Dry Type Transformer – Real Life Stories – Cable Fault Avoided
Two quick qualifiers: One, switchgear manufacturers get it right most of the time. And two, it often takes a pair of fresh eyes to spot the obvious. Now that some perspective has been established we can continue with impunity.
An educational facility had a 13.8 kv primary dry type transformer located in a basement substation. The transformer panels (the skin) had just been pulled per a routine scheduled shutdown testing and maintenance procedure. What our techs found staggers the imagination, the scene echoing with “what were they thinking?” terminology. No, it was not Al Capone’s hidden treasure or Indiana Jones’s arc of the covenant. But the word arc is getting close.
Lying on the concrete floor, like an extension cord, were the standard 15 kv non-shielded switchgear cables. The cables ran from the primary switch compartment to the transformer compartment and had a white chalk like substance running the length of the cable where it made contact with the floor. The chalk like substance was the result of corona (ionization of nitrogen in the air) induced by the intense electrical field between the cables and ground, the concrete floor.
A chemical cocktail soon forms as the corona goes about its business and over time arcing takes place causing carbon tracking (dark carbon deposits) and eventual destruction of the cable or an electrical fault. The cables were replaced and were properly supported in open air with proper clearances. A certain disaster was avoided.