Main Contact Faults
Severe Sparking During On/Off of Moving and Static Main Contacts
Sparking occurs when the moving and static main contacts are turned on or off. The high temperature of the arc forms irregular pits on the contact surface, reducing the contact area, increasing current, and worsening sparking. To repair damaged contacts, first check the damage degree—only contacts with a thickness remaining more than 2/3 of the original can be repaired. During repair, place fine emery cloth on a horizontal surface, grind the damaged contacts flat on the emery cloth, check the repair progress until all damaged points are removed, and finally deburr the contacts.
Fusion Adhesion of Moving and Static Main Contacts
The main causes of this fault include load short circuit, main circuit short circuit, reduced load impedance, and improper selection of AC contactors. Due to operational needs, AC contactors are used at frequencies ranging from low to high. During frequent on/off cycles, the contact surface temperature rises, and under the action of electric arcs, the moving and static main contacts will eventually fuse and adhere. There are generally two treatment methods: 1. Replace the AC contactor with a higher voltage and current rating. 2. Repair the AC contactor by replacing contacts with the same specifications, cleaning carbon deposits around the moving and static contacts, and connecting Resistor-Capacitance (RC) arc-extinguishing devices in parallel with each of the three pairs of main contacts.
Auxiliary Contact Faults
Excessively High Contact Resistance of Moving and Static Auxiliary Contacts
There are two main causes: 1. A large amount of oil, dirt, and dust accumulates on the contacts. 2. An oxide layer forms on the contact surface. Based on the undervoltage protection mechanism of AC contactors, the control circuit stops working when the voltage across the contactor coil is lower than 85% of the rated voltage. The solution is to remove the contacts, wipe them dry with clean gauze, and gently polish the contact surface with fine emery cloth.
Severe Sparking During On/Off of Moving and Static Auxiliary Contacts
The main causes of this fault may include short circuits in the controlled circuit or reduced impedance of energy-consuming components in the control circuit.