Classification Of Relays

Question 1

Types of Relays

Answer 1

Electromechanical, Static, Digital, Numerical-Microprocessor

Question 2

Advantages and disadvantages of Static relay

Answer 2

Advantages: No moving parts, less space, more settings

Disadvantages: need auxiliary power, not long lasting

Question 3

Features of digital relay

Answer 3

No moving parts
Stable
More protection functions
Fault current/event recording
Communication facility
HMI display
Self supervision

Question 4

Numerical-Microprocessor relay features

Answer 4

All functions of digital + auto recloser functions, power quality measuring, interlock, time stamping

Question 5

What is over current relay

Answer 5

Picks up current above a set threshold to protect power system elements

Question 6

Magnitude of short current and fault clearance time

Answer 6

5-20 times full load current (millisecond clearance required)

Question 7

What is the voltage rating of over current device

Answer 7

Should be equal or greater than circuit voltage

Question 8

Process of Relay during fault

Answer 8

Main relay activated once CT senses fault
Main relay activation energizes trip relay
Trip relay pulses CB trip coil