What is the most serious failure of high-voltage motors?

There are many reasons for the failure of AC high-voltage motors. For this reason, it is necessary to explore a set of targeted and clear troubleshooting methods for various types of failures, and propose effective preventive measures to eliminate failures in high-voltage motors in a timely manner. , so that the failure rate of high-voltage motors is reduced year by year.

What are the common faults of high-voltage motors? How should they be dealt with?

1. Motor cooling system failure

Failure analysis

Due to production needs, high-voltage motors start frequently, have large vibrations, and have large mechanical impulses, which can easily cause the motor circulation cooling system to malfunction. This mainly includes the following types:

First, the external cooling pipe of the motor is damaged, resulting in the loss of cooling medium, which in turn reduces the cooling capacity of the high-voltage motor cooling system. The cooling capacity is blocked, causing the motor temperature to rise;

Second, after the cooling water deteriorates, the cooling pipes are corroded and blocked by impurities, causing the motor to overheat;

Third, some cooling and heat dissipation pipes have high requirements for heat dissipation function and thermal conductivity. Due to the different shrinkage degrees between objects of different materials, gaps are left. Problems of oxidation and rust occur at the joint between the two, and cooling water penetrates into them. As a result, the motor will have a “shooting” accident, and the motor unit will automatically stop, causing the motor unit to not work properly.

Repair method

Supervise the external cooling pipeline to minimize the temperature of the external cooling pipeline medium. Improve the quality of cooling water and reduce the probability of impurities in cooling water corroding pipes and blocking cooling channels. Lubricant retention in the condenser will reduce the heat dissipation rate of the condenser and restrict the flow of liquid refrigerant. In view of the leakage of aluminum external cooling pipelines, the probe of the leak detector moves near all possible leakage parts. At the parts that need to be inspected, such as joints, welds, etc., the system is run again so that the leak detection agent can be used again. The actual plan is to adopt the maintenance methods of stamping, stuffing and sealing. When conducting on-site maintenance, glue must be applied to the leakage area of the aluminum external cooling pipe of the high-voltage motor, which can effectively prevent the contact between steel and aluminum and achieve a good anti-oxidation effect.

2. Motor rotor failure

Failure analysis

During the starting and overload operation of the motor, under the influence of various forces, the short-circuit ring of the internal rotor of the motor is welded to the copper strip, causing the copper strip of the motor rotor to slowly loosen. Generally, because the end ring is not forged from a single piece of copper, The welding seam is poorly welded and may easily cause cracking due to thermal stress during operation. If the copper bar and the iron core are too loosely matched, the copper bar will vibrate in the groove, which may cause the copper bar or end ring to break. In addition, the installation process is not carried out properly, resulting in a slight roughening effect on the surface of the wire rod. If the heat cannot be dissipated in time, it will seriously cause expansion and deformation, causing the rotor vibration to intensify.

Repair method

First of all, the welding breakpoints of the high-voltage motor rotor should be inspected, and the debris in the core slot should be carefully cleaned. Mainly check whether there are broken bars, cracks and other defects, use copper materials to weld at the welding breaks, and tighten all the screws. After completion, normal operation will begin. Conduct a detailed inspection of the rotor winding to focus on prevention. Once found, it needs to be replaced in time to avoid serious burning of the iron core. Regularly check the condition of the core tightening bolts, reinstall the rotor, and measure the core loss if necessary.

3. High-voltage motor stator coil failure

Failure analysis

Among high-voltage motor faults, faults caused by damage to the stator winding insulation account for more than 40%. When a high-voltage motor starts and stops quickly or changes load quickly, mechanical vibration will cause the stator core and stator winding to move relative to each other, causing insulation breakdown due to thermal degradation. The increase in temperature accelerates the deterioration of the insulation surface and changes the condition of the insulation surface, thereby causing a series of changes related to the condition of the insulation surface. Due to oil, water vapor and dirt on the winding surface and discharge between different phases of the stator winding, the red anti-halo paint on the surface of the high-voltage lead insulation layer at the contact part has turned into black. The high-voltage lead part was inspected and it was found that the broken part of the high-voltage lead was at the edge of the stator frame. Continued operation in a humid environment resulted in the aging of the insulation layer of the high-voltage lead wire of the stator winding, resulting in a decrease in the insulation resistance of the winding.

Repair method

According to the construction site conditions, the high-voltage lead section of the motor winding is first wrapped with insulating tape. According to the “hanging handle” technique commonly used by maintenance electricians , slowly lift the upper slot edge of the faulty coil 30 to 40 mm away from the inner wall of the stator core and try to fix it. Use a simple baking clamp to initially clamp the newly wrapped insulating part, use powder mica tape to half-wrap the straight section of the upper layer to insulate it from the ground for 10 to 12 layers, and then wrap the noses of both ends of the adjacent slot coil to insulate it from the ground, and the bevel edge of the coil end Apply high-resistance semiconductor paint to sections with a brush length of 12mm. It is best to heat and cool twice each. Tighten the die screws again before heating for the second time.

4. Bearing failure

Failure analysis

Deep groove ball bearings and cylindrical roller bearings are most commonly used in high-voltage motors. The main reasons for motor bearing failure are unreasonable installation and failure to install according to corresponding regulations. If the lubricant is unqualified, if the temperature is abnormal, the performance of the grease will also change greatly. These phenomena make the bearings prone to problems and lead to motor failure. If the coil is not firmly fixed, the coil and the iron core will vibrate, and the positioning bearing will bear excessive axial load, which will cause the bearing to burn out.

Repair method

Special bearings for motors include open and closed types, and the specific selection should be based on the actual situation. For bearings, special clearance and grease need to be selected. When installing the bearing, pay attention to the selection of lubrication. Sometimes grease with EP additives is used, and a thin layer of grease can be applied on the inner sleeve. Grease can improve the operating life of motor bearings. Correctly select bearings and use bearings accurately to reduce the radial clearance of the bearing after installation and use a shallow outer ring raceway structure to prevent it. When assembling the motor, it is also necessary to carefully check the matching dimensions of the bearing and the rotor shaft when installing the bearing.

5. Insulation breakdown

Failure analysis

If the environment is humid and the electrical and thermal conductivity is poor, it is easy to cause the motor temperature to rise too high, causing the rubber insulation to deteriorate or even peel off, causing the leads to loosen, break or even arc discharge problems. Axial vibration will cause friction between the coil surface and the pad and core, causing wear of the semiconductor anti-corona layer outside the coil. In severe cases, it will directly destroy the main insulation, leading to breakdown of the main insulation. When the high-voltage motor gets damp, the resistance value of its insulation material cannot meet the requirements of the high-voltage motor, causing the motor to malfunction; the high-voltage motor has been used for too long, the anti-corrosion layer and the stator core are in poor contact, arcing occurs, and the motor windings break down, causing the motor to eventually malfunction. ; After the internal oil dirt of the high-voltage motor is immersed in the main insulation, it is easy to cause short circuit between turns of the stator coil, etc. Poor internal contact of the high-voltage motor can also easily lead to motor failure.

Repair method

Insulation technology is one of the important process technologies in motor manufacturing and maintenance. In order to ensure the stability of the motor for a long time, the heat resistance of the insulation must be improved. A shielding layer of semiconductor material or metal material is placed inside the main insulation to improve the voltage distribution along the surface. A complete grounding system is one of the important measures for the system to resist electromagnetic interference.