Study on Self-Excitation of Power Factor Compensation Capacitor during Output Variation of Induction Generator

Induction generators are widely used in mini- or micro-scale hydroelectric power plants. In the case of hydroelectric power generation in which changes in flow rate and head are large, the operation of the induction generator is often lower than the rated output. An induction generator is an inductive load and has a lagging power factor, and when operated at rated output, the power factor is around 0.8. The utility recommends that the customer compensate for the low power factor. The power factor compensation is planned so that the power factor of the induction generator will be about 0.95 under the condition of operating at the rated capacity. When the output of the induction generator decreases, the reactive power required for magnetization has a low change, but the active power decreases and the power factor is further lowered. At this time, a self-excitation phenomenon in which the reactive power for power factor compensation becomes higher than the reactive power required for magnetization may occur. When the self-excitation phenomenon occurs, electrical stress is provided to the induction generator, so in order to reduce the occurrence probability, the extent to which the generator's output can be operated was analyzed. As a result of the analysis, it was confirmed that the possibility of self-excitation can be reduced if the output of the induction generator is operated not to be less than 60% of the rated value. Copyright © The Korean Institute of Electrical Engineers.