Common faults and maintenance methods for low-voltage electrical appliances - Solutions - Huaqiang Electronic Network

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Low-voltage electrical devices are widely used in various circuits, and each has a unique structure. To ensure their proper functioning, it's essential to first understand the common faults and maintenance techniques of their basic components, then move on to the specific issues found in commonly used low-voltage devices. This knowledge helps technicians quickly identify and resolve problems, ensuring safe and efficient operation. 1. Common Faults and Repairs of Low-Voltage Components 1.1 Contact Failure and Maintenance (1) Contact Overheating: When contacts close, current flows through them. Under normal conditions, they should not overheat. However, if the contact resistance is too high or the current exceeds the rated value, overheating can occur. Excessive heat may degrade contact performance or even cause welding. Common causes include excessive system voltage, overloaded equipment, or improperly sized contacts. To prevent this, regular inspections and cleaning of contact surfaces are crucial. If the contact resistance increases due to dirt or wear, the surface should be cleaned using appropriate tools like scrapers or fine sandpaper. For larger contacts, smoothing the surface is necessary, while smaller ones require careful handling to avoid damage. In some cases, replacing worn springs or adjusting contact pressure can also help. To test contact pressure, a thin strip of paper (0.01 mm thick) can be inserted between the moving and stationary contacts. If the paper can be easily pulled out, the pressure is insufficient. If it tears, the pressure is too high. Adjusting the spring or replacing it when damaged ensures optimal contact performance. (2) Contact Wear: There are two types of contact wear—mechanical and electrical. Mechanical wear occurs due to friction during contact closure, while electrical wear results from high temperatures caused by arcs. Over time, contacts become thinner and may need replacement when they reach about half their original thickness. If wear is rapid, the root cause must be identified and addressed promptly. (3) Contact Welding: This occurs when the contact surfaces melt and fuse together, preventing the contacts from opening. It often happens due to improper selection of contact size, excessive load, or faulty springs. If welding occurs, new contacts must be installed. In some cases, increasing the contact capacity can prevent future issues. 1.2 Electromagnetic System Faults and Maintenance (1) Noisy Iron Core: A slight "click" sound is normal, but loud or abnormal noise indicates a problem. Poor contact between the armature and iron core, deformation, or contamination can cause vibrations and noise. Cleaning or repairing the affected areas usually resolves the issue. Additionally, a damaged short-circuit ring can lead to noise and requires repair or replacement. (2) Coil Failure: The coil may overheat or burn out due to high current, insulation damage, or incorrect voltage. If the coil is burned, it should be rewound. In some cases, removing a few damaged turns can save the rest of the coil without significant impact on performance. (3) Arc Suppression System Failure: Issues such as moisture, carbonization, or broken arc angles can hinder arc extinction. These problems can be resolved by drying, cleaning, or replacing damaged parts. 2. Common Low-Voltage Electrical Faults and Maintenance 2.1 Contactor Faults and Maintenance Other common issues include phase loss, contact welding, and phase-to-phase short circuits. Phase loss can cause the motor to run slowly and emit unusual sounds. Contact welding prevents the motor from stopping even after pressing the stop button. Proper interlocking mechanisms and regular maintenance can help avoid these issues. 2.2 Thermal Relay Faults and Maintenance Thermal relays may fail due to blown elements, misadjustments, or incorrect settings. Regular checks and proper calibration are essential to ensure they function correctly. If the relay trips, it should not be reset immediately; instead, wait for the bimetallic strip to cool down before resetting. 2.3 Time Relay Faults and Maintenance Air-type time relays can experience issues due to air leaks or dust buildup. Disassembling and cleaning the internal components, or replacing damaged parts, can restore proper timing functions. 2.4 Speed Relay Faults and Maintenance Speed relays may fail to brake the motor properly. This could be due to misadjusted screws or broken components. Inspection and adjustment of internal parts usually resolve the issue. By understanding these common faults and maintaining the components regularly, technicians can ensure the reliability and safety of low-voltage electrical systems.