Value of security: modeling time-dependent phenomena and weather conditions

Deterministic security criteria provide a degree of security that may be insufficient under some operating conditions and excessive for others. To determine an appropriate level of security, one should perform a probabilistic cost/benefit analysis that balances the cost of the security margin against its benefits, i.e. the expected societal cost of the avoided outages. This paper shows how a previously published method based on Monte Carlo simulation can be enhanced to take into account time-dependent phenomena such a cascade tripping of elements due to overloads, malfunction of the protection system and potential power system instabilities. In addition, the importance of using failure rates that reflect the weather conditions is discussed. Studies based on the south-western part of the transmission network of England and Wales demonstrate the validity of the models that have been developed.