The case where the three-phase asynchronous motor winding is Y-connected: After the power supply is out of phase, the motor can continue to run, but the same speed decreases significantly, the slip becomes larger, and the rate of the magnetic field cutting conductor increases. At this time, the B-phase winding is opened. The A and C two-phase windings become in series relationship and the passing current is too large, and long-term operation will cause the two-phase windings to burn out at the same time.
First, the causes and countermeasures of partial burning of motor windings
1. Due to poor sealing of the motor itself, and environmental leakage, the internal combustion of the motor or other corrosive liquids or gases, the insulation of the motor winding is eroded, and the most severe part or the weakest point of insulation occurs to the ground. Phase-to-phase short circuit or turn-to-turn short circuit, resulting in partial burnout of the motor winding.
Corresponding countermeasures: 1 Try to eliminate the process and mechanical equipment "target=_blank> mechanical equipment leakage phenomenon; 2 pay attention to the sealing of each part of the motor when repairing, for example, apply a small amount of 704 sealant on each flange, in the bolt Apply grease to the terminal, if necessary, install a drip-proof box at the junction box, etc. If the motor is leaking, it should be used as a protective cover in places where liquid and dirt are easily invaded. 3 Shorten the repair and operation of the motor running in this environment. Repair the cycle, in case of serious, timely repair.
2. Due to bearing damage, shaft bending and other reasons, the stator and rotor friction (commonly known as broom) cause the core temperature to rise sharply, burn the slot insulation, turn-to-turn insulation, and cause short-circuit between winding turns or “shooting†on the ground. In severe cases, the stator core may be inverted, misaligned, the shaft is worn, and the end cap is scrapped. Bearing damage is generally caused by the following reasons: 1 improper assembly of the bearing, such as unevenly tapping the inner ring of the bearing during cold assembly, causing the shaft to be worn, resulting in the bearing inner ring and the bearing cooperating to lose the interference or the interference is reduced, and the running inner ring appears. Phenomenon, when the motor end cover is installed unevenly, the end cover bearing chamber and the outer ring of the bearing are too loose to run the outer ring phenomenon. Whether running the inner ring or running the outer ring will cause the bearing temperature rise to rise sharply and burn out, especially if the running inner ring fault will cause serious wear and bending of the rotating shaft. However, the intermittent running outer ring generally does not cause a sharp rise in the bearing temperature. As long as the bearing is intact, the intermittent running outer ring phenomenon is allowed. 2 The bearing cavity is not cleaned or the grease is not clean. For example, the tiny rigid material in the bearing cage is not completely cleaned, and the bearing raceway is damaged during operation, causing the temperature rise to be too high to burn the bearing. 3 bearing re-replacement processing, after the motor end cover is nested, the interference is large or the ellipticality exceeds the standard, causing the bearing ball clearance to be too small or uneven, causing the friction force to increase when the bearing is running, and the temperature rises sharply until it burns. 4 Due to the axial misalignment of the stator and rotor core or the lack of precision after machining the shaft, the inner and outer rings of the bearing are not on one cutting surface, causing the bearing to run “eaten†and then the temperature rises until it burns. 5 Because the temperature rise of the motor body is too high, and the bearing is added and grease is not timely, the bearing is short of oil or even burned. 6 Bearing damage due to mixing of different types of grease. 7 Bearings have manufacturing quality problems, such as raceway rust, inflexible rotation, over-standard clearance, and cage deformation. 8 The standby machine does not run for a long time, the grease is deteriorated, the bearing is rusted and the repair is not carried out.
Corresponding countermeasures: 1 When unloading the bearing, it is generally necessary to heat the bearing to 80 ° C ~ 100 ° C, such as bearing heater, transformer oil cooking, etc., only in this way, to ensure the assembly quality of the bearing. 2 Before installing the bearing, it must be carefully and carefully cleaned. No impurities can be left in the bearing cavity. It must be cleaned when adding grease. 3 Try to avoid unnecessary shaft machining and motor end cap nesting work. 4 When assembling the motor, it must be ensured that the stator core is centered and must not be misaligned. 5 The motor casing is clean and the original color is required. The ventilation must be guaranteed. The cooling device must not have scale and the blades should be kept intact. 6 It is forbidden to mix a variety of lubricating grease. 7 Before installing the bearing, the bearing should be thoroughly and thoroughly inspected. 8 For motors that are not used for a long time, the necessary disassembly inspection must be carried out before use to update the bearing grease.
3. The winding is partially burnt out due to the long or partial damage of the winding ends and the friction of the end cover or other accessories.
Corresponding countermeasures: When the motor is updating the winding, it must be welded according to the original data. When the motor is inspected, any rigid objects are not allowed to touch the windings. When the motor rotor is cored, the rotor must be lifted to prevent the rotor core from rubbing against each other. When using an open flame, the winding must be isolated from the open flame and guaranteed to be at a certain distance. Before the motor is reloaded, the integrity of the winding should be carefully checked and diagnosed.
4. Due to long-term overload or overheating operation, winding insulation aging accelerates, and the weakest point of insulation carbonization causes inter-turn short circuit, phase-to-phase short circuit or short circuit to ground, causing partial burning of the winding.
Corresponding countermeasures: 1 Try to avoid overloading the motor. 2 Ensure that the motor is clean and well ventilated. 3 Avoid frequent motor starting, and if necessary, do a dynamic balance test on the rotor of the motor.
5. The insulation of the motor winding is affected by mechanical vibration (such as high current impact at start-up, vibration of the driven equipment, unbalanced rotor of the motor, etc.), causing undesirable phenomena such as loose turns and insulation cracks in the windings, and the damage effect is continuously accumulated. The expansion and contraction causes the winding to be rubbed, thereby accelerating the insulation aging and eventually causing the first carbonized insulation to break until the winding is burned.
Corresponding countermeasures: 1 Avoid frequent starts as much as possible, especially high voltage motors. 2 Ensure that the vibration value of the driven device and motor is within the specified range.
2. Reasons and countermeasures for burning or overheating one-phase or two-phase windings of three-phase asynchronous motors
If the one-phase or two-phase winding of the motor burns out (or overheats), it is usually caused by phase loss. There is no deep theoretical analysis here, just a brief description.
When the motor is out of phase for any reason, the motor can continue to operate, but the speed decreases and the slip becomes larger. The two phases B and C become series and then connected in parallel with the A phase. Under the same load, The phase A current is too large and runs for a long time, and the phase winding must be overheated and burned.
The case where the three-phase asynchronous motor winding is Y-connected: After the power supply is out of phase, the motor can continue to run, but the same speed decreases significantly, the slip becomes larger, and the rate of the magnetic field cutting conductor increases. At this time, the B-phase winding is opened. The A and C two-phase windings become in series relationship and the passing current is too large, and long-term operation will cause the two-phase windings to burn out at the same time.
It should be specially pointed out here that if the stopped motor lacks a phase power supply to close, generally only a click will occur and it will not start. This is because the motor passing into the symmetrical three-phase alternating current will generate a circular rotating magnetic field in the stator core. However, when a phase power source is missing, a single-phase pulsating magnetic field is generated in the stator core, which does not cause the motor to generate starting torque. Therefore, the motor cannot start when the power supply is out of phase. However, during operation, the elliptical rotating magnetic field with high harmonics of the three phases is generated in the air gap of the motor. Therefore, the running motor can still operate after the phase is missing, but the magnetic field is distorted and the harmful current component is sharply increased. , eventually causing the winding to burn out.
Corresponding countermeasures: Regardless of whether the motor is static or dynamic, the direct harm caused by the lack of phase operation is that the one-phase or two-phase winding of the motor is overheated or even burned out. At the same time, the insulation aging is accelerated due to the overcurrent operation of the power cable. Especially in the static state, the phase loss will generate several times the stall current of the rated current in the motor winding. The speed at which the windings burn out is faster and more severe than the sudden phase loss in operation. Therefore, while we perform routine maintenance and overhaul of the motor, we must carry out comprehensive inspection and testing of the corresponding MCC function unit of the motor. In particular, it is necessary to carefully check the reliability of the load switch, power line, and static contact. Eliminate the lack of phase operation.
Http://news.chinawj.com.cn Editor: (Hardware Business Network Information Center) http://news.chinawj.com.cn
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