Mho relays are used for the protection of which of the following lines?

A. short transmission lines only

B. long transmission lines only

C. medium transmission lines only

D.  none of the above


Answer: B. long transmission lines only


Explanation:


Relays and their applications:
1. Reactance relays ----- Short transmission lines
2. Impedance relays ------ Medium transmission lines
3. Mho relays ------------- Long transmission lines
In long transmission lines power swings are more frequent. It is not a fault but impedance relay and admittance relay mall operates during power swings. To overcome this problem mho relay is used.


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