Frequency Quality Degradation and Measures in Western Japan

Western Japanese power system, where the standard frequency is 60 Hz, has exhibited noticeable degradation in frequency quality under normal operating conditions. Such degradation can weaken system resilience during disturbances, requiring prompt and effective countermeasures. This paper analyses the causes of the degradation and identifies key drivers, including the rapid growth of variable renewable energy—which has reduced available control reserves—along with inter-area differences in balancing-response speed and the high control speed of frequency converter stations. Based on this analysis, we examine countermeasures using time-domain simulations, including increasing control reserves, applying ramp commands to tie-line set-points, moderating the ramp rate of frequency converter stations, and implementing a new frequency-control scheme. The findings provide valuable insights not only for the Western Japanese power system but also for other systems operating under similar conditions or with high shares of variable renewable energy.