impulse current testing according iec

Lightning Protection Forum Shanghai June 2004

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Impulse current testing

Michael Gamlin

Haefely Test AG, Basle, Switzerland

Abstract: IEC time parameter definitions for impulse currents are explained and an overview of the IEC standards 60060-1, 60099-4, 61643-1 and 61312-1 in regards to impulse current testing is given. The differ-ent impulse currents such as exponential current im-pulses (ECI), lightning current impulses (LCI) and rectangular current impulses (RCI) are analytically described by their simplified circuit diagrams. The generation of the lightning current impulses (LCI) is more detailed explained and the impulse current sys-tem of the Shanghai Metrology Institute delivered by the Haefely AG is introduced especially in regards of lightning current impulse testing. 1. Introduction The IEC standards 60060-1, 60099-4, 61643-1 and 61312-1 specify parameter tolerances for the different exponential current impulses (ECI), rectangular cur-rent impulses (RCI) and lightning current impulses. IEC 61312-1 standard gives a guideline how a light-ning current impulse (LCI) for test purposes can be achieved. 2. Time parameter definitions for impulse currents according to IEC standards 2.1. Exponential current impulse (ECI)

Figure 1. Time parameter ECI T1: Front time T2: Time to half value O1: Virtual origin

2.2. Rectangular current impulse (RCI)

Figure 2. Time parameter RCI Td: Duration of peak of a rectangular impulse Tt: Total duration of a rectangular impulse current 2.3. Current rise

Figure 3. Parameter current rise ∆i: I90% - I10% ∆t: t90% - t10% 3. Overview of impulse current definitions according to IEC standards 3.1. IEC 60060-1: High Voltage Test Techniques; Part 1: General definitions and test requirements IEC 60060-1 defines several exponential current im-pulses as well as several rectangular current impulses by time parameters, peak values, polarity reversal and the permitted tolerances (see Figure 4.).


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3.2. IEC 60099-4: High Voltage Test Techniques; Surge arrestors; Part 4: Metal-oxide surge arres-tors without gaps for a.c. systems IEC 60099-4 defines several exponential and rectan-gular current impulses by time parameters, peak val-ues, polarity reversal, needed energy and the permitted

tolerances (see Figure 5.). Compared with IEC 60060-1 the tolerances for the time parameter for ECI varies. Furthermore the RCI is defined by time parameters and an energy demand for the test object. To simulate service conditions of an arrestor 4/10, 8/20, 30/80 and long duration cur-rent impulses are combined with the rated

Figure 4. IEC 60060-1 impulse current definitions

Figure 5. IEC 60099-4 impulse current definitions


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arrestor AC voltage (operating duty test ODT).

3.2. IEC 61312-1 (Annex C): Protection against lightning electromagnetic impulse, Simulation of the lightning current for test purposes, First light-ning stroke

Simulation parameters: Peak current: Ipeak Charge: Specific energy: Current rise: ∆i= I90% - I10%, ∆t= t90% - t10% IEC standard 61312-1 (Annex C) splits up the first lightning stroke current into a high energy portion and a fast rise time portion. Both portions can be applied independently or in combination 3.2.1. IEC 61312-1 (Annex C): High energy portion

“The parameters Ipeak, Qs, and W/R with their toler-ance4s are to be obtained in the same impulse. This can be achieved by an approximately exponentially decaying current with T2 in the range of 350 µs.” (see figure 6.)

3.2.2. IEC 61312-1 (Annex C): Fast rise time por-tion “The simulation conducted in accordance with this method covers the rate of rise of the current of short duration strokes ∆i / ∆t. The tail of the current is of no consequence for this kind of simulation.” (see figure 7.) 4. Simplified analytical description of different impulse currents 4.1. Simplified principle circuit diagram for expo-nential current impulses (ECI) Figure 8. Simplified circuit diagram ECI

∫∞

=0

s dt)t(iQ

∫∞

=0

2 dt)t(iR/W

Figure 6. IEC 61312-14 (Annex C) High energy portion

Figure 7. IEC 61312-14 (Annex C) Fast rise time portion


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0.00

0.50

1.001.50

2.00

2.50

3.00

0 1 2 3 4 5 6 7 8 9 10

R / R0

t peak

in µ

s4.1.1. Aperiodic damped circuit (1/<20 wave shape) Figure 9. normalized aperiodic damped ECI Above formulas show that the higher the damping (R ?) the shorter is the rise time (T1 ?) but the lower is the current peak (Ipeak ?) and the longer is the time to half value (T2 ?). Figure 10. Rise time versus damping for aperiodic damped ECI 4.1.2. Periodic damped circuit (4/10, 8/20, 30/80, switching current)

Figure 11. normalized periodic damped ECI 4.2. Simplified principle circuit diagram for rec-tangular current impulses (RCI) An RCI impulse generator consists of 8 to 12 distrib-uted constant impulse generators.

Figure 12. Distributed constant impulse generators for RCI The formula below describes the relation between the used lattice network and the duration of the peak T90% (or Td). Figure 13. Rectangular current impulse RCI, class 5 arrestor, Urated= 12 kV, 60 kJ

CL1

)CL1CLln(t

),CL

1tsinh(e

CL

4R

U2)t(i

,criteriondampingCL

1,

L2R

2

2

peak

2t0

2

⋅−

⋅⋅+−⋅⋅=

⋅−⋅⋅⋅

⋅−⋅=

⋅>

⋅=

⋅−

δ

δδ

δ

δδ

δ

s1Ts7.1tF9C,H1L

CL1

;CL

2R

1peak

20

µµµµ

δ

≈=>===

⋅=⋅=

)arctan(1

t

,CL

1

),tsin(eL

U)t(i

,criteriondampingCL

1,

L2R

peak

2

t0

2

δω

ω

δω

ωω

δδ

δ

⋅=

−⋅

=

⋅⋅⋅⋅

=

⋅<

⋅=

⋅−

12..8n,CnC,LL;CL)1n(2

T1.1ntot

n

1iitottottot

%90 =⋅==⋅=−⋅

⋅⋅ ∑=

1 ms 2 ms 3 ms 4 ms 5 ms 6 ms 7 ms

100 A

200 A

300 A

400 A

500 A

600 A

700 A

RCIIpk : 623.919 ATd : 3.500 msTt : 4.318 ms

1

0.0

0.2

0.4

0.6

0.8

1.0

0 10 20 30 40 50 60 70 80 90 100

t in µs

i(t)

/ I m

ax

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

0 10 20 30 40 50 60 70 80

t in µs

i(t)

/ I m

ax


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Figure 13. Impulse current system SSGA 100-150 (100 kV, 150 kJ) for arrestor testing according to IEC 60099-4 with ECI, RCI and operating duty testing 4.3. Simplified principle circuit diagram for light-ning current impulses (LCI) Figure 14. Simplified circuit diagram LCI Figure 15. normalized simplified LCI

5. Lightning current impulse generation (LCI, “10/350”) 5.1. Detailed LCI circuit diagram

Figure 15. Detailed circuit diagram LCI 5.2. Function principle LCI circuit By the ignition of the main spark gap the energy stored in the charging capacitors capacitance C1 is transferred to the external inductance L2. Shortly be-fore the impulse current reaches its peak value the crow bar spark gap 1-2 is triggered by the impulse voltage generator. To achieve a fast rise time of about a few hundred ns for the impulse voltage generator current an extremely low inductive peaking circuit has to be integrated. The voltage drop of this fast dis-charge current across the main circuit inductance L1 finally ignites the crowbar spark gap 2-3 and the crowbar switch is closed. A crowbar switch is a spe-cific spark gap arrangement being able to be triggered under virtually no voltage condition. To fulfil the fast rise time portion the external induc-tance value L2 has to be chosen quite low (some µH) whereas for the high energy portion the external in-ductance value L2 has to be in the range of some ten µH. As soon as the crow bar switch is closed the time to half value T2 is determined by the time constant (L2+Lcrowbar)/(R2+Rcrowbar+RDUT). All component in this external circuit (crowbar, external inductance) must have a low resistive design and the current is meas-ured by a Rogowski coil and not by a shunt. Due to the inherent crowbar inductance Lcrowbar to-gether with the charging capacitors capacitance C1 an oscillation closely after the current peak occurs as to be seen in figure 16 and 17. To insure reproducible LCI impulse the controls of the main impulse current circuit and the impulse voltage generator must work together in a master/slave mode. The benefit of the master/slave mode is that a delay time can be adjusted and a triggering is only possible when both circuits are charged up.

ωπ

ω

ωπ

ω

ωπ

ω

ωπ

⋅≥⋅

+⋅=

⋅=

+⋅=

⋅≤≤⋅⋅

+⋅=

⋅−−

2t,e

)LL(U

)t(i

2t,

)LL(C1

2t0),t(sin

)LL(C

U)t(i

2LR

).2

t(

21

0

121

210

0

0.2

0.4

0.6

0.8

1

0 500 1000 1500 2000

t in µs

i(t)

/ I m

ax


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Figure 16. Fast rise time portion LCI

Figure 17. Energy portion LCI 5.3. LCI circuit components Figure 18. Impulse current system SSG 200-180 (200 kV, 180 kJ) for SPD testing with ECI and LCI

Figure 19. Motorized crowbar electrodes with tungsten copper insertion to ensure a reliable performance Figure 20. Control unit GC 223 for the impulse current circuit (bottom) and crowbar control CBC 220 (top) for adjusting and displaying the crowbar electrode distances Figure 21. Low resistive, reliable resin cast coil design

1 ms

20 kA

40 kA

60 kA

80 kA

100 kA

120 kA

140 kA

CH2 : Shunt:5.000 mOhm Level:100% Sampling:7.500 Ms/s Range:800.0 Vpp Trigger:Level 10%

No. 1LCIIpk : 107.243 kAdi : 85.794 kAdt : 9.887 usdi/dt : 8.677 kA/usT1 : 12.359 usT2 : 363.876 usQs : 46.187 AsW/R : 2.647 MJ/Ohm

1

1 ms

20 kA

40 kA

60 kA

80 kA

100 kA

120 kA

140 kA

CH2 : Shunt:5.000 mOhm Level:100% Sampling:7.500 Ms/s Range:800.0 Vpp Trigger:Level 10%

No. 20LCIIpk : 116.885 kAdi : 93.508 kAdt : 9.876 usdi/dt : 9.468 kA/usT1 : 12.346 usT2 : 357.878 usQs : 50.635 AsW/R : 3.135 MJ/Ohm

1


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Figure 22. Motorized, low inductive crowbar design with peaking circuit Figure 23. Test chamber with connected SPD ready for testing

Figure 24. SPD exploded during LCI testing 6. Technical data impulse current system SSGA 200-180 and future extension possibili-ties Wave shape max. current

Ipeak max. charging voltage

max. load

8/20 200 kA 100 kV 100 mΩ

“10/350” 100 kA 200 kV 50 mΩ

Extension possibility by integrating additional damping resistors and external inductances

(metal oxide arrestor testing according to IEC 60099-4)

1/20 30 kA 200 kV Ur= 12 kV

4/10 150 kA 200 kV Ur= 12 kV

30/80 60 kA 100 kV Ur= 12 kV

Switching current

3 kA 100 kV Ur= 12 kV

Author address: Michael Gamlin Manager Engineering HVT Haefely Test AG, Lehenmattstr. 353 CH-4052 Basle, Switzerland Email: [email protected]