Auto reclose after transmission bus differential trip?

[cbradley75]

I'm hoping someone here is familiar with this approach. The utility I came from before relocating to Georgia never used such a practice. The basic issue is this: Say you have a transmission substation (100kV and above) that is constructed in the single bus configuration (i'm assuming because it's cheapest). Next you have a bus diff relay operate and clear the bus. A few seconds later, this scheme is such that a 'test-breaker' comes closed to test the bus and if the fault is gone, all the other breakers on the bus reclose.

Does anyone know the background of that scheme or seen it elsewhere? Is it unique to georgia? I'm curious because I'm trying to get a good rule of thumb on how I choose which line breaker should be the 'test-breaker' for the bus.

Thanks


"Don’t argue with idiots. They drag you down to their level and beat you with experience."
--Greg King, Comedian

 

[bacon4life]

I have heard of it in highly lightning prone areas.

 

[davidbeach]

Yep, if the utility has experienced too many false trips of the bus diff due to lightning, they may well try a single reclose to see if there really was a fault.

 

[cbradley75]

I don't know that lightning plays a big part, but it's possible. From my perspective it seems like when you have a single bus configuration, it's not unreasonable to want to restore it for a fault that could likely be temporary. Unlike ringbus, or breaker and half schemes, every line would be tripped in the single bus scheme.

I wonder, though, is there any industry guideline that I could reference on how the 'test-breaker' is chosen. I've heard a couple of scenarios about using the 'strongest source' or 'weakest source'; but it all seems subjective.