Arc in circuit breakers can be extinguished using two methods. These are High resistance and Low resistance methods.
In the high resistance method, arc resistance is made to increase with time. Since current and resistance are inversely related, as a result, current is reduced to a value that is insufficient to maintain the arc. The current is thus interrupted and the arc is extinguished.
Disadvantages of High Resistance Method
The principal disadvantage of this method is that enormous energy is dissipated in the arc.
Due to the aforementioned restriction, the method is employed only in DC circuit breakers and low-capacity AC circuit breakers.
Methods to increase the resistance of the arc
- Lengthening the arc: The resistance of the arc is directly proportional to the length. This can be achieved by increasing the gap between contacts.
- Reducing the cross sectionals area of the arc: By reducing area, the voltage necessary to maintain the arc is increased. In simple terms, the resistance of the arc path is increased. The cross-section of the arc can be reduced by letting the arc pass through a narrow opening or by having smaller area of contacts.
- Cooling the arc: Doing so enables the deionization of the medium between the contacts which in turn increases the arc resistance.
- Splitting the arc: The resistance of the arc can also be increased by splitting the arc into number of smaller arcs in series. Each one of these arcs experiences the effect of lengthening and cooling. The splitting of arc can be achieved by introducing some conducting plates between the contacts.