AHFA-a real-time expert system for the incremental diagnosis of multiple faults on a transmission network using the sequence and timing of switching indications

A real time Alarm Handling and Fault Analysis (AHFA) expert system has been developed to assist Area Control Engineers by diagnosing multiple faults in real time on the power system from switching indications received at the Control Centre. Switching indications are received passively through a serial link from the Control Room printer. The reasoning strategy used in AHFA goes beyond the ´generate and test´ approach used in most other comparable expert systems, incrementally following the sequence and timing of messages according to a generalised protection ´signature´. Consequently the diagnosis is fast and of high confidence, removing the need for any verification by simulation to generate the expected switchings. There is no need for a fixed time-window and both multiple faults and imperfect data can be handled. AHFA has undergone a two-month evaluation trial at an Area Control Centre, where it has operated continuously, successfully diagnosing about 95% of faults despite telemetry data problems. Under demonstration conditions, AHFA has diagnosed 20 simultaneous faults, including adjacent faults involving the same circuit breaker. AHFA is implemented in Smalltalk-80, allowing portability to workstations and PCs.