Surge Arrester Specification 2

[charz]

In the datasheet of surge arrester, the residual voltage at certain waves are mentioned as below,
a)Residual voltage at 8/20us
b)Residual voltage at 30/60us
c)Residual voltage at 1/..us
However the surge arrester is selected based on 8/20us only.
1.Why? why not based on wave at 30/60us and 1/..us?
2.Is there any other names for the a), b) and c)?
3.What is power frequency spark over voltage? Is it same as rated voltage?
4.What is Impulse spark over voltage? Is it same as residual voltage at 8/20us?
5.If the surge arrester conducts for more than micro seconds say in milli seconds or seconds, whether it is possible for the over current/ground fault protection getting activated as when it starts conducting it is a phase to ground fault?
6.Does surge arrester conducts only on lightning impulse voltages or even for power frequency over voltages beyond rated voltage?
7. What is steep front residual voltage? Is it same as residual voltage at 1/..us?

 

[Power0020]

1- because the surge of 8/20 us of current usually results in a voltage pulse similar to 1.2/50 us (standardized BIL wave).
2- "discharge voltage"
3- housing FO voltage
4- same as 3
5- this is too long time for SA, it may be unable to withstand such Temporary OV (TOV), also, it will conduct usually few amperes at TOV, not a full short circuit current (protection will not sense that in most cases, it will see it a star load!)
6- by design, it must not conduct on power system normal or abnormal power frequency voltages, otherwise, it will explode!
7- usually yes

 

[cuky2000]

1. Why not based on wave at 30/60us and 1/..us? The 8/20 waveshape was chosen those many years ago and has remained the standard discharge current waveshape even though it is known not to simulate all lightning current waveshapes. As the understanding of lightning current waveshapes evolved, faster waveshape tests were introduced. To simulate the discharge current of a switching surge on a power line, the slow front and long tail waveshape was adopted.


2. Is there any other names for the a), b) and c)? Yes, the are associated with the protective level of the discharge or residual voltage waveshapes as follow:

a) 8/20us : Lightning Protective Level (LPL): is the discharge voltage resulting from a discharge current with an 8-10μs rise time. The IEC term for this is Lightning Impulse Protective Level (LIPL).

b) 30/60us: Switching Protective Level (SPL): is the discharge voltage resulting from a discharge current cresting in 45-60μs. The IEC term for this is Switching Impulse Protective Level (SIPL). NEMA in the USA stipulate a discharge voltage waveshape ranging from 45 to 90μs.

c) at 1/..us : Front-of-Wave Protective Level (FOW PL): is the discharge voltage with a rise time of approximately 5μs. The IEC equivalent to this is the steep current impulse protective level and is the residual voltage across the arrester resulting from a discharge current cresting in 1 μs.

See below supplementary information related with the surge arrester standard waveshape test and typical sample of surge arrester discharge voltage.

 

[edison123]

Thanks cuky.

Muthu

http://www.edison.co.in