The extinction of arc is one of the important applications of vacuum circuit breaker, because the arc not only damages the equipment circuit but also affects personal safety.
There are four common methods of arc extinguishing:
Mechanical arc extinguishing: the arc is quickly elongated by the limit device. This method is mostly used in switchgear.
Magnetic blow arc extinguishing: under the action of the magnetic field generated by the magnetic blow coil in series with the contact, the arc is elongated by the electromagnetic force and blown into the arc extinguishing cover composed of solid dielectric, where the arc cools and extinguishes.
Narrow slot (longitudinal slot) arc extinguishing method: under the action of the electromagnetic force of the magnetic field generated by the arc, the arc can be elongated and enter the narrow (longitudinal) slot in the arc extinguishing cover. Several longitudinal slots can divide the arc into several sections and contact with solid dielectric, so that the arc will be extinguished quickly. This structure is mostly used in AC contactors.
Grid arc extinguishing method: when the contact is separated, the arc generated is segmented into several sections and pushed into a group of metal grids under the action of the electromagnetic force. Each isolated metal grid is equivalent to an electrode, so there are many anode-cathode voltage drops.
For AC arcs, there will be a dielectric strength of 150V ~ 250V near the cathode at the zero crossing of the arc, which makes the arc unable to continue to maintain and extinguishes.
Since the grid arc extinguishing effect is much stronger than that of DC, grid arc extinguishing is often used in AC electrical appliances.
These methods are mainly for some low-voltage circuit breakers. To understand the reasons for using these methods, it is necessary to clarify the principle of arc extinguishing of vacuum circuit breaker.
At the moment of vacuum circuit breaker breaking, due to the existence of capacitance between two contacts, the insulation between contacts is broken down and a vacuum arc is generated. Due to the shape and structure of the contacts, the vacuum arc column rapidly expands to the vacuum area outside the arc column.
When the current being disconnected approaches zero, the temperature and pressure of the arc between the contacts drop sharply, making the arc unable to continue to maintain and extinguishes. Within a few microseconds after the arc is extinguished, the withstand voltage level of the vacuum gap between the contacts quickly recovers.
At the same time, the distance between the contacts has also reached a certain distance, which can withstand a high recovery voltage.
Therefore, after the current passes through zero, the arc will not reignite and will be disconnected. This is the principle of its arc extinguishing.
In the case of high voltage and large current, the switch often uses more complex methods and structures for arc extinguishing, while the high voltage drop vacuum circuit breaker only needs a simple rubber tube to achieve smooth and effective arc extinction, mainly because: first, the current of the high voltage drop fuse is not very large, and the arc generated is not very large. Second, it uses air to extinguish the arc, which is similar to the principle of arc extinguishing of air circuit breaker, only the structure is different.