How is a typical medium voltage tie breaker relay set ?

[bdn2004]

I'm trying to model this tie breaker that's on a 13.8kV system tying the two switchgear busses together. And to see if the settings make sense. It has a relay but I don't know how the CT's are connected. on both sides? This particular tie in the pick is set to 1200A and a 5 sec time delay, it TCC plots the same as the main but offset by 200A less.

I can see 6 scenarios with this tie breaker: 1) Open, both sources energized, 2) Open, one source energized, 3) Open , the other source energized, 4) Closed both sources energized 5) Closed one source energized 6) Closed the other source energized. I was going to pick the worst case scenario for an arc flash determination. Is this the way this is generally done?

 

[Overvoltage]

You might verify whether both ties can be closed. Some sources require an open transition (i.e. an open upstream breaker) before closing a tie bus. If so, that would greatly reduce the amount of fault current available (by not having option 4 you listed).

 

[bdn2004]

I'm sure I'll get the feedback if the open transition is required. But, from my own experience it seems places
like this don't like ever having to lose power and much prefer a closed transition and have the systems designed that way.

 

[Overvoltage]

They may not have a choice depending on whether they are taking service at high voltage or at medium voltage. If they take service at high voltage and step down to medium voltage on their equipment it's their choice. If it's at medium voltage, utility practices/regulations may apply.