(1) Classification of electrical contacts

Electrical contacts can be divided into the following three types according to their contact methods

1) Fixed connection contacts. Refers to electrical contacts that cannot move relative to each other between the conductors that are connected by contact. Such as busbar joints, lead connections of electrical equipment, etc.

2) Slide the contacts. A contact method in which the conductors can keep in contact with each other, but allows one contact surface to move relative to the other, is called a sliding contact.

Such as: the expansion joint of the bus, the brush of the motor, etc., are all sliding contacts.

3) Breakable contacts. If the contacts can be closed or broken during normal operation, they are called breakable contacts. The contacts of various switches are breakable contacts.

(2) Breakable contacts are classified according to their structure:

1) Butt-type contacts.

The docking contact is the plane butting of the moving contact and the static contact. This type of contact is more common in older multi-oil switches. Its characteristics are: simple structure, fast breaking speed.

The disadvantages are: the contact surface is unstable and changes greatly with the change of pressure; there is no self-cleaning effect during the opening and closing process; it is easy to bounce when the moving contact and the static contact are just in contact; there is no auxiliary contact, The main contact is easy to burn out.

2) Socket contact.

Socket contacts are widely used in various types of oil-less circuit breakers, and their structure is shown in the figure below. It has both dynamic and static contacts. The moving contact is rod-shaped, and the static contact is composed of a plurality of contact fingers, each of which passes current; the contact pressure is maintained by the spring 2 . The advantages of the socket contact are: self-cleaning during the opening and closing process; in the closing state, the moving contact contact rod contacts the inner side of the static contact contact finger, and the arc during opening and closing is not. Appears at the ends of the moving contact and the static contact, so it can maintain the stability of the contact resistance in the closed state; when the socket contact passes a short-circuit current, the current flows between the contact fingers, between the contact fingers and the moving contact rod The direction is the same, so the electric force is suction, which increases the pressure between the moving and static contacts and ensures that the contacts are good. Therefore, the electrical stability of the socket contact is high. And because the contact pressure direction and the moving direction of the moving contact are perpendicular to each other, the bounce of the contact is small when the contact is closed; the end of the contact finger can also be welded with an alloy with a high melting point, so that the metal vapor is reduced when the short-circuit current is cut off.

The main disadvantages of the socket contact are: complex structure, difficult to manufacture, when the rated current increases, the closing power of the mechanism will increase (because the pressure of the contact finger on the moving contact needs to be increased, the closing resistance will increase); The breaking time of socket contacts is also longer.

3) Finger contacts

Finger contacts are widely used in isolating switches, and also in oil-less circuit breakers. The structure is shown in the figure;

The advantages of finger contacts are: high electrical stability, not limited by the rated current; the contact surface also has a self-cleaning effect during the opening and closing process.

The disadvantage of the finger contact is that it is not easy to use with the arc chute. Therefore, this contact is mostly used in isolating switches. In oil-less circuit breakers, the finger contacts are mainly used as main contacts and not as arc-extinguishing contacts. In order to increase the current that the contacts allow to pass, the contact fingers of the contacts can be composed of multiple pieces in parallel.

3) Knife contact.

Knife contacts are widely used in high voltage isolating switches and low voltage knife switches. The blade contact can be divided into two types: plane contact and line contact according to its own contact status. Knife contacts are widely used because of their simple structure, obvious opening and closing positions, and easy operation and maintenance.