Question

Which type of distance relay is inherently “directional” and does not require an additional directional unit?

• A. Impedance relay
• B. Reactance relay
• C. MHO relay
• D. Plain offset relay

Hint:

MHO relay is inherently directional, while impedance and reactance relays generally need additional directional control.

Answer 1

The Correct Option is C

Concept: Distance relays operate according to the impedance seen from the relay location to the fault point. Common types are impedance relay, reactance relay, and MHO relay.

Step 1: An impedance relay responds mainly to impedance magnitude.

Step 2: A reactance relay responds mainly to reactance and is less affected by fault resistance.

Step 3: A MHO relay has a circular characteristic passing through the origin on the R-X diagram.

Step 4: Because of its characteristic, the MHO relay naturally responds to faults in one direction.

Step 5: Therefore, it is inherently directional and does not require a separate directional unit. Hence, the correct answer is: \[ \boxed{\text{MHO relay}} \]