Protection on 6 kV Station Board.

[iphapppi]

We Have two Station Service Transformer (SST) to supply our 6,3 kV Station Board A&B on a Coal fired Power Plant. The SST rating is 150 / 6,3 kV and primary side (150kV) supplied from the 150 kV transmission line through GIS (Gas Insulated Switchgear). There was a black out on the system so the SST completely loss the voltage. but on that fault the 6,3 kV Station board incoming CB didn't Trip. The station board itself provide with Bus Under Voltage (27) protection Relay and it works after the SST loss the voltage. But The trip contact did not connencted to the incoming breaker.
My quenstion is : is that a standard that the incoming CB must trip because off loss voltage of the SST (like my example)? because we are affraid of accidental energization if the Transmission line suddenly energize and the station board incoming CB still at close position and all the load are connected. It will shock the busbar.

 

[davidbeach]

You have to have an open between the normal source and the bus when running on the alternate source. Could be on the high side of the SST or on the low side of the SST, or somewhere on the station board.

 

[ScottyUK]

I think the OP is asking whather his 6.3kV incomer should be automatically tripped if the source upstream of that incomer has a severe undervoltage or blackout event, and whether this is mandated in a standard. I'm not aware of any standard which would require this, although it might be a good idea depending on system configuration, which as usual we have no knowledge of. And I might just not understand the question.

 

[cranky108]

If you figgure most motor load should have some rotating mass that will continue to rotate following a complete loss of voltage, it is possible to have a small time delay on low voltage, then transfer to the other source. Most plants do that. The operating methods may be different, and usually have part or all the motor load on the unit while it is operating, and will switch on a trip of said unit.

But, I don't know the plant configuration.

We use a lockout on the unit to trip all breakers, and to prevent any of the breakers to close. The problem is once the lockout is reset any breaker may be closed. So the operators should not reset the lockout until the unit is ready to run.

Being this is a power plant and it is desired to keep power to the customers, some loss of motor life should be expected in the way of keeping the unit running. So an under voltage setting of 50% or lower with some time delay is not beyond belief.

Most bus bar is rigid enough that shocking it should not be a problem.

 

[iphapppi]

Sorry if my english a little bit confusing to all, my point is just like ScottyUK says. The main rules for energizing a load is from upstream to down stream ( power source to the load). I wonder if there is any standard (e.g IEEE, IEC) that stated that if the power on the upstream off because it's breaker off, the Breaker connected on the down stream have to open also to protect the load in case of accidental energization. thank youy

 

[cranky108]

I think the answer is it depends. If the load is sensitive to sudden energization then yes. If it is lighting load, then people will probally be happy the lights came back on. As far as standards are concerned, I don't know of any.