Page 204 - Practical Power System and Protective Relays Commissioning
P. 204
204 Practical Power System and Protective Relays Commissioning
18.5.3.3 Discrimination by Current and Time
The grading can be done with both time and current.
18.5.4 EARTH FAULT PROTECTION
This protection can be done using the following CT connection in the resid-
ual path, as shown in Fig. 18.5.5.
FIGURE 18.5.5 Residual connection of current transformers to earth fault relays.
18.5.5 DIRECTIONAL RELAYS
Directional relays are used to trip in one direction only by taking a voltage
vector as reference to the current vector. The reference voltage is called a
polarizing signal.
