Types of earth fault relays are similar to over current relays but with only one coil for current in the case of instantaneous, definite time, or inverse time earth fault types. One voltage coil is added in the case of directional earth fault relays.
Instantaneous, Definite Time, and Inverse Time Types
Tripping characteristics instantaneous Earth Fault, definite time earth fault, or inverse time earth fault relays are similar to the case of over current type. Different connection of current circuits are exist .
- Current coil may be connected to return path (neutral) of a current transformer as shown in figure (16).
- Current coil may be connected to the secondary of current transformer which is installed at the stare point of power transformer as shown in figure (17) .
- Current coil may be connected to secondary of ring type current transformer installed at power cables as shown in figure (18).
