Why did relaying fail to clear this fault? 1

[Mbrooke]

Talk of the year, looks like a bus fault:

https://www.youtube.com/watch?v=Wvz6j_xBzsI

Good birds eye view of the damage:

https://www.youtube.com/watch?v=NgBQ_oCrXkw

But my question is why did this fault persist for a whopping 8 minutes? Why didn't bus-bar differential catch it? Breaker fail if the case? Why didn't zone 2 or zone 3 pickup at the remote ends when all local relaying apparently failed to do so? Has me scratching my head...

 

[davidbeach]

From what I can gather looking at the substation in Google Earth is that the failed CVT is on a section of ring bus, so there wouldn't be any bus differential per se. Some how the other end of the line needed to open so any communication mentioned in the video (haven't taken the time to watch yet) was probably intended to transfer trip the remote end.