Number
of pilot wires required for protecting 3-phase transmission lines using
translay system of protection is
6
4
3
2
2
Number
of pilot wire required for protecting 13- 
transmission lines using translay system of protection is
two. Translay scheme is mainly applied for differential protection of feeders.
Here two sets of current transformer have connected either end of feeder. The
compensating device neutralizes the effect of pilot - wires capacitance
currents and effect of inherent balance between the two current transformers.
Hence,
the correct option is (D).
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