WHAT IS CIRCUIT BREAKER AND BASIC PRINCIPAL?
Circuit Breaker: It is a device that close or open the electrical contact in a chamber (interrupter) in normal as well as abnormal (fault) condition.
OR
A device that isolate the electrical equipment (transformer, generator etc) by breaking the contact from faulty circuit.
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| Circuit breaker panels |
Basic principal of operation of circuit breaker:
The working principal of circuit breaker can be explain by given two parts:
1.Opening of contacts of circuit breaker
2.Extinguishing of arc produce between contacts.
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| Working diagram circuit breaker |
According to figure the trip coil is connected with current transformer and it is also connected with automatic operated device (for automatic operation of circuit breaker).In normal condition current flow from circuit.When the current above normal condition (at the time of fault), then current transformer excited and the increase current also flow in trip circuit.Thus trip coil energized and it attract the mechanical device and the handle connected with movable end move (as shown in figure) and it disconnect from fix end, thus it is break the circuit.
2.Extinguishing of arc: When the contact of circuit breaker opened, then a high current flow between contact, that produce spark and heat between the contact.Due this the air or oil between the contact ionized.Thus resistance between contact decreases and voltage drop across contact also decreases.Thus spark between the contact increases gradually.So, it is important to stop the arc at this time.Because if it persists for some time, it may be become more dangerous.
The extinguishing of arc in circuit breaker take place by given method:
1.High resistance method: In this method the arc is extinguish by increasing the resistance between contact.This method is used in low and medium voltage air circuit breaker.It is also used in DC circuit breakers.The following methods is used for increasing the resistance between contacts:
a) Reducing ionized particles: The ionization of air or oil depends upon the potential gradient and temperature between contacts.So, by decreasing the potential gradient and temperature between contact we can reduce the ionization of particles.We can reduce potential gradient by increasing the distance between contacts.By cooling the arc we can decrease the temperature between contacts.
b) Increasing the length of arc: We know that resistance is directly proportional to length.Thus by increasing the length between contacts.The length of produce arc increases.So, resistance between contact increases and it extinguish the arc.
c) Decreasing the cross section area of the arc: We know that resistance is inversely proportional to cross section area.So, by using thin contacts we can decrease the cross section area of arc.Thus the arc suppress easily.
d) Splitting the arc: By inserting conducting plates between produce arc.We can split the arc.Thus arc extinguishes easily.
2.Low resistance method: This method is used for AC circuit breakers only.Because in this method the arc is suppress at the time of zero condition of AC.Thus it does not re-strike to produce arc again.It is also know as ZERO POINT method.
In this method between the arc produces between contact is cooled by the acceleration of pressure free air or gas.So, the air or oil between the contact is not ionized by arc.
→This method is used for high capacity breakers.
Desired requirements in circuit breaker: The desired requirements in circuit breaker is given below.
1.Safety: It should be work properly in normal and abnormal condition.
2.Quickness: It should be work quickly.At the time of fault it should be break the faulty circuit quickly.
3.Selectivity: At the time of abnormal (fault) condition, it should be break the only faulty circuit without disturbing the normal circuits.
4.Reliability: It should be operate only in fault condition.
5.Sensitivity: It should be sensitive for fault.At the time of fault it should be operates quickly.
Duties of circuit breaker: The duties of circuit breaker is given below.
1.It should be work properly on full load (without rise the temperature).
2.It should be open and close on no load.
3.It should be operate at time of fault.
4.At normal condition, it should be open and close.
Conclusion: The final conclusion is that circuit breaker behaves like a switch as well as a protective device.With the help of circuit breaker we can open or close the circuit at normal condition and at time of fault it operates quickly and protect the electrical system.
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