Behavior of transformer insulation under short-time overvoltage
This paper reports on a series of tests made on transformer insulation samples with automatically applied short-time a.c. overvoltages above the corona inception level to determine the conditions under which damaging corona occurs. Modified dielectric tests for power transformers are discussed.
The Effect of Test and Abnormal System Voltages on Transformer Insulation
In service, a transformer will be subjected throughout its life to three different types of voltages. These are: power frequency, switching surge, and impulse voltages. Recent computer studies and field investigations of EHV systems have provided data on the magnitudes and durations of these voltages. Laboratory tests and factory tests of transformer insulator structures have provided new data on performance. Impulse test levels have been defined for many years. Modern lightning arresters can be selected to provide adequate protection against switching surges.
Insulation Levels for VEPCO 500-Kv Substation Equipment
A detailed study has been made of the Virginia Electric and Power Copmany (VEPCO) 500-kv transmission sytem to determine optimum insulation levels for the substation equipment. Results of this study depend on both economic and technical considerations. For the VEPCO system, a 70% arrester can be used at the generator step-up transformer locations, and a 75% will be required at step-down substations. Adequate impulse and switching surge margins permit a transformer BIL (basic impulse insulation level) of 1,300 kv to be used at all locations. The most practical circuit breaker BIL, consistent with good engineering practice and economy of application, is 1,550 kv.