PILOT RELAY PROTECTION FOR TRANSMISSION LINES
Pilot wire differential relays are high-speed relay which is designed for the protection of distribution and transmission lines mostly they are used in short lines which is less than 40 km. it is the fastest power relay in switchgear relays and the working of this scheme requires communication channel so that it can carry system voltage and current information to the control section the main purpose done by the pilot relay is to remote control the circuit breaker Pilot relaying is used in high voltage transmission line to transmit “trip or don’t trip” between two or more substations the function of the relay is to trip the circuit breaker when a fault appears
PILOT CHANNELS To transmit a trip or don’t trip signal pilot relay use different channels • Line tuner is used for the transmission of signals through the power line the signal will be coupled by the tuner, wave traps are used and this combination is called as (PLC) power line carrier • Telephone lines can be used to transmit the signals • Microwave tower can be used to transmit the trip signal if the line of sight is clear between the two substations • Fiber optic cables can be used for the transmission of the signal in order to use fiber optic cable the T- lines must be short if so the optical cables can be connected to relays on both ends of the line
DISTANCE RELAY The distance relays will respond to the ratio of voltage to current and it would react to impedance and impedance component Features of distant relays • Distance relay could detect the fault within the preset distance in a transmission line from its location • Because of the resistance generated by the power line, the total impedance will be the function of its length of distance • A distance relay compares voltage and current and it will calculate the impedance
