Classification, structure and application 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 be moved relative to each other by the conductors that are connected in contact. Such as busbar connectors, lead connections for electrical equipment, etc.
2) Slide contacts. A contact method that guides the bodies to maintain mutual contact, but allows one contact surface to move relative to each other along the other contact surface, called a sliding contact.
Such as: the telescopic knot of the busbar, the brush of the motor, etc., are all sliding contact.
3) Breakable contacts. If the contacts can be closed or broken during normal operation, they are called breakable contacts. The contacts of the various switches are breakable contacts.
(2) Breakable contacts are classified according to their structure:1) Docking contacts.
The butt-type contact is a movable contact of the movable contact and the fixed contact. Such contacts are more common in older multi-oil switches. Its characteristics are: simple structure and fast breaking speed.
The disadvantages are: the contact surface is unstable, and there is a big change with the change of pressure; there is no self-cleaning effect in the process of splitting; the bounce is easy to occur when the moving contact and the static contact are just in contact; there is no auxiliary contact, The main contacts are easily burned out.
2) Socket contacts.
Socket contacts are widely used in various types of oil-less circuit breakers, and their structures are as follows. It has two types of contacts. The moving contact is in the shape of a rod, and the static contact is composed of a plurality of fingers, each of which receives a current; the contact pressure is maintained by the spring 2. The advantages of the socket type contact are: self-cleaning during the closing and closing process; in the closing state, the moving contact contact rod is in contact with the inner side of the stationary contact contact finger, and the arc during the splitting and closing is Appears at the end of the moving contact and the static contact, so that the contact resistance can be kept stable when the closing state is maintained; when the socket contact passes the short-circuit current, the current flows between the fingers, the contact finger and the moving contact rod The direction is the same, so the electric power is suction, which increases the pressure between the moving and static contacts and ensures that the contacts are good. Therefore, the socket type contacts have high electric stability. Moreover, since the direction of the contact pressure and the moving direction of the movable contact are perpendicular to each other, the bounce is small when the contact is closed; the alloy with a high melting point can also be welded to the end of the finger, so that the metal vapor is reduced when the short-circuit current is cut off.
The main disadvantages of the socket type contacts are: complicated structure, difficult manufacturing, and increased rated current, which will lead to an increase in the closing power of the mechanism (because the pressure of the finger to the moving contact is increased, so that the closing resistance is increased); The socket contacts also have a longer break time.
3) Finger contact
Finger contacts are widely used in isolating switches, and are also used in oil-less circuit breakers, the structure of which is shown in the figure;
The advantages of the finger contact are: high motor stability, not limited by the rated current; in the process of closing, the contact surface also has self-cleaning effect.
A disadvantage of the finger contacts is that they are not easy to use with the arc extinguishing chamber. Therefore, such contacts are often used in isolating switches. In a low oil circuit breaker, the finger contact is mainly used as a main contact and not as an arcing contact. In order to increase the current allowed by the contacts, the contact fingers of the contacts may consist of a plurality of parallel connections.
3) Blade contact.
Knife contacts are widely used in high voltage disconnectors and low pressure knife switches. The blade contact can be divided into two types: a planar contact and a line contact according to its own contact condition. The blade-shaped contact is widely used because of its simple structure, obvious position and position, easy operation and maintenance.
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