Accelerated testing of 25 kV/6.25 kV potential transformers for E.M.U. stock (TM-ETR-4)

In 1968, two potential transformers mounted on the roofs of AM3 units on Scottish Region failed explosively, causing considerable damage to other roof-mounted equipment. The failures were caused by insulation deterioration in the epoxy impregnated winding. The insulation had deteriorated due to the action of discharges in voids, caused either...