Mechanism of Quasi‐Power‐Frequency Resonant Overvoltage Triggered by Multiple Lightning Strikes in High‐Voltage Alternating Current Systems Equipped With Shunt Reactor

This paper investigates the generation mechanism of quasi‐power‐frequency resonant overvoltage triggered by multiple lightning strikes in high‐voltage alternating current (HVAC) systems equipped with shunt reactors. Based on field measurements from a 500 kV AC system, equivalent and simplified circuit models have been established to analyse the system resonant characteristics. A comprehensive theoretical framework is then developed through both frequency‐domain and time‐domain approaches, in which, the frequency scanning reveals the existence of quasi‐power‐frequency resonances for unbalanced HVAC systems. Whereas, the time‐domain analysis identifies the role of lightning continuing current in resonance excitation. Through the analysis, essential conditions for generation of resonant overvoltage are identified, that is, initial lightning strike causing single‐phase double‐end tripping, subsequent lightning strikes during the tripping period and continuing current with sufficient magnitude to cause shunt reactor saturation. Validation of the model against field data demonstrates satisfactory accuracy, with relative errors below 4% for both peaks and duration of the overvoltage waveform. These findings provide insights for enhancing insulation coordination and lightning protection design, thereby supporting the reliable operation of HVAC systems.