What are the troubleshooting and key points of common voltage electrical appliances?

1. General troubleshooting

1. Voltage circuit breaker failure

If the contact is overheated, you can smell something in the power distribution control cabinet. After inspection, it is found that the moving contact is not fully inserted into the static contact, and the contact pressure is insufficient, resulting in a decrease in the switch capacity and contact overheating. At this time, adjust the operating mechanism so that the moving contact is fully inserted into the static contact.

When the power is turned on, there is an arc flash and a loud noise. After inspection, it is found that the load is too heavy for a long time, the contacts are loose and the contact is poor. When repairing this fault, you must pay attention to safety and prevent the arc from harming people and equipment. After repairing the load and contacts, you can first turn on the power without load to check the operation until it is normal. For this fault, you must pay attention to the daily maintenance of the equipment to avoid unnecessary harm.

2. Contactor failure

The contact is broken. Due to the poor contact of one phase contact or the loose screws on the terminal, the motor runs in a phase-loss state. At this time, the motor can rotate but makes a buzzing sound. Stop the machine immediately for inspection.

Contacts are welded. When the "Stop" button is pressed, the motor does not stop and may make a buzzing sound. This type of fault is caused by welding of two-phase or three-phase contacts due to overload current. The power should be cut off immediately, and the load should be checked before replacing the contactor.

The armature does not attract when the power is on. If there is no vibration or noise when the power is on, it means that the moving part of the armature is stuck and the fault is just a coil circuit break. The coil can be removed and rewound according to the original data, then dipped in paint and dried.

3. Thermal relay failure

The thermal equivalent element is burnt out. If the motor cannot start or there is a buzzing sound when starting, it may be that the fuse in the thermal element of the thermal relay is burnt out. The cause of this type of failure is that the operating frequency of the thermal relay is too high or the negative side is overloaded. After troubleshooting, replace the appropriate thermal relay and readjust the setting value after attention.

The thermal relay "misoperates". This kind of fault is generally caused by the following reasons: the setting value is too small, so it operates without overload; the motor starts for too long, causing the thermal relay to operate during the startup process; the operating frequency is too high, causing the thermal element to be frequently impacted. Re-adjust the setting value or replace the appropriate thermal relay to solve the problem.

The thermal relay does not work. This kind of fault is usually caused by the current setting value being too large, so that it does not work after being overloaded for a long time. The setting current should be adjusted according to the load working current.

The thermal relay should be checked regularly for reliability after long-term use. When the thermal relay trips, wait until the bimetallic strip cools down before resetting it. Do not press the reset button too hard, otherwise the operating mechanism will be damaged.

2. Troubleshooting and maintenance of common voltage electrical appliances and their essentials

All voltage appliances with contact action are mainly composed of three parts: contact system, electromagnetic system and isolation device. They are also the focus of maintenance.

1. Contact troubleshooting

Contact failures generally include overheating, welding, etc. The main causes of overheating are insufficient contact pressure, surface oxidation or uncleanness, and insufficient capacity; the main cause of contact welding is a large arc generated when the contact is closed and severe contact jumping.

Check the oxidation condition and dirt on the contact surface. If there is dirt on the contact, clean it with gasoline.

The oxide layer of the silver contacts not only has good electrical conductivity, but also will be reduced to metallic silver during use, so no repair is required.

If there is an oxide layer on the copper contacts, you can use an oil file to file it flat or use a knife to gently scrape off the oxide layer on the surface.

Observe the contact surface for burns and burnishes. If the copper contact is burnished, it can be trimmed with an oil file or a knife. The contact surface does not need to be too smooth when trimming. It is not allowed to trim with emery cloth to avoid residual sand particles being embedded in the contact when the contact is closed, causing poor contact. However, if the silver contact is burnished, it does not need to be trimmed.

If the contact is welded, it should be replaced. If it is caused by insufficient contact capacity, an appliance with a larger capacity should be selected when replacing it.

Check if the contact is loose. If so, tighten it to prevent the contact from jumping. Check if there is mechanical damage to the contact that causes the spring to deform and cause insufficient contact pressure. If so, adjust the pressure to make the contact contact well. The empirical measurement method of contact pressure is as follows: To measure the initial pressure, place a piece of paper about 0.1mm between the bracket and the moving contact. Its width is wider than the contact. The paper is compressed by the spring. At this time, pull the paper with one hand. When the paper can be pulled out and there is a sense of force, it can be considered that the initial pressure is relatively appropriate. To measure the final pressure, clamp the paper between the moving and static contacts. When the contacts are energized and attracted by the electrical appliance, pull the paper in the same way. When the paper can be pulled out, it can be considered that the final pressure is relatively appropriate. For large-capacity electrical appliances, such as those above 100A, use the same method to pull the paper. When the paper is torn when it is pulled out, it can be considered that the initial and final pressures are relatively appropriate.

The above contact pressure measurement method has been effective in many repair tests. If the measured pressure value cannot be restored by adjusting the spring, the spring or contact must be replaced.

2. Troubleshooting of electromagnetic system

Due to poor end contact of the moving and static iron cores, skewed iron cores, damaged short-circuit rings, too low voltage, etc., the armature will make loud noises and even the coil will overheat or burn out.

(1) The armature makes a loud noise. When repairing, the coil should be removed to check whether the contact surface between the armature and the static core is flat and free of oil stains. If it is not flat, it should be filed or polished; if there is oil stain, it should be cleaned with gasoline.

If the moving iron core is crooked or loose, it should be corrected or tightened.

Check whether the short-circuit ring is broken. If it is broken, replace it with a copper plate according to the original size, or knock the thick copper wire into a square section and install it according to the original size.

(2) The armature does not release immediately after the electromagnetic coil is powered off. The main reasons for this failure are: the moving part is stuck;

The size of the core air gap, the residual magnetism is too large; the spring is fatigued and deformed, the elasticity is insufficient, and there is oil on the contact surface of the core. It can be repaired after disassembly to leave a 0.02-0.03mm air gap between the end face of the middle column and the bottom end face of the core, or replace the spring.

(3) Coil fault inspection and repair. The main fault of the coil is that the current passing through is too large, causing the coil to overheat and burn out.

This type of fault is usually caused by coil insulation damage, low power supply voltage, loose contact between the moving and static iron cores, which can also cause the coil current to be too large, the coil to overheat and burn out.

If the coil is burned due to short circuit, it should be rewound. The wire diameter and number of turns can be measured from the burned coil. The wire diameter and number of turns of the coil can also be found from the nameplate or manual. Make a wire mold according to the cross section of the column in the iron core. After the coil is wound, put it in an oven at 105-110℃ for 3 hours, cool it to 60-70℃ and dip it in 1010 asphalt paint. Other insulating paints can also be used. After dripping off the remaining paint, dry it in an oven at a temperature of 110-120℃ and cool it to room temperature before use.

If the number of turns of the coil short-circuited is small and the short-circuit point is close to the end of the coil, and the rest of the coil is intact, the power supply should be cut off immediately to prevent the coil from burning.

If there is no vibration or mechanical noise after the coil is powered on, check the connection of the coil lead wire and see if it is loose. Use a multimeter to check if the coil is broken or burned. If there is vibration and noise after power is turned on, check if the moving part is stuck, if there is any conductive material between the static and dynamic cores, and if the power supply voltage is too low. Treat them differently and handle them in time.

3. Inspection and maintenance of fire extinguishing equipment

Remove the arc extinguishing cover, check the integrity of the arc extinguishing coral and remove the smoke marks and metal fines on the surface. The outer shell should be intact.

If there are any cracks in the arc extinguishing hood, it should be replaced in time. A special note is that electrical appliances originally equipped with arc extinguishing hoods must not be used without arc extinguishing hoods to prevent short circuits.