Under certain circumstances, the vacuum circuit breaker can force the current in the circuit to zero before the natural zero (and reversal of current) in the alternating-current circuit. If interrupter operation timing is unfavorable with respect to the AC-voltage waveform (when the arc is extinguished but the contacts are still moving and ionization has not yet dissipated in the interrupter), the voltage may exceed the gap's withstand voltage. This can re-ignite the arc, causing abrupt transient currents.It is possible to reduce the current level at which chopping occurs by selecting a contact material which gives out sufficient metal vapour to allow the current to come to a very low value or zero value, but this is rarely done as it affects the dielectric strength adversely.
Nowadays, with very low current chopping, vacuum circuit breakers will not induce an overvoltage that could reduce insulation from surrounding equipment.
Vacuum arc extinguishing chamber, also known as vacuum switch tube, is the core component of power switch. Its main function is to make the circuit quickly extinguish the arc and suppress the current after cutting off the power supply through the excellent vacuum insulation in the tube, so as to avoid accidents and accidents.
The contacts carry the circuit current when closed, forming the terminals of the arc when open. They are made of a variety of materials, depending on the vacuum interrupter's use and design for long contact life, rapid recovery of voltage withstand rating, and control of overvoltage due to current chopping.
A vacuum interrupter has shields around the contacts and at the ends of the interrupter, preventing any contact material vaporized during an arc from condensing on the inside of the vacuum envelope. This would reduce the insulation strength of the envelope, ultimately resulting in the arcing of the interrupter when open. The shield also helps control the shape of the electric-field distribution inside the interrupter, contributing to a higher open-circuit voltage rating. It helps absorb some of the energy produced in the arc, increasing a device's interrupting rating.