One of the most popular types of electric motors is a three-phase squirrel-cage induction motor. It can be from tens of watts to several megawatts with a starter winding voltage of up to 6 kW. Repair of an induction motor requires not only knowledge of the matter, but also an understanding of the design of the device. Difficulties that may arise during operation are speed regulation and the small potential for full load in idle mode.
Squirrel cage rotor problems
If we talk about the design of the engine, then it consists of a fixed part, which is called the stator, and a rotating part, which is called the rotor. The stator parts include a housing and a special core with a metal winding.
The rotor consists of a core with a winding and a shaft. During operation, the rotor shaft rotates in special bearings, which are located in protective shields. Repairing an induction motor can take anywhere from a few minutes to an hour.
To prevent the engine from overheating, it is cooled by blowing from the outer surface of the housing. The air flow is created by rotating the centrifugal fan, which is covered by a casing so that parts and parts from the external environment do not get there. During the repair of the induction motor, the casing may open. At the time of repair of engine malfunctions, to quickly change the direction of rotation of the rotor, change the speed, and also to reverse the motor, it is necessary to change the direction of rotation of the magnetic field, which is created during the operation of the stator winding.
This effect can be achieved by switching two phases, that is, 2 out of 3 wires that connect the stator winding to the electrical network. Thanks to high-quality repair of the induction motor, the device can be brought into normal operation.
Phase Type Problems
The main malfunctions that can occur in this type of engine include the impossibility of developing the nominal speed of rotation, increased noise emission, poor development of speed and excessive rotation at idle. Malfunctions can also include impossibility of rotation of the rotor and vibration of the entire machine.
Possible causes of such shortcomings are worn bearings, misalignment of bearing shields, changes in the bending of the shaft. These problems can be repaired very quickly with special tools. In the process of operation, an engine diagram is used, behind which you can distinguish the location of all necessary elements.
Repair of an asynchronous motor with a phase rotor is carried out after preliminary diagnosis of the device. Improper work of the windings may interfere with incorrect connections of the windings or breakage of the rotor winding rod. These types of breakdowns include a short circuit in the winding or contamination of the same windings through the ventilation ducts. With a low motor resistance, not only contamination of the windings, but also aging of the insulation is possible.
Preparing the machine for repair
The machine, which arrives for repair or inspection, must be equipped with all necessary parts, cleaned of dirt, and the upper elements must be removed. This will allow you to quickly and efficiently conduct surface diagnostics and find out the causes of malfunctions.
To measure the insulation resistance, a special device is used - a megaohmmeter. To conduct a quality check of the windings, the masters recommend using a universal resistance bridge or special probes. During the overhaul of asynchronous motors, the temperature of individual accessible places is better determined using shelf-type alcohol thermometers, which are cylindrical in shape and small in size.
This will allow you to use the thermometer in hard to reach places and correctly determine the temperature. To avoid damage during the inspection, it is advised to wrap the thermometer tank with a special foil - this will help to press the device more tightly to a heated surface.
The temperature of the bearing can be much higher if it is damaged or there is no special lubrication. The results of the inspection must be recorded in a protocol or journal.
Squirrel cage rotor
In the process, the degree of heating of the housing and bearings is checked, the uniformity of the air gap between the starter elements and part of the rotor is revealed, the presence or absence of abnormal noise during engine operation is indicated. Repair work also includes standard cleaning and dynamic blowing without disassembling the engine, quick tightening of contact joints in captive shields.
By changing and adding oil in the bearing, the operation of an induction motor improves. It may be necessary to completely disassemble the engine and flush parts.
Malfunctions in the work relate to the winding, so it is washed, impregnated, dried, coated with a special varnish. Repair of a squirrel-cage induction motor also implies a possible flushing of the bearings, complete or partial replacement of the winding, cleaning and assembly of the electric motor and its technical testing under heavy load.
In the case of quality work, the electric motor will be able to serve an even greater amount of time. Be sure to take the result after the repair or make a copy of the sheet from the journal, where the output was entered after the wizard.
Machine disassembly
Masters begin work by removing the upper casing, which covers the fan blades from dust and dirt from the outside. The disassembly process should be carried out as carefully as possible in order to avoid hammer blows or great efforts. This can lead to damage to parts of the electric motor and malfunction.
In the process of repairing a three-phase induction motor, bearing caps and bearing shields are removed. At the time of disassembling the elements from the shields, it is necessary to put marks on the case, according to which, when reassembling the machine, the shield is installed in the right place.
If the machine is small, then the rotor is removed from the stator manually. When the dimensions are large, the element is removed using special lifts, the process is carried out along the axis of the machine.
As for the removal of bearings, there are several options. Elements of bushings or inserts can be knocked out or protruded from special panels. Efforts cannot damage core elements.
Repair of components and parts
Before starting work, an inspection point on the asynchronous motor repair routine is mandatory. Thanks to preliminary diagnostics, the problem and the specific malfunction are determined.
A plan is being made to remove it. The main malfunctions include loosening of the pressing, swelling of the teeth, heating of the core, burnout of individual sections, deformation of the steel during fast operation. The repair procedure includes the diagnosis of spacers and bolt tightening.
Some masters, in order to eliminate the weakening of the pressing in the event of breaking off or loss of individual teeth, recommend hammering and strengthening special wedges that will perform the necessary work and not slow down the electric machine. When the core is heated, the masters do not only clearing, but also completely replacing the insulation, since this affects the operation of the coupling bolts. If the insulation begins to break through the winding of steel, a complete cleaning and winding of new elements is done.
Mechanical repair
When repairing a shaft, the following damage can be detected in the form of irregular bends, cracks or deformations, small fumes and scratches from the necks. Malfunctions also include general shaft production, camber of special channels, collapse and thread wear at the ends of the shaft.
This is a responsible process that requires not only an understanding of the matter, but also the presence of an electric motor circuit, since specific features require special tools and an understanding of the core device. In the process of repairing the bed, an emphasis is placed on fast and high-quality welding of cracks and welding of broken legs.
It is also possible to eliminate the elements in the seats and restore the broken thread in the holes with the removal of the remaining torn elements. High-quality maintenance and repair of the induction motor allows you to keep the machine in good condition for a long period of time.
Seal Repair
When there is a problem with the electric motors, grease from the bearings may enter other elements, thereby causing malfunctions or malfunctions. This can happen both in the case of wear of the main parts, and with improper installation of seals or the same application of grease.
It is advised to inspect the electric motor once a year in order to make sure that it is working and check for lack of lubrication on additional elements of the device. If there is a severe leakage of grease, it can be eliminated using the oil of the reflective ring with an inclined reflector, which is mounted on the shaft inside the machine.
Maintenance and repair of an asynchronous motor requires not only care, but also a high level of professionalism, since the further work of both a separate element and the entire device together depends on it.
Rotor balancing
To ensure a high-quality process of operation of an electric machine, balancing is performed. Static and dynamic balancing are distinguished, the first option is used for machines with a low speed, the 2nd option is used for elements whose speed exceeds 1000 rpm.
In the process of dynamic balancing, the location of the problem is determined by the vibration that occurs during the rotation of the rotor. The machine, which is used for dynamic balancing, consists of a balanced rotor, a special dial indicator, a coupling and a drive.
Stator full rewind
To begin work, it is necessary to release the frontal coils from the fastening elements, in the process the connections between the coils and phases are cut, and for a complete inspection, the wizard sets the starter on a special tilter. The measurement of the length and width of the groove and verification of operability begins. In the course of the case, the craftsmen are advised to make a template, prepare insulation material for further work.
The process of installing sleeves and laying the belts takes time and care, it is carried out after winding the stator coils on a special machine and unpacking the bay.
Occupational Safety and Health
In the course of work, craftsmen should wear special clothing that will protect them from small parts and possible injuries.
When repairing the rotor of an asynchronous motor, one should beware of grabbing clothes or additional material by rotating parts. Do not touch live parts or grounded wires on the machine with your hands.
To do this, use special tools that have insulated handles. Otherwise, you need to turn off the engine and only then continue repair work.
When impregnating and drying the windings, the impregnated chamber must be equipped in accordance with safety requirements. In the room where the electric motor is being repaired, it is forbidden to smoke and use open flame.
Masters Tips
Depending on the type of breakdown, repairs can take a long period of time. If there are no specific skills in working with electric motors, understanding the circuit of the device itself, additional details, it is not recommended to engage in repairs on your own.
In case of improper operation of the engine, you can re-diagnose or correct its elements. A mandatory point of correctly performed work is to conduct tests of dielectric strength of the insulation and check the engine in test mode.