Vacuum fault interrupter
Vacuum fault interrupter
(OP)
There are two vista switchgears, one fed from A-side and the other one fed from B-side. These switchgears serves transformers.
Since the B vista switchgear is energized through the closed loop switch in each transformer a fault on a primary conductor will be fed direct from the utility and also through the primaries feeding the other transformers. The loop feed switch at the transformers creates a direct connection between the A and B side primary conductors without going through the transformer.
The VFI feeding the faulted line and the A side should open first and the B side VFI should also open since it will be back fed through the other transformer primary conductors. Currently both the VFIs are set as
Pick up - 200A
U2 Inverse - 0.5
Instantaneous - 1000
Definite time - 96ms
If I bring down the definite time setting of the A-side VFI to 80ms,will this solve the issue?
Thanks
Since the B vista switchgear is energized through the closed loop switch in each transformer a fault on a primary conductor will be fed direct from the utility and also through the primaries feeding the other transformers. The loop feed switch at the transformers creates a direct connection between the A and B side primary conductors without going through the transformer.
The VFI feeding the faulted line and the A side should open first and the B side VFI should also open since it will be back fed through the other transformer primary conductors. Currently both the VFIs are set as
Pick up - 200A
U2 Inverse - 0.5
Instantaneous - 1000
Definite time - 96ms
If I bring down the definite time setting of the A-side VFI to 80ms,will this solve the issue?
Thanks






RE: Vacuum fault interrupter
Why is it necessary that the A side open first? With the closed loop, both sides will open for a fault. Who cares if one opens 16 ms earlier?
Do your settings provide coordination with transformer fuses?
RE: Vacuum fault interrupter
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If we learn from our mistakes I'm getting a great education!
RE: Vacuum fault interrupter
jghirst- Yes the settings provide coordination with the transformer fuses. I don't have a good knowledge about the closed loop system and currently I am doing the coordination study using the SKM powertool analysis. My manager asked me to do this. So I am kind of confused with this. He said the A side should trip before B side inorder to protect other transformers in the loop
RE: Vacuum fault interrupter
RE: Vacuum fault interrupter
RE: Vacuum fault interrupter
I think Scotty is right - a directional scheme is needed, but this is not an option on the Vista switch. I believe that you need to have the B feeders normally open as well to prevent backfeeding faults. You would need to open all Switch A positions if Source A is lost and close all Switch B positions.