Transfer Trip Required?

[ThePunisher]

One the existing system we are operating are described as follows:

13.8kV substation (via 34.5kV output circuit breaker) is feeding a remote 13.8kV padmounted switchgear(to the 13.8kV input circuit breaker) via overhead distribution lines. The 13.8kV padmounted switchgear further (via 13.8kV outgoing circuit breaker) feeds a 13.8-4.16KV dry type power transformer and the transformer feeds a 4.16kV switchgear (connected to 4.16kV input circuit breaker.

There are protective relays that protect and trip each of the circuit breakers stated above.

One of our engineering colleagues recommended that there should be a transfer trip from the upstream 13.8kV circuit breaker to the remote 13.8kV padmounted switchgear input circuit breaker and vice-versa.

Our point is that it is not required since if there is a fault at the 13.8kV overhead distribution, the upstream 13.8kV protective relay will trip the associated upstream relay (via 86). Hence, even though the downstream 13.8kV padmounted switchgear input breaker remains closed, the upstream breaker is "locked out".

Will this logic be acceptable in your personal experience? The upstream and downstream equipment are all owned by the plant.

Thank you.

 

[davidbeach]

Does the plant generate power in parallel with the utility source or is it entirely just load?

 

[ThePunisher]

Hi David, the plant does not have its own generation and is solely dependent from the utility.

 

[davidbeach]

Then it doesn't sound like transfer trip would buy much.

 

[magoo2]

I don't see that it buys you anything at all. For a fault between the 2 breaker, you'd have to reset 2 breakers if you had transfer trip. Keep it simple. You don't need transfer trip in your situation.

 

[slavag]

Hi.
What Davis saied.
Transfer trip is needed only in case of distribueted power generation.
From other hand, in case of some selectivity problem you can send BFP (50BF) signal from remote substation to the upstream substation. But this case must be study, this is a very special case.

Godd luck.
Slava

 

[ThePunisher]

Thanks gentlemen for the prompt response.

Out of curiousity.

Why does a transfer trip (from the remote downstream 13.8kV substation to the upstream 13.8kV substation for a fault between the usptream and downstream substation)would be significant in my case if the upstream 13.8kV has in in-plant generation in parallel to the utility if both utility connection and in-plant generation are on both upstream 13.8kV plant buses?

 

[SMB1]

Hi everyone,

it is needed in your case if the generation is from downstream.

i.e if the fault in the 13.8 feeder thw two ends will be feeding the fault.

thank you

 

[jghrist]

Why does a transfer trip (from the remote downstream 13.8kV substation to the upstream 13.8kV substation for a fault between the usptream and downstream substation)would be significant in my case if the upstream 13.8kV has in in-plant generation in parallel to the utility if both utility connection and in-plant generation are on both upstream 13.8kV plant buses?

If there is no source on the downstream substation, how would you have transfer trip from the remote downstream substation to the upstream substation for a fault between the substations? The upstream breaker would be the only one to see fault current and trip.

 

[ThePunisher]

Thanks Jghrist for the clarification. Now it is clear to me.