Lead wire on a surge arrestor

[jeebusmn]

Hi,

We have a power pole with a surge arrestor on it. The surge arrestor will redirecting a lightning strike to ground to prevent our electrics from being damaged. I am trying to determine the maximum length the lead wire can be so that its inductance doesn't interfere with the surge arrestor. This is what I have found:

PM = Protection Margin: set to 0.1
Vp = Voltage drop per a foot of the lead arrestor wire =6KV/FT
BIL = Basic Insulation Level of the power cable = 8KV
Va = Arrestor switch voltage = 18.5 KV



The equation I was using was

PM = (BIL - 2*VA - L*VP)/BIL

I solved for L with the above values and got about 5ft. Is this correct or is there a table someplace I should be using?

 

[jghrist]

Seems to me that

PM = (8 - 2*18.5 - 5*6)/8 = -1.125

As long as your arrester switch voltage is more than half the BIL, you have no protective margin no matter how short the lead is.

 

[cuky2000]

See if the enclosed link could help:

http://www.hubbellpowersystems.com/powertest/literature_library/pdfs4lib/OB/EU1509WB.pdf