Failure Analysis of Electrical Contact

Common control electrical products such as AC contactors, electromagnetic relays, electrical switches and air switches contain electrical contacts, and contacts are one of the most important components of these products. The reliability and service life of the product depend to a large extent on the contact performance, which is affected by factors such as contact material, load type, contact pressure, operating frequency and use environment. When these factors can not meet the requirements, there will be contact electrochemical corrosion, welding between contacts, fire, contact wear, contact resistance increase and other problems, resulting in unreliable operation, functional failure and even security risks.

In the energized state, if the current of the open circuit exceeds a certain limit, or if the voltage on the contact gap exceeds a certain limit after opening, an arc will appear in the contact gap. Arc is a discharge phenomenon of gas between contacts under the action of strong electric field. Sparks and strong light are generated and emitted with high temperature. The arc will corrode the metal surface of the contact, shorten the service life of the electrical appliance, extend the breaking time of the circuit, and cause the contact failure of the contact. In severe cases, it can cause a fire or gas accident.

When the moving contact and the stationary contact are in contact, external pressure must be applied to ensure good electrical contact between the moving contact and the stationary contact, which is usually called the contact pressure of the contact.

Contact pressure has the following functions:

Ensure good contact between the moving and stationary contacts and keep the contact resistance as small as possible.

and (B) reduce the generation of surface oxide films and contamination of contact surfaces.

Suppress contact rebound.

The contact pressure of the contact is an important parameter of the electrical product contact, which can only be selected after many tests in the initial design of the product. If the contact pressure of the contacts is selected to be relatively small, the requirements for reliability of the relay cannot be met. If the contact pressure of the selected contact is relatively large, it is necessary to increase the operating work of the relay, and the requirements for the reaction spring also need to be increased, which is technically uneconomical.