How to extinguish an electric arc in electrical devices

Breaking the electrical circuit of the apparatus is a process of transition of the switching body of the apparatus from the state of a conductor of electric current to the state of a non-conductor (dielectric).

For the arc to be extinguished, it is necessary that the deionization processes exceed the ionization processes. To extinguish the arc, it is necessary to create conditions in which the voltage drop on the arc exceeds the voltage supplied by the power supply.

Forced air movement

Arc extinguishing in a stream of compressed air produced by a compressor is very effective. Such extinguishing is not used in low-voltage devices, since the arc can be extinguished in simpler ways without the use of special equipment for compressing air.

To extinguish the arc, especially at critical currents (when conditions for extinguishing the electric arc occur, they are called critical), a forced blow of air created by the parts of the moving system when moving during the tripping process is used .

Quenching an arc in a liquid, for example in transformer oil, is very effective, because the resulting gaseous products of oil decomposition at the high temperature of the electric arc intensively deionize the arc cylinder. If the contacts of the disconnecting device are placed in oil, then the arc that occurred during the opening leads to intense gas formation and evaporation of the oil. A gas bubble is formed around the arc, which consists mainly of hydrogen. The rapid decomposition of the oil leads to an increase in pressure, which contributes to better arc cooling and deionization. Due to the complexity of the design, this method of arc quenching is not used in low voltage devices.

Increased gas pressure makes it easier to extinguish the arc because it increases heat transfer. It was found that the arc voltage characteristics in different gases at different pressures (higher than atmospheric) will be the same if these gases have the same convection heat transfer coefficients.

Extinguishing under increased pressure is carried out in closed cartridge fuses without a filler of the PR series.

Electrodynamic effect on the arc. At currents above 1 A, the electrodynamic forces occurring between the arc and adjacent live parts have a major influence on arc quenching.It is convenient to consider them as the result of the interaction of the arc current and the magnetic field created by the current passing through the live parts. The simplest way to create a magnetic field is to correctly place the electrodes between which the arc burns.

For successful hardening, it is necessary that the distance between the electrodes gradually increases in the direction of its movement. At low currents, none, even very small steps (1 mm high) are undesirable, as the arc may be delayed at their edge.

Magnetic filling. If it is not possible to achieve cooling by proper arrangement of the current-carrying parts using acceptable contact solutions, then in order not to increase too much, so-called magnetic cooling is used. To do this, in the area where the rainbow burns, create magnetic field by means of a permanent magnet or an electromagnet whose arc extinguishing coil is connected in series with the main circuit. Sometimes the magnetic field created by the current loop is amplified by special steel parts. The magnetic field directs the arc in the desired direction.

With a series-connected arc extinguishing coil, a change in the direction of current in the main circuit does not result in a change in the direction of arc travel. With a permanent magnet, the arc will move in different directions depending on the direction of current in the main circuit. Normally, the design of the arc chute does not allow this. Then the device can work in one direction of the current, which is a significant inconvenience. This is the main disadvantage of the permanent magnet design, which is simpler, more compact and cheaper than the arc coil design.

The way to extinguish the arc using a series connected coil is that the highest field strength should be created at critical currents that are small. The arc extinguishing field becomes large only at high currents, when it is possible to do without it, since the electrodynamic forces become significant enough to blow out the arc.

Magnetic silencing is widely used in apparatus designed for normal atmospheric pressure. In automatic air switches for voltages up to 600 V (except high-speed), arc quenching coils are not used, since these are primarily manually operated devices and it is easy to create a sufficiently large contact gap for them. However, field reinforcement with steel clamps covering live parts is often used. Arc extinguishing coils are used in single pole electromagnetic contactors direct current because the contact solution must be reduced a lot to avoid using too large a retracting electromagnet.