Common ground fault detection methods are: shake table inspection method; test lamp test method; multimeter test method. If it is found that the winding is damp, it can be heated and dried by 0.6 times the rated current of the stator winding. If the winding is grounded and the grounding point is often out of the slot (ie, notch) at the coil, then it can be inserted with bamboo or insulating paper Between the core and the winding; if the grounding point in the tank, you must replace the winding. Stator Winding Wire Breaking Faults Since the stator winding ends and the lead fixing structure at the end of the welding, welding or mechanical damage caused by the winding nose and lead to greater vibration, or even double the frequency vibration, will make the parts of the wire occurs Fatigue fracture, resulting in a serious short-circuit the accident. According to the insulation results of the stator winding, it can be seen that the electromagnetic force of the upper winding in the same phase with the slot is 3 times of that of the lower winding. Under the action of electromagnetic force, loose wires rub against each other until the residual strands are worn away, resulting in a short circuit. In the short-circuit parts will have additional losses and temperature rise, thus exacerbating the aging of the main insulation, and the wire friction with each other, will make the wire itself grinding, grinding off. Fractures of the wires often form sharp points, causing local electric fields to concentrate and accelerating the aging or breakdown of the main insulated wires in the vicinity. Measures to prevent wire breakage are: to improve and improve the stator winding wire in the manufacture of gelling and molding process to ensure that its operation is not loose, the main insulation and the insulation between the shares do not separate, no shelled, no air gap; improve Stator end and slot windings fixed structure, so that the winding copper wire and insulation in the operation of the vibration value does not exceed the allowable limit. Insulation between stator core pieces Damaged motor The stator core is one of the most important components of a motor and should have the specified mechanical, magnetic and electrical characteristics throughout its operation. The stator core is coated with a varnish film between each piece. When the insulation of the high-grade teeth or teeth of the effective core is damaged, a closed circuit of current is formed, causing a high temperature and even a serious accident of melting the effective core. This is the reason why the insulation of the stator winding is damaged, short-circuited with the case and short-circuited. Causes of damage to the stator core are: the effective iron core or its individual regions loose fit, causing individual sector damage, resulting in the main stator winding insulation damage; short circuit caused by the stator core damage. When the motor appears a little grounding, if the ground capacitor current and duration of more than a certain value, it may be accompanied by stator core burning accident. Therefore, with the stand-alone capacity increases, the motor single-phase ground protection requirements will be more stringent. Rotor winding grounding rotor winding insulation fault to the ground are: rotor winding overheating, insulation is damaged; rotor winding to slip ring lead and conductive screw insulation damage, brush holder fixed screw insulation damage and excitation fault grounding; due to rough manufacturing process The formation of local defects, the rotor insulation in the transport process of moisture, dirt and other causes of winding ground fault. Grounding of rotor windings can result in burning of large motor shaft, severe vibration and severe magnetization. Salient pole synchronous motor rotor winding used in the pump station should be protected by a little grounding signal device, when the signal action, should be promptly processed. Rotor winding inter-turn short circuit caused by vibration. Calculated according to the electromagnetic field theory, the electromagnetic force between the stator and the rotor is proportional to the square of the flux density and inversely proportional to the square of the number of short-circuited turns. For a salient pole rotor, an inter-turn short circuit in a pole winding will directly affect the main magnetic flux on one side of the pole and cause a sharp drop in the magnetic pulling force, which has a much more serious impact on the vibration, and the amplitude and excitation The current size, the relationship is a tendency to saturation curve. Given the uneven air gap between the rotor caused by vibration in the air gap generated by the electromagnetic force B for the air gap flux density (T); for a pole displacement (cm); for the set, the average gap between the rotor ( cm); is the angle between the displacement pole and the left and right adjacent pole centerlines. If the air gap between the rotor and the stator is not uniform, the one-way magnetic force will be the largest when the magnetic pole passes the minimum air gap and the one-way magnetic force will be the minimum when passing through the maximum air gap. The frequency of this electromagnetic force is 2 times the power frequency, causing vibration. Stator core assembly junction relaxation. Due to the uneven assembly of the stator core to form a magnetic circuit in the reluctance of different sizes, such as a large pump station installed 7000kW synchronous motor, the stator core assembly using split-site, may be the case. If the seam is not good, then there is an air gap around the stator core, resulting in uneven flux, so that the motor amplitude increases. Rotor center position offset. Rotor center position offset is also one of the reasons the motor magnetic imbalance. The electromagnetic force acting on the rotor in the direction of the minimum air gap is the logarithm of the number of poles. The rest of the physical quantities have the same meanings as mentioned above. In the case of salient pole rotors, the center position of the rotor sometimes becomes an individual part. Analysis of Main Motor Running Faults and the Causes of Preventing Damage. Due to the premature investment, the synchronous motor is greatly impacted. The large pulse torque causes the unit to oscillate violently. Under certain conditions, even the resonance of the electrical or generator sets causes the bolt of the bottom corner of the motor to loosen and the insulation of the stator coil becomes worn. The end of the coil is loosely bound, increasing temperature rise and noise. If a 3000kW motor pump unit, due to start-up speed did not rise to the sub-synchronous speed, the excitation device automatically cast encourage strong vibration so that the core of the stator core bolts loose, forcing the unit overhaul. The following measures can be taken to prevent such accidents: Adoption of new technologies to improve the safety of the equipment; During startup, operation or shutdown, the unit can not damage the motor due to the excitation device; Replace the original plug-in with a microcomputer excitation controller Has a good overall performance. Motor mechanical failure Motor mechanical failure of bearings, end caps, iron core and other parts of the loose, wear, deformation, fracture and poor lubrication and so on. These failures are easy to cause the motor rotor stuck. In the above mechanical failure, the bearing part of the fault occurred the most common. Therefore, the use of bearings in a certain period of time, should be oil or oil change. Filling oil or oil change time should be motor working conditions, working environment, cleanliness and type of lubricant may be, the added oil should be the provisions of the grade, two different lubricants do not mix, there should be no precipitation of oil Or foam. The way to improve the reliability of the main motor of the pump station The main problem of the reliability of the main motor of the pump station is the design and manufacture quality. The motor manufacturer shall take strict measures in every link such as design, construction, production, delivery, installation and commissioning to ensure the inspection quality of each operation and lay the foundation for the reliable operation of the motor. Ensure the safety and quality of construction of units, improve the operation and management mechanism of pumping stations and improve the overall quality and technical level of operators. Comprehensive measures should be taken to minimize the occurrence of faults and accidents; in the event of faults and accidents, prompt and proper measures should be taken to reduce losses and impacts, effectively improve the performance of pumping stations and give full play to the efficiency of pumping stations. According to the needs of pumping station operation, the Company carried out intelligent on-line monitoring aimed at eliminating potential motor failures, preventing sudden accidents and reducing accident losses, enhancing diagnostic techniques and strengthening on-line monitoring and diagnosis technologies for pumping stations.
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