Directional Overcurrent Relay

The directional overcurrent relay defines the direction of fault and help in tracing the fault as precise as possible. Basically it is called unidirectional or forward direction relay. Let see figure and try to understand the working phenomenon of directional Overcurrent relay.

Figure 1

There is two input of relay as voltage and current, voltage will be considered as reference voltage here with angle zero degree.

Commonly the impedance of line is reactive in nature, when fault occurred at P1, then fault current flow from bus 1 to bus 2, and as we knew that the impedance is of reactive nature so the voltage in circuit lead the current by 90 degree.

Let see one figure also, this figure is trip-block figure of directional overcurrent relay.

Is the angle of current with respect voltage and is the angle difference of 2 to 8 degree, this angle difference is the difference between block and trip states of relay.

Operation condition is

-180 degree< -