How to maintain and maintain the motor
1、 Preparation before installation of electric motor
Newly installed or idle motors for more than three months must undergo safety, electrical, and mechanical inspections before use to ensure safe and reliable operation of the motor.
1. Check the insulation resistance of the motor winding. Open the junction box and use a megohmmeter above 500V to measure the insulation resistance between the winding and the base. The normal resistance value should be>5M ohms. Remove the terminal connection piece and measure the insulation between the winding phases. The normal resistance value should be>10M ohms. If there is a serious low resistance during the above measurement process, the motor should be disassembled to find the cause. If there are no fault points, it indicates that the insulation performance of the motor has decreased due to moisture. Baking and moisture removal should be carried out until the insulation is qualified before installation and use.
2. Measure the resistance value of the three-phase winding. Observe whether the resistance values are the same. If there is a significant difference in resistance values, check the motor winding leads for poor contact or other reasons.
3. Check if the mechanical part of the motor is qualified. Rotate the rotating shaft by hand to check for flexibility and for any abnormal friction, jamming, shaft movement, and abnormal noise. At the same time, check whether all components are complete, whether the sturdy screws are tightened, and whether the coupling or pulley is installed and calibrated properly.
2、 Motor installation and commissioning
Before wiring the motor, check whether the control circuit and protection circuit are normal, whether the selection of fuses is appropriate, and whether the connection points between the control appliances are firm. If normal, connect the motor power supply and start without load, observe whether the motor's running direction meets the equipment requirements. If the direction of rotation is opposite, simply swap any two incoming wires of the motor wiring board for each other. After the startup test is normal, connect the motor to the load for trial operation and check if its working current is normal. If the current is too high, the machine should be shut down for inspection.
If the motor does not rotate or the speed is very low, or there is abnormal humming after being loaded, it should be immediately powered off. If the power is on for a slightly longer time, it is highly likely to burn the motor winding, even damage the control circuit and equipment. Generally, this type of condition is caused by mechanical overload or jamming, and the electrical device is caused by phase failure operation. At this point, the cause of the fault should be carefully checked and the test run can only be resumed after the fault is eliminated.
Usually, the starting current of the motor is 5-7 times the operating current. When starting the motor, the number of consecutive starts should be controlled within three to avoid the accumulation of high temperature caused by excessive starting current and burning the insulation of the motor winding.
3、 Maintenance during motor operation
The normal operation of the motor can be judged by the sound, speed, temperature, working current, and other phenomena emitted by the motor. If the motor experiences leakage, sudden decrease in speed, severe vibration, abnormal noise, overheating and smoke, or if the control electrical contacts ignite and smoke during operation, one of these phenomena should be immediately shut down for maintenance. Listen to the sound emitted by the motor during operation, and if there is a loud buzzing sound, it is either a high current or a lack of phase operation. If there is an abnormal friction sound, it may be due to bearing damage and cleaning phenomenon. If there is a slight abnormal sound, use a wooden stick or long rod screwdriver, with one end pressed against the motor bearing and the other end pressed close to the ear, to carefully distinguish whether the sound is abnormal. If there is an abnormal sound, it indicates that there is a problem with the bearing. It should be replaced in a timely manner to avoid damaging the bearing cage, causing friction between the rotor and stator to sweep the bore, and burning the motor stator winding. Observe whether the control electrical contacts and motor wiring contacts are loose, abnormally heated or ignited, and whether the insulation is aging. Is there any abnormal vibration or sound in the contactor, and is there any ignition after the contact is closed? If such problems are found, they should be dealt with and resolved as soon as possible to avoid accidents.
During regular inspections, it is important to regularly check the motor for overheating. The maximum allowable temperature for commonly used E-pole insulated motors is 105%: in actual operation, the winding temperature of the motor should be much lower than this limit temperature. When measuring, the actual temperature of the motor winding is determined by adding 15-20 ℃ to the surface temperature of the motor. For motors with excessively high temperature rise, the working current should be measured. If the current is too high and the three-phase voltage is normal, it indicates that the load is too heavy. Mechanical maintenance personnel should check the mechanical equipment. If the motor is found to have a long-term overcurrent of more than 20%, the protection device will not operate and will not automatically power off. This indicates that the set current value of the thermal relay is too large, and the set current value should be reduced.
4、 Dismantling and maintenance of electric motors
Motor disassembly steps: Use a puller to remove the pulley or coupling, remove the rear fan cover of the motor, and remove the front bearing outer cover screws and front and rear end cover screws. For larger motors, use a scribe to mark the original fixed positions on the two end covers and the frame before disassembly. Use a wooden hammer to hit the top of the front shaft to loosen the rotor and rear cover from the frame, and then remove the rotor from the stator. Be careful not to scratch the insulation of the stator winding end when removing the rotor.
Observe whether the motor bearings are damaged and whether the lubricating oil has deteriorated or dried up. Grasp the outer ring of the bearing by hand and shake it back and forth to see if it is too loose. If the bearing is checked to be normal, it does not need to be disassembled. Clean the bearing with kerosene or diesel. If there are any problems during the inspection, the bearing can be removed with a puller.
If the fit between the shaft and the bearing is too tight or rusty, heating can be used to solve the problem. Wrap the shaft with asbestos rope, quickly and evenly heat the bearing to around 250 ℃ using a torch type acetylene flame, and use a puller to pull it out while it is hot. The cold disassembly method is to pad the damaged bearing with a wooden block, use an iron hammer to break the periphery, remove the outer ring, use a handheld polishing machine grinding wheel to cut a hole in the bearing inner ring (without cutting through to avoid damaging the rotor journal), and then use a hammer to hit the inner ring to break the cut and remove the inner ring.
When replacing bearings, direct installation can easily scratch the rotor journal. Generally, smaller bearings can be directly installed. When replacing larger bearings, it is best to place the bearings in an oven for heating. When the temperature reaches around 100 ℃, cover the bearings on the rotor journal while they are hot, and use a steel pipe to cover the shaft against the inner ring of the bearing. Evenly tap the steel pipe to make the shaft move in place. Attention: When installing bearings, the side with the model engraved on the bearing should face outward for future alignment and replacement.
Add lubricating grease to half the capacity of the bearing's internal space, with slightly less grease added at high speeds and slightly more grease added at low speeds. Excessive oiling can cause the lubricating oil to become thinner and flow out after the bearing overheats, which is swept by the rotor blades on the stator winding, reducing the insulation performance between the windings, causing breakdown and short circuit, and burning the motor winding. Commonly used lubricating oils include calcium based grease, sodium based grease, lithium based grease, etc. Calcium based lipids have good water resistance, but poor heat resistance (≤ 70 ℃), while sodium based lipids have good heat resistance (≤ 120%), but poor water resistance. Lithium based grease has the advantages of both, but its price is relatively high. Please refer to the hardware manual for an introduction to the use of lubricating grease. Users can choose according to their actual needs.
Pay attention to the cleanliness of the lubricating grease and do not mix it with dust, iron filings, or sand particles. If contaminated lubricating grease is added to the bearing, it will cause accelerated bearing wear and premature bearing damage. In summary, there are many cases where the rotor is swept due to bearing damage, resulting in the burning of the motor winding, which should be given special attention.
5、 Daily maintenance of electric motors
Daily maintenance is crucial for reducing and avoiding motor malfunctions during operation, with the most important aspect being patrol inspections and timely elimination of any root causes of abnormal phenomena. After an accident occurs, careful accident analysis and countermeasures are necessary to reduce the number of accidents and improve the efficiency of motor operation when repairing and stopping the machine. Daily maintenance of the motor is certainly very important for its normal operation, However, motors in operation often encounter many unexpected situations, such as short circuits, overloads, and interruptions. In order to prevent the motor from being damaged under these conditions, some operational protection measures must be taken.
Keep the motor clean. It is not allowed to enter water droplets, oil stains, dust, etc. inside the motor, and regularly clean the dust inside and outside the motor.
Pay attention not to exceed the rated load current.
Pay attention to checking the heating and oil leakage of the bearings, especially refueling according to regulations.
The temperature rise of the motor cannot exceed the rated value.
1. Listen to the sound of the motor running. If there is any abnormality in the sound of the motor running, immediately replace the bearing. When replacing the bearing, confirm that the accuracy of the shaft and bearing chamber is damaged.
2. Regularly check the temperature of the motor, and if the temperature of the motor is too high, stop or reduce the load. If the temperature is high under normal load, check if there is insulation damage.
3. Regularly oil the bearings of the motor, clean the fan and casing, and the specific time depends on the working environment.
6、 Regular maintenance and upkeep of motors
In order to ensure the normal operation of the motor, in addition to using it according to the operating procedures and paying attention to normal monitoring and maintenance during operation, regular inspections should also be carried out to do a good job in motor maintenance and upkeep. This can eliminate some problems in a timely manner, prevent faults from occurring, and ensure the safe and reliable operation of the motor. The time interval for regular maintenance can be determined based on the form of the motor and the operating environment.
