A stochastic study of hidden failures in power system protection

Recent studies have shown that power systems protection mechanisms have pla yed a major role in propagating disturbances. All of the last five major We stern Systems Coordinating Council (WSCC) events (the North Ridge earthquak e, December 14, 1994, July 2 and 3, 1996, and August 10, 1996), involved ei ther false trips of line protection relays or generator protection equipmen t. Using an importance sampling based algorithm on the 179-bus WSCC equival ent system, we modeled the sequence of rare events involving generator trip s and incorrect zone 3 relay operations. Due to possible loss of generation and load, frequencies were monitored for the necessary of load shedding. T he algorithm uses the Newton-Raphson method for accuracy but reverts to DC load flow when the Newton-Raphson algorithm fails to converge within three iterations. The resulting sequence of rare events and its corresponding pro bability are used to detect weak links in the power system. This informatio n can be beneficial not only in areas such as service and maintenance sched uling and in planning, but also in determining locations where an investmen t in improving the protection system is warranted. (C) 1999 Elsevier Scienc e B.V. All rights reserved.