Restricted earth fault protection of transformers,
generators and motors differential protection of
bus bars, motors and generators.
RESTRICTED EARTH FAULT RELAY JRD 013
Principle of Operation:
The Relays JRD 011 & JRD 013 are current operated Microprocessor based, differential relays which work on the high impedance principle. An external series stabilizing resistor is used with this relay to make it a voltage operated relay. The voltage setting of the relay is adjusted to be higher than that developed by the current transformers used for maximum external fault conditions. JRD 011 is a single pole relay where as JRD 013 is a triple pole relay.
The sensing current is converted to voltage by an internal resistor and this voltage is fed to a harmonic
network which is tuned to fundamental frequency. The output of filter is fed to voltage comparator. When the sensing current signal at the fundamental frequency exceeds the set value,the comparator gates a train of pulses to the processor. The program residing in the CPU performs the function of control and also gives output signals for relay and LED driver circuits. The operation of the relay is indicated by the glowing of a 'Red' LED,which has to be reset manually by means of a 'RESET' push button provided on the front of the relay. A 'Trip Test' push button is also provided in the relay to enable testing of the trip and alarm circuits. When this push button is pressed, the output element of the relay is energized and its contacts close to
energize the trip and alarm circuits.
The relay will not operated at third harmonic currents upto 25 times the setting.