Inverter control motor does not rotate or the speed is abnormal: in-depth analysis and solution
一、 Summary
In the field of industrial automation control, frequency converters are widely used in motor speed control. However, the motor does not rotate or the abnormal speed is a thorny problem often encountered during the use of the inverter. Not only does this affect productivity, but it can also cause damage to equipment. This article will delve into the various causes that cause the motor not to rotate or the speed is abnormal, including the inverter parameter setting, external control signals, the failure of the motor itself, and the connection line problem, etc., and elaborate the corresponding solutions for each cause, aiming to help electrical engineers, equipment maintenance personnel and related technology enthusiasts quickly and accurately diagnose and solve such problems, and ensure the stable and efficient operation of the inverter and motor system.
二、 Introduction
With the rapid development of modern industry, inverters have been widely used in many fields due to their excellent energy-saving effect and precise speed regulation performance. From production equipment in the manufacturing industry to elevators and ventilation systems in the construction industry, AC drives play a vital role. However, in the actual operation process, the phenomenon that the motor does not rotate or the speed is abnormal occurs from time to time, which brings a lot of inconvenience to production and operation. Therefore, it is of great practical significance to understand the causes of this problem and grasp effective solutions.
三、 Analysis of the reasons why the motor does not rotate or the speed is abnormal
(1) The problem of inverter parameter setting
1. The output frequency is set improperly
The output frequency of the inverter directly determines the speed of the motor. If the output frequency is set to 0 or too low, the motor will not be able to reach its normal operating speed or even not rotate. For example, during the start-up of some automated production lines, if the operator mistakenly sets the incorrect frequency of the inverter, the motor may only flutter slightly without rotating.
In addition, the setting of the upper and lower frequency limits may also affect the speed range of the motor. If the upper limit is set too low, the motor will not be able to achieve the expected high-speed operation even at full load.
2. The motor parameter setting is incorrect
The inverter needs to correctly set the parameters of the motor before operation, such as the number of poles of the motor, the rated voltage, the rated current, the rated power, etc. If these parameters do not match the actual motor, the inverter will not be able to accurately control the operation of the motor. For example, if the number of poles of the motor is set incorrectly, the synchronous speed calculated by the inverter will not match the speed characteristics of the actual motor, resulting in abnormal motor speed.
Taking a 4-pole motor as an example, if it is incorrectly set to the parameters of the 2-pole motor, the inverter calculates the speed corresponding to the output frequency according to the speed formula of the 2-pole motor, which will cause the actual speed of the motor to deviate from the normal range, and the speed may be too high or unstable.
3. The acceleration and deceleration time is not set reasonably
If the acceleration and deceleration time is too short, the motor will generate a large impulse current when it starts or stops, which may lead to the overcurrent protection action of the inverter and stop the motor from rotating. For example, when some load equipment with large inertia, such as large fans or centrifuges, is started, if the acceleration and deceleration time is set too quickly, the motor may trip due to excessive current at the moment of start-up, and cannot start normally.
Conversely, too long acceleration and deceleration times can make the motor start and stop process too slow, affecting productivity, and in some cases may lead to instability such as jitter or creep when the motor is running at low speeds.
(2) Problems with external control signals
1. Missing or abnormal operating signals
The inverter needs to receive the correct operating signal to start the motor. If the control circuit is faulty, the PLC output signal is wrong, or the external control button is damaged, the operating signal cannot be properly transmitted to the inverter, and the motor will not rotate. For example, in an automated production line controlled by a PLC, if the PLC program is wrong, the motor operation signal is not output under the predetermined conditions, or the signal transmission line is broken, the inverter will not receive the start command, and the motor will naturally not work.
In addition, some inverters have a multi-stage speed control function, and if there is an error or interference in the multi-stage speed selection signal, the motor will not be able to run at the expected speed, and the speed may jump or stay in the wrong speed section.
2. Analog input signal failure
When a frequency converter uses an analog quantity, such as a voltage or current signal, to control the motor speed, the accuracy of the analog input signal is critical. If the analog signal source fails, such as a damaged potentiometer, an abnormal sensor output, or an interference in the signal transmission line, the inverter will receive the wrong speed given signal, resulting in abnormal motor speed.
For example, in a control system that uses a potentiometer to adjust the speed of the motor, if the potentiometer is not in good contact, the voltage signal input to the inverter may be unstable, and the motor speed will fluctuate, and even sudden stops or acceleration may occur.
(3) The motor itself is faulty
1. Short circuit or open circuit in motor winding
A short circuit in the motor winding is one of the more common faults. Short circuits can occur between turns, phases, or ground. When the winding is short-circuited, the equivalent impedance of the motor decreases and the current increases, which may lead to the overcurrent protection action of the inverter and the motor cannot operate normally. For example, in a humid environment, the insulation performance of the motor winding is reduced, which is easy to cause turn-to-turn short circuits. At this time, the motor may emit an abnormal humming sound and heat up, and the speed may not be increased or even gradually decreased to a stop.
If the motor winding is broken, the motor circuit will not be able to pass, and the rotating magnetic field cannot be generated, and the motor will naturally not rotate. This condition may be due to the long-term operation of the motor resulting in loose winding joints, desoldering of weld joints, or breakage of windings due to mechanical damage.
2. Motor bearing damage
Damage to the motor bearing will increase the rotational resistance of the motor and make the motor load heavier. In this case, the motor speed decreases, and vibration and noise increase. In severe cases, the bearing will be stuck and the motor will not be able to rotate. For example, in some dusty or poorly lubricated working environments, bearings are prone to wear, and defects such as scratches and pittings appear on the surface of the balls or raceways, resulting in unsmooth motor operation.
In addition, the failure of the connecting parts between the motor shaft and the load, such as loose coupling, belt breakage or slippage, etc., will also make the output power of the motor unable to be effectively transmitted to the load, resulting in the motor seemingly running normally, but the load does not rotate or the speed is abnormal.
(4) Connection line issues
1. The connection cable
between the inverter and the motor is broken or in poor contact
A broken connection cable breaks the electrical connection between the motor and the inverter, and the motor is unable to obtain drive current and thus does not rotate. This condition can be caused by long-term mechanical pulling, abrasion, or rat bites. For example, in some mobile devices or places with harsh installation environments, cables are susceptible to damage by external forces.
Poor contact will cause the current to be unstable when the motor is running, and the speed may fluctuate, and the phenomenon of rotating and stopping may occur. For example, loosening, oxidation, or untightened screws at cable joints will increase the contact resistance and affect the normal operation of the motor.
2. Control line connection error or interference
The control circuit of the inverter includes running signal, fault signal, analog input and output lines. If these lines are incorrectly connected, such as the signal line is reversed, missed or short-circuited, the inverter will not be able to receive or process the control signal normally, which will affect the operation of the motor. For example, if the forward and reverse signals of the inverter are reversed, the motor will turn in the opposite direction.
In addition, if the control line is subject to electromagnetic interference, such as large motors, welding machines or high-frequency equipment running nearby, the control signal will be distorted, resulting in abnormal motor speed or malfunction. For example, on some factory floors, when a welder is working, it may cause interference to nearby inverter control lines, causing the motor speed to change or stop suddenly.
四、 the solution
(1) Parameter inspection and adjustment
1. Check and correct the output frequency parameters
First, use the inverter’s operating panel or commissioning software to check the set value of the output frequency. If you find that the frequency is set to 0 or too low, adjust the output frequency reasonably according to the rated speed and load requirements of the motor. For example, for a 4-pole motor with a rated speed of 1450r/min operating at 50Hz, the output frequency of the inverter can be set to 25Hz if the motor is required to run at 725r/min.
At the same time, check the setting of the upper and lower frequency limits to ensure that they meet the operating requirements of the motor. Generally speaking, the upper limit of frequency can be set according to the rated frequency of the motor and the overspeed capacity of the load, and the lower limit of the frequency can be set according to the process requirements.
2. Check and correct motor parameters
Carefully check whether the motor parameters set in the inverter are consistent with the nameplate parameters of the actual motor. If an error is found, correct it in a timely manner. For the setting of the number of poles of the motor, it should be adjusted in strict accordance with the actual number of poles of the motor. For example, for a 6-pole motor, the number of poles should be set to 6 in the inverter parameters.
Parameters such as rated voltage, rated current and rated power must also be set accurately to ensure that the inverter can be accurately controlled according to the characteristics of the motor. After the setting is completed, the motor parameter self-learning function can be carried out (if the inverter has this function), so that the inverter can automatically detect the parameters of the motor and optimize the setting to improve the control accuracy.
3. Optimize the acceleration and deceleration time settings
According to the load characteristics and inertia of the motor, the acceleration and deceleration time is reasonably adjusted. For loads with large inertia, such as large fans, water pumps, etc., the acceleration and deceleration time should be appropriately extended to reduce the inrush current when starting and stopping. For example, for a 55kW centrifugal fan, the acceleration time can be set to 15 20 seconds and the deceleration time to 20 30 seconds.
For some occasions with high requirements for response speed, such as the spindle motor of CNC machine tools, the acceleration and deceleration time can be appropriately shortened under the premise of not exceeding the rated current of the motor, but it is necessary to pay attention to determine the best setting value through experiments and monitoring, so as to avoid overheating of the motor or inverter failure due to too fast acceleration and deceleration.
(2) Investigation and repair of external control signals
1. Check the operating signaling pathway
Use a tool such as a multimeter or oscilloscope to check that the inverter’s operating signal input port has the correct signal input. If it is PLC control, check whether the logic in the PLC program about the operation of the motor is correct, and whether the signal transmission line between the PLC output module and the inverter is normal. For example, check whether the signal line is open, short-circuited or poorly contacted, and repair or replace the damaged wire in time for the broken line; For joints with poor contact, reconnect and make sure the connection is secure.
If the control is controlled by an external button, check whether the contacts of the button are normal and whether there is any adhesion or damage. For multi-speed control signals, the signal source and transmission line should also be checked to ensure that each speed signal can be accurately communicated to the frequency converter.
2. Deal with analog input signal problems
For inverters that use analog speed control, first check whether the analog signal source is normal. If it is a potentiometer control, check whether the resistance value of the potentiometer is normal, whether the rotation is flexible, and whether there is any poor contact. For the sensor as the signal source, check whether the working status of the sensor and the output signal range meet the requirements.
At the same time, check whether the transmission line of the analog input signal is disturbed. If interference is found, a shielded cable can be used to transmit an analogue signal and the shield can be well grounded. In addition, a filter can be added to the analog input port of the inverter to filter out interfering signals and improve the stability and accuracy of the signal.
(3) Motor fault diagnosis and repair
1. Detect and repair motor winding faults
Use an insulation resistance meter (megohmmeter) to check the insulation resistance of the motor windings to determine if there is a short circuit or ground fault. For the detection of turn-to-turn short circuits, the turn-to-turn short circuit tester can be used or by measuring the resistance value of the three-phase winding of the motor for comparative analysis. If a short circuit in the windings is found, different repair measures are taken depending on the severity of the short circuit. For minor inter-turn short circuits, they can be dealt with by local repair of insulation; For severe short circuits or phase-to-phase short circuits, it may be necessary to replace the motor windings.
If the winding is broken, check the resistance value of the three-phase winding of the motor one by one through the multimeter to determine the phase and specific location of the open circuit. For the case where the break point is at the end of the winding, you can try to re-weld the repair; If the break point is inside the winding, it may be necessary to disassemble the motor for repair or to replace the winding.
2. Replace the damaged motor bearing
When it is found that the motor bearing is damaged, the first thing to determine is the type and specification of the bearing. Then, use a suitable tool to remove the damaged bearing, such as a puller. When installing new bearings, pay attention to cleaning the bearing seat and journal, apply an appropriate amount of grease, and adopt the correct installation method, such as hot or cold installation, to ensure that the bearing is installed in place and the installation accuracy meets the requirements.
For the failure of the connecting parts between the motor shaft and the load, such as the coupling is loose, the connecting bolts of the coupling should be re-tightened, and the coaxiality should be checked to see if it meets the requirements; In the case of belt drives, check that the tension of the belt is appropriate, and if necessary, replace the worn or broken belt.
(4) Inspection and maintenance of connecting lines
1. Check and repair the connection cable between the inverter and the motor
Double-check the connecting cables for breakage, open circuits, or poor contact. For broken cables, repair or replace them according to the degree of damage. If the contact at the cable gland is poor, reconnect the cable gland to ensure a reliable connection and do a good job of insulation. For example, the oxide layer at the cable glands should be sanded clean with sandpaper before being connected.
In the process of cable laying, it is necessary to pay attention to avoid mechanical damage to the cable, such as avoiding the cable being squeezed by heavy objects, scratched by sharp objects, etc. For cables that have been in a moving or vibrating environment for a long time, flexible cables should be used, and the fixation and wear of the cables should be checked regularly.
2. Troubleshoot and solve control line problems
Refer to the schematic diagram of the control circuit of the inverter, and carefully check whether the connection of the control circuit is correct. For the wrong signal line, correct it in time. At the same time, check whether the wiring of the control line is reasonable and whether it is laid separately from the power line to reduce electromagnetic interference.
If the control line is interfered with, the following measures can be taken: first, increase shielding measures, such as using shielded cables or shielding the control line; The second is to stay away from the interference source, and keep the control line away from large motors, welding machines and other strong interference equipment as much as possible; The third is to add a filter or reactor at the input end of the control line of the inverter to suppress the incoming interference signal.
5. Summary
The motor does not rotate or the speed is abnormal, which is a common problem in the application of the inverter, and its causes are complex and diverse, involving the parameter setting of the inverter, the external control signal, the motor itself, and the connection line. In the actual troubleshooting and problem solving, it is necessary for technicians to have solid electrical knowledge and rich practical experience, and gradually troubleshoot in the order from easy to difficult, from software to hardware. By carefully inspecting and analyzing various possible causes and taking corresponding solutions, we can effectively solve the problem of motor not rotating or abnormal speed, ensure the stable and reliable operation of the inverter and motor system, improve production efficiency, and reduce equipment failure rate and maintenance costs. At the same time, in the daily maintenance and management of equipment, it is necessary to pay attention to the regular inspection, maintenance and parameter backup of the inverter and motor system to prevent the occurrence of such problems and provide a strong guarantee for the smooth progress of industrial production.
In short, it is of great importance to have an in-depth understanding of the reasons and solutions for the inverter-controlled motor not to rotate or the abnormal speed to ensure the stable operation of the industrial automation control system. Whether it is equipment manufacturers, electrical engineers or equipment maintenance personnel, they should take this issue seriously and continue to accumulate experience to improve the ability to diagnose and solve faults to meet the needs of increasingly complex industrial automation environments.
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