Inverter output imbalance failure: uncover the root cause and unlock the cheats of efficient repair!

The inverter outputs full analysis of unbalanced faults and efficient solution strategies

I. Introduction

        In industrial automation and production process control, the inverter plays a vital role as the core component of the electric drive system. However, the inverter output unbalance fault, as a common electrical fault, often has a significant impact on the stable operation of the production line. In-depth analysis of such faults not only helps to eliminate hidden dangers in time, but also provides a solid guarantee for the production safety and efficiency of enterprises. This article will comprehensively analyze the output imbalance fault of the inverter from the aspects of fault phenomenon, cause analysis, diagnosis methods, solutions and preventive measures, aiming to help equipment maintenance personnel improve the fault handling ability and efficiency.

二、the fault phenomenon

        When the output of the inverter is unbalanced, the most direct manifestation is the abnormal operation of the motor. The motor may vibrate violently, accompanied by harsh noise, its torque output is unstable, the speed fluctuates obviously, and in serious cases, it may even cause the motor to stop, which directly affects the normal operation of production equipment, thereby reducing product quality and production efficiency. From the perspective of electrical parameters, the amplitude of three-phase voltage or current is unequal and the phase is out of order, which is a typical feature of the output unbalance fault of the inverter.

三. Analysis of the cause of the failure

(1) The motor itself fails

        1. Winding short circuit: During the long-term operation of the motor, the winding insulation layer may age due to harsh environments such as humidity and high temperature, which will cause a short circuit in the winding. Once a phase winding is short-circuited, its resistance value will decrease significantly, resulting in an increase in the phase current, thus breaking the equilibrium state of the three-phase current.
        2. Winding break: Frequent start and stop of the motor or external impact may lead to poor welding or fracture of the winding joint, making a certain phase current zero, resulting in a serious imbalance of three-phase current.
        3. Rotor failure: Under the condition of overload or frequent forward and reverse rotation, the rotor squirrel cage bar of the motor may break, and the end ring may crack, resulting in uneven distribution of the rotor magnetic field, which in turn causes uneven torque output of the motor and three-phase current loss balance.

(2) External connection problems

        1. Cable damage: The industrial site environment is complex, and the cable may be damaged due to factors such as extrusion, erosion, or high temperature. Once the cable insulation is broken, it can cause a short circuit or open circuit fault, resulting in a three-phase current or voltage imbalance.
        2. Poor cable contact: The cable joint is not firmly connected or loose, and the motor vibration is easy to lead to poor contact. The increase of the contact resistance increases the voltage drop of the phase, which in turn causes a voltage imbalance.

四、fault diagnosis methods

        1. Visual inspection method: first, observe the appearance of the inverter and motor, and check whether there are abnormal phenomena such as smoke and odor. At the same time, check whether the motor shell, windings and cables are intact, whether the joints are loose, and preliminarily judge the fault location.
        2. Electrical parameter measurement method: use multimeter, oscilloscope and other tools to measure the input and output voltage, current and other electrical parameters of the inverter. Focus on measuring the output three-phase voltage and current, compare the amplitude and phase relationship, if the three-phase voltage amplitude difference is large or the current unbalance exceeds the normal range, the output unbalance fault can be diagnosed.
        3. Component replacement method: When it is suspected that a component inside the motor, cable or inverter is faulty, normal parts can be used to replace it and observe whether the inverter operation is restored to normal. However, it should be noted that the replacement operation needs to be cautious to avoid secondary damage.
        4. Motor off-line test method: separate the motor from the inverter, use professional equipment to measure the motor winding resistance and insulation resistance, and conduct no-load and load tests to determine whether the motor is faulty.

五、 the solution

(1) Fault handling of the motor itself

        1. Winding short circuit or open circuit repair: For winding short circuit fault, if the fault is minor, the short circuit point can be insulated or the short circuit winding can be replaced; If the fault is serious, such as a large-area short circuit or a multi-phase open circuit, it needs to be sent to the motor maintenance plant for winding rewinding. After repair, a comprehensive test is required to ensure that the motor performance returns to normal before connecting the inverter.
        2. Motor rotor fault handling: For rotor squirrel cage bar fracture or end ring cracking fault, it can be repaired by welding or replacement. After repair, a dynamic balance test is required to ensure that the rotor runs smoothly. Then install the motor back in place and debug and test it with the inverter to ensure that it is well matched.

(2) External connection problem solving

        1. Cable damage treatment: After determining the fault point of short circuit or open circuit of the cable, for the short circuit fault, you can use the insulation resistance meter to troubleshoot, cut off the damaged part and replace the new cable; For the open circuit fault, you can use the multimeter resistance file to trace, find the broken point and repair it and do a good job of insulation.
        2. Solve the poor contact of the cable: check the connection of the cable joint, tighten the screws to ensure the connection is firm. Clean the oxide layer and dirt of the joint, and apply conductive paste to reduce the contact resistance. After processing, the operating status of the inverter and motor needs to be re-tested.

6. Preventive measures

        1. Regular equipment inspection: Establish a regular equipment inspection system, and professionals will conduct regular inspection and maintenance of key components such as frequency converters, motors and cables. The inspection content includes but is not limited to the heat dissipation of the inverter, dust accumulation, and electrical connection; Motor appearance, bearing wear, temperature changes; Cable wear, aging, joint firmness, etc. Identify and deal with potential problems in a timely manner to ensure the stable operation of the equipment.
        2. Optimize the operating environment of the equipment: keep the operating environment of the inverter and motor clean and dry, and ensure that the heat dissipation channel of the inverter is unobstructed and the temperature is appropriate. Conditioning equipment such as air conditioners can be installed to control indoor temperature and humidity. At the same time, avoid overload operation of the motor, reasonably adjust the load and start-stop times, and prolong the service life of the equipment.
        3. Correct equipment selection and installation: according to the load characteristics and working environment, select the appropriate inverter and motor model and parameters. When installing, it is necessary to operate strictly according to the instructions to ensure that the cable connection is correct, firm and well insulated. At the same time, avoid installing the inverter near the interference source to reduce the impact of electromagnetic interference on the equipment.

七、 Conclusion

        As one of the common electrical faults in the field of industrial automation, the impact of inverter output unbalance fault cannot be ignored. Through in-depth analysis of fault phenomena, causes and diagnostic methods, and taking effective solutions and preventive measures, we can effectively improve the fault handling ability of equipment maintenance personnel and ensure the stable operation of the production line. At the same time, the implementation of measures such as strengthening equipment inspection, optimizing the operating environment, correct selection and installation, personnel training and technical reserves will also provide a solid guarantee for the production safety and efficiency of the enterprise. In the future development of industrial automation, with the continuous progress of technology and the in-depth expansion of applications, the development of inverters and related technologies will be more mature and perfect, injecting new vitality and power into the production and development of enterprises.