Bus bar differential protection

[jan63]

Working in a power station where the switchyard is 500KV.The bus bar is in two section with a tie breaker/bus sectionalizer inbetween.
Presently the bus bar has high impedence bus bar differential protection with zone I covering one half of the bus and zone II covering second half.
In an upgradation project the equipment on one side of sectionalizer has been changed.Protection now is low impedence.
This will mean low impedence on one side of tie breaker and high impedence on second side.
IS THERE ANY DRAW BACK?

 

[marks1080]

The main thing that comes to my mind would be checking to make sure the low impedance bus protection CTs are not going to saturate. I'm assuming that's why you have the high impedance bus protection in the first place.

 

[davidbeach]

Good, modern, low impedance bus diff relays can figure out what's going on in the first 1/4 to 1/2 cycle, before CT saturation can begin to throw things off.

 

[marks1080]

I'm thinking for a close in external fault outside the bus zone.

 

[HamburgerHelper]

High impedance differential provides security for out of zone faults and you only have to size the CTs for in zone faults. Out of zone fault CT saturation helps secure the relay and prevent out of zone tripping.

Davidbeach,

Will it secure the differential for out of zone faults that take longer to clear than the time it could take for the CTs to saturate?



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If you can't explain it to a six year old, you don't understand it yourself.

 

[davidbeach]

The ones I’m familiar with go into a high security mode when they’ve determined it to be external and the CTs start to saturate.

 

[RRaghunath]

There is no draw-back in having one half of busbar protected by LowZ and other half by HiZ bus differential protection. Since these two schemes are independent completely.
Hope you also have Check zone differential protection! Separate Check zone protection is standard with HiZ busbar differential protection schemes.

Rompicherla Raghunath

 

[Prot123]

Is there any particular requirement for having low impedance bus diff installed? if not then High impedance bus diff relays are quite robust and have satisfactory performance. Having digital relays on Lines and feeders offers advantage of fault recording, however, for a bus bar we don't expect to see faults that often when eliminates the requirement of fault recording.
Anyways, I don't think there is any draw back of mixing Low and High impedance protection.