The number of pilot wire required for protecting 3-
phase transmission lines using translay system of
protection is
Answers
Number of pilot wire required are Two
Explanation:-
Number of pilot wires required for protecting 3-phase transmission lines using translay system of protection are two
The principal reason is that there would have tobe too many interconnections between current transformers (CT’s) to make current-differential relaying economically feasible over the usual distances involved intransmission-line relaying. For a three-phase line, six pilot conductors would be required,one for each phase CT and one for the neutral connection, and two for the trip circuit.
Because even a two-wire pilot much more than 5 to 10 miles long becomes more costly than a carrier-current pilot, we could conclude that, on this basis alone, current-differential relaying with six pilot wires would be limited to very short lines.