Translay relay is used for

• The translay relay is a differential relay
• The arrangement is similar to overcurrent relay, but the secondary winding is not closed on itself
• These types of relays are used in the feeder protection and the scheme is called Translay scheme.
• In this scheme, two such relays are employed at the two ends of feeder as shown in the Fig

[ alt="RRB JE 2019 D1" src="//storage.googleapis.com/tb-img/production/19/06/RRB%20JE%202019_D1.PNG">

• The secondaries of the two relays are connected to each other using pilot wires
• The connection is such that the voltages induced in the two secondaries oppose each other
• The copper coils are used to compensate the effect of pilot wire capacitance currents and unbalance between two currents transformers
• Under normal operating conditions, the current at the two ends of the feeder is same
• The primaries of the two relays carry the same currents inducing the same voltage in the secondaries
• As these two voltages are in opposition, no current flows through the two secondaries circuits and no torque is exerted on the discs of both the relays
• When the fault occurs, the currents at the two ends of the feeder are different, hence unequal voltages are induced in the secondaries
• Hence the circulating current flows in the secondary circuit causing torque to be exerted on the disc of each relay
• But as the secondaries are in opposition, hence torque in one relay operates to close the trip circuit while in other relay the torque just holds the movement in unoperated position
• The care is taken that at least one relay operates under the fault condition