Complex Imaginary Variation 2 #5- simple protection system question

[ElecPwrPEOct11]

This is a basic question about protecting a transmission line. If there's a fault at point D and breaker 5 fails to trip, which breakers should trip next? I would pick 2 & 4 since they are the next ones up-stream. If 2 & 4 fail to trip, then I would say 1 & 3 should trip.

The problem says 1 & 3 would trip if 5 failed to trip. Am I crazy with all this studying?

 

[vdubEE]

Seems like for a fault at D, Breakers 5 and 6 would trip first. If Breaker 5 failed to trip then Breakers 2 and 4 would trip next. If Breakers 1 and 3 are tripping, I would think this is due to overreach by those Breakers.

EDIT: I see what the problem states now and it says for a Fault at Point D, Breakers 1,3 and 6 trip. What breaker more than likely failed?

My answer would be 5. If 5 fails then Breakers 2 and 4 should trip. If Breakers 2 and 4 fail, then Breakers 1 and 3 trip. However, it all starts with Breaker 5 failing.

I think this is what CI was aiming for and unfortunately it seems the problem is worded confusing. I don't have Variation 2 so I cannot see the whole problem. For breakers 1 and 3 to trip before breakers 2 and 4, it would seem they are overreaching beyond breaker 2 and 4.

 

[ElecPwrPEOct11]

^ - Thanks for your thoughts, they definitely make sense. Your interpretation of the original problem is correct. I was just trying to understand the whole problem as the CI solution didn't mention anything about 2 & 4 failing as well.