Revising tests for transformer insulation

THE MARGINS obtained and the degree of co-ordination between transformers and other insulation in transmission systems depends largely on the possibilities inherent in the insulation design of the transformer. Recently some units have been designed which take full advantage of the impulse characteristics of insulating materials as compared to their 60-cycle strengths. These designs are core-form, or at least have concentric coils, and it is likely that they might be considered to have maximum impulse characteristics compatible with present 60-cycle test requirements. It is believed that these characteristics affect and should be given consideration in the setting of future required impulse levels and tests, and perhaps in the 60-cycle tests which are required.