Surge arrester failure

[type2jim]

We have had a failure of a 22yr old porcelain ZnO surge arrester on a 66kV 10/12.5MVA DYN11 transformer fed from an OHL. Last inspection showed no evidence of any issues. We do not have a spare and the suppliers come in at a 6-8 week lead time. The other two arresters appear to be ok. This unit is connected to generating plant and there is some urgency in returning this to service.

We have little expertise with surge arresters and would not know how to quantify the risk to the transformer of energising and operating without surge protection on one phase until a replacement is obtained so we are looking to source a replacement with some urgency. Any suggestions?

 

[cranky108]

Maybe not a complete evaluation, but if you know the chances of storms you have part of the answer. Another is the length of the line, and distance between this tap ant the next arrestored tap.
If you have an overhead line, why would you not keep spare arrestors for that line? Do you keep transformer bushings? They fail also.

Have you tried to borrow an arrester from another utility? Or looking at other manufacturers?