Classification, construction and application of electrical contacts
(1) classification of electrical contacts
Electrical contacts can be divided into the following three types according to their contact modes
1) fixed contact. An electrical contact that cannot be moved relative to a conductor connected by contact. Such as bus connections, electrical equipment, such as lead connections.
2) sliding contact. A contact that guides the body to maintain contact with one another, but allows one of the contacts to move relative to one another, known as a sliding contact.
Such as: bus telescopic knot, motor brush and so on, are sliding contact.
3) broken contacts. When normal operation, the contacts can be closed or broken, which is called a broken contact. The contacts of various switches are broken contacts.
(2) broken contacts are classified according to their construction:
1) butt contact.
The butt contact is the movable contact and the static contact plane butt joint. This kind of contact is more common in old type multi oil switch. The utility model has the advantages of simple structure and fast breaking speed.
The disadvantage is that the contact surface is not stable, with the change of pressure changed; no self-cleaning effect in the process of closing bounce; prone to dynamic contact and static contact between the rigid contact; no auxiliary contact main contact, easy to burn out.
2) socket type contact.
Socket contacts are widely used in all kinds of less oil circuit breakers, and their structures are shown below. It has two kinds of contacts. The movable contact is rod shaped, the static contact is composed of a plurality of contact fingers, each contact finger passes through an electric current, and the contact pressure is kept by the spring 2. The advantages of socket contact is: in the opening and closing process of self-cleaning effect; in the closing state, moving inside contact contact rod and static contact contact means, and the arc of the closing, it appears in the end of the moving contact and the static contact, so stable contact resistance keepingshutting state socket contact; through the short-circuit current, the fingers, finger touch and move the same direction of current flow between the contact rod, so the electrical power is suction, which increases the contact pressure between the contact, ensure good. Therefore, the electric stability of socket type contacts is high. Because the contact pressure direction and the moving direction of the moving contact are perpendicular to each other, when the contact is closed, the bounce is small; the end of the contact finger can also weld the alloy with high melting point so as to reduce the metal vapor when the short circuit current is cut off.
The main disadvantage of socket contact is: complex structure, difficult to manufacture, the rated current increases, will lead to increased power (because of closing mechanism to increase the contact of the moving contact pressure, the closing resistance increases); socket contact time is longer.
3) finger contact
Finger contacts are widely used in isolating switches, and are also used in less oil circuit breakers;
The advantage of finger contact is that the electric stability is high, and it is not limited by the rated current. During the switching process, the contact surface also has self-cleaning function.
The disadvantage of finger contact is that it is not easy to match with arc extinguishing chamber. Therefore, the contact is used in the isolating switch. In the less oil circuit breaker, the finger contact is mainly used as the master contact instead of the arcing contact. In order to increase the current allowed by the contact, the contact point of the contact can be composed of parallel pieces of parallel contacts.
3) knife shaped contact.
The cutter contact is widely used in high voltage disconnector and low voltage cutter head. The cutter contact can be divided into two types: flat contact and linear contact. Because of its simple structure, the knife contact is widely used because of its obvious location and convenient operation and maintenance.