Introduction to contact systems

Update:20-03-2020
Summary:

The contact system is the actuator of an electrical app […]

The contact system is the actuator of an electrical appliance, and it functions to open and close the circuit. Therefore, the quality of the contacts directly affects the working performance of the entire appliance. There are many types of contact mechanisms, and according to their contact types, they can be divided into three types, namely point contact, line contact and surface contact.

It is a straight line, and the contact is a rolling contact during the on-off process. At the beginning of the contact, the static and dynamic contacts are contacted at point A, and the spring pressure is used to roll through point B to point C. Do the opposite motion when disconnected. In this way, the oxide film on the surface of the contact can be automatically removed, and at the same time, the long-term working position is not at point A, but at point C, which ensures good contact of the contact. This rolling wire contact is mostly used for contacts of medium capacity, such as the main contact of a contactor.

 (C) Surface contact is shown, which allows larger currents to pass. This contact is generally inlaid with an alloy on the contact surface to reduce contact resistance and improve wear resistance. It is mostly used as the main contact for larger capacity contactors. When the contact is in the closed state, when the static contact is in full contact with the working current, it is called electrical contact. The condition of the electrical contact will affect the reliability and service life of the contact. The main factor that affects the working of electrical contacts is the contact resistance of the contacts. When the contact resistance is large, the contacts are likely to heat up and the temperature rises, which will cause the contacts to fuse. This will affect the reliability of the work and reduce the Point of service life. The contact resistance of a contact is not only related to the contact form of the contact, but also to the contact pressure, the contact material, and the condition of the contact surface. In order to make the contacts come closer, to reduce the contact resistance and eliminate the vibration generated at the beginning of the contact, a contact spring is installed on the contact, so that the contact will generate initial pressure when it is just contacted, and will close with the contact Increase contact mutual pressure.

During the contact closing process, when the moving contact has just come into contact with the static contact, the contact spring is compressed in advance for a period of time, thereby generating an initial pressure F1. After the contact is closed, a final pressure is generated due to the spring's continued deformation in the over-travel. F2 The distance the spring compresses is called the over-travel of the contact. Compression distance. With overtravel, there is still a certain amount of pressure in the event of contact wear. Replace if worn out.