Search

Blackouts usually occur when a heavilyloaded transmission interconnection is subjected to a disturbance that pushes it over the stability limit. In this case, a blackout was caused by multiple lightning strikes to a transmission link consisting of three parallel 500 kV power lines carrying a small fraction of their rated load. The incident caused the islanding of seven power stations, the shedding of 663 MW of generation, a regional blackout in British Columbia, Canada that affected 34,500 customers and damage to the equipment of a major customer. One of the subject lines experienced a double line-to-ground fault, and the other two lines experienced single line-to-ground faults. It took about 3.25 hours to end the blackout and totally restore the system to its pre-outage condition. The following unusual phenomena were encountered during this incident: a) 9 Hz ferroresonance currents that triggered the relay of the shunt reactor bank of the 500 kV line which experienced the double line-to-ground fault, and; b) Ferranti Effect overvoltages that reached 148% at the remote end of a chain of 138 kV & 230 kV lightly-loaded lines that became electrically connected in series, with no voltage control at the intermediate points. This paper gives a review of both this incident and a prior unreported one which also caused a regional blackout, and presents the lessons learned from them. more...