Lightening Arrester Rating

[RIA123]

Guys – Need your help in selecting right sized Lightening Arrester.

I have to select an L.A. for the Primary of a substation transformer which has delta connected Primary at 115 kV. This substation transformer 115kV, Delta-Primary/ 23kV Secondary Y-solidly grounded, is being fed by a utility transformer (approx. 8.5kM away) 115kV, Y-solidly grounded secondary.

My question is – will I choose the L.A. based on delta winding (substation tfmr) or based on solidly grounded utility transformer?

Appreciate your comments.

Regards

 

[mgtrp]

Is there a source on the LV of the transformer? If not, then I'd size as a grounded system, if not then I'd be considering whether I could inadvertently be backfeeding an ungrounded system.

 

[RIA123]

Thanks mgtrp
There is no source on the LV side.
Could you please explain the concept of a source on LV side influencing the LA selection criteria?. Also how does the backfeeding an ungrounded system affect the LA rating?.I was trying to select it on the basis of MCOV rating based on the grounding conditiones of the system.
Regards