Emergency control of frequency on the NIE system

The authors present the solutions used by NIE (Northern Ireland Electricity) to reconcile the conflicting requirements of overall generation cost minimisation and supply reliability. The performance of the procedures is assessed, and possible improvements presented. The existing approach to emergency frequency control on the NIE system is based on scheduling sufficient emergency reserve to cover 80% of the largest infeed. The difficulties discussed include inaccurate information regarding generating unit response, and the co-ordination of under-frequency relay settings with system dynamics. The management and further development of the system is designed to ensure that the load shed following a major loss of generation does not exceed the scheduled amount. To this end, work is aimed at improving the accuracy of generating-unit emergency reserve data. NIE is also examining ways of improving the reserve available from each unit, and is proposing to fit load controllers on major generators