Insulation coordination

[chuckd83]

I have a surge arrester at the 69 kV transformer bushing which adequately protects it (per IEEE C62.22-2009 Section 5.2). The transformer is connected to GIS 30 feet away by overhead line. I'm trying to determine if the GIS is protected by the same arrester. Can this be done without EMTP? I'm looking through the same standard Annex C and I'm lost. Can I even use it as the first line says "This annex provides a simplified procedure for calculating acceptable separation distances for simple air insulated substations..."

 

[jdsmith]

I am going to assume that this transformer has a 69 kV primary and some level of MV secondary - if this is not the case then these comments may not apply. I'll ask a few questions that may help you think through this:

If the primary of the transformer is properly protected per C62.22, is the transformer secondary protected as well?

What is the BIL of the transformer secondary winding and what is the BIL of the switchgear? Does the switchgear have any arrestors at any location? Depending on the type of interruptor used (SF6 puffer type contacts or vacuum bottles in SF6) arrestors may be provided for switching transient mitigation, although this is a whole different discussion.

Do you consider the line between the transformer secondary and the switchgear to have any exposure to lightning surges?