Factors Influencing the Insulation Coördination of Transformers-II

Supplementing a previous paper, data given here verifies the coördination between transformer major insulation and standard edge gaps for surges of short duration. Insulation deterioration caused by high surge voltages is shown to occur at relatively constant voltages regardless of wave length or polarity. Direct strokes are Found to be the cause of principal damage, use of overhead ground wires for apparatus protection is recommended.