Economic dispatch of a small utility with a frequency based reserve policy

The provision of emergency reserve within short time scales, the order of a few seconds, following the loss of an on-line generator is an important part of a small utilities system integrity. It is primarily made up of generator response, demand behaviour and load shedding. Economic dispatch of on-line units must take account of these factors in order to minimise operating cost while maintaining security of supply. Present reserve policies generally take account of generator response only. The minimum frequency reached following a contingency would be a more appropriate measure of system security and would represent an enhanced reserve policy. In this paper a method is described where the economic dispatch for a small utility is performed with a frequency based reserve constraint. A system model is used to evaluate the network behaviour following a contingency and is linked to an optimisation algorithm. A comparison is made with a generator based reserve policy; reduction in system costs while maintaining acceptable levels of security is noted