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.