CONVENTIONAL CIRCUIT BREAKERS
Automatic Switch
The simplest circuit interruption device is the knife switch shown in Fig. 19.3. By closing the switch against the action of a spring, energy is stored. By applying a small force on the latch, the stored energy is released and the contacts open within a short time.
Air-Break Circuit Breakers
Air-circuit breakers cool the gases to naturally deionize them, causing arc interruption. The arc can be stretched. Its resistance can be increased by increasing its length. The increase in resistance is significant so that the current and voltage are brought into phase.
If the phase difference between the system voltage and the short-circuit current is reduced, when the current is interrupted at its zero value, the recovery voltage is very low at that instant.
The application of high-resistance interruption is limited to low- and medium-power ac circuit breakers. It is also used for low- and medium-power dc circuit breakers.
METHODS FOR INCREASING ARC RESISTANCE
The following methods increase the arc resistance:
1. Arc lengthening. The resistance is approximately proportional to the arc length.
2. Arc cooling. A decrease in temperature increases the voltage required to maintain ion- ization. Therefore, cooling effectively increases the resistance.