Estimation of power system inertia constant and capacity of spinning-reserve support generators using measured frequency transients

A procedure for estimating the inertia constant M (=2H) of a power system and total on-line capacity of spinning-reserve support generators, using transients of the frequency measured at an event such as a generator load rejection test, is presented. In estimating the inertia constant, a polynomial approximation with respect to time is applied to the wave form of the transients in order to obtain the change rate of the frequency just after the onset of the event, without the influence of the oscillatory component produced by the synchronizing power between the generators. In estimating the capacity of the spinning-reserve support generators, a simple and low order model based on the idea of average system frequency is assumed, where the difference in the dynamic response of the power output to the frequency change between the once-through boiler plants and drum boiler plants is taken into account. As for the parameters of the model, the estimated value of the inertia constant for each event is used and other values are set to those which are considered to be general, except for the capacity of the spinning-reserve support generators. The value of the capacity is estimated separately for the once-through plants and the drum plants by comparing the transients and the simulation result obtained from the model for each event. The results of the estimation using the transients at 10 events show that the inertia constant of the 60 Hz power system of Japan is around 14 to 18 seconds in the system load base, and the capacity of the spinning-reserve support generators is 20 to 40 percent of the system load. Figure 1 shows the comparison between the transients and the simulation results, which reveals the validity of the presented procedure for estimating the inertia constant and the capacity of the spinning-reserve support generators. The proposed procedure is expected to be tested by Kansai Electric Power Company with increased number of events. This effort will contribute to estimate and evaluate the dynamic behavior of the system frequency in loss of generation or load.