A qualitative simulation of faults on NGC´s transmission system

The National Grid Company´s (NGC´s) supergrid consists of about 200 substations inter-connected by over 7000 km of transmission lines. The supergrid can suffer failures like any other complex system. The system is continually monitored by protection systems which automatically open circuit-breakers to isolate the affected items of plant. Low level messages reflecting these switching events and some of the protection events are transmitted automatically to an Area Control Centre (ACC) where the control engineer has to interpret these messages in order to ascertain what has transpired on the system. NG RDC have been developing an expert system (ES) to assist the engineer in firstly, keeping track of the state of the system and secondly, in diagnosing the fault on the basis of the messages received at the ACC. An integral part of this ES is a discrete event qualitative simulator of the response of the transmission system and its protection systems to a fault. For a specified fault the simulator emulates the resultant sequence of protection operations and switching events. It also reproduces the list of messages that would have been transmitted to the ACC