According to statistics, approximately 85% of the electrical faults in the operation of three-phase asynchronous motors used in production are caused by winding burnout, while approximately 15% are caused by mechanical and other faults. The main reasons for winding burnout are missing phase operation or overload operation, winding grounding, and short circuit between windings or turns. The next most common causes are mechanical issues such as friction between the stator and rotor, and broken bars. Here, the focus is on analyzing the causes of winding burnout from an electrical perspective and proposing corresponding solutions.
1. Running with phase deficiency
1. Fault phenomenon
The motor cannot start, even though it can start without load, the speed increases slowly with a buzzing sound; the motor smokes and heats up, accompanied by a burning smell.
2. Check results
Remove the motor end cover, and you can see that the winding end has 1/3 or 2/3 of the pole-phase winding or variable focus or turns dark brown.
3. Causes of failure and troubleshooting methods
(1) The contact of the motor power supply circuit fuse circuit is poor or damaged by mechanical means, resulting in the melting of a phase fuse.
(2) The three-phase fuse specifications in the power supply circuit of the motor are different, and the fuse with a smaller capacity burns out. The fuse should be replaced with one of the same specifications according to the power of the motor.
(3) Poor contact of switches (isolation switches, rubber cap switches, etc.) and contactors in the power supply circuit of the motor (burned or loose). Repair and adjust the moving and static contacts to ensure good contact.
(4) There is a missing phase in the circuit. Locate the break and make a secure connection.
(5) The virtual soldering between the motor windings leads to poor contact. Carefully inspect the motor winding connection wires and solder them securely.
The electric motor current exceeds the rated value; the electric motor temperature rise exceeds the rated temperature rise.
2. Check results
All three sets of motor windings are completely burned; bearings have no grease or damaged sand frames; stator and rotor iron cores rub against each other, commonly known as "scraping the barrel".
3. Causes of failure and troubleshooting methods
(1) When the load is too heavy, consider reducing the load appropriately or replacing the motor with a suitable capacity.
(2) If the power supply voltage is too high or too low, it is necessary to install a three-phase power supply voltage stabilizing compensation cabinet.
(3) If the motor is severely dampened or corroded by corrosive gases for a long time, the insulation resistance will decrease. Depending on the specific situation, a major overhaul or replacement of a closed motor with the same capacity and specifications should be carried out.
(4) Bearing oil shortage, dry friction, or rotor mechanical eccentricity can cause the rotor of the motor to rub against the stator, resulting in the motor current exceeding the rated value. First, carefully inspect the bearing for wear. If it is not up to standard, replace it with a new one. Secondly, clean the bearing and inject an appropriate amount of lubricating grease. Then, check the motor end cover. If the center hole of the end cover is worn, causing the rotor to be eccentric, the end cover should be treated or replaced.
(5) The transmission part of the mechanism malfunctions, causing the motor to overload and burn out its winding. Check for faults in the mechanical part, take measures to handle and resolve them, making it rotate smoothly.
The motor cannot start when it is unloaded; the motor power supply circuit fuse is blown or the switch trips.
2. Check results
The stator slot winding and iron core have burn marks, and there is copper melting; the winding inside the slot is broken through the iron core; the insulation of the lead-out wire of the winding is damaged.
3. Fault Causes and Handling Methods
(1) When repairing the electric motor, if the bamboo wedge is not inserted carefully, it may damage the insulation of the slot winding. If the bamboo wedge is old and aged, the insulation may be poor. It is necessary to select high-quality bamboo wedges and ensure proper insulation treatment according to the offline process of the motor. When taking the motor offline, be careful not to scratch the wires with the bamboo wedge.
(2) For motors that are exposed to moisture for a long period of time or operate in corrosive gases, they should be replaced with enclosed-type motors.
(3) Open-type motors may have their winding insulation damaged due to the entry of metal or metal chips into the motor. In this case, protective nets or plates should be installed around the motor.
(4) The rotor balance block is loose or detached, causing damage to the insulation of the motor winding. The balance block should be readjusted and securely fixed, and any damaged winding should be repaired.
(5) For those without lightning arresters or with failed lightning arresters, lightning arresters should be installed or rechecked.
4. inter-turn short circuit
1. Fault phenomenon
The motor cannot start; the motor power supply circuit fuse blows or the switch trips; the motor winding smokes and has a burnt smell.
2. Check results
Multiple strands of wire at the short-circuited area have burned and there is copper melting around it.
3. Causes of failure and troubleshooting methods
(1) For motors with scratched insulation on the surface of the conductors or poor insulation at the ends of the windings when they are taken offline, the burnt conductors should be separated, cleaned, soldered, and insulated with insulation tape. After being placed in the slot, they should be coated with insulation varnish and dried. If it cannot be repaired, it should be rewound according to the original data.
(2) The sleeves for inter-winding connections and reference lines must be compatible with the insulation class of the motor windings. The insulation sleeves for connections should be 15-25mm longer than the solder joints.
The motor is smoking, with excessive local temperature rise and a burnt smell.
2. Check results
Electric Motor three-phase current imbalance; several turns or one coil become bare wire.
Motor three-phase current imbalance; several turns or one coil become bare wire.
(1) When a few turns or one coil is burned out, if the slot filling rate is not high, it can be repaired by rewinding.
(2) For the remaining parts, please refer to the processing method in item 4.
Timely detection and prompt elimination of electrical equipment failures can prevent accidents and ensure smooth production. Therefore, it is necessary to regularly inspect and maintain electrical equipment according to regulations, accurately diagnose and handle operational failures of electrical equipment, reduce equipment accident losses, and ensure normal production.
professional electric motor manufacturer -Dongchun motor China.
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