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I. selection of motor. The following steps should be followed in the selection of motors:
The view appearance: Motor surface paint layer should be smooth, nameplate signs complete; correct installation, closed motor seat ribs should be intact, complete accessories;
The manual rotation: axis, rotation should be flexibly rotated by hand, momentum is good, no axial movement; the bearing power: listen to run 15-25 minutes, the bearings should be smooth, no stagnation. The sound of uniform harmony; bearing temperature is not high, no oil leakage, oil leakage phenomenon; after stopping operation, with a motor cover and the end touch does not feel the heat; check the wiring: open the box to see the line marks is clear and complete, the contact piece is compacted tightly, the nut is complete; the measurement of resistance: manual megabytes of rated voltage 500V ohm meter, measuring line between the end line and phase line and the line between the base of the insulation resistance, insulation resistance of normal motor should be greater than 1 megohm. It can measure the current. In operation, with the clamp type ammeter to measure the phase current of the motor without load, the deviation of the average value of any phase and three-phase in the three-phase current shall not exceed 10% of the average value, and the no-load current is generally 25-50% of the rated current.
Two 、 motor maintenance. Practice has proved that the focus of motor maintenance is to prevent the motor from burning down. The following methods are effective:
1, keep the starting equipment in good state of technology, and the technical status of the motor startup equipment is directly related to the smooth start. Practice shows that the vast majority of burned motors are not start smoothly and burned, such as starting equipment technical condition caused by bad phase start; contactor arc ignition, resulting in voltage and current change etc.. Measures to keep the equipment in good condition are: check, clean and tighten regularly. If the contact is not clean, oxidation erosion, will result in the increase of contact resistance, heating, ablation of contacts, thus forming and burning of motor winding phase operation; contactor coil core with rust and dust, will pull lax and makes strong noise, and increasing the coil current, until the burning coil. Therefore, the electrical control cabinet should be located in a dry, ventilated and convenient location; dust removal, cleaning and regular contact; the core to increase the anti rust measures; often fastening the connecting parts; check contactor, ensure good contact, mechanism of action should be flexible, accurate, is to ensure that these necessary conditions start smoothly.
2. Keep the motor clean and a good cooling environment. Keep it clean at the inlet of the motor. Around the air inlet may not have dust, oil, water and other straw debris, to prevent this kind of thing sucked inside the motor form a short medium or damage to the motor winding insulation layer; or blocking the motor ventilation cooling and temperature, lead to burn.
3. Keep the motor working under the rated current to avoid the overload operation of the farm motor. When the motor is in overload operation, the motor speed drops, the current increases, the temperature increases, the winding coil is overheated. The main reason is the excessive drag caused by load, the voltage is too low or the dragging machine card etc.; if the overload for a long time, motor overload to absorb a large number of active power from the grid, the current will increase sharply, with the temperature rise. In the high temperature operation of the motor, insulation material easily aging, failure and burn winding coil, which is the main reason for burning the motor. Therefore, one should always pay attention to check the unit transmission device is flexible, reliable operation, check and adjust belt tightness, prevent seizure; two should pay attention to machinery not long time of work overload; three to maintain voltage stability, especially not low voltage operation, so as to ensure the normal work of the motor at rated current.
4 keep the interphase current balanced. For agricultural three-phase asynchronous motors, the difference between the current value of any phase and the average value of other two-phase currents shall not exceed 10%, which is a necessary condition for the safe operation of the motor. If the difference is over 10%, the motor has been found to be out of order. It must be stopped immediately to find out the cause and can continue to work until it is out of order. Otherwise, the fault will be expanded rapidly until the motor is burnt out.
5. Keep the temperature and temperature of the motor in the normal range. In the operation of the motor, it is necessary to check the temperature of the bearing, stator, shell and other parts 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 damage, it will inevitably cause the temperature to rise. In the vicinity of bearings, airframe temperature rise, it is necessary to stop immediately to check bearings, may be refueling, and if still invalid, it should be removed bearing identification. If the roller, raceway surface cracks, scratches or damage, or gap becomes larger, the inner ring in the bearing on the rotation, appear any one, should replace bearings. Otherwise, continue to use the bearings will cause further damage, collapse, motor burned accident such as sweeping. To monitor the motor temperature or temperature rise has no change, use the following methods: simple monitoring of the motor plug hole, thermometer, use cotton plugged fixed, can monitor the temperature change of motor, machine and shell is usually 1 DEG C temperature.
6, in time to detect and deal with motor abnormalities, motor operation should be no vibration, noise and odor. If the vibration occurs, it will cause the motor to connect the load as the axis of the machine, different degrees of heart, and then load increases, the load current also increases, causing the temperature rise and burn the motor. So, always.
