To determine the characteristic of Directional -Overcurrent Relay

Phase Shifter

3 Ph400 V

AC

Reference Phase

Variable Phase

220V/6V Transformer

3600

ohm

V

A

PC

CC

220VDC

SPST

Wattmeter

Trip Indicating Lamp

3 4 6 9 10 7 8

Directional Overcurrent Relay

Circuit diagram for Directional Overcurrent Relay

Procedure:

1. Connect the circuit as shown in the figure. 2. Chose a setting for the Overcurrent Relay (say plug setting of 2.5 A) 3. Decide the equipment rating based on the Relay setting. 4. Set the input Voltage to 110V (7 and 8) and current 3 A through 9 and 10. 5. Change the position of the phase shifter to vary θ (can be calculated from V, I and W) and note

down whether the relay indicates ‘Trip’ or ‘Block’ signal. In case of ‘Trip’, note the time of operation.

6. Repeat for different θ, over the entire range of (00-3600) at a step of 100. Precaution:

1. Switch OFF the current circuit once the relay indicates ‘Trip’ signal. Report:

1. Plot the graph showing the characteristic of directional relay. 2. Plot the operating time Vs angle characteristic.

Discussion:

1. How is the time related to the characteristic of the relay? Find the Maximum Torque angel. 2. Explain with circuit diagram, any one use of directional relay in power system.