In industrial production and daily applications, motors are the core equipment that converts electrical energy into mechanical energy, and their stable operation is crucial. However, the problem of abnormal magnetic field position in motors often troubles equipment maintenance personnel and engineers. Abnormal magnetic field position not only leads to a decrease in motor output power and efficiency, but may also cause vibration, noise, and even damage to the motor, affecting the normal operation of the entire production system. Thoroughly exploring the causes of its occurrence and developing targeted solutions is the key to ensuring the reliable operation of the motor.
1、Common causes of abnormal magnetic field position in motors
（1）Motor winding fault
The motor winding is a key component that generates a magnetic field, and its state directly affects the distribution of the magnetic field. Winding short circuit is one of the common faults. Due to aging, moisture or mechanical damage of the insulation material, the insulation between turns or phases of the winding fails, and the current does not flow along the normal path, resulting in magnetic field disorder. Open circuit faults can also damage the integrity of the magnetic field, such as loose welding points, broken wires, etc., which can prevent some windings from participating in the generation of the magnetic field and cause the position of the magnetic field to shift.
（2）Rotor issue
The rotor plays a crucial role in the operation of the motor, and rotor eccentricity is an important factor leading to abnormal magnetic field position. During the manufacturing and installation process of the motor, or after long-term operation, bearing wear, shaft deformation, etc., may cause the rotor to deviate from the stator center axis, resulting in uneven air gap. Uneven air gaps can cause uneven distribution of magnetic field in the circumferential direction, thereby affecting the performance of the motor. In addition, for squirrel cage asynchronous motors, rotor bar breakage can disrupt the normal distribution of rotor current and affect the generation of electromagnetic force; For permanent magnet motors, damage or demagnetization of the permanent magnet can change the strength and direction of the magnetic field, causing abnormal magnetic field position.
（3）Sensor malfunction
Modern motor systems are often equipped with position sensors for precise detection of magnetic field position to achieve efficient control. However, sensors may malfunction due to environmental factors such as high temperature, humidity, electromagnetic interference, or their own quality issues. Damaged or offset sensors can result in inaccurate magnetic field position signals detected, and the control system adjusts based on the erroneous signals, ultimately causing abnormal magnetic field positions in the motor. Even if the sensor is not damaged, if it has not been properly calibrated, it will still affect the detection accuracy.
（4）Control system issues
Advanced motor control systems, such as vector control and direct torque control, rely on precise algorithms and parameter settings to control the magnetic field. If there are loopholes in the control algorithm, or if the parameter settings of the current loop, speed loop, etc. are unreasonable and cannot accurately adjust the current and voltage of the motor, it will be difficult to maintain a stable magnetic field position. In addition, the software version of the control system is outdated and may have compatibility issues or functional defects, which can also have adverse effects on magnetic field control.
2、Solution strategy for abnormal magnetic field position of motor
（1）Troubleshooting and repair of winding faults
Use an insulation resistance tester to test the insulation resistance of the motor winding. If the resistance value is lower than the specified standard, further inspection of the winding short-circuit point is required. Voltage drop method, segmented testing with megohmmeter, and other methods can be used to locate the short-circuit position. For situations with fewer short-circuit turns, local repairs can be carried out; If the short circuit is severe, the winding needs to be rewound. Measure the winding resistance phase by phase using a multimeter to determine if there is an open circuit. Once the open circuit point is found, perform welding repair or replace the damaged wire. At the same time, check the winding wiring terminals to ensure that the wiring is firm and correct, avoiding magnetic field abnormalities caused by wiring errors.
（2）Rotor fault handling
Measure the air gap between the rotor and stator using a dial gauge. If the air gap deviation exceeds the allowable range, adjust the rotor position. For motors using sliding bearings, the rotor center can be calibrated by adjusting the position of the bearing seat; For rolling bearing motors, check the wear of the bearings and replace them if necessary to ensure the accuracy of rotor installation. For squirrel cage asynchronous motors, a broken bar detector is used to detect the breakage of rotor bars. If a broken bar is found, welding or replacement of the bar can be used to repair it. For permanent magnet motors, use a magnetic performance tester to test the performance of the permanent magnet. For demagnetized or damaged permanent magnets, replace them with permanent magnets of the same specifications and pay attention to the installation direction and position.
（3）Sensor maintenance and calibration
Check the appearance of the position sensor, inspect for any damage, deformation, etc., and check if the connecting wires are loose, short circuited, or open circuited. Use tools such as oscilloscopes to detect sensor output signals and determine if they are normal. For situations where signals are abnormal due to electromagnetic interference, measures such as shielding and filtering can be taken to eliminate the interference. According to the requirements of the sensor manual, perform calibration operations under specific conditions, such as adjusting the installation position and parameters of the sensor when the motor is stationary or running at low speed, so that its output signal accurately corresponds to the actual magnetic field position.
（4）Optimization of control system
Thoroughly analyze the control algorithm and check for any logical errors or improper parameter settings. Based on the actual operating characteristics of the motor, parameters such as current loop and speed loop can be optimized using methods such as trial and error and engineering design to determine appropriate parameter values. Timely monitor the software update information released by the control system manufacturer, download and install the latest version of the control program, fix known software issues, and improve the stability and control accuracy of the control system.
3、Measures to prevent abnormal magnetic field position of motors
To reduce the occurrence of abnormal magnetic field positions in motors, it is necessary to strengthen the daily maintenance and upkeep of motors. Regularly check the insulation performance and wiring condition of the motor winding, and replace aging insulation materials in a timely manner; Regularly lubricate and inspect the bearings to prevent rotor eccentricity caused by bearing wear; Keep the operating environment of the motor clean and dry, and avoid damage to the motor caused by dust, moisture, etc. At the same time, in the process of motor selection and installation, strict adherence to technical requirements is carried out to ensure the installation accuracy and quality of the motor.
Abnormal magnetic field position of a motor is a complex problem that involves multiple components and control systems of the motor. By conducting in-depth analysis of the causes of anomalies, adopting targeted solutions, and carrying out daily preventive work, it is possible to effectively solve the problem of abnormal magnetic field position in motors, ensure stable operation of motors, and improve production efficiency and equipment reliability. In practical work, it is necessary to continuously accumulate experience, combine new technologies and methods, and further improve the ability to diagnose and handle motor faults.
Hengda Electric has always been dedicated to the research and development, production, and service of various types of motors. With advanced technology and equipment, lean manufacturing processes, reliable product quality, and satisfactory after-sales service, the company provides customers with the most suitable motor professional solutions and creates greater social value.
