Question

Impedance relay is used on______ transmission lines. 
1. Short
2. Medium
3. Long
4. All

Answer 1

Correct Answer - Option 2 : Medium

Distance Relay

• A distance protection relay is a name given to the protection, whose action depends on the distance of the feeding point to the fault.
• The time of operation of such protection is a function of the ratio of voltage and current, i.e., impedance.
• This impedance between the relay and the fault depends on the electrical distance between them.
• Types of distance relays are impedance relays, reactance relays, and the mho relays.

 

Transmission line	Length &  Operating voltage	Distance Relay
Short-line	(0-80) km (0-20) kV	Reactance relay
Medium line	(80-200) km (20-100) kV	Impedance relay
Long-line	(>200) km (>100) kV	Mho relay