Relays can be designed to respond to changes in resistance, reactance or impedance voltage and current, light intensity, temperature.
Description : IDMT relays are used to protect the transformer against : (A) Internal short -circuits (B) Open circuits (C) External short circuits (D) Oil leakage
Answer : IDMT relays are used to protect the transformer against : External short circuits
Answer : The inverse definite mean time relays are used for over current and earth fault protection of transformer against internal short-circuits.
Answer : The single phasing relays are used for the protection of three phase motors.
Answer : Impedance relays are used for phase faults on long line.
Answer : Discrimination between main and back up protection is provided by the use of relays which are slow.