Emergency Operation of Electrical Power Plants: Effects of Thermal Unit Controls on Frequency Transients

The effect of thermal plant response on system frequency control is investigated in the paper using the results of computer simulation studies. Particularly, when islanding conditions for loss of generation or loss of heavy import are involved, the frequency deviation is largely influenced by the prime mover energy supply system as well as by the governing characteristics. As the response time frame of large steam units is on the order of minutes, the problem of the evaluation of grid frequency behaviour is cast in the so-called mid-term period. Consequently, interactions between the electrical grid and boiler turbine units are here evaluated on the basis of a mid-term modelling of the overall system. The time response of the system frequency and of some typical thermal variables are simulated for different operating modes or boiler turbine controls; the trend of such variables are correlated and compared in order to give an insight of the effects of the thermal dynamics on the frequency behaviour of an isolated power system.