Power plant islanding with the aid of a controlled resistor

This paper investigates the stability of a typical thermal power plant utilizing a controlled high-energy resistor as an aid for power plant islanding, or 'trip to house-load' operation. Such a resistor may be used in addition to mechanical means to quickly reduce the plant output during the transition to islanded operation. In addition, the resistor may be used to load the islanded plant to overcome mechanical limitations related to low-load operation. The stability is investigated using frequency-domain and time-domain methods. Simulations were performed using detailed models of the generator, exciter, turbine, control systems, and the resistor. The investigation indicated that the use of the resistor requires additional control actions to stabilize the plant during islanded conditions. A suitable control action was found to be a feedback signal to the excitation system, similar to a conventional power system stabilizer. The proposed control loop represents a simple method of stabilizing the power plant when a resistor is connected to the generator terminals during islanded operation.