Analyzing the Possibility of Improving Waveform Shape in Lightning Impulse Testing of Distribution Transformers

In the high-voltage laboratories, engineers attach significant importance to generating standard Lightning Impulse (LI) waves while testing distribution transformers. The transformer windings with small inductance or large capacitance can lead to high-frequency resonances and excessive overshoot in the resulting $L I$ voltage waveform. These outcomes impose substantial stress on the transformer insulation and increase the risk of breakdown. This paper focuses on the potential of incorporating series and parallel compensators with the transformer under test to achieve the desired standard waveform. Initially, a Frequency Response Analysis (FRA) measurement is conducted to derive the black box model of the transformer. Subsequently, the utilization of a parallel capacitor to dampen the oscillations and enhance the front time of the LI waveform is presented. Afterwards, the inability of Glaninger and Haefely Patented Overshoot (HPO) compensators to mitigate the excessive overshoot observed during testing of the Low Voltage (LV) winding is investigated. Finally, the necessary to readjust the parameters of the Impulse generator (IG) to achieve a waveform that closely resembles the standard one. Then, some compensators are utilized to correct the tail time and overshoot. The research aims to provide valuable insights into preventing high-frequency resonances, improving LI waveform characteristics, and ensuring the reliable performance of distribution transformers.