Correct Answer - Option 4 : High resistance interruption.
Methods of Arc Extinction:
There are two methods of extinguishing the arc in circuit breakers:
| Sr. No |
Method |
Application |
| 1 |
Low Resistance or Current Zero Method |
AC Circuit Breakers |
| 2 |
High Resistance Method |
DC Circuit Breakers, Low Capacity AC Circuit Breakers |
1. High resistance method:
- In this method, arc resistance is made to increase with time so that current is reduced to a value insufficient to maintain the arc.
- Consequently, the current is interrupted or the arc is extinguished.
- The principal disadvantage of this method is that enormous energy is dissipated in the arc. Therefore, it is employed only in DC circuit breakers and low-capacity AC circuit breakers.
- The resistance of the arc may be increased by:
- Lengthening the arc
- Cooling the arc
- Reducing X-section of the arc
- Splitting the arc
2. Low resistance or Current zero Method
- This method is employed for arc extinction in AC circuits only.
- In this method, arc resistance is kept low until the current is zero where the arc extinguishes naturally and is prevented from restriking in spite of the rising voltage across the contacts.
- All modern high-power AC circuit breakers employ this method for arc extinction.
- In an AC system, the current drops to zero after every half-cycle.
- At every current zero, the arc extinguishes for a brief moment.
- Now the medium between the contacts contains ions and electrons so that it has small dielectric strength and can be easily broken down by the rising contact voltage known as restriking voltage. If such a breakdown does occur, the arc will persist for another half cycle.
- If immediately after current zero, the dielectric strength of the medium between contacts is built up more rapidly than the voltage across the contacts, the arc fails to restrike, and the current will be interrupted.
