I. Project requirements

When the three-phase AC squirrel-cage asynchronous motor is dragged, the stator winding is completely damaged due to improper use or other reasons.

It's broken. This motor needs overhaul. After the overhaul, the test meets the requirements of various technical indexes and can be put into normal operation.

1. Time requirement: 30 class hours.

2. Quality requirements: all technical parameters of the original motor can be accurately restored. The rated power is 5.5 kW, 1440 rpm,

Rated current 1 1.3A Temperature rise of 75℃ No-load current 3.8-4.3A Phase-to-phase insulation of three-phase winding: above 500 megohms, III.

Insulation of phase winding to ground: more than 500 megohms.

3. Safety requirements: The project shall be operated in strict accordance with the safety operation regulations.

4. Civilized requirements: consciously carry out project operations in accordance with civilized production rules.

5. Environmental requirements: Try to operate the project according to environmental requirements.

(According to the school's own teaching site or enterprise production environment, formulate the operation procedures of each project)

Second, the project analysis

This is the most basic project of mechatronics, and the basic work of three-phase asynchronous motor must be understood before this project is carried out.

Principle and structure. Through practical operation, students can correctly master the disassembly and assembly methods of motor and three-phase squirrel-cage asynchronous motor.

Stator winding rewinding and wire embedding technology and how to strengthen insulation technical requirements, master the parameter test of motor no-load operation, and master the judgment and treatment methods of typical faults during motor no-load operation.

To complete this project, we must do well in the following four aspects:

(1), disassembly (2), maintenance (3), installation (4) and testing.

1, motor stator winding disassembly:

Schematic diagram of motor structure

Three-phase AC squirrel-cage asynchronous motor is mainly composed of stator and rotor in structure:

(1) Stator: The stator is the fixed part of the motor, which consists of stator core, stator winding, frame and end cover.

(3) Rotor: The rotor is the rotating part of the motor, and the magnetic conduction generates the induced electromotive force and electromagnetic torque of the rotor, dragging the load.

Before disassembling the motor, you should know its structure and master the correct disassembly method. Demolition cannot be carried out blindly.

Operation. Disassembly should be carried out in the correct order to avoid damage to parts.

Disassembly method and key points:

(1) Remove the cover of the external fan and the external fan (unscrew the screw fixing the external fan on the rotating shaft or the snap ring screw of the fan to remove it).

(2) Remove the three screws fixing the rear bearing outer cover and the rear bearing inner cover, and remove the rear bearing outer cover.

(3) Unscrew the fixing screws for fixing the rear end cover and the front end cover. Make original records of the parts where the front and rear covers are matched with the base.

Sign. Then use a flat shovel to reach into the gap between the mating surface of the base and the rear end cover, pry open the rear end cover and remove it.

(4) Use a wooden pad at the rear shaft end of the rotor and knock the front end with a hammer to remove the front end cover together with the rotor.

(5) After removing the screws of the outer cover and the inner cover of the front bearing, you can check the bearing (clean the bearing first to check whether it can be used continuously,

Do not meet the requirements must be replaced with new bearings).

(6) Cut off one end of the motor stator winding with a special chisel and hammer, and then cut off the effective edge of the coil with a special chisel.

Cut out from the slot (special attention: it is easy to damage the stator core when cutting out and cutting out the coil).

(7) Record all technical parameters of the motor stator winding.

2. Repair of motor stator winding

The repair of motor stator winding is the most important operation link of this project. Can the motor reach the quality after repair?

Indicators depend on the following steps:

(1) coil winding (2) motor embedding (3) winding connection (4) insulation treatment

Coil winding:

According to the recorded data of the removed motor stator winding, make the winding die for winding the coil, and the size of the winding die must be made.

Accuracy, too large or too small size will affect the final quality. So you can leave a relatively complete line when disassembling the coil.

Circle, take the smallest number of turns as the shape and perimeter of the winding die. Winding method and matters needing attention:

(1) When winding the machine, the rotating speed should not be too fast, which may easily lead to broken wires, uneven arrangement and crossed lines.

Usually, the speed of the winding machine is 150 ~ 200 rpm.

(2) When winding coils, the wires must be arranged neatly to avoid crossing. Because passing through the conductor will increase the conductor in the core groove

Area, making it difficult to bury and easy to cause turn-to-turn short circuit.

(3) The number of turns of the coil must meet the design requirements. Not too much, because too much will not only waste wires, but also make the slot content

Can't take it, at the same time, the leakage reactance increases, and the maximum torque and starting torque decrease; The number of turns should not be too small, because too few turns will increase the no-load current of the three-phase motor and reduce the power factor.

(4) The number of turns of the three-phase winding must be equal. If one phase is equal, the three-phase current will be unbalanced and the three-phase will be charged.

The performance of this machine has declined.

(5) The wire diameter of the conductor must meet the design requirements. Too thick, it is difficult to embed lines, and it also wastes materials; Too fine, not only easy.

Breaking will also increase the DC resistance of the three-phase motor winding, which will directly affect the performance of the three-phase motor.

(6) When winding, the insulation layer of the conductor must be protected, and no damage is allowed, otherwise it will cause turn-to-turn short circuit of the coil.

Barriers.

(7) The joint or damage of wires shall not exceed one place in each coil and two places in each phase winding; exist

No more than four three-phase motors per unit. The connector must be at the hypotenuse of the coil end, and it is not allowed to leave the connector in the core slot.

Motor embedding:

Embedding is a highly technical job, which needs careful operation and can't be careless at all, because the embedding level is related to the quality of the motor and directly affects the electrical characteristics of the rewinding motor.

Basic operating methods and technical requirements for embedding wires;

(1) First, the cut slot insulating paper is longitudinally folded into a U shape and inserted into the slot so that the smooth surface of the slot insulating paper faces inward to insulate the slot.

The paper should be double-layered, the upper layer should extend out of the notch to facilitate off-line, and the length of both ends of the slot insulating paper should be uniform.

(2) When embedding wires, the right hand inclines the rear end of the effective edge of the flattening coil to the notch of the end face of the iron core, and the left hand moves away from the stator.

The other end extends into the connecting coil, and both hands press the effective edge near the left section into the notch as much as possible, and then the left hand slowly moves.

When pulling left, the right hand should not only prevent the wire from slipping out of the notch, but also comb the wire at the back, and hold it down with both hands while pushing.

Pull back and forth so that the effective edge of the wire is completely embedded in the groove. If there are still wires not embedded, you can use a scribing board.

Pull this part of the wire into the slot one by one.

(3) Because the motor is a single-layer winding, when the first two coils are embedded, only one effective side is embedded first, and the other one has

The effect edge is not embedded for the time being, and the slot is left. After all coils are embedded, they are embedded again.

(4) After each coil is embedded, the notch shall be sealed. First, press the conductor with the wire pressing plate, and then insert the straw cover for insulation.

Into, or fold the insulating paper of the groove to clamp the wire. Then the insulating paper is pressed by the wire pressing plate, and the insulating paper is pressed by the wire pressing plate.

The gap is inserted into the slot wedge. If it is difficult to insert the wedge, you can beat the slot wedge with a wooden hammer.

(5) After all coils are embedded, insert interphase insulating paper to shape the end of stator winding. End stage

Before placing the insulating paper, it is advisable to cut the insulating paper into a half-moon shape, carefully identify the polar groups and insert them one by one.

Insulation paper. Then tap the winding end with a setting tool and a wooden hammer to form a bell mouth, which is convenient for the stator winding to pass through.

Wind dissipates heat. But the bell mouth should not be too big, so as not to affect the insulation performance when the coil end touches the bushing, or even

Resulting in winding short circuit to ground.

Winding connection:

After embedding, each coil in the stator should be connected according to certain rules to form a complete three.

Phase winding. According to the original data recorded when dismantling the old winding, it is necessary to make clear the form of the winding, the number of parallel branches and the connection mode of the pole-phase group, and then make wiring according to the winding development diagram of the motor. The following is the connection development diagram of the motor stator winding:

Wiring method and process requirements:

(1) Measure the wires to be overlapped along the winding ends, keep the required length, and cut off the rest.

(2) Put a sleeve on the wire to be connected. Casing generally adopts glass fiber yellow wax pipe, and the size depends on the specific situation.

The situation determines. Plastic sleeves can't be used because they are easily damaged at high temperature. After putting on the sleeve, push it aside to expose the threaded end of the connecting part.

(3) Scrape the paint on the thread head to be welded with an electrician's knife and polish it with gauze to remove the oxide layer and oil stain on it.

Dirt and so on. , and then connect the two ends of a single or multiple wires according to the method of electrical wiring.

(4) The original cable lead of the old motor can continue to be used if it is intact, and the cable lead with damaged insulation layer must be reused.

Replace. Its cross-sectional area can be selected according to the rated current of the motor.

The specification of outgoing line is selected in the following table:

(5) Welding methods: There are three main welding methods: brazing, gas welding and arc welding. (This project only needs welding.)

Welding: This is the most common welding method. First, apply flux (rosin or other flux) to the cleaned wire connector, and preheat the electric soldering iron under the connector. When the flux smokes, the welding rod is quickly stuck to the soldering iron and melted at the joint, and the solder will automatically dissolve into the gap of the joint under the action of the flux. When welding, solder must be prevented from dripping on the winding. In addition, the soldering iron should not be overheated, so as to avoid sharp oxidation of the soldering iron and tin hanging. After welding, the soldering iron should be moved away in parallel to avoid the solder leaving a tip on the joint and damaging the insulation. As for the power of the soldering iron, it depends on the thickness of the wire. Generally, this kind of motor can use 100W or 150W soldering iron.

(6) Binding of winding ends:

After welding the terminals of the winding, wipe the terminals clean, cover the joints with glass wax pipes, and then place the connecting wires of each pole group neatly at the end of the winding, and then tie them tightly with wax wires to prevent looseness. There are two binding methods. One is to bind the lead wire, connecting wire and its sleeve with the coil end, which is firm. The other is not directly tied to the coil, but to tie the lead wire and the connecting wire separately. Six outgoing lines shall be marked (i.e. the "head" end and "tail" end of each phase shall be clearly defined).

Insulation treatment:

Links to project-related knowledge: (there are mainly seven knowledge points)

Knowledge point (1): working principle of three-phase asynchronous motor.

The working principle of asynchronous motor is to generate electromagnetic torque through the interaction between air gap rotating magnetic field and induced current in rotor winding, so as to realize energy conversion, so asynchronous motor is also called induction motor.