Protection Riddle No.90 – Directional Earth Fault testing

The overcurrent unit of a directional relay should be checked similarly to the overcurrent relay, with the directional unit blocked closed. The directional relay should be tested for minimum pickup, maximum torque angle, contact gap, and clutch pressure. If the phase power supply is not available, the directional unit can be tested by applying single-phase voltage and current in phase. Usually, this test will give large variations in in-phase pickup, because of in-phase angle being far different from maximum torque angle.