Evaluation of Lightning Impulse Voltages Superimposed with Oscillations and Overshoot using the Test Voltage Function

The frequency and amplitude of the superimposed oscillations or overshoot near the peak in Lighting Impulse (LI) voltage have an influence on the 50% Break-Down Voltage (BDV). The evaluation of test voltage incorporating frequency dependent test voltage function known as -factor takes the physical breakdown behaviour of the different dielectric materials. The paper presents two methods for implementation of -factor and the complete procedure to evaluate the test voltage magnitude and time parameters of lightning impulse voltage waveform. The first method is based on mean curve approach using Double Exponential (DE) function whereas second method uses Single Exponential (SE) function fitting on the tail of the measured impulse. The standard IEC 61083-2 Test Data Generator (TDG) waveforms are used for evaluation and comparison of these methods