High Resistance Interruption
High Resistance Interruption is a topic of switchgear protection. In this method are resistance is made to increase with time so that the current becomes insufficient to maintain the arc.
- The rate at which the resistance is increased or the current is decreased is not abnormal so as to cause harmful induced voltages in the system.
- Because of the resistive nature of the arc discharge, most of the energy in the system will be received by the circuit breaker.
- The main drawback of this interruption is that the energy dissipation is high.
- Hence it can be used only in low and medium circuit breakers and in d.c. circuit breakers.
Arc resistance can be increased by:
(a) Lengthening the arc:
Arc resistance is directly proportional to the length of are so as to increase resistance, the separation between the contacts is increased.
(b) Cooling the arc:
Cooling helps in deionization of medium thus increasing arc resistance.
(c) Splitting the arc:
The resistance can be increased by splitting the is into a number of smaller arcs in series. Each arc experiences the effect of lengthening and cooling. Arc may be split by introducing some conducting plates between the contacts.
(d) Reducing cross-section of the arc:
When the area of the arc is reduced, the voltage required to maintain the arc to be increased i.e. resistance is increased. Allowing the arc to pass through a narrow opening can reduce the cross-section area.