Translay scheme CANNOT be used for line voltages beyond _________.

T​ranslay scheme of feeder protection

• The translay scheme is a differential relaying scheme used for feeder protection, employing two relays at opposite ends of the feeder. 
• Two differential relays are used, one at each end of the feeder. The secondaries of the two relays are connected using pilot wires. The connection is designed so that the voltages induced in the two secondaries oppose each other. 
• Under normal conditions, the current at both ends of the feeder is the same, inducing the same voltage in the secondaries. 
• When a fault occurs, the currents at the two ends of the feeder become different, leading to unequal voltages induced in the secondaries. 
• This difference in voltages causes a circulating current to flow in the secondary circuit, exerting torque on the discs of both relays. 
• The relays are designed to trip the circuit breakers quickly, isolating the faulted section of the feeder. 

Limitations of Translay Scheme:

• Cannot be used for voltages above 33 kV due to increased phase shift and CT magnetization effects.
• Requires pilot wires, which may introduce communication delays over long distances.
• Not suitable for very long transmission lines, where distance protection is more effective.