Ground Fault Coordination Time Intervals

[timm333]

I have a question about the ground fault coordination time interval. The phase protection of LV breaker is coordinated with upstream MV phase 50/51 relay with a time delay of 0.22 sec. And the ground protection of LV breaker is coordinated with upstream MV ground 50G/51G relay with a time delay of 0.1 sec.

Do we also need to provide the coordination of the ground protection of LV breaker with the upstream phase 50/51 relay, what should be the time delay in this case? Thanks

 

[jim dungar]

How will a ground fault on the LV side be seen by the HV side?

Don't all faults on the LV side get seen as phase-phase faults as they 'pass through' a transformer?

 

[timm333]

How about if the voltage is same: for example, 480V main incoming feeder of a switchboard, and 480V outgoing feeder from switchboard to load. Will it be needed to coordinate the “ground” protection of the outgoing feeder with the “phase” protection of the upstream main incoming feeder?

 

[jim dungar]

Will it be needed to coordinate the “ground” protection of the outgoing feeder with the “phase” protection of the upstream main incoming feeder?

In my opinion, yes. But the bigger issue would be the main GFP coordinating with the feeder 'phase' protection.

 

[timm333]

In case we do it, what should be the coordination time interval, between the curve of ground-protection of the outgoing feeder, with the phase-protection of the upstream main incoming feeder?