Ground-fault Protection This bulletin is an application guide for installation cases with:- A supply from two separate sources- A solidly grounded neutralIt contains:- Installation diagrams- A table for selecting the type of ground-fault protection for equipment asshown in the installation diagrams- Important recommendations- Options available for implementationThe diagrams show how to prevent:- Nuisance tripping due to current flow in the grounding system- Failure to trip at the displayed setting due to partial measurement of the fault current- Disconnection of the external current transformer (CT) secondary when the primary is energized, which would result in an overvoltage condition and probable destruction of the CT
Ground-fault Protection
Residual type ground-fault equipment protection performs a vectorial
summation of phase and neutral currents utilizing an external current sensor
(CT) in each phase (and neutral in four-wire system). The rating of the neutralCT is the same as the rating of the phase CTs
Ground-fault Protection Source ground return type ground-fault equipment protection monitors the current on the conductor connecting the transformer neutral-to-ground.
The only grounding connection must be in the switchgear. No grounding
connection can be connected to Xo of the transformer in the transformer
cabinet or throat. The rating of the neutral or external CT must be the same
as the rating of the circuit breaker CTs.
connection can be connected to Xo of the transformer in the transformer
cabinet or throat. The rating of the neutral or external CT must be the same
as the rating of the circuit breaker CTs.
