Analysis of Self-Excitation Magnetic Fault in a 220 kV Hydroelectric Power Station's Generator

Large substations are generally located far from the load center and require long-distance and high-capacity transmission through EHV. When the generator operates with no-load long lines, it is prone to self excitation overvoltage phenomenon. If the voltage is too high, it may cause related equipment malfunction or even damage. In this paper, taking the startup and commissioning of hydro generator as an example, the cause of burning of bus Voltage transformer during startup and commissioning is analyzed. According to the process of the accident, on-site inspection and fault record chart are analyzed. It was found that high overvoltage during the fault process was the main cause of equipment failure. Based on the self excitation criterion of the charging characteristic method of the generator with no-load long line, combined with the actual data on site, the self excitation characteristics of the generator in the hydropower station are analyzed and calculated. The results indicate that the self excitation criterion is correct, reliable, fast, and practical. In order to solve the problem of self excitation of small hydropower stations at the end caused by long-distance transmission lines' capacitance to the ground, suppression measures such as damaging resonance parameters, adjusting operation mode, and changing transformer taps have been proposed to suppress self excitation. It has certain reference significance for operation and maintenance work.