Transmission Lines Protection Questions Answers

What is meant by Tine Graded Protection?

Time Graded protection is a scheme of over current protection, in which the discrimination is incorporated i.e, the time setting of the relays is so graded that in the event of the fault, the smallest part of the system is disconnected

What are the main elements of current carrier protection?

The main elements of the carrier current protection are: Transmitter, Receiver, Coupling equipment and Line trap.

Why Merz-Price Protection is not suitable beyond 33kV?

Difficulties are experienced in balancing the secondaries of the CTs and this is why Merz-Price protection is not employed beyond 33kV.

What types of relays are suitable for the protection of radial feeders?

Induction type IDMT relays are more suitable for protection of the radial feeders because the time current characteristics are similar in shape and in no case they cross each other at any time.

What is the purpose of Line trap and Coupling capacitors in carrier channels?

Line trap is an LC network inserted between the busbar and connection of coupling capacitors to the line and tuned to resonance at the high frequency and are used to confine the carrier currents to the protected section so as to avoid interference with or from adjacent carrier current channel.

Coupling capacitors is used to connect the high frequency (carrier) equipment to one of the line conductors and simultaneously serves to isolate the carrier equipment from high power line voltage.

What is Unit Protection?

Unit system of protection is one in which the protection responds to the faults in the protected zone alone and it does not respond to through faults (faults beyond the protected zone). None unit systems does not have zone boundry.

What is the minimum time interval set for two adjacent circuit breakers to operate in radial feeders?

It will be usually around 0.4 sec