Static pressures developed in distribution transformers due to internal arcing under oil

In this paper equations are derived to calculate static pressures which may occur within faulted oil filled distribution transformers as a result of arcing and gas generation, under known conditions such as tank dimensions, air space, specific fuses, and specific pressure relief devices; and unknown quantities such as actual fault current, arc length, arc location, and gas temperatures. The behavior of arcs under oil, the character of pressures in transformers, and the effect on distribution transformer pressure of various fusing means are discussed in the paper. Calculated transformer static pressure values are useful not only for the design of the transformer enclosure, but also for the design of the distribution system, the selection of protective fusing, and the formulation of operating procedures. The paper is largely based on Electric Power Research Institute (E.P.R.I.) project and report RP 325-1.