GFP for Feeders/SDS

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ron

ron

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215.10 requires ground fault protection for feeders that are "1000 amperes or more and installed on solidly grounded wye electrical systems of more than 150 volts to ground, but not exceeding 600 volts phase-to-phase" unless "ground-fault protection of equipment is provided on the supply side of the feeder" etc.

The following examples are not services, but feeders:
If there was GFP on the primary of a delta-wye solidly grounded transformer (1000kVA, 480/277V secondary, separately derived source), would you consider the feeder on the secondary side of the transformer GF protected on it's supply side?

Is your answer the same if the input feeder to a 1000kVA UPS module, 480/277V output, separately derived source, is protected upstream by GFP? Is the output feeder of the module GF protected on it's supply side?
 
In my opinion, the intent of the code is that the secondary of an SDS (especially one with a new bonding conductor) needs to be treated as a new "service" and does not get to take advantage of anything on the primary side.

Is the UPS a dual conversion style? Again I feel GFP is required. When the UPS is acting as the source the normal incoming protection is no longer part of the circuit.
 
It is a dual conversion type UPS, and considered a separately derived source.

For a SDS, the equipment grounding conductor is electrically continuous with the upstream OCPD/GFP. What is the scenario that would make you concerned about the upstream GFP not "seeing" the fault?

A ground fault on the secondary of the xfmr or the output of a dual conversion UPS, would still cause a disruption upstream. Generally, a UPS module can offer 4-6 times FLA to a fault.
 
Ron,

Ground fault current on the secondary of a wye connected SDS will "return" to the X0 point of the SDS. The primary side GFP may never see enough ground current to trip.
 
The ground fault current sourced by the primary and drawn by the secondary will be proportional to the turns ratio.
Do you suspect that the ground fault protection on the primary will not see enough, after settings are applied to the GFP per a coordination study?
 
The primary will not see secondary ground current as a fault. As far as the primary GFP is concerned the secondary grounded and grounding conductors are the same because they are common at the SDS X0 bond.
 
Jim,
Power in = power out + losses
If there is a ground fault on the output of a SDS, it must be the input that is sourcing that current. The primary protection will see this additionally sourced current. Where else would it come from :)
 
Ron
If the fault is on the secondary side of the UPS/SDS how would the primary side see enough of the fault on the EGC, when the fault current is flowing to the secondary side of the UPS/SDS?

The primary side EGC should not pick up any of the secondary side fault current... if it does, I think there is some wiring configuration within the building that may cause this issue and others as well.
 
Ron,

Yes the current is coming from the primary, but how does the primary know it is ground fault current and not simply a load current.
 
If the current on the primary is high enough to activate the ground fault trip setting, then it doesn't much matter to me whether it is ground fault current or fault current.
Most of the three phase delta GFP that I've seen looks for an imbalance change between phases, to determine a fault.
 
Ron, most of the GFP systems I have seen are of the Zero-Sequence type. This means they expect to see as the same amount of current flowing "back in" as is flowing "out". They do not care about the actual current imbalance between conductors nor the direction of the imbalance. Differential ground fault schemes operate slightly different but even these will not be able to see a secondary ground fault.

In the case of a delta primary to wye secondary SDS, all secondary currents are seenas phase currents on the primary. 1200A of L-G secondary current is provided by the primary phase conductors exactly the same way that 1200A of L-N single phase loading would be.
 
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