Circuit Breaker(Protective Device)


Circuit Breaker

It is a device, which is use to protect electrical power system, when fault is occur. Circuit breaker is a protective device which can be operated manually as well as automatically for protection of power system.

There are two main function of circuit breaker,

  • To Act as switch for normal condition.
  • To automatically isolate or open the faulty part during faulty condition.

Circuit Breaker is operate on only under faulty condition. when short circuit is occur in the power system high current flow through the circuit breaker and it will operate during this arc is produce between the two contact of circuit breaker. CB is a piece of equipment which can break a circuit either manually or by remote control under normal condition, make circuit either manually or by remote control under fault condition. break circuit automatically under faulty condition.

basic Circuit Breaker

Operating principle of Circuit Breaker

CB is consist of two contact one is moving contact and another is fix contact, known as electrodes. these contacts are remain close,under normal operating condition.It will not open automatically until the fault is occur in power system. the contacts are can be open and close by manually or by remote control. when fault is occur on any equipment of the system, the tripping coil gets energized and the moving contact are pulled by some mechanism and CB will operate,and circuit is open.

Arc is induced between contact, when CB is operate under faulty condition. current  is able to continue until the discharge. the production of Arc not only the delay the current but it also generate heat which causes to damage CB and power system. therefore production of Arc is main problem in CB. hence make the CB as Arc production time is shortest as possible so heat generated by it may be not more danger.

During the arcing time, current flowing between the contacts depends upon the arc resistance.if arc resistance is greater, the smaller current flowing through contacts.

Selection of Circuit Breaker:-

Following parameter are consider for the selection of CB,

  1. Momentary current rating
  2. operating Speed of CB
  3. Normal working voltage
  4. Rated interrupting KVA and working power level
  5. Rated short circuit current

The speed of CB is define as the time between fault is occur to the opening  time of contact .for the selection of short circuit current take the multiplying factor is 1.0 to 1.5 to get maximum interrupting current. the calculated value is less then to the short circuit current rating.

Types of Circuit Breaker

According different application there are different types of CB.

According to their arc quenching medium:

  1. Oil circuit breaker.
  2. SF6 circuit breaker.
  3. Air circuit breaker.
  4. Vacuum CB.

According to the voltage level:

  1. High voltage CB.
  2. Medium voltage CB.
  3. Low voltage CB.

According to their services:

  1. Indoor CB
  2. Outdoor CB

According to the operating mechanism:

  1. Spring operated CB.
  2. Hydrolic CB.


if any query about CB

comment below…………………. ?



Please enter your comment!
Please enter your name here