How is the axial force of a three-phase asynchronous motor generated? Whether it is a high-voltage or low-voltage electric motor, shaft displacement problems or axial force causing bearing temperature to rise are reported from time to time. The best operating condition for the motor is that there is no force in the axial direction and an ideal connection between the motor and the load is guaranteed; in fact, different three-phase asynchronous motors have more or less axial force.
In a three-phase asynchronous motor, when the stator winding is connected to the power supply, a rotating magnetic field is generated, so that an induced current is generated in the rotor due to electromagnetic induction, and the rotor is magnetized and generates a rotating electromagnetic attraction.
After excitation, the synchronous induction motor rotates at a synchronous speed, and the rotation of the three-phase asynchronous motor produces a slip. The gravity of the rotating magnetic field of the motor is generated based on the shortest characteristics of the magnetic lines of force. The electromagnetic force makes the motor run on the electromagnetic center line, that is, the electromagnetic forces of the motor stator and rotor are balanced with each other in the radial direction, and no axial magnetic force is generated. However, in actual operation, axial force will be generated due to the following factors.
What are the causes of the axial force of the Sima motor?
-The axial force generated by the cooling air flow when the motor rotor fan is running at no load.
-Due to factors such as manufacturing process and assembly error of three-phase asynchronous motor, the mechanical center line and electromagnetic center line of the motor are deviated, and the stator and rotor will generate axial force.
-In order to reduce the influence of tooth harmonics, the stator or rotor adopts a skewed slot structure. When the load is running, the electromagnetic force forces the rotor to bend to one end to generate axial force.
-The electromagnetic center line of the three-phase asynchronous motor is the reference line for the connection between the motor shaft and the driven mechanical equipment coupling. However, since there is no electromagnetic center line mark in the motor design and manufacturing, the calibration dimensions of the installation drawings in the accompanying documents are based on the mechanical center design when the motor and coupling are installed.
In this way, in the actual operation of the engine, due to the misalignment of the mechanical center line and the electromagnetic center line, the following situations will inevitably occur: H Due to the installation error of the motor and coupling and the axial force generated. The direction of the axial force is the push or pull axial force on the driven mechanical equipment, resulting in damage to the motor and bearings of the driven mechanical equipment or the entire machine. For brushless excitation synchronous motors with higher safety, the factors are greater, so from the perspective of process manufacturing and processing, the stamping quality is improved and the stamping burrs are reduced; discipline, ensuring the length of the stator and rotor cores, avoiding human installation and assembly errors, requiring the company's technical personnel to have high technical quality and good assembly skills, is the process guarantee for reducing axial force.
In addition, the designer must be familiar with the manufacturing process and product assembly process, and the size and direction of the axial force caused by inherent factors such as structural design, motor rotation, fan position and chute direction must be considered in the structural design so that they can offset each other or minimize them. At the same time, product assembly technicians must participate in the initial startup attempt after product assembly. During the trial run, more importantly, the test technicians are required to accurately require assembly in the technical documents based on the actual displacement data of the center line of the three-phase asynchronous motor and the actual electromagnetic center tested in the no-load and load tests during the prototype test assembly test. Then, the motor adjusts the displacement value and shifts the shift direction to the rotor position during the process.