7.2.2 Ground fault protection
The method of grounding affects the amount of protection that is provided by a differential relay.
When the generator is solidly grounded, as in Figure 7.7, there is sufficient phase current for a phaseto-
ground fault to operate almost any differential relay. If the generator has a neutral impedance
to limit ground current, as shown in Figure 7.8, there are relay application problems that must be
considered for the differential relays that are connected in each phase. The higher the grounding
impedance, the less the fault current magnitude and the more difficult it is for the differential relay
to detect low-magnitude ground faults.