what are circuit breakers? design of circuit breaker for given load, installation of circuit breaker, working principle of circuit breaker, classification, selection and maintinence

History Of Circuit Breaker

                 An early form of circuit breaker was described by Thomas Edison in an 1879 patent application , although his commercial power distribution system used fuses.Its purpose was to protect lighting circuit wiring from accidental short circuits and overloads.

Installation Of First Circuit Breaker

               The BOSTON Electric light company in 1898 used the first installed breaker at the local     L Train Station.

Working Principle Of Circuit Breaker

               Circuit Breaker essentially consists of fixed and moving contacts .Whenever a fault occurs on any part of the system,the trip coil of the breaker gets energized and the moving contacts are getting apart from each other by some mechanism , thus opening the circuit.

Design Of Circuit Breaker For Given Load

                  The following example can explain that what value of circuit breaker we could select for the given value of load.

Let

        Connected Load =40kw

        Voltage=380v

         P.f = 0.8

         C.B.=?

         KVA=KW/P.f

                  =40/0.8   =50kva

          Current I= Connected Load /Sqr 3  * V

                          =50*1000/sqr3*380

                           =75.96A

   Circuit Breaker Required=Current *25% Safety Factor

                                             =I*1.25

                                              =75.96*1.25=  94.5A

So, we can use 100A C.B. because 95A is not available.

Classification of Circuit Breakers

                      There are several methods of classification of circuit breaker.The most general way of the rating of a circuit breaker is by the Arc extinction medium.The arc extinction can easily be done by using the different medium like air ,insulator,gas,vacuum,dielectric etc.

                       By the arc extinction medium, the circuit breaker is categorized into four types. They ate the air circuit breaker, air blas circuit breaker, Sulphur hexafluoride circuit breaker and vacuum circuit breaker.

• Circuit Breaker:  Circuit Breaker have two main categories.

1.  Ac Circuit Breaker
2. DC  Circuit Breaker.

DC Circuit breakers are further sub divide into HVDC circuit breaker.
AC Circuit breakers are further sub divide into

1. High Voltage Circuit Breaker.
2. Low Voltage Circuit Breaker.

High Voltage Circuit Breaker are further sub divide into.

1. Oil Circuit Breaker.
2. Oilless Circuit Breaker.

Oil Circuit breaker are further subdivide into

1. Bulk oil circuit breaker.
2. Low oil circuit breaker.

Oil less circuit breakers are further subdivide into.

1. Air break circuit breaker.
2. Air blast circuit breaker.
3. SF6 circuit breaker.
4. Vacuum circuit breaker.

Selection Of a Circuit Breaker

               There are few different criteria to consider when selecting a circuit breaker.

• Voltage Rating.
• Frequency.
• Maximum Interrupting Capacity.
• Continuous Current Rating.

A Typical Operating Conditions

                 

                       When selecting a circuit breaker it is crucial to have in mind the user location. Each breaker is different and some are better suited for more unforgiving environments. Below are a few scenarios to keep in mind when determining what circuit breaker to use.

• High ambient temperature.
• Corrosion and Moisture.
• high shock probability.
• Altitude 
• Resting Position.
• Testing .

1. UL factory testing .
2. Field testing.

Maintenance

                              For the most part molded case breakers have an exceptional track record of reliability mostly due to the fact that the units are enclosed.The enclosed minimizes exposure to dirt,moisture,mold,dust other containments and tampering.Part of proper maintenance is making sure that all terminal connections be tightened to proper torque value as set by the manufacturer.Breakers also need to be cleaned regularly.Improper cleaning and loose terminations can cause excessive heating and weakening of the breaker.Circuit breakers that are not used on a regular basis an intermittent start up of the breaker is required to refresh the system.