Distance Protection on one end

[HamidEle]

We are doing a retrofit project. A substation new is being built. There is distance protection on the main incomer, working with utility Distance protection relay to trip on the incoming line fault instantaneously. There is another distance protection relay on one of the outgoing feeder to protect the internal line to another plant. However, there is no distance protection on the other end as it is already up to running.
The client does not want to shut the plant for adding the distance protection relay on the other end.

Wonder if there is any protection scheme to allow the 21 trip within 10 cycles to protect this internal line?

Any insights would be appreciated.

Thanks

 

[davidbeach]

Please explain why you think it's a problem. I'm not seeing an issue, so I don't know if there's something missing in your description or if you're just overly concerned.

 

[HamidEle]

The issue is, the 21 has zone 1 and zone 2 settings.zone1 is instantaneous t cover 90% line. Zone2 has time delay. If the fault happens on 10% of the line. The Zone 2 tripping will trip the line with a time delay, which would not be 10 cycles.

 

[davidbeach]

Okay, so you have a distance relay on the other end and nothing changes about what you just said. Although I wouldn't recommend it, you can set the zone 2 time at 10 cycles.

Much more than a lack of a distance relay it seems you're missing a transfer trip scheme.

What's at the other end of the line? If it's just a transformer you can have zone 1 reach into the transformer. Is there a source at the other end or just load? What's critical about 10 cycles?

 

[HamidEle]

On the other side of the line, there are 50/51 and 87B to protect the substation. There is no source on the other end, just loads. However, the utility asks us to trip within 10 cycles. Direct transfer is difficult to achieve as we additional telecom or hard wire is required.