A 35 kV PT explosion in a thermal power plant caused busbar outages and grid risks. Explore root causes, fault progression, protection response, and how to prevent similar failures with insulation testing and resonance overvoltage mitigation. Abstract— It is shown in this paper that single-phase fault s in a 110 kV supply network result in the occurrence of resonant overvoltages, which are dangerous for substation equipment at the 35 kV side where capacitive current compensation via Petersen coils is used. Analysis after on - site investigation: 1. Common methods of protecting busbars include overcurrent-based interlocking schemes, overcurrent-based differential protection, high-impedance differential protection, and percentage differential protection. The series resonance withstand voltage test is a critical step in ensuring the insulation performance of high-voltage equipment such as 35kV cables used in prefabricated substations (commonly referred to as “box transformers”). Due to the fact that the short-circuit levels of bus bars.