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Several practical methods for motor repair.

Several practical methods for motor repair.

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Industry Information
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2017/10/10 10:12
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  In motor repair, there will be a variety of situations, such as taking a reasonable approach, in the repair can avoid detours, achieve the effect of half the effort. Summarize the experience and understanding of daily maintenance work, as a practical method of several kinds of motor repair, mainly including motor insulation resistance decrease, stator winding groove inside the ground, winding interturn short circuit, cage rotor broken bars, between motor and head shot, demolition of the old winding and rotor shaft neck and deal with the problems of the bearing chamber wear repair method, for reference.
 In this paper, the problems of motor maintenance are summarized, and several practical methods are introduced in the repair work.
1. After loading the end cover, the insulation resistance of the motor will be reduced.
 When the cage motor is repaired without two caps, the windings are insulated well. After loading, the insulation resistance decreases. This phenomenon can be judged to occur at both ends of the winding end. Causes the insulation resistance to be reduced. It may be that the paint film on the enameled wire has a partial touch or a winding mode. The insulation resistance of the winding is reduced due to the close or contact fault point of the end cover.
 To rule out the fault, which side should first judge fault in the machine, judgment method is: to be packed in a head end cover, with a 500 v insulation resistance meter measuring winding insulation resistance, such as low, shows the end winding fault exists. Then removed the head end cover, and then put on another end cover, measure the insulation of the winding resistance, such as is low, then the other end of the fault also exist, in the process of disassembly and assembly end cover, rotor is not loaded.
 To determine the fault after the end of the general winding end plastic slightly, and can never paint, if not solve the problem, can be easy to contact with the inside of the end cover on the outside of winding ends in a layer of thin film mat green shell paper, fault can generally be eliminated.
2. Find and process the location in the stator windings.
The stator winding groove is grounded, usually in the slot. As slot insulation paper in the rabbet mat, damage, or in the rabbet for referrals and scribing carelessly, put enameled wire in the bottom of the tank insulation paper, or in the groove when into the slot wedge insulation paper crowded broken, thus caused earth fault.
For this kind of fault, first of all, it is necessary to determine whether the motor winding is damped. If the motor is baked in the damp, the result is invalid, and the fault is judged to be grounded.
There are several ways to find a location:
(1) carefully check lead and trough and ends, and found that the lead wire in good condition, trough and slot insulation on both ends are no damage, motor inside and outside clean, no dust everywhere, and the oil, it shows the location in the groove.
(2) solve the y-type connection point of the stator winding, and measure the relative insulation resistance respectively, and find out the phase of the ground fault.
(3) with a single phase voltage regulator, which is the output phase line to ground fault phase lead at the end of the line, zero line motor shell, then put the voltage regulator for booster from scratch, to smoke inside groove, then immediately cut off the power supply and voltage regulator output voltage drop to zero, the smoke is ground, the whole operating process should pay attention to safety, to put a piece of motor insulation MATS, cut off the power before person cannot contact motor.
The treatment method is: carefully remove the slot wedge with the earthing slot, then put the motor into the oven to add the pad, bake the soft winding, and then carefully remove the inside turn of the tank to check the insulation of each wire. The insulation is damaged to be painted, dried, and then placed in the groove to place the insulation paper, and then the removed line turns into the groove, into the slot wedge, winding paint, drying.
If discover enameled wire has been burn out, will give each of the two bolt head to the end of the winding, then find a thread of the same diameter enameled wire in the groove, on both ends of winding wire, connector to twisted soldering, coating, drying, combined with insulation casing, strapping end, must pay attention to the strapping connectors.
3. Judgment of the short-circuit fault of the stator windings.
Stator winding turn short circuit fault, the general is judged by measuring the dc resistance of the three-phase winding, but the capacity of the large motor stator winding dc resistance is very small, and the influence of the relationship between the accuracy of the instrument and the measurement error, not easy to correct the judgment, but can use the following method to judge.
Don't break motor, with a capacity appropriate since the single phase coupling voltage regulator, gradually step up from scratch, to one of the common low-voltage alternating current (ac), at the same time with a clip-on ammeter to measure current, make the current up to 1/3 of the motor rated current. Then stop booster, the other two phase induction voltage is measured with a multimeter, respectively, if a phase have interturn short circuit fault, the induced voltage is lower than the other, and then replace the same electricity, in the same way to measure the other two phase induction voltage. According to whether the induction voltage is the same, it can be determined whether there is a fault in turn. Short circuit fault between stator turns. Motor winding is usually required in maintenance.
4. Judgment of rat cage bar breaking.
Cage rotor broken bar, generally is no-load running normally, but a plus load, motor speed is lower, the stator current, motor vibration, temperature, and will be accompanied by abnormal noise, the greater the load, the more breaks, the above phenomenon is more serious.
The method of determining whether to break a bar is as follows:
(1) electricity method: a single phase voltage regulator with appropriate capacity is used to connect the winding of the motor to low voltage ac. Voltage regulator from zero to open such as step up slowly, at the same time using the clip-on ammeter, measure current, current rise to about half of the motor rated current, stop the booster, then slowly rotating the shaft of the motor with the hand, observe the clip-on ammeter pointer, if the pointer is not moving or swinging slightly, table rotor in good condition, if the pointer periodic oscillation, and the oscillation amplitude is larger, article suggests that turns the mouse cage with article break fault.
(2) substitution method, is to look for a seat number on the same aircraft as the motor, with the core issue of the motor rotor, replace the installation on the defective motor, with the same load test, the failure to eliminate, thus proving the motor turns the mouse cage bars have a problem.
5. Repair after the "and headgear" of the motor.
When a short circuit is worn between the linear motor and the head set, the line head is usually burned off, and the method of extension can be used when repairing. The specific method is as follows:
Use 1-2 250W infra-red light bulbs to partially heat and soften the end of the rotor end, remove the copper foam, and then bend the burnt (flat) copper wire head slightly (so that it is suitable for welding). Long wire can be silver or tin soldering. Pay attention to protect windings during welding, so as to avoid burning (protect by wet asbestos cloth). After the copper wire is straightened out, the outer layer is coated with a glass strip, coated with insulating paint, and dried with an infrared light bulb. When the wire is placed in its original position, a thin film of thin film paper is placed, then the excess part of the copper wire is cut off. The wire is inserted into the head cover, and the tin soldering is finished. And the first set of copper shall be made according to the original size.
6. The removal of the old motor winding.
Generally, it is necessary to bake the soft windings before removing the wires, but the larger capacity of the motor, the drying and the disassembly are more difficult, so the following method can be used to dismantle the old winding. Remove one end of the winding with a flat shovel and flush with the notch. The other end of the winding is cut open with a metal shears, and then a thick and fine copper rod is used to flush the enameled wire out of the slot and finally clear the slot. If the groove is suitable, the operation method is correct, the conductor in each tank can be rushed out together, when using the spade, be careful, do not shovel the broken iron core.
With the above method, the drying process can be saved, saving time, saving energy and saving energy. However, this method is suitable for motors with a capacity of less than 7.5kw, because the small motor or micro motor has small housing, and it is inconvenient to operate with the flat shovel.
7. Grinding of new brushes.
Update is wound rotor motor brush dc motor or rotor, when the brush and commutator surface vertical, to study the method is: mo brush on the commutator surface pave a piece of sandpaper, same model in hand, the new brush along the axial reciprocating friction, commutator brush by grinding mill will soon be out in conformity with the surface of the commutator surface. Use coarse sandpaper first, then fine sandpaper. When grinding, the hand should hold the brush to be positive, the back and forth movement should be along the direction of the axis of the commutator, can not deflect, the reciprocating trip should not be too long. Attention should be paid to prevent the commutator and the brush powder into the armature groove, the brush into brush after grinding, starting motor no-load running a few minutes behind each brush inspection, interface is typically accounts for over 80% of the total area, otherwise, be reground until qualified.
When the brush holder of the motor is not perpendicular to the commutator surface, it is appropriate to apply the following method to lay the sandpaper on the flat surface, and make a bevel with the Angle of the brush holder. Then brush in brush, turn the motor rotor by hand, so that it will be on the inclined plane of brush grinding out bright point, and then with shining point of sand paper burnish, polishing, then brush, brush fit into the rotation of motor rotor with the hand, also can be ground out bright spot, the area will be the first time. Several times, the contact surface of the brush will become larger and larger, forming an arc. When polishing bright spot, don't polish too much every time, especially the last time, must be careful, as long as use fine sandpaper to brush a little bit can, if wipe more, will become smaller. It is proved by practice that this method can be used to grind the tilting brush.
8. Emergency repair of wear of rotor journal and end bearing chamber.
Specific methods and procedures:
(1) use ethanol or gasoline to wash and apply the coating repeatedly.
(2) heat the ternary nylon ethanol solution into a transparent liquid, with a small hair brush dipped in the liquid thin layer on the wear and tear, the wear quantity is larger, can be appropriately extended heating time make the solution besmear again a bit thick, generally need to paint a few times, meet the requirements of thickness, the besmear after the first time, to be placed about 3 minutes, put dry on its own, to not glue the hand can apply for the second time.
(3) dry up after coating, can be heated (temperature is not more than 80 degrees, time is 0.5-1 hour), also can let it dry naturally (at room temperature 20, put in ventilated place about 36 hours).
Within 0.10 mm (4) wear, after good dry coating, can be used, the wear quantity is greater than 0.10 mm, in order to ensure the motor assembly, fixed, rotor concentricity, besmear after turning processing is needed. If the original bearing outer ring and inner ring dimension are within its tolerance range, the repair end bearing chamber can be machined according to P6, such as repairing shaft neck, which can be processed according to r6.
When the nylon solution is completely dry, it has sufficient adhesion and hardness, which can guarantee the requirement of motor assembly.
This method is only suitable for a small amount of wear, only a few millimeters.