The motor is composed of a stator frame, windings and insulating materials, a rotor, bearings at both ends and end covers, which is relatively simple. The causes of motor failure are: power supply phase failure, incorrect voltage or frequency; Winding short circuit, open circuit, grounding; Poor operation of the carrier; Dirty inside and outside, poor heat dissipation (too thick paint outside is also the reason for poor heat dissipation), and bad cooling fan with its own, poor ventilation; Poor mechanical equipment; Long-term high load operation; High ambient temperature, etc. Most of the damage to the motor is caused by poor daily inspection and insufficient maintenance by maintenance personnel. As long as you insist on carefully watching, listening, touching, measuring and doing, most of the failures can be prevented and avoided,
1. Look: Check the size and change of the working current of the motor during daily inspections, and see if there is any water leakage or dripping around, which will cause the motor to burn out due to low insulation breakdown. It also depends on whether there are objects that affect the ventilation and heat dissipation environment around the motor. Whether the fan end cover, fan blades and the outside of the motor are too dirty and need to be cleaned? It is necessary to ensure its cooling and heat dissipation effect. Whoever finds the problem should deal with it in time.
2. Listen carefully to whether the running sound of the motor is abnormal. Due to the loud noise in the machine room, you can listen close to the two ends of the motor with the help of auxiliary tools such as screwdrivers or listening sticks. If you listen frequently, you can not only find the bad vibration of the motor and its driving equipment, but also judge the amount of internal oil, so as to make corresponding measures such as adding oil or replacing new ones in time, avoid the motor pin bearing oil dry grinding and blocked rotation, go outside the circle, sweep the chamber burned.
Pay attention to open the lower oil drain port or remove the bulkhead screw on the other side when refueling the motor, so as to squeeze out the old oil to prevent the oil from squeezing into the motor due to high pressure during refueling, and splashing on the stator and rotor during operation, affecting The heat dissipation function of the motor, etc.
3. Touch: probe the temperature around the motor with the back of your hand. In the case of good bearing conditions, the temperature at both ends will generally be lower than the temperature of the middle winding section. If the temperature at both ends of the bearing is high, it is necessary to check the bearing in combination with the measured sound of the bearing. If the overall temperature of the motor is high, it is necessary to check the load, equipment and ventilation of the motor in combination with the working current.
According to the insulation level of the insulating material used in the motor, the limit temperature at which the winding insulation can be used for a long time during the operation of the motor, or the allowable temperature rise of the motor (the actual temperature of the motor minus the ambient temperature), can be determined. Insulation grade standards vary from country to country, but they are basically divided into: Y, A, E, B, F, H and C grades, of which Y grade has the lowest allowable temperature rise (45 ℃) and C grade has the highest allowable temperature rise (above 135 ℃). Considering the bearing oil and other materials, the temperature measured by the thermometer is preferably controlled below 85 ℃.
4. Measurement: When the motor stops running, the insulation resistance of each relative ground or 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. If any defects are found, the insulation shall be improved by baking with a damp lamp, and the motor shall be prevented from burning out due to low insulation (recommend value> 1 megohm). Do not turn off the heating switch at will unless special circumstances. Pay special attention to the waterproof, moisture-proof and drying of the motor in wet weather and winter. Special attention should be paid to the watertightness of the motor in the open air and wet places, and the motor that is suspected of being seriously damp or splashed with water should be carefully checked before use. If the motor is found to be soaked in water, as long as the rotor is drawn out after the motor is disassembled, and dried with compressed air, then bake with a baking lamp from both ends of the motor stator to stop the insulation of the motor from rising to normal.
Some motor winding leads only three, can not detect the insulation between windings, rewinding motor insulation resistance should not be less than 5 megohm.
When the motor is running, its three-phase working voltage and current can be measured to see if it is balanced. The voltage should be basically equal, and the error between each phase current and the average value should not exceed 10%. If the difference between each phase current measured by 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 2 poles are about 2800rpm (rated current);4 poles are about 1600rpm; 6 poles are about 900rpm,. It will vary depending on the number of poles and capacity. In addition, the Y and △ shape connection of the motor cannot be mistaken. If the Y shape is connected into △ shape by mistake, the working current will increase. These points can help us judge the condition of the motor in daily operation.
5. Do: Not only should remedial measures be taken in time for the problems found in the inspection, but also the screws and wiring of the motor should be tightened, disassembled and inspected, and cleaned and maintained according to the maintenance cycle (monthly). If all four fixing screws of the motor end cover are loose, it will cause the chamber sweeping operation to burn out. The loose and false connection of the motor wiring bolts causes the missing phase to burn out. The fan blade of the motor falls off and resists the machine body, causing blocking and burning. The motor burns out due to poor lubrication and high operating temperature, and failure to replenish lubricating oil or replace the motor in time causes breakdown due to the decrease of insulation resistance due to wet weather and failure; the motor in the workshop section is burned out because it is not checked and fastened in time. Or is it because although the problem has been found, it has not been maintained and remedied. Whether you don’t look or don’t do, or just look and don’t do, it will eventually cause a malfunction or accident.
If you need to replace the motor when dismantling the motor, you should use imported as much as possible, the domestic will have a lot of refurbished old bearing, the quality is difficult to guarantee. If it is found that the outer circle of the end cover is not closely matched with the outer circle, that is, when the outer circle of the end cover is taken, according to its different degree, depending on the situation, the end cover is used to play pitting, pad copper skin or inlaid copper sleeve to eliminate. Be sure to set the center point or it will be damaged again soon. Before putting into operation, it is necessary to reconfirm the tightening of the radial swing of the extended end and the end cover, whether the rotor rotates flexibly, whether the winding lead is connected correctly, etc.