DIFFERENCE BETWEEN RELAY, CIRCUIT BREAKER, & ISOLATOR|Online electrical engineering & Electrical Interview Questions

Saturday, November 20, 2010


What is the difference between Relay,Circuit Breaker,Isolator?

Relay is a protective device which senses the faulty conditions in a power system line and initiates the operation of circuit breaker to isolate the faulty part from the rest of the healthy power system.Examples of relays are Over Current relay,Directional relay,etc..

Circuit Breaker is a device which can
  • Make or break circuit under normal conditions either manually or through remote control.
  • Break circuit automatically under faulty conditions.
  • Make or break circuit under faulty conditions either manually or through remote control.
Some types of circuit breakers are Air blast circuit breakers,Vaccum Circuit Breakers ,SF6 Circuit Breakers,etc.You can notice the circuit breakers near to the transformers.Next time when you see a transformer search for the circuit breaker.Mostly it will be SF6 Circuit Breakers.

Isolator or Isolating Switch is a device which is used to disconnect a part of the system for maintanance purpose and repairs.Isolator can open a circuit under no load condition only.If two isolators are connected on either sides of circuit breaker,then the circuit breaker must be opened before opening the isolators.
After perfoming maitanancee work on the circuit breaker,isolators must be closed first and then the circuit breaker must be closed to bring the system into operation.


Anonymous said...

Nice one ..thank u for the information

priya said...

optimum answer i would like to know the answer for this question..."Is there any DC tansmission in tamilnadu "

bagi said...

Isolator can be operated in no load condition only what is meant by no load condition can any one explain that clearly.....

bagi said...

the isolator can be operated in the no load condition only.Can any one explain what is meant by the no load condition.If there is no load then why we are using the isolator.

anshul singhal said...

"no-load condition" means the condition in which the input of an external power supply is connected to the mains power source, but the output is not connected to any primary load....

sudhanshu said...

isolator is a off load device which is used for isolating
the downstream circuits from upstream circuits for the
reason of any maintanance on downstream circuits. it is
manually operated and does not contain any solenoid unlike
circuit breaker. it should not be operated while it is
having load. first the load on it must be made zero and
then it can safely operated.

MaheSh said...

excellent answer ... thanks for this information.......!

adposting said...

Isolator using onely break the voltage. No load condition means current is zero.

Urvashi Gupta said...

is it necessary that there should be isolators on both the sides of a circuit breaker?