Here is the latest:
http://msn.foxsports.com/nfl/story/Utility-Bad-device-caused-Super-Bowl-blackout-020813
Sounds like the relay that tripped out the MV feeder cable was protecting the cable from a fault.
Something like a Pilot Wire Relay or some sort of differential type device for cable protection.
No doubt it was solid state and not the old reliable electro-mechanical relays of yesteryear.
Maybe that's why nuclear plants still use the electro-mechanical protection relays! :slaphead:
In the opening the article indicates that the reason it tripped was that the relay was set too low. Then later on it stated that the one relay was defective! :? Duh!! Which is it. :rant:
Usually a complex relay of this type has diagnostics to give you a history of what the V and I levels were before the trip occurred. Who is to say that there was not an actual fault on the line? Some rodent crawling around in an underground vault or some animal crawling around the insulators on top of a nice warm transformer
Wonder if there was a line disturbance analyzer monitoring these circuits. This would indicate whether the relay did see an intermittent fault or that the relay nuisance tripped and is defective.
They also got the facts wrong about what happened at Candlestick Park. A transformer did not blow up! A overhead cable splice in a 12kv PG&E line that feeds the park opened up then whipped around and shorted the other 2 lines causing 2 separate explosions. That was the first outage. The second outage was caused by operator error: shutting down a 480V generator that was still feeding tower lights.
Yeah, it will be interesting to see how this all plays out.
