Frequency response analysis of displacement governing in synchronous power systems

The paper describes the application of the frequency-response concept to the analysis of displacement governing in a synchronous machine system. The governor loop is shown to combine with the basic closed-loop pattern of the generator and modifies only the feedback element in the original basic loop. The analysis is used to compare stability boundaries for different governor conditions, these boundaries being derived by the application of the Nyquist stability criterion. The results obtained by this method, although based on small-displacement theory, were found to be in agreement with those obtained from a power-system simulator. The effects of phase lags, arising in the steam header of the turbine and the servo mechanism operating the throttle valve, on the stability of the system are considered together with that of a second-derivative stabilizer. An examination is also made of the damping in the system, as this provides a useful appraisement when comparing the relative stability of different configurations in the governor loop.