Correct Answer - Option 4 : Closing timed over current relay
- In an overcurrent relay, the actuating quantity is only current but not any voltage coil.
- When the current in the magnetic coil increases above a certain level of current, the defecting force generated by the magnetic field of the coil crosses the restraining force.
- After that, the relay operates and sends the signal to the circuit breaker.
Types of overcurrent relay:
1) Instantaneous overcurrent relay
2) Definite time overcurrent relay
3) Inverse time overcurrent relay
4) Inverse min. definite time overcurrent relay
The setting of overcurrent relay:
Two types of settings are used in the overcurrent Relay.
1) plug setting multiplier (PSM)
2) Time setting multiplier (TSM)
Plug setting multiplier:
It is the ratio of fault current in the relay to its pickup current.
PSM = (Fault current) / (Rated CT secondary current × current setting)
Time setting multiplier:
The operating time of an electrical relay mainly depends upon two factors.
- How long distance to be traveled by the moving parts of the relay for closing relay contacts and
- How fast do the moving parts of the relay cover this distance.
