De‐excitation and Rotor Overvoltage Protection of Synchronous Generator

A fast de‐excitation system can only accelerate the attenuation of the rotor excitation current in the vertical axis excitation winding circuit but cannot make the energy stored in the generator rotor and the horizontal axis damping winding quickly disappear to achieve fast de‐excitation. For a steam turbine with a static self‐excitation system, de‐excitation is achieved with the field circuit breaker and the de‐excitation resistor provided in the generator main excitation circuit. For a synchronous generator, when the generator is operating in the event of a loss of excitation or a loss of synchronization or a pole slip, depending on the active power, a slip is generated between the generator's stator and rotor, and an overvoltage is generated on the rotor excitation‐winding side. The chapter describes the performance characteristics of the widely used Metrosil series of SiC nonlinear resistors from the United Kingdom's M&I.