Circuit Breaker Theory

OIL CIRCUIT BREAKER

These are one of the oldest type of circuit breaker which employs oil as ac quenching medium. The contacts of the circuit breakers are separated in the oil. The bubbles of gas formed which prevent resitriking of the arc after the current reaches zero point of the cycle. 

There are two type of circuit breakers

1. circuit breakers using large quantity of oil or the bulk oil circuit breakers

2. circuit breakers using minimum quantity of oil called minimum oil circuit breakers.

PLAIN BREAK OIL CIRCUIT BREAKER

It consists of a strong, weather tight earthed tank containing oil upto certain level and air above the oil level. both the fixed and moving contacts are immersed in oil.

 when the contacts are separated, an arc is struck between the contacts with production of large amount of heat. this with increase the temperature to near about 5000 k which will vapourize the oil into gases such as hydrogen with small percentage of methane,ethylene and acetylene. with the withdrawal of moving contacts, arc length increase and gas formation rate decreases as temperature lowers.

when distance between fixed contact and moving contact reaches at critical value, the arc gets extinguished at some current zero.

There are two types of plain- break oil circuit breakers,

1. Single break oil circuit breaker

2. double break oil circuit breaker.

Single break oil circuit breaker

The single break oil circuit breaker principle is represented in fig . The in and out of the current is through the terminal bushing. There is only one arc which is struck between the fixed and moving contact. The current breaks at one bushing and the moving contact is supported by the other bushing through sliding contact.

Double break oil circuit breaker

The principle of this type of circuit breaker is shown in the fig. There are two fixed contacts associated with terminal bushing which makes contacts with the moving contacts during normal operating condition. The lever containing the moving contacts can be operated with the help of crank.

  When the contacts are separated, two arcs are drawn. Thus there are two breaks  in series. This can achieve rapid arc lengthening which eliminates the need for a specially fast moving contact speed.