Surge Arrester Zinc Oxide Gapless 1

[Linspire]

Guys,
I would like to seek clarification what is current wave (30/60 us - slow-front/switching), (8/20 us- fast-front/lightning), 1/(2-20 - steep-front)us

 

[Marmite]

Steep current impulse: Current impulse with a virtual front time of 1μs and a virtual time to half-value on the tail not longer than 20 μs. The steep current impulses are used to determine the voltage-current characteristic. They have amplitudes up to 20 kA and roughly reproduce steep current impulses like those which may appear with disconnector operation, re-striking,back flashes, and vacuum circuit breakers.
Lightning current impulse: Current impulse with the wave shape 8/20 μs. The virtual front time is 8 μs and the time to half-value on the tail is 20 μs. The lightning current impulse reproduces approximately the current impulse produced by a lightning stroke in a conductor after an insulator flashover. This current impulse travels as a transient wave along the line.
Switching current impulse: Peak value of discharge current with a virtual front time between 30 μs and 100 μs, and a virtual time to half-value on the tail of roughly twice the virtual front time. The switching current impulses are used to determine the voltage-current characteristic, and in connection with the line discharge class are also used to determine the energy which has to be absorbed by the surge arrester during the operating duty test. The current amplitudes lie between 125 A and 2 kA, and roughly reproduce the load of an arrester produced by overvoltages, which were caused by circuit breaker operation.

Regards
Marmite

 

[Linspire]

Does virtual front time mean surge arrester can absorb the current for certain period ?
Whereby half-value of tail mean surge arrester take certain period of time to discharge the current energy into half.