Daily inspection and maintenance of motor
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The motor is composed of stator frame, winding and insulating materials, rotor, bearings at both ends and end covers, which is relatively simple. The causes of motor failure include: power phase failure, wrong voltage or frequency, short circuit of winding, open circuit, poor operation of grounding bearing, dirty inside and outside, poor heat dissipation, too thick paint on the outside, bad self-contained cooling fan, poor ventilation and poor mechanical equipment, long-term high load operation, high ambient temperature, etc. More than 90% of the motor damage is caused by the poor daily inspection and insufficient maintenance by the maintenance personnel. As long as we insist on watching, listening, touching, measuring and doing carefully, the vast majority of faults can be prevented and avoided.
1. Look
During daily inspection, check the size and change of motor working current, check whether there is water leakage and dripping around, and whether the motor will be burned due to low insulation breakdown winding resistance. It also depends on whether there are objects outside the motor that affect its ventilation and heat dissipation environment, whether the fan end cover, fan blade and the outside of the motor are too dirty and need to be cleaned to ensure its cooling and heat dissipation effect. Whoever finds a problem should deal with it in time.
2. Listen
Carefully listen to whether the operation sound of the motor is abnormal. Due to the high noise in the machine room, you can listen close to both ends of the motor with the help of auxiliary tools such as screwdriver or listening stick. If you listen often, you can not only find the bad vibration of the motor and its driving equipment, but also judge the amount of internal bearing oil, so as to timely take corresponding measures such as adding bearing oil or replacing new bearings, so as to avoid locked rotor, walking outer circle and burning out due to lack of oil and dry grinding of motor bearings.
Considering the difficulty of disassembling and replacing bearings of large motors, most manufacturers will use open bearings regularly (2000h). When refueling with oil * * *, pay attention to use the bearing oil (- 35 ℃ - + 140 ℃) marked by the motor nameplate, and open the oil drain port at the lower end or disassemble the bulkhead screw on the other side, so as to squeeze out the old oil (pay attention to the quota of supplementary oil), Prevent the oil from being squeezed into the motor due to high pressure during refueling, splashing on the stator and rotor during operation, affecting the heat dissipation function of the motor, etc.
3. Touch
Probe the temperature around the mold motor with the back of your hand. When the bearing is in good condition, the temperature at both ends will generally be lower than that of the intermediate winding section. If the temperature at the bearings at both ends is high, check the bearing in combination with the measured bearing sound. If the overall temperature of the motor is too high, check the load, equipment and ventilation of the motor in combination with the working current and deal with it accordingly. According to the insulation grade of the insulating material used by the motor, the limit temperature that the winding insulation can be used for a long time when the motor is running, or the allowable temperature rise of the motor (the actual temperature of the motor minus the ambient temperature). There are differences in insulation grade standards among countries, but they are basically divided into y, a, e, B, F, h and C. among them, the allowable temperature rise of Y is the lowest (45 ℃) and that of C is the highest (above 135 ℃). In consideration of bearing oil and other materials, the temperature measured by the motor with a thermometer should preferably be controlled below 85 ℃.
4. Survey
(1) Off line: when the motor stops running, the insulation resistance of each relative or phase to phase shall be measured regularly (monthly) with an insulation meter and compared with the test results of last month, so as to find insulation defects in time. In case of any defect, bake with a damp lamp to improve the insulation and avoid damaging the motor due to winding breakdown due to too low insulation (recommended value > 1 megohm). Do not turn off the heating switch of the motor with electric heating for drying moisture at will unless under special circumstances. In wet weather and winter, pay special attention to the waterproof, moisture-proof and drying of the motor. Pay special attention to water tightness of motors in open and humid places; Motors suspected of being seriously damp or splashed with water shall be carefully checked before use. If the motor is soaked in water, just disassemble the motor, extract the rotor, dry it with compressed air, and then bake it from both ends of the motor stator with a baking lamp until the motor insulation rises to normal. Some motor windings have only three leads, so the insulation between windings cannot be detected. The insulation resistance of rewound motor shall not be less than 5 megohm.
(2) Online: when the motor is running, the three-phase working voltage and current can be measured to see whether it is balanced. The voltage shall be basically equal, and the error between the current of each phase and the average value shall not exceed 10%. If the difference between the current of each phase measured by the clamp meter is too large, there may be inter turn short circuit. Sometimes it is necessary to disconnect the load to measure the no-load current. Generally, the 2-pole is about 2800rpm, 1 / 3 ie (rated current), the 4-pole is about 1600rpm, about 40% ie, and the 6-pole is about 900rpm, 55% ie. It will vary depending on the number of poles and capacity. In addition, the Y and △ connection method of the motor shall not be mistaken. If the Y is wrongly connected into △ shape, the working current will increase, otherwise, it will decrease. At the same time, if the winding wiring of the motor is wrong, or the number of winding turns is reduced, and the air gap between the stator and rotor of the old motor is too large (normally 0.2-1.0mm), the no-load current will increase. These key points can help us judge the condition of the motor in daily operation.
5. Do
Not only take remedial measures for the problems found in the inspection in time, but also fasten the screws and wiring, disassemble, inspect, clean and maintain the motor according to the maintenance cycle (monthly). For example, all 4 fixing screws on the motor end cover are loose, resulting in burning out during chamber sweeping operation; Loose and false connection of motor connecting bolts, resulting in phase loss and burning; The fan blade of the motor falls off against the body, causing blockage and burning; The motor bearing is poorly lubricated and the operating temperature is high, but the lubricating oil is not supplemented or the bearing is not replaced in time, resulting in motor burnout; Due to wet weather, the insulation resistance of the motor decreases, and the insulation is not improved in time, resulting in breakdown. The motor in the section was burnt out because it was not checked and fastened in time, or because it was found that the problem was not repaired. Whether you don't look at it or just look at it, it will eventually cause failure or accident.
When disassembling and inspecting the motor, if the bearing needs to be replaced, it shall be imported as far as possible. Many domestic bearings will be refurbished old bearings, and the quality is difficult to guarantee. If it is found that the outer circle of the bearing does not fit closely with the end cover bearing seat, that is, when the bearing goes through the outer circle, it is necessary to eliminate the pitting, copper skin or copper sleeve on the inner ring of the end cover bearing seat according to its degree, and be sure to fix the center point, otherwise it will be damaged soon. Before putting into operation, it is necessary to reconfirm the radial swing of the extended end of the shaft and the fastening of the end cover, whether the rotor rotates flexibly, whether the winding leads are connected correctly, etc.
There are also many motors. When the pump connected to them leaks, they usually pressurize (stuffing box) to eliminate the leakage. When adding and changing packing, experienced maintenance workers will first turn it by hand to see the rotation, tighten the gland screws evenly, and then start and stop for a short time for two or three times to see whether the working current is normal; The inexperienced new maintenance workers only know to tighten and eliminate the leakage, and do not pay attention to the related motor. As a result, the motor breakdown winding is burned out due to too large locked rotor starting current and too late thermal overload protection. In addition, during the maintenance, disassembly, inspection and reassembly of the mechanical equipment driven by the motor (reducer, water pump, oil pump, etc.), the axis line between the motor and the driven machinery shall also be carefully checked and corrected to ensure good alignment. The coupling shall be light and flexible when rotating by hand. Only by doing each step earnestly and carefully can the intact rate of equipment be improved.
