How to choose and buy Motor maintenance steps
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1、 Selection of motor. The following steps shall be followed for the purchase of motor:
(1) check the appearance: the paint layer on the motor surface shall be smooth and flat, the nameplate shall be installed correctly and the marks shall be complete; The cooling ribs of the enclosed motor base shall be intact and the accessories shall be complete; (2) manual rotation: rotate the electric shaft by hand. The rotation shall be flexible, the inertia momentum is good, and there is basically no displacement in the axial direction; (3) diagnosis and hearing bearing: the bearing shall be stable and light without stagnation after being powered on for 15-25 minutes. The sound is even and harmonious; The bearing temperature is not high, and there is no oil leakage and oil throwing; After the operation stops, touch the motor base and end cover by hand to avoid heating; (4) check the wiring: open the junction box to see whether the phase line marks of each phase are clear and complete, whether the connecting piece is compacted and compressed, and whether the nuts are complete; (5) resistance measurement: use a manual megohmmeter with rated voltage of 500V to measure the insulation resistance between the phase lines at the outlet end and between the line and the base. The insulation resistance of normal motor shall be greater than 1 megohm. (6) measure the current. During operation, use a clamp type ammeter to measure the current of each phase of the motor under no-load. The deviation between any phase of the three-phase current and the three-phase average value shall not be greater than 10% of the average value, and the no-load current is generally 25-50% of the rated current.
2、 Maintenance of motor. Practice has proved that the focus of motor maintenance is to prevent motor from burning, and the following methods are effective:
1. Keep the technical state of starting equipment intact, and the technical state of motor starting equipment is directly related to whether it can be started smoothly. Practice shows that the vast majority of burned motors are burned out due to poor start-up, such as phase loss start-up caused by poor technical state of starting equipment; The voltage and current change greatly due to arcing and ignition of contactor contact. The measures to keep the starting equipment in good technical condition are: regular inspection, cleaning and fastening. If the contactor contact is not clean and the oxidation and ablation are serious, the contact resistance will increase, causing heating and ablation of the contact, resulting in phase loss operation and burning of the motor winding; The iron core of the contactor pull-in coil is rusted and dusty, which will make the pull-in loose and make strong noise, and increase the coil current until the coil is burned. Therefore, the electrical control cabinet shall be set in a dry, ventilated and easy to operate position; Dust removal and contact cleaning shall also be carried out regularly; Rust prevention measures shall be added to the coil core; Fasten all connecting parts frequently; Check the contactor contact to ensure good contact and flexible and accurate mechanism action, which are the necessary conditions to ensure smooth start.
2. Keep the motor clean and a good cooling environment. The air inlet of the motor must be kept clean frequently. There shall be no dust, oil stain, water stain and other straw sundries around the air inlet to prevent such things from being sucked into the motor, forming short-circuit medium or damaging the insulation layer of motor winding; Or block the ventilation and cooling of the motor and the temperature rises, resulting in burning.
3. Keep the motor working under the rated current to avoid overload operation of agricultural motor. When the motor runs in overload state, the motor speed decreases, the current increases, the temperature increases, and the winding coil is overheated. The main reason is that the driving load is too large, the voltage is too low or the driven machinery is stuck; If the overload time is longer, the overload motor absorbs a large amount of active power from the power grid, the current will increase sharply, and the temperature will rise. When the motor operates at high temperature, the insulation material is easy to burn the winding coil due to aging and failure, which is the main reason for burning the motor. Therefore, first, always check whether the transmission device of the unit operates flexibly and reliably, and check and adjust the tightness of the transmission belt at any time to prevent jamming; Second, pay attention not to overload the operating machinery for a long time; Third, keep the voltage stable, especially do not operate at low voltage, so as to ensure the normal operation of the motor under the rated current.
4. Maintain phase to phase current balance. For agricultural three-phase asynchronous motor, the difference between the current value of any phase and the average current value of other two phases shall not exceed 10%, which is a necessary condition to ensure the safe operation of the motor. If the difference exceeds 10%, it indicates that the motor has failed. It must be shut down immediately to find out the cause and eliminate the fault before continuing to work, otherwise the fault will expand rapidly until the motor is burned.
5. Keep the motor temperature and temperature rise within the normal range. During the operation of the motor, it is necessary to check whether the temperature of the bearing, stator, housing and other parts is abnormal at any time, especially for the motor without overload protection, it is more important to monitor the temperature. If the bearing is short of oil or damaged, the temperature will inevitably rise. When the temperature of the machine body near the bearing rises, stop the machine immediately to check the bearing. Add oil first. If it is still invalid, remove the bearing for identification. If the surface of rolling element and raceway is cracked, scratched or damaged, or the gap becomes larger, and the inner ring rotates on the bearing, replace the bearing in case of any item. Otherwise, continued use will further damage the bearing, resulting in major accidents such as frame collapse, motor sweeping and burning. To monitor whether the temperature or temperature rise of the motor changes, the following simple methods can be used: insert a thermometer in the hole of the motor and plug it tightly with cotton ball to monitor the temperature change of the motor at any time. The temperature difference between the outside of the machine and the inside of the shell is usually 1 ℃.
6. Find and handle motor abnormalities in time, and there shall be no vibration, noise and peculiar smell during motor operation. If vibration occurs, it will cause the increase of different centrality of the axis of the load working machine connected to the motor, and then the load will increase, and the load current will also increase, resulting in the increase of temperature and the burning of the motor. Therefore, the anchor bolts, motor end covers, bearing glands, etc. causing vibration shall be checked frequently without looseness, and the connecting devices must be reliable, especially for high-power motors, they must be found and eliminated in time. Noise and peculiar smell are important signs of abnormal motor operation and precursors of major accidents. They must be found out in time and the causes must be found out and eliminated immediately. Otherwise, the opportunity will be delayed and the fault range will be expanded, resulting in a serious accident of burning the motor.
