1. Application of electrical contact materials in MCB

    MCB is mainly used for low-voltage terminal power distribution in residential buildings and buildings for short-circuit protection. Although the rated current of MCB is low, it has short-circuit breaking capability and requires high anti-adhesion performance of the contacts. AgC contacts tips are most suitable for MCB. AgC contains Ag 95%~97% and C 3%~5%, which makes it have good conductivity and excellent welding resistance.

    AgC contacts tips have excellent electrical properties, but the preparation process and production equipment of AgC are demanding, so the cost of the contacts is high. At present, the contact part used in MCB in China is the AgCdO contact tips made by the alloy internal oxidation method.

2. Application of electrical contact materials in MCCB

    MCCB can connect, carry and break current under normal circuit conditions. It is mainly used in branch circuits of power distribution systems. Its working characteristics require that the contacts should have high resistance to welding and arc burning. In this regard, one contact material can no longer meet the requirements at the same time, and asymmetric pairing is generally used. Generally, the static contacts have good resistance to welding, while the moving contacts have good resistance to arc burn damage.

    Because graphite has excellent resistance to welding and has certain electrical conductivity, the material is easy to obtain and the cost is low. Generally, static contacts contain 3%-5%, such as AgWC12C3 and AgC5 contacts. AgWC12C3 contacts are widely used in domestic MCCBs. In addition to the conductive material 85% Ag and the welding resistance material 3% C, the AgWC12C3 contact also contains 12% WC. The existence of WC increases the electrical wear resistance of the static contact.

    When MCCB is broken in a short circuit, the arc is mainly elongated upward and eventually extinguished. The main damage caused by arc burning is the moving contacts, especially during the Icn limit short circuit breaking test, the burning of the moving contacts is more serious. Therefore, the moving contact material should contain refractory metal. Low melting point Ag should be able to be bound and not easy to splash. W is a metal with a higher melting point and has good resistance to arc burn damage. The contact base prepared by the infiltration method is Ag, which is not easy to spatter and is beneficial to improving the resistance to arc burn damage. AgW50 contacts are widely used in MCCB movable contacts in China.

3. Application of electrical contact materials in ACB

    ACB mainly distributes electric energy and protects lines and power equipment from overload, undervoltage, short circuit, single-phase grounding and other fault hazards. It is used in the main circuit of the power distribution system. ACB has selective short-time delay short-circuit protection and short-term withstand segmentation capabilities. This working characteristic requires the contacts to have higher resistance to welding and superior resistance to arc burning. Generally, in addition to asymmetric pairing, ACB contacts also add arc contacts, making them more conducive to arc extinguishing and protecting the main contacts.

    The main contacts are made of the same materials as MCCB, such as static contacts AgNi30C3 (containing 3% graphite), and moving contacts AgW50, AgWC40 (containing W or WC). Due to the higher rated operating current and short-circuit breaking index, the contact cross-sectional area is larger. Generally, the static contact is a large-sized contact, and the moving contact is composed of multiple small contacts. The arc contact should have good resistance to arc burning. CuW70 is a good arc contact material. It has both high content of refractory metal (70% W) and Cu (30% Cu) with good arc conduction. At the same time, Cu-based products are relatively cheaper than Ag-based products.

——The content of the article comes from the Internet