Page 243 - Practical Power System and Protective Relays Commissioning

240 Practical Power System and Protective Relays Commissioning

FIGURE 18.7.4 Low-frequency injection method for 100% stator earth fault protection for
generators.

FIGURE 18.7.5 100% Stator EF scheme with third harmonic voltage scheme.

18.7.4 RESTRICTED EARTH FAULT PROTECTION

This is a high-impedance protection, and it is instantaneous and protects
90% 95% of generator winding; all CTs are similar and should be class X.
Refer to Fig. 18.7.8 for Restricted Earth Fault (REF) protection for a
generator.