Description

The contact is one of the key components of switch appliances, and the main performance and lifespan of switch appliances largely depend on the quality of the contact material. Contact materials typically require good conductivity, low contact resistance, high resistance to fusion welding, high resistance to arc erosion, and resistance to material transfer. For vacuum contact materials, It also requires a small cutoff value, high withstand voltage strength, and high breaking capacity. The microstructure of contact materials has an important impact on their macroscopic properties. The electrical properties of contact materials, such as resistance to welding, arc erosion, and pressure resistance, are not only related to the composition of the contact material, but also to the size of the constituent material grains.

Application

Electric contacts are the main conductive contact materials widely used in relays, contactors, load switches, medium and low voltage circuit breakers, as well as household appliances, automotive appliances (horns, headlights, ignition) and other switch appliances. Switching devices are widely used to separate/close voltage/current in circuits, and their reliability directly affects the reliable operation of the entire power system, and electrical contacts are one of the important components of switching devices. Contact products are the "heart" components of these products.

Electrical Contact classification

Breakable contacts are an indispensable part of switch appliances, and can be divided into the following types according to their different structures:

(1) Knife shaped contact: Its structure is simple, divided into surface contact and line contact, widely used in low-voltage switches and high-voltage isolation switches.

(2) Docking contact: It has the characteristics of simple structure and fast action speed, but the contact surface is unstable and varies greatly with pressure. It is prone to bouncing during action and has no self-cleaning effect. The contact is easily burned by electric arcs. This type of contact is commonly used in distribution circuit breakers with rated currents below 1000A and below 500A.

(3) Wedge shaped (contact finger) contact: composed of paired contact pieces and wedge shaped contact blocks pressed on the conductive base with double headed bolts and springs. Generally, wedge shaped contact blocks are used as moving contacts, but there are also cases where the wedge shaped contact blocks are used as static contacts and the contact pieces clamped on the conductive base are used as moving contacts. This type of contact rubs against each other during the contact between the moving and stationary contacts, and the contact surface can be automatically cleaned. Its electric stability is high, and it has a self-cleaning effect. Increasing the number of contacts and wedges may increase the rated current, but the lateral size also increases, making assembly difficult. The working current is generally limited to below 5000A, with a maximum of 12000A. The working surface of the contact is prone to arc burns, and it is generally only used as the main contact rather than the arc extinguishing contact.

(4) Insert type (plum blossom shaped) contact: The static contact is composed of multiple trapezoidal contact fingers. It is divided into two types: flexible conductive sheet and non flexible conductive sheet. A socket with flexible conductive sheets has a groove on the contact finger, in which an insulation sleeve is embedded. A spiral spring is inserted to ensure the pressure of the contact finger on the conductive rod. The other end of the spring is supported by a circular ring, and the position of the contact finger can be slightly adjusted around the conductive rod (moving contact). The contact finger is connected to the contact base through a flexible conductive sheet. The socket without flexible conductive sheets eliminates the complex structure and unstable performance of conductive sheets, and uses springs to directly press the contact finger onto the conductive base. The moving contact is a circular copper conductive rod. In order to increase the arc resistance of the contact, a copper tungsten alloy protective ring is often added at the end of the outer sleeve of the contact seat, and a copper tungsten alloy arc resistant head is added at the end of the conductive rod. When connected, the conductive rod is inserted into the socket, and the trapezoidal contact finger is pressed on the conductive rod by the spring. By using the appropriate fit between the inner diameter of the socket and the conductive rod, each contact finger forms two line contacts with the conductive rod, ensuring reliable contact. At the same time, the pressure direction between the moving and stationary contacts is perpendicular to the direction of movement, and the bounce when the contacts are connected is small. Friction occurs when the moving and stationary contacts move relative to each other, which has a self-cleaning effect. When a short-circuit current passes through, due to the consistent direction of current between the fingers and between the fingers and the conductive rod, the electrodynamic force tends to guide the fingers towards the electric rod, resulting in good dynamic stability. However, this type of contact structure is relatively complex, and the allowed current is also limited, and the breaking time is longer. It is also commonly used in distribution networks below 35KV. Sliding contacts are connections that maintain relative motion between moving and stationary contacts without separation. It is divided into Z-shaped finger sliding contacts and rolling sliding contacts.

(5) Z-shaped finger sliding contact: Similar in structure to socket type contact. It is composed of a Z-shaped contact finger installed inside a conductive base, held in position by a spring, and the two sides of the contact finger are respectively pressed against the guide pole and the conductive base. Its advantages are: small height, assembly