Quantitative grading of insulation damage to distribution transformers caused by high-altitude electromagnetic pulse based on partial discharge detection

Distribution transformers may experience insulation breakdown or degradation when exposed to the influences of high-altitude electromagnetic pulse (HEMP), thus posing significant threats and uncertainties to the safety and stable operations of power systems. Therefore, this study constructs a HEMP impact-test platform for distribution transformers, evaluates and analyses the development patterns of partial discharge (PD) under the action of different amplitude conduction environments, decomposes and identifies the types of damage defects, proposes a quantitative classification method for the degree of HEMP damage to distribution transformers based on PD detection. And reveals the damage mechanism of distribution transformers exposed to HEMP at different damage levels. The results show that distribution transformers undergo insulation breakdown when subjected to the influences of HEMP and that performance degradation often occurs before breakdown. As the amplitude of the HEMP environment increases, the degree of transformer damage continues to deteriorate, and both the amount of PD and the repetition rate of discharges exhibit a step-wise increase, with the increase in the repetition rate lagging behind that of the discharge amount. Based on the patterns of discharge quantity and repetition rate, transformer damage is categorised into three stages: undamaged, latent defect discharge, and severe defect discharge.