Fault current capability of distribution transformers with under-oil arresters

Fault current withstand capability testing of distribution transformers with under-oil arresters is discussed. The tests performed simulate the effect of an arrester failure under oil within the transformer. Experience with different test methods used to demonstrate withstand capability is described. The advantages of an internally mounted arrester are reviewed, and the effect of an arrester failure is reviewed. The way in which the arrester fails affects the resulting arc energy and peak pressure within the enclosure. The test circuit parameters, the arc energies, and the effects on the transformer are presented. Based on the test data, recommendations are made for current-limiting fuse protection at specific fault current levels and arrester ratings