Prevention of high-fault rupture of pole-type distribution transformers

Violent rupture of distribution transformers has occurred with increasing frequency in recent years. The problem appears greatest with pole-type units at locations with high available short-circuit currents. This paper concerns the rupture of pole-type distribution transformers subjected to internal, submerged, arcing faults of high current magnitude. An analysis of a probable rupture process and tests of faulted transformers were used to obtain a simple semi-empirical equation for the internal transformer pressure rise. Limiting the I²t during the fault with current limiting fuses is shown to be a practical means of minimizing the probability of transformer rupture.