Arc cause and arc extinguishing method in switchgear - News - Global IC Trade Starts Here Free

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Electric orphan is a kind of gas discharge phenomenon. It has two characteristics: First, there are a large number of electrons and ions in the arc, so it is electrically conductive. The electric orphan does not extinguish the circuit and continues to conduct. After the arc is extinguished, the circuit is officially disconnected; Second, the temperature of the arc is very high, and the arc temperature is above 4000-5000 degrees Celsius. The high-temperature arc will burn the equipment and cause serious accidents. Therefore, measures must be taken to quickly extinguish the arc.

The physical process of arc generation and extinction is briefly described as follows: During the disconnection of the switch, the contact surface between the moving and static contacts is continuously reduced due to the movement of the moving contact, the current density is continuously increased, and the contact resistance is in contact with The reduction in surface is getting larger and larger, and thus the contact temperature rises, generating thermal electron emission. When the contact is just separated, the electric field strength is very high due to the small gap between the moving and static contacts. Under the action of the electric field, the electrons on the metal surface continuously escape from the metal surface, and the free electrons move between the contacts. This phenomenon is called field emission. The free electrons generated by the thermal electron emission and field emission accelerate to the anode under the action of the electric field force, and continuously collide with the nature point on the way, and collide the electrons in the medium property point. This phenomenon is called collision free. Due to the chain reaction of collision free, the free electrons increase exponentially (positive ions also increase), a large number of electrons rush toward the anode, a large number of positive ions move toward the negative pole, and the gap of the switch contacts becomes the channel of the current. The medium between the gaps is broken down to form an arc.

Due to the high arc temperature, under the action of high temperature, the medium nature point at high temperature generates strong irregular thermal motion due to high temperature. When the medium nature points collide with each other, it will be free to form electrons and ions. The freeness caused by thermal motion is called thermal release. Thermal free generation produces a large amount of electrons and ions to maintain an arc between the contact gaps. The arc is generated mainly by the collision, and the arc is maintained mainly by heat.

What are the commonly used methods for arc extinguishing in switchgear?

The commonly used methods for arc extinguishing in switchgear are as follows:

(1) Extinguish the arc with a gas or oil. Various types of arc extinguishing chambers are used in the switchgear to generate a huge pressure of gas or oil and blow strongly to the arc gap. The arc is strongly cooled and freed in the gas stream or oil stream, and the free matter therein is not When the free material is replaced, the arc is quickly extinguished. There are two types of gas or oil blowing: vertical blowing and horizontal blowing. The vertical blowing makes the arc cool and then extinguishes. The horizontal blowing is to cut the arc and extinguish it. Many circuit breakers use vertical and horizontal hybrid blowing to achieve better arc extinguishing effect.

(2) Adopt multiple fractures. High-voltage circuit breakers are often made with two or more series-connected fractures per phase, so that the voltage applied to each fracture is reduced and the arc is easily extinguished.

(3) Parallel resistance is added to the breaker breaker. In high-voltage large-capacity circuit breakers, arc-gap parallel resistors are widely used to improve their operating conditions. If there are two pairs of contacts in each phase of the circuit breaker, one pair is the main contact, the other pair is the auxiliary contact, and the resistance is connected in parallel on the main contact. When the circuit breaker is in the closed position, the main and auxiliary contacts are closed. When the circuit is disconnected, the main contact is first disconnected. At this time, the resistance connected in parallel with the break of the main contact acts as a shunt during the disconnection of the main contact, which is beneficial to the arc breaking of the main contact. After the arc of the main contact is extinguished, the shunt resistor is connected in series in the circuit, effectively reducing the recovery voltage value and the voltage recovery speed on the contact. In addition, the parallel resistor can limit the overvoltage generation when the small inductor current or capacitor current is cut off.

(4) Adopt new media. Use new media with superior arc extinguishing performance, such as SF6 (sulfur hexafluoride) circuit breakers and vacuum circuit breakers.

(5) The arc is extinguished by the metal arc chute. The metal arc chute is made of ferromagnetic material. When the arc occurs, the arc is immediately attracted into the grid, and the long arc is divided into a series of short arcs. When the arc crosses zero, 150 ~ will appear near each short arc. The dielectric strength of 250 volts is extinguished immediately if the voltage applied between the contacts is less than the sum of the strengths of the individual media. This arc extinguishing method is used in many low voltage switches.