Several Practical Methods in Motor Maintenance
Various situations may be encountered during motor maintenance. If reasonable methods are adopted, detours can be avoided during the maintenance process, achieving twice the result with half the effort. Summarize the experience and experience in daily maintenance work into several practical motor repair methods, mainly including methods for handling and repairing problems such as reduced insulation resistance of the motor, grounding point of stator winding slot, inter turn short circuit of winding, broken cage rotor bar, and "parallel top cover" photography between motors, dismantling of old winding, wear of rotor journal and end cover bearing chamber, for reference. This article summarizes common problems in motor maintenance and introduces several practical methods in maintenance work.
1. Treatment for reducing the insulation resistance of the motor after installing the end cover
During the maintenance process of the cage motor, the insulation between the winding and the casing is good before installing the covers at both ends. After installation, the insulation resistance decreases. This phenomenon can determine that the fault occurred at both ends of the winding. The reason for the decrease in insulation resistance. This may be due to local damage to the paint film on the enameled wire or offset of the winding mold, resulting in a longer extension of the winding end. Due to the inner wall of the end cover being close to or in contact with the fault point after being covered, the insulation resistance of the winding decreases.
The first step to eliminate this type of fault is to determine which end of the motor has malfunctioned. The judgment method is to first install the end cover and use a 500V insulation resistance meter to measure the insulation resistance of the winding. If it is very low, it indicates a fault at this end of the winding. Then, remove this end cover, install another end cover, and measure the insulation resistance of the winding. If it is also very low, it indicates that there is also a fault on the other end. During the process of removing and installing the end cover, it may not be possible to install the rotor.
After determining the faulty end, it is usually only necessary to slightly reshape the winding end and paint it. If the problem is not resolved, a layer of thin film green shell paper can be placed on the outer side of the winding end that easily contacts the inner side of the end cover, which can generally eliminate the fault.
2. Search and handling of stator winding slot grounding points
The grounding in the stator winding slot usually occurs at the slot. Due to offset or damage to the slot insulation paper at the slot, or improper threading or marking at the slot, the enameled wire is placed under the slot insulation paper, or the slot insulation paper is squeezed when entering the slot wedge, resulting in a grounding fault. For this type of fault, the first step is to determine whether the motor winding is damp. If the motor is damp, it should be baked. If the result is invalid, it is judged as a ground fault.
There are several ways to find a grounding point:
(1) Carefully inspect both ends of the outgoing line and slot, and it is found that the outgoing line is intact and undamaged. The insulation at both ends of the slot is not damaged, the inside and outside of the motor are clean, and all parts are free of dust and oil stains. This indicates that the grounding point is inside the slot.
(2) Unlock the Y-shaped connection point of the stator winding, measure the insulation resistance of each phase to ground, and identify the grounding fault phase.
(3) Using a single-phase voltage regulator, connect the output phase line to one end of the ground fault phase and the zero line to the motor casing. Then, boost the voltage regulator from zero until smoke rises in the slot. At this point, immediately reduce the output voltage of the regulator to zero and cut off the power supply. The smoking point is the grounding point. Pay attention to safety during the entire operation process and place the motor on an insulation pad. Do not touch the motor before cutting off the power.
The treatment method is to carefully remove the slot wedge with a grounding slot, then place the motor in a padded oven, dry the soft winding, and carefully remove the wire turns inside the slot to check the insulation of each wire. If the insulation layer is damaged, it should be painted and dried, and then the insulation paper should be placed again in the slot. The removed wire turn should be placed in the slot, inserted into the slot wedge, and the winding should be painted and dried. If it is found that the enameled wire has been burnt out, the two disconnected wire ends should be pulled to the end of the winding, and then a enameled wire with the same diameter should be placed in the slot. The wires and joints at both ends of the winding should be twisted,