- The reason why the contact resistance is too large
The increase of contact resistance often causes a large voltage drop on the contact, which reduces the input power of the load equipment. If the contact resistance of one or two contacts increases, the three-phase voltage of the load equipment will be unbalanced, resulting in phase-loss operation; if the contact resistance is too large, the electrical appliance itself will also overheat, reducing its reliability. There are many reasons for the excessive contact resistance of the contact. In addition to the reasons described above, there are the following:
1. There is dust, lint, grease and metal particles on the contact surface.
2. During maintenance, flux, rosin and other debris are left in the electrical appliance, and the organic vapor escaping at high temperature contaminates the contact.
3. The contact surface is rusted or burned by the arc.
4. The environment is humid, and the water vapor on the contact surface may condense into frost at low temperatures.
5. The corrosive gas and steam in the surrounding medium cause erosion to the contact, and the contact surface is covered with a harmful insulating film.
6. Electrical wear and mechanical wear of the contact.
- To detect and eliminate the contact resistance fault, follow the following methods:
To check the contact resistance, you can use the voltage range of the multimeter to measure it, that is, touch the two sides of the contact with the multimeter probe when the power is on, and the range will gradually decrease. If the measured voltage drop is large, it means that the contact resistance is large; if the voltage drop is zero, it means that the contact is in good contact. In addition, you can also use the resistance range of the multimeter to directly measure the contact resistance of the contact when the power is off, but it must be noted that the contact resistance of the contact is related to the pressure applied to the armature. Therefore, after disconnecting the wiring at both ends of the contact, measure the resistance on both sides of the contact when the coil is powered on.
In order to repair the fault of the contact resistance, in addition to the contact treatment method described above, the arc extinguishing cover should be removed regularly to check and clean the contact to prevent accidents. In addition, for electrical appliances working in harsh environments (such as acids, alkalis, salts and hot steam), it is advisable to use sealed ones with isolation covers and adopt appropriate protective measures.
- Preventive measures for excessive contact resistance
1. The connection between wires and wires, and between wires and electrical equipment must be firm and reliable.
2. Regularly inspect the running lines and deal with loose joints or heating phenomena in a timely manner.
3. The connection between wires with large cross-sectional areas should be welded or crimped.
4. When copper and aluminum wires are connected, copper-aluminum transition joints should be used. You can also pad tin foil between copper and aluminum wires or tin the copper wire nose. In order to check the temperature rise of the contact head, you can also apply color-changing paint or candles to the parts with large contact resistance to monitor the heating of the contact points.
5. Conduct electrical safety inspections regularly, and repair or replace problems in a timely manner if they are found.
