Interview Questions and answers - Electrical engineer,Electrician and Electrical apprentice trainee.
1.What is meant by reach point of a relay?
Ans - The farthest point from relay location,which is still inside the zone of protection,is called the reach point.
2.What is difference between fuse and breaker?
Ans - Fuses are burnt when over current flows in the circuit but circuit breaker will just open during over current.Thus fuses are used for only once but breakers can be used by multiple number of times.
3.What is the difference between isolators and electrical CB?
Isolators are mainly for switching purpose under normal conditions but they cannot operate in fault conditions. Actually they used for isolating the CB for maintenance. Whereas CB gets activated under fault conditions according to the fault detected.
4.Explain the working of an OC relay and mention type of it?
An over-current relay has a single input in the form of ac current.The output of the relay is normally open contact,which changes over to closed state when the relay trips.
The relay has two settings.These are the time setting and the plug setting.The time setting decides the operating time of relay while the plug setting decided the current required for the relay to pickup.
Three types of over current relay.
1.Instantaneous over current relay
2.definite time current over relay
3.Inverse time current over relay.
5.Explain the working of an IDMT relay?
In an IDMT (Inverse definite minimum time) relay,the operating principle is based on the idea that with the more severe a fault is,the faster it should be cleared to avoid damage to the apparatus. It is inverse in the sense,the tripping time will decrease as the magnitude of fault current increase.