high

voltage

6.6kVpower supply


electrical device

earthing for

enclosure of device

Figure 6. Condition of distribution of lightning current which strikes the air termination rod

ground resistance of structure 2Ω

earthing for

low voltage coil of

transformer

Induced voltage caused by lightning currentIn the case that

the electrical installation circuit is separated from the down conductor

lightning current


Figure 7. Mutual Inductance M2 in the case that the square circuit of electrical

installation inside of the structure is separated from the down conductor and separated

distance is S

Difference of lightning current waveform

waveform

[µs]

peak current

[kA]

total charge amount

[kAs]

ratio

(direct/induced)

Direct lightning

current10/350 100 0.04863852 24.92171277

Induced impulse

current8/20 100 0.001951652 ―

10

Figure 8. Comparison of waveform between direct lightning current and

induced impulse current


--- 10/350 (peak value : 100kA)

― 8/20 (peak value : 100kA)

Characteristic values of lightning current in each LPL

LPL

sign unit ⅠⅠⅠⅠ ⅡⅡⅡⅡ ⅢⅢⅢⅢ/ⅣⅣⅣⅣ

first stroke

peak value

of first stroke currentI max kA 200 150 100

charge of

first stroke currentQ short C 100 75 50

specific charge energy

of first stroke currentW/R MJ/Ω 10 5.6 2.5

wave form T1/T2 µs/µs 10/350 10/350 10/350


wave form T1/T2 µs/µs 10/350 10/350 10/350

subsequent

stroke

peak value

of subsequent strokeI max kA 50 37.5 25

average steepness of

current rise of

subsequent stroke current

di/dt kA/µs 200 150 100

wave form T1/T2 µs/µs 0.25/100 0.25/100 0.25/100

long stroke

long stroke chargeQ long C 200 150 100

duration of

long stroke currentT long S 0.5 0.5 0.5

Operating characteristic

IEC 61643-1 : 1998

Surge protective devices connected to low-voltage power distribution systems

- Part 1 : Performance requirements and testing methods.

Typical SPD

voltage switching type SPD ( air gap ) … Class Ⅰ(Figure 9)

voltage limiting type SPD ( ZnO varistor ) … Class Ⅰ(Figure10)

(10/350µs) (10/350µs)


Figure 9. Terminal voltage change during

operation of voltage switching type SPD

Figure 10. Terminal voltage change during

operation of voltage limiting type SPD

SPD energy coordination

SPD is basically installed at the transition point of interface in the LPZ as this figure

shows.

Impulse withstand categories for each circuits or devices are determined in

accordance with each LPZ.

LPZ1

impulse withstand category ⅣⅣⅣⅣ : 6 kV

LPZ0


Figure11. Energy coordination between lightning current arrester(classⅠⅠⅠⅠ)

and surge arrester(classⅡⅡⅡⅡ)

service entrance for

electrical power line

(the transition point of

interface in the LPZ ) lightning current arrester (classⅠⅠⅠⅠ)

wave from (10/350µs)

surge arrester (class ⅡⅡⅡⅡ)

wave form (8/20µs

decoupling inductance

Type 1 varistor-based SPD Type 1 spark-gap-based SPD

Comparison of the coordination behavior

of a spark gap and a varistor

total currenttotal current

Current flowing

through the type 1

SPD (spark gap)

current flowing

through the varistor

of the terminal

device


Figure 12. Current characteristic for a decoupling inductance in length of 10m

total current: 1.25kA 10/350µs)

Current flowing through

the varistor of the terminal device

The wave form indicated in green flows into the classⅡⅡⅡⅡSPD.

current flowing through the type 1 SPD(varistor)

SPD locations

conductor

power supplyclassⅡⅡⅡⅡSPD

low voltage

200V

high

voltage

6.6kV

LIGITNING PROTEC TAKETANI Co.,

Ltd. 15

earthing for

low voltage coil of

transformer

earthing

for enclosure

of device

classⅠⅠⅠⅠSPD

200V

Figure 13. The locations of classⅠⅠⅠⅠSPD and classⅡⅡⅡⅡSPD

TN system : One part is earthed directly at the power supply, and the exposed conductive

part of the installation is connected to that point by protective conductor.

Earthing system of power distribution line

installation

power

supply

supply cable

(if any)

power

exposed conductive part

terminal

device

16

(a)(a) JIS C 60364JIS C 60364--11 figure 31. A1 figure 31. A1 (b) example of single phase / 2 wire(b) example of single phase / 2 wire


Figure 14. TNS system which has neutral line and protective conductor separately

throughout the whole system

earthing at

power supply

earthing inside of the

supply cable

earthing of the system

which is connected via

more than one earth electrode

exposed conductive part

power

supplydevice

earthing for

low voltage coil of

transformer

earthed at the power supply

TT system The exposed conductive part of installation is connected to the earthing

electrode which is electrically separated from the earthing of power supply.

power

supply

supply cable

(if any) installation

power

supply

terminal

device

exposed

conductive

part

17

Figure 15. TT system which has neutral line and protective conductor

separately throughout the whole installation

(a)(a) JIS C 60364JIS C 60364--11 figure 31. F1 figure 31. F1 (b) example of single phase / 2 wire(b) example of single phase / 2 wire


earthed at

power supply

protective earthing

inside of the installation

exposed conductive part Each earthare separated.

earthing for

low voltage coil of

transformer

earthing for

enclosure of

device

SPD connection in the TT system

MCCB

Protective measure for short-circuit failure of SPD :

backup circuit breaker = MCCB

Electric

shock R

18

SPD

earthing for low voltage coil

of transformer

earthing for

enclosure of device

Figure 16. Lightning current path in the case of the short-circuit failure of SPD

(back up: MCCB)

Power supply voltage is

added to the enclosure

of the device via

protective conductor.

earth fault current

MCCB cannot detect

earth fault current because

this current is too small.

short


PE

SPD connection in the TT systemProtective measure for short-circuit failure of SPD

R

short

MCCB

short circuit

current

SPD is installed between L and N

Due to the N-PE gap,

hazardous voltage is

19

Figure 17 . Lightning current path in the case of the short-circuit failure of SPD

(back up: MCCB)

N-PE gap

Because of the short circuit current,

interruption by MCCB is possible.

hazardous voltage is

not added to the

enclosure of the

device.



of transformer

earthing for

enclosure of device

PE

SPD connection in the TT system

ELB

It’s possible to interrupt

the earth fault current.

protective measure for short-circuit failure of SPD:

backup circuit breaker = ELB

RIn this case, earth

fault current is small

because impedance of

earth fault circuit is

large. (earthing for low

voltage coil of

transformer and

earthing for enclosure

of device) However

ELB can detect this

small fault current and

20

SPD

Figure 18. Lightning current path in the case of the short-circuit failure of SPD

(back up: ELB)

earth fault current

short

small fault current and

interrupt it.

Therefore there is no

danger of electric

shock.

DISADVANTAGE

ELB often trips

because ELB is

sensitive.

This occurs problem

on supply

discontinuity.



of transformer

earthing for

enclosure of device

PE

Combination of MCCB and SPD

MCCB or fuse

MCCB or fuse

R

S

TELB

21

Figure 19. SPD installed at the side of power supply of ELB in TT system

(according to IEC 60364-5-53 Annex B, figure B.1)


N-PE gap

( rated follow current

extinguish capacity≧≧≧≧100A)

Combination of ELB and SPD

MCCB or fuse

MCCB or fuse

R

S

T

IΔ

ELB

22

Figure 20. SPD installed at the side of terminal device of ELB in TT system

(according to IEC 60364-5-53 Annex B, figure B.2)

No necessity

of N-PE gap


Interruption capacity of follow current

for N-PE gap requires over 100AR

MCCBSPD

I1

23

Figure 21. Follow current extinguish capacity of N-PE gap

N-PE gap

I1,I2 divert in inverse ratio to the

resistance at point A. I1 I2

⇒⇒⇒⇒Interruption capacity of follow current

of N-PE gap requires over 100A

(IEC 60364 )

I2

A

earth fault current


earthing for

enclosure of device

earthing for

low voltage coil

of transformerPE

mechanism of lightning and the latest lightning protection

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