What is an arc？
An arc is a gas discharge phenomenon. An instantaneous spark produced by an electric current passing through some insulating medium (such as air). An arc is a self-sustaining gas that conducts electricity (electrical conduction in an ionized gas), and most of its carriers are electrons generated by a single electron emission. The metal surface of the contact is caused by an electron emission (thermionic emission, field emission or photoelectric emission), and the gas atoms or molecules in the gap will generate electrons and ions due to ionization (collision ionization, photoionization and thermal ionization). In addition, bombardment of the emission surface by electrons or ions can cause secondary electron emission. When the ion concentration in the gap is sufficiently large, the gap is electrically broken down and an arc occurs.
Components of an arc
The arc is usually divided into three areas: cathode area, arc column area, and anode area
Cathode and cathode area
From a microscopic perspective, the current in the arc is the result of the movement of electrons and positive ions under the action of an electric field. The movement of the electrons constitutes the main part of the current. The role of the cathode is to emit a large number of electrons, which tend to the anode direction under the action of the electric field, thereby forming a current in the cathode region.
The cathodic region of thorium arc is of great significance to the occurrence of the arc and the physical process. Most of the electrons forming the arc discharge are generated in the cathode region or emitted by the cathode itself. During arc discharge, not the entire cathode actually participates in the discharge process. The discharge on the surface of the cathode is concentrated in a few small areas. This small area is called the cathode spot. It is a very concentrated, small area with bright areas. Its current density is large. It is the source of powerful electron flow in arc discharge.
There are two mechanisms for the emission of electrons from the cathode: thorium emission and field emission.
The surface of the cathode emits electric current only in the cathode region. Partial conduction of the arc column requires that a large number of free electrons can also appear in the arc column region. This requires the gas atoms in the arc column region to be released. There are usually two types of gas atom release: electric field release and thermal release.
Tritium is similar to a reversible chemical reaction. On the one hand, positive ions and electrons are constantly increasing due to thermal release. At the same time, there is a de-dissociation effect, which reduces positive ions and electrons. Dissociation includes two methods of recombination and diffusion.
The characteristics and physical processes of the arc column play an important role in the arc. The main research in the switching arc is the characteristics of the arc column.
Anode and anode area
The anode can be divided into two types: passive and active.
In the passive type. The anode only serves to collect electrons. In the active type, the anode not only collects electrons but also generates metal vapor, so it can also supply charged particles to the arc column.
Anode spots also exist on the anode surface.
The effect of the above three areas on the arc varies depending on the circumstances of the arc. For arcs with a length of only a few millimeters. The arc voltage is mainly composed of the voltage drop in the cathode region and the voltage drop in the anode region. The physical process plays a major role in the arc. This arc is called a short arc. For a longer arc, the arc column plays a major role, and the cathode and anode processes do not play a major role or can be ignored. This kind of arc is called a long arc. Arcs in switches are generally long arcs.
Classification of arcs
<1> According to the type of current, it can be divided into: AC arc, DC arc and pulse arc.
<2> According to the state of the arc, it can be divided into: free arc and compression arc (such as plasma arc).
<3> According to the electrode material, it can be divided into: melting electrode arc and non-melting electrode arc.
Conditions under which the arc occurs
1. Arc occurs when the circuit is open
When the contacts start to separate. The contact pressure between them will be reduced, the contact area will also be reduced, and the contact resistance and the heat released from the contacts will increase. The heat is concentrated in a small volume, and the metal is heated to high temperatures to melt it. A liquid metal bridge is formed between the contacts, and finally the metal bridge is pulled apart to form a transitional or stable arc between the contacts. If the discharge is stable, it is the so-called breaking arc. Discharge stability is related to many factors, such as the current at break, the characteristics of the contact circuit, and the speed of contact separation. In order for the arc to ignite, a certain minimum current value is necessary.
2, the arc occurs when the contacts are closed
3, breakdown of vacuum and gas gap
4. Transition from glow discharge to arc discharge
5. The transition from spark discharge to arc discharge
Can arc lighters kill people electrically?
Because the voltage is high and the current is small, as long as the air is penetrated to generate an arc. Generally it is 2.5 amps. Occasionally call for refreshment. But arc burns are still quite painful. Anyway, it will not die.