When the motor is running, one or other faults may occur, causing the motor to malfunction or even burn out. At this time, it must be repaired. So how should it be repaired? The following is the repair and maintenance of the motor that I have compiled for you. I hope it can help you.
Repair and maintenance of motors
1 Repair of motor stator windings
1.1 Winding requirements of motor stator windings
Windings are the main components of motors One of the main components and a key part of energy conversion. It is composed of many coils connected. All the wound coils are placed in the stator core slots, and then connected in series or parallel according to certain rules to become the motor windings. Whether the winding design is reasonable or not will affect the torque, speed, loss, efficiency and temperature rise of the motor. Therefore, the following requirements are put forward for the motor winding: ① The electric potential and magnetic potential of each phase winding must be symmetrical, and the resistance and reactance must be balanced. That is, the winding structures of the three phases are exactly the same; ② shorten the connection part, save copper, and reduce winding short-circuit loss; ③ the winding heat dissipation must be good, and the insulation and mechanical strength must be reliable; ④ the construction process of the winding structure is good.
1.2 Several important parameters of motor windings
1.2.1 Pole pitch. The range occupied by each magnetic pole along the inner circle of the motor stator core is called pole pitch.
1.2.2 Pitch. The number of slots spanned between two active sides of a winding element is called the pitch.
1.2.3 Electrical angle. Electrical angle = number of pole pairs?360?.
1.2.4 Number of slots per pole and phase. The number of slots occupied by each phase winding under each magnetic pole.
1.3 Types of motor windings
1.3.1 Composition principles of three-phase stator windings:
The number of coils in each phase of the three-phase stator winding is equal and the layout is The same, the intervals between phases are 120° electrical angle in the slot, which conforms to these two principles, that is, a three-phase symmetrical winding is formed. Only in the three-phase symmetrical winding can a balanced three-phase electromotive force be induced.
1.3.2 The types of three-phase stator windings include single-layer windings and double-layer windings
There is no interlayer insulation problem in the single-layer winding slot, so there will be no layer insulation in the slot. Inter-phase and phase-to-phase insulation breakdown fault. Both winding and embedding are more convenient; the disadvantage is that the selection of short-pitch coils is limited, and the electromagnetic waveform is not ideal, so it is generally used in small-power motors. Its coils are wound with round electromagnetic wires into multi-turn scattered embedded coils. The advantage of double-layer winding is that you can choose any suitable short-pitch coil. The technical indicators of the motor are better than those of single-layer winding. It is generally used for large and medium-sized motors.
1.4 Replacement and repair of motor stator winding
1.4.1 Coil winding
①Loose coil: The loose coil is wound with insulated coil wire , the geometric size is guaranteed by the winding die. The winding die must be of appropriate size and the pulling force should not be too large. The wires must be arranged sequentially in the wire mold; the wires are not crossed neatly, which not only makes it difficult to embed the wires, but also easily causes short-circuit faults between turns; during the winding process, the broken wires should be welded to the hypotenuse of the end of the coil, and the joints are not allowed to remain in the coil groove part.
② Formed coils: Formed coils are more complicated to manufacture than loose coils. Generally, when repairing and replacing coils, spare coils are used or coils are ordered from the manufacturer according to the motor model.
1.4.2 Offline, wiring and inspection. Preparation work before offline: including the preparation of insulation materials and coils, slot wedges, welding materials, slot insulation, cleaning of the iron core, cleaning of the work site, etc. At the same time, you must be familiar with the drawings and clearly understand the number of motor poles and winding sections. distance, lead direction, etc. to avoid errors in the production line.
1.4.2.1 The process of removing the embedded winding is:
① Remove the lower edge of the first pitch coil. Determine the position of the first slot based on the buckle slot of the iron core or the outlet hole of the machine base, embed the lower coil edge slot by slot, and pad the upper coil with cardboard;
②Embed the remaining coils.
After placing the lower coil edge, pad the interlayer insulation, lower the upper coil edge into the groove with the corresponding pitch, use a scribing board to straighten the coil edge in the groove, and press the end lightly with your hands to prevent it from warping, and then Fold over the slot insulation and drive in the slot wedge;
③ Lower the last pitch coil, lift the upper edge of the first pitch coil, and lower it into the lower edge of the last pitch coil. Then remove the upper edge of the next pitch coil, fold the slot insulation, and drive in the slot wedge;
④ Shape the end, use a rubber hammer or a bamboo board to make the end into a bell mouth, the diameter The size must be appropriate. If it is too small, it will affect the placement of the rotor and ventilation and heat dissipation. If it is too large, the end will be too close to the casing, which will affect the insulation of the motor;
⑤ End wrapping. Trim the same insulation paper at the end neatly;
⑥Insulation test. Check the tightness of the protruding slot wedge at the end and whether the insulation is damaged, and perform a withstand voltage test on the phase-to-phase insulation and the ground insulation;
⑦Connection between pole groups. Connect the coils of the same group according to the "normal series" or "reverse series" regulations, and lead out the cables, weld them firmly, wrap them with insulation, and then bundle the connecting wires tightly;
⑧Inspection and testing. Check the wiring and welding quality;
⑨Dip paint. Dip and dry the paint and spray insulating paint on the winding surface.
1.4.2.2 Wiring
①Connect the individual coils into pole phase groups according to the 60° phase distribution;
②Connect the pole phase groups of the same phase, Make it a winding for each phase;
③ Lead the beginning and end of the three-phase winding to the junction box with wires. All connectors must be welded and insulated.
1.4.2.3 Inspection
Before dipping in paint, the stator winding should be inspected, including: ① Whether the winding is grounded; ② Whether the winding is short-circuited; ③ Whether the winding is open-circuited; ④ Check whether the winding is connected incorrectly or reversely.
After confirming that there are no above-mentioned problems, proceed with dipping and drying.
1.4.3 Dip paint and drying
After rewinding or partially replacing the stator winding, the process of dipping paint and drying can make the gap between the winding and the iron core and the wires The gap between the wire and the wire is filled with insulating paint, so that the winding and the iron core form a whole. It enhances the moisture resistance of the winding and improves the insulation strength, heat dissipation capacity and mechanical strength of the winding. Therefore, the paint dipping and drying of the stator winding is a very important process in motor repair. There are roughly the following procedures;
1.4.3.1 Pre-baking:
The function of pre-baking is Moisture removal from the winding is usually carried out in an oven, with the temperature controlled at around 120°C and a time of about 4h-8h. Use a 500V megger to measure the insulation resistance of the winding to ground every 1 hour. When the insulation resistance value stabilizes, pre-baking can be completed.
1.4.3.2 Paint dipping:
After the stator core temperature drops to 60℃--70℃, paint can be dipped. When dipping paint for the first time, the viscosity of the paint should be Lower so that the insulating paint can penetrate into the winding as much as possible. For the second dip, the viscosity should be higher so that a thicker paint film can be formed on the surface of the winding. Under normal circumstances, the method of pouring paint can be used, and the pouring should be repeated several times evenly.
1.4.3.3 Drying:
Drying is to evaporate the solvent and moisture in the paint so that a stronger paint film can be formed on the winding surface. The drying process is best divided into two processes. ① Low temperature stage. The temperature is controlled at 70℃--80℃, about 2h--4h; ② High temperature stage. The temperature is around 130℃ for about 8h~16h in order to form a solid paint film. At this time, the insulation resistance of the winding to ground should be measured every 1h with a 500V megger. Until the last 3h, the insulation resistance value is stable above 5M? The winding is considered drying complete.
1.4.4 Repair of stator winding end wear
The stator winding of an AC motor is subject to electromagnetic forces with alternating directions during operation, because of the electromagnetic force generated between adjacent windings. The magnitude of the electromagnetic force is proportional to the square of the current flowing through it. Therefore, when the motor is started, short-circuited, or blocked, the maximum electromagnetic force sometimes reaches dozens of times the normal value.
Therefore, the end structure of the winding with the end painted and cured can easily cause insulation wear, which is a very common fault of AC motors. The reasons are:
① Thermal shrinkage of the end binding rope after heat curing The amount is not enough, so it cannot tighten the ends of each phase winding after the paint is solidified, so that the winding ends cannot effectively bind and fix the windings in the direction of the force vibration. Therefore, once the motor is subjected to alternating tangential force and axial force, the force point is added to the contact point between the winding and the end binding, causing vibration displacement. This is one of the main reasons for accelerating the insulation wear there;
② Binding the ends when taking off the line causes damage to the end insulation crimping line;
③ Painting and curing process of the ends The rigidity of the rope after curing cannot be guaranteed;
④The gap in the slot increases, and the coil vibrates in the slot, causing the coil to wear at the slot.
1.4.5 Local repair of stator winding. If one or part of the motor winding is burned out, local maintenance should be considered. First of all, it is necessary to find out the exact fault point of the faulty coil and heat the motor winding to 100℃--130℃ to soften the winding insulation. Then remove the slot wedge and faulty coil while they are hot. When removing the old coil, be careful not to damage the good coil. . After the faulty coil is removed, a new coil is replaced, and then the slot wedge is driven in and the paint is dipped and dried.
2 Troubleshooting of the motor core
2.1 The role of the motor core
The iron core of the motor is not only a key component for electromagnetic energy conversion, but also the iron core in the motor. The core also has to withstand the combined effects of mechanical vibration, electromagnetic force, and thermal force. In order to reduce the eddy current loss in the iron core, a certain insulation resistance value is required between the iron core punching sheets.
2.2 Repair of common iron core faults
2.2.1 Individual teeth of the core tooth pressure plate open outward along the axial direction
This is due to the iron core stacking The teeth of the tooth pressure plate were not leveled during assembly. After the iron core was pressed and installed, the punched sheet appeared wavy, and the teeth of the iron core were warped, or individual teeth of the tooth pressure plate were pried off when the stator iron core was touched when the rotor was pulled out. From now on, when repairing, just use a copper rod to flatten the individual teeth that open outwards.
2.2.2 Partial burnout of the iron core
The arc generated when the winding has a phase-to-phase short circuit or a grounding short-circuit fault sometimes burns out the iron core partially. If the burnt area is not large, you can repair it without dismantling the iron core. First use files, chisels, grinding wheels and other tools to flatten or smooth the partially burned areas of the iron core, and then use a knife to remove the silicon steel sheets piece by piece. Coat the surface of the iron core with a layer of self-drying insulating paint, and then press the iron core tightly. If the burnt area is large, the iron core should be replaced or the damaged punching sheet should be replaced.
2.2.3 Radial looseness of the iron core
Radial looseness of the iron core can occur in the following two situations:
① Small-sized iron cores using external press-fitting technology The motor is caused by the loose fit between the outer circle of the iron core and the inner hole of the base, or the loose positioning screw between the iron core and the base. The repair method is to tighten the positioning screws. If necessary, you can add additional positioning screws to the machine base, or you can weld the iron core and the machine base;
② Large and medium-sized machines that use internal pressure-installed iron core technology The motor is caused by the radial positioning device of the iron core being open or loose, or the welding between the iron core and the machine base being desoldered. The repair method is to tighten the positioning device and install anti-loosening screws or repair welding at the desoldered area.
3 Troubleshooting of squirrel-cage rotors
Broken bars are a common fault of squirrel-cage asynchronous motors. Most of them are caused by desoldering of the welding joints between copper bars and end rings. Clean the desoldering area and solder it firmly with silver solder.
In addition, there are often some defects in the rotating shaft. For example: the rotating shaft is bent; the keyway is worn, the bearing gear is worn, etc. Depending on the situation, these can be solved by welding, straightening, re-milling a keyway, plating a layer of chromium on the bearing files by electroplating or spraying, etc.
Repair tips for water in the motor
1. Use a hot air gun to remove water by evaporation
If the motor wheel is made of aluminum, use a hot air gun to blow dry the water on the surface of the inner magnet steel and proceed. Remove water by evaporation! If the magnet steel is wet and the surface of the magnet steel is oxidized and rusted in the future, the internal force of the motor will be greatly lost, causing a large discharge current and the motor to heat up, which wastes electricity! Over time, sludge and rust will accumulate in the motor's internal bearings, which are prone to damage and damage. Clean up! The motor current will increase during riding and the mileage will be shortened. The friction of the motor will cause the vehicle components to run hard!
2. Blow away the accumulated water inside the stator winding with a hot air gun
Use a hot air gun to dry out the accumulated water inside the stator winding, and ensure that the insulation resistance of the winding is greater than 10 megohms before installation. It should be noted that when blowing the stator with a hot air gun, pay attention to the Hall. Do not let the high temperature destroy the Hall. Er? Dissolved, otherwise the water will dry out and the Hall will be "baked", causing the installation and operation to be abnormal.
3. Observe the two end covers of the motor.
Observe the two end covers of the motor to see if the protection frame in the bearing is rusted or stuck or the rotation is inflexible due to water ingress. If The operation is not slippery. Apply lubricating oil appropriately. If necessary, please replace it in time to prevent the coil from being damaged due to the falling off of the bearings and steel eggs during use of the motor, resulting in scrapping!
4. The ends of the motor cover Sealing treatment