1. The main contacts and auxiliary silver contacts of the switchgear have different tasks.

1) The main contacts are located in the main circuit

The task of the main circuit is to perform the transmission and control of electrical energy. Therefore, the main contacts of the switchgear must withstand short-circuit currents and overload currents, and strong overvoltages can occur.

Therefore, the main contacts must meet the dynamic stability requirements of the switchgear and can withstand large temperature rises.

2) Auxiliary electrical contacts (silver contacts) are located in the auxiliary circuit

The task of the auxiliary circuit is to perform signal amplification, control and transmission. Therefore, the auxiliary silver contact electrical contacts of the switchgear must ensure low current signal transmission
2. The materials of the main contacts and auxiliary silver contacts of the switchgear are different.

The main contact materials are mainly silver and tungsten alloys, which can withstand the impact of the arc, and there is complementarity between the moving contact and the static contact to improve the welding resistance;

The auxiliary silver contacts are mainly silver-based alloys to improve the electrical conductivity of the contacts.

The main contacts of circuit breakers are mainly line contacts. The contact of the line contact is friction, which can grind off the oxide layer of the contact to ensure a good contact; the auxiliary electrical contact is mainly a point contact.

3. The dynamic thermal stability of the main contacts and auxiliary silver contacts of the switchgear is different.

Let's look at the dynamic thermal stability of the contacts:

When a short circuit current flows through the contacts, the contact material heats and even welds. If the contact opens, the contact material will melt and form a metal bridge, which will then open and arc. Explosive arc gases can splatter molten contact material, and metal vapor arcs can also occur.

The coordination relationship between the main contact material of some switchgear and the action time of the upper-level switchgear performing line protection is called SCPD coordination. This relationship is necessary for the main contacts and also for the coordinated testing of the switchgear.

For auxiliary contacts, SCPD type testing is not required.

Therefore, the main electrical contacts are usually equipped with arc extinguishers, while the auxiliary electrical contacts are not equipped with arc extinguishers. After all, the breaking current of the auxiliary silver contacts is usually no more than 5A.