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I. Analysis and Processor of Common Electrical Faults of Motor
(1) It is difficult for the motor to start, and the speed is low when the rated load is added.
The possible reasons are: (1) lower power supply voltage; (2) misconnection of angle connection into star connection; (3) detachment, loosening or fracture of cage bar end of squirrel cage rotor.
Processing methods: (1) Increase the voltage; (2) Check the nameplate wiring method, correct the stator winding wiring mode; (3) After inspection and symptomatic treatment.
(2) When the timing is switched on, the motor cannot start, but there is a buzz.
The possible reasons are: (1) the power supply is not fully connected to single-phase start; (2) motor overload; (3) being stuck by traction machinery; (4) winding motor rotor circuit is open to break; (5) stator internal head position is wrong, or there are breaks or short circuits.
Processing methods: (1) Check the contacts of power supply wire, motor lead-out wire, fuse and switch, find out the position of breaking circuit and remove it; (2) Start without load or half load after unloading; (3) Check the tracted machinery and remove the fault; (4) Check the connection of brush, slip ring and starting resistance contactors; (5) Check the connection of brush, starting resistance contactors. (3) Re-judge the beginning and end of the three-phase, and check whether the three-phase winding has a canned wire and short circuit.
(3) Low insulation resistance
Possible reasons: (1) damp windings or dripping water into the motor; (2) dust on windings, oil mat; (3) aging of stator windings insulation.
Processing methods: (1) heating and drying stator and rotor windings; (2) cleaning winding end with gasoline; (3) inspecting and restoring the insulation of lead-out wire or replacing the insulation board of junction box; (4) replacing all windings in general.
(4) Heating beyond the temperature rise standard or smoking after starting of motor
Possible reasons: (1) too low power supply voltage, motor temperature rise under rated load is too high; (2) poor ventilation or high ambient humidity of motor; (3) motor overload or single-phase operation; (4) motor starting frequently or too many times of positive and negative rotation; (5) stator and rotor friction.
Processing methods: (1) Measuring no-load and load voltage; (2) Checking motor fans and cleaning ventilation ducts to strengthen ventilation and reduce ring temperature; (3) After checking the current of each phase with clamp-type ammeter, symptomatic treatment; (4) Reducing the number of positive and negative turns of motor, or replacing the motor adapted to frequent starting and positive and negative turns; (5) Checking. The treatment of aunt's symptoms after investigation.
(5) Live motor housing
Possible reasons: (1) insulation of motor lead-out wire or insulation board of junction box; (2) end of winding touching housing; (3) no reliable grounding of motor housing
The treatment methods are: (1) restoring the insulation of the motor lead-out wire or replacing the insulation board of the junction box; (2) if the grounding phenomenon disappears after the end cover is removed, the end cover can be installed after the end of the winding is insulated; (3) grounding the motor shell reliably according to the grounding requirements.
(6) abnormal sound of motor during operation
Possible causes: (1) incorrect connection of stator windings, local short circuit or grounding, resulting in three-phase current imbalance and noise; (2) foreign bodies or serious lack of lubricant in bearings.
Processing methods: (1) Check separately and prescribe medicines accordingly; (2) Replace new lubricants after cleaning bearings
(7) Motor Vibration
Possible reasons are: (1) uneven installation foundation of motor; (2) unbalanced rotor of motor; (3) unbalanced pulley or coupling; (4) bending of shaft head or eccentric pulley; (5) unbalanced fan of motor.
Processing methods: (1) the motor base is padded flat and fixed after the timing is horizontal; (2) static or dynamic balancing of the rotor; (3) balancing of the pulley or coupling; (4) straightening the shaft, aligning the pulley to the rear mounted heavy vehicle; (5) calibrating the fan.
II. Analysis and Treatment of Common Faults of Motor Machinery
(1) Troubleshooting of Stator and Rotor Cores
The stator and rotor are made up of insulated silicon steel sheets, which are the magnetic circuit parts of the motor. The damage and deformation of stator and rotor cores are mainly caused by the following reasons.
(1) Excessive wear and tear of bearings or poor assembly cause friction between stator and rotor, resulting in surface damage of iron core, resulting in short circuit between silicon steel sheets, increase of iron loss of motors, resulting in excessive temperature rise of motors. At this time, fine files and other tools are used to remove burrs, eliminate short joints of silicon steel sheets, coat insulating paint after cleaning, and heat drying.
(2) When removing old windings, excessive force is exerted to make the inverted slot open obliquely. At this time, small mouth pliers, wooden hammers and other tools are used to repair, so that the alveolus is reset, and hard insulating materials such as green paper, bakelite board and so on are added between the slit silicon steel sheets which are not easy to reset.
(3) The surface of iron core is corroded due to dampness and other reasons. At this time, sandpaper should be used to polish the surface, and insulating paint should be applied after cleaning.
(4) High heat burns iron core or tooth due to grounding of winding. Use chisel or scraper and other tools to remove the deposits and coat them with insulation to dry.
(5) The combination between the iron core and the machine base is loose, and the original positioning screw can be tightened. If the positioning screw fails, the positioning hole can be re-drilled and tapped on the machine base, and the positioning screw can be tightened.
(2) Maintenance of Bearing Faults
Rotary shaft rotates through bearing support, which is the heaviest part of load and easy to wear.
Inspection in operation: When the rolling bearing is short of oil, it will hear the sound of being busy. If you hear the discontinuous stemming, it may be that the ring of the bearing is broken. When the bearing is mixed with sand and other impurities or the bearing parts are slightly worn, a slight noise will be produced.
Inspection after disassembly: first inspect whether the bearing rollers, inner and outer steel rings are damaged, rusted, scarred, etc., and then pinch the inner ring of the bearing by hand, and make the bearing level. The other hand pushes out the steel ring by force. If the bearing is good, the outer steel ring should rotate smoothly, without vibration and obvious sticking phenomenon in rotation, and the outer ring disappears after stopping rotation. There is a backward phenomenon, otherwise the bearing can no longer be used. The left hand holds the outer ring, the right hand holds the inner ring, and pushes hard in all directions. If it feels loose when pushing, it will be worn seriously.
The rust spots on the outer surface of the bearing can be erased with sand paper No. 00 and then washed in gasoline; or new bearings should be replaced when there are cracks in the bearing, cracks in the inner and outer rings or excessive wear of the bearing. When replacing new bearings, the same bearings as the original type should be selected.
(3) Inspection and repair of chassis and end cover
If there are cracks in the shell and end cap, surfacing welding should be carried out. If there is too large gap in the bore hole of the bearing, the bearing end cap matches too loosely. Usually, the bearing bore wall can be uniformly punched out with a punch, and then the bearing can be punched into the end cap. For the motor with larger power, the method of inlaying or electroplating can also be used to finally process the shaft. Bear the required size.
(4) Troubleshooting of Rotary Shaft
(1) shaft bending
If the bending is not large, it can be repaired by polishing the diameter of the shaft and the sliding ring. If the bending exceeds 0.2 mm, the shaft can be placed under the press and corrected under pressure at the bending point. The corrected surface of the shaft can be machined and polished by a lathe. If the bending is too large, a new shaft needs to be replaced.
(2) Journal wear
When the wear of the journal is small, a layer of chromium can be plated on the journal and grinded to the required size; when the wear is large, surfacing welding can be carried out on the journal and then grinding on the lathe; if the wear of the journal is too large, turning 2-3 mm on the journal, then turning a set of cylinders on the journal while it is hot, and then turning to the required size.
(3) Axis crack or fracture
When the transverse crack depth of the axle does not exceed 10%-15% of the diameter of the axle and the longitudinal crack does not exceed 10% of the length of the axle, surfacing can be used to remedy the crack, and then finishing to the required size. If the crack of the axle is serious, a new axle needs to be replaced.
The motor has the characteristics of simple structure, reliable operation, convenient use and low price. In order to ensure the normal operation of the timing, the running motor should be checked according to the requirements of the motor quality standard. The axis of the motor in operation and the driven equipment should be aligned, there is no obvious vibration in operation, and good ventilation and wind wings must be maintained. To observe and measure the voltage and normal working current of the motor network at all times, the change of voltage should not exceed (+5%) of the rated voltage. The rated load current of the motor should not always exceed the rated current, in order to prevent overheating at the time, and check whether the motor starting protection device is flexible and reliable. Check whether the temperature rise of each part of the motor is normal, and check the bearing temperature frequently. Sliding bearings should not exceed the degree, rolling bearings should not exceed 70 degrees, and the sound of rolling bearings should be clear and noiseless. For the running environment of the motor, it should be anti-smash, anti-shower and moisture-proof. For poor environment, regular movement, frequent start-up, overload operation and other aspects should be strengthened daily maintenance and maintenance, timely detection and elimination of hidden dangers.