In the years of equipment maintenance, I have observed that many faults are caused by the aging of various low-voltage electrical components and a lack of regular upkeep. Below are some examples from my maintenance work that illustrate how to troubleshoot and maintain low-voltage electrical devices effectively.
First, let's look at some common voltage-related electrical issues:
1. **Faulty Circuit Breaker Contacts**
During inspections, I found that overheated contacts in a circuit breaker could be detected by a burning smell coming from the control panel. Upon checking, it was discovered that the moving contact wasn't fully inserted into the static contact, resulting in insufficient pressure and reduced switching capacity. Adjusting the mechanism to ensure full insertion resolved the issue.
Another case involved arcing when power was turned on, which was due to loose connections and an overloaded circuit. Safety precautions were taken during the repair, and after fixing the load and tightening the contacts, the system returned to normal operation. Regular maintenance is crucial to avoid such issues and prevent potential damage.
2. **Contactor Contact Issues**
A misaligned contact in one phase caused the motor to run out of phase, even though it still rotated and produced a buzzing sound. This required immediate maintenance. In another instance, the contacts were welded shut, and the "stop" button failed to stop the motor, with a clicking sound indicating a possible short. This was caused by high current due to overload, so the contactor was replaced after checking the load.
Additionally, if the armature doesn’t pick up, it may be due to a broken coil or mechanical jamming. The coil can be rewound using original specifications and then dipped in insulating paint for protection.
3. **Thermal Relay Failures**
Thermal relays often fail due to blown fuses in their thermal elements. If a motor won’t start or makes a clicking noise, this could be the cause. Faults like false tripping can result from incorrect settings, long starting times, or high operating frequency. Adjusting the settings or replacing the relay helps resolve these problems.
When a thermal relay fails to trip, it might be due to an overly high current setting. Adjusting the setting based on the actual load current is necessary. It’s also important to regularly test the reliability of thermal relays. When tripped, the bimetallic strip should be cooled before resetting to avoid damaging the mechanism.
Second, the key points in repairing common low-voltage electrical devices include checking the contact system, electromagnetic system, and arc extinguishing device.
1. **Contact System Faults**
Common contact issues include overheating, welding, or poor conductivity. Overheating is often due to insufficient pressure, oxidation, or dirt on the contact surfaces. Cleaning with gasoline or gently scraping oxide layers (for copper) can help. For silver contacts, the oxide layer naturally reduces during use, so no repair is needed.
If contacts are burned or deformed, they should be replaced. Ensuring proper spring tension is essential. A simple method to measure contact pressure involves using paper strips between the contacts. If the paper can be pulled out with resistance, the pressure is suitable. For larger appliances, a tearing effect indicates proper pressure.
2. **Electromagnetic System Troubleshooting**
Noisy armatures are usually caused by dirty core surfaces, skewed iron cores, or broken short-circuit rings. Cleaning the surfaces, realigning the core, or replacing the short-circuit ring can fix this.
If the armature doesn’t release after power is cut, it may be due to a stuck mechanism, improper air gap, or weak spring force. Adjusting the air gap or replacing the spring ensures proper operation.
Coil failures often occur due to excessive current, which can burn the coil. Rewinding the coil with correct wire diameter and turns, followed by insulation treatment, is essential for safe operation.
3. **Arc Extinguishing Device Inspection**
The arc extinguishing cover must be checked for cracks or damage. If damaged, it should be replaced immediately. Never use a device without its arc extinguisher, as this can lead to dangerous short circuits.
Low-voltage electrical devices come in many types, and the methods discussed here are practical for diagnosing and maintaining similar equipment. Regular inspection and proper maintenance are vital to ensuring safe and reliable operation.
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