The heat dissipation of the ordinary asynchronous motor is cooled by the fan behind the motor butt. If it is running for a long time at a low frequency (that is, it is running below the rated frequency of the motor for a long time, the fan speed of the motor is low, so that the motor is not well cooled, too hot. The motor will burn out. If the motor has a problem, the motor current will increase. If the maximum current of the inverter is exceeded, the inverter will implement a protection stop output and report a fault code to the user.
The inverter shows that OC means overcurrent. The solution is to replace the motor with a special motor for frequency conversion, or add a cooling fan to the motor. Or it is a motor with a larger power.
Second, the interpretation of burning machine technology
"The inverters that burn the motor are basically short-circuit between the turns, short-circuit between phases and short-circuit to the ground. Why is the inverter easy to burn the motor, and most of them are inverter motors, which are related to the technical indicators?"
In the case of power frequency power supply, the motor winding input is a three-phase 50Hz sine wave voltage, the induced voltage generated by the winding is also low, and the surge component in the line is small.
In the case of variable frequency power supply, the inverter part converts the DC voltage into a three-phase AC voltage, and controls the switching of the six bridge arms to turn on and off to realize the output of the three-phase AC voltage. After the inverter is connected, the carrier frequency is about several thousand to ten kilohertz, which makes the stator winding of the motor withstand a high voltage rise rate, which is equivalent to applying a steep voltage to the motor, which makes the motor Inter-insulation is subject to a more severe test. The increase of the voltage change rate dv/dt makes the motor winding turn-to-turn voltage change rate dv/dt high, the winding voltage distribution becomes very uneven, and the power supply condition of the motor becomes "bad". The fault that shorts the winding turns is increased, and the motor failure rate is increased. The PWM waveform output by the inverter also generates harmonic voltages of various components in the motor winding power supply loop. It can be seen from the inductance characteristics that the faster the rate of change of the inductor current flows, the higher the induced voltage of the inductor.
The induced voltage of the motor winding is increased compared to the power frequency. Insulation defects that are not exposed during power frequency power supply are not resistant to the impact of the induced voltage under the high frequency carrier, so voltage breakdown between turns or phases of the windings is generated. Everyone knows that the inverter has a perfect protection circuit. If the inverter is used, the motor will not burn. The answer is definitely no, the protection circuit of the inverter is not a panacea. Compared with the power frequency power supply, with the upper frequency converter, the motor is easier to burn. The phase-to-phase, inter-turn short-circuit or grounding of the motor windings causes a sudden short circuit of the motor windings, which may blow up the module or burn the motor during operation. The output voltage waveform of the inverter, under the influence of the high-speed switching of the semiconductor switch, the impact will cause the voltage to be superimposed on the operating voltage of the motor, and a pulse overvoltage will be generated at the motor terminal, and the peak value is about twice the voltage of the DC part. Ground insulation poses a threat, and ground insulation will accelerate aging under repeated impacts of high pressure.
Third, the cause of the motor burning caused by the inverter
The fault of the motor is actually not the cause of the motor itself. Most of them are caused by the non-standard debugging of the inverter or the use of the non-inverter motor when the inverter motor is used. The main reasons are as follows:
1.Use ordinary motor as variable frequency motor. Since the ordinary motor cooling fan is connected with the rotating shaft, when the inverter is used for speed regulation, the speed is unstable, and the rated speed of the motor cannot be reached. The cooling fan can not play a normal role, causing the motor to dissipate heat badly; plus the ordinary motor is not Designed according to the frequency conversion requirements, so that the motor heats up or burns.
2. The variable frequency motor and the inverter are directly connected together without being debugged. The two most common methods used by the inverter to control the motor are vector control and V/F curve control. Each type of control must first type the motor (synchronous, asynchronous, with or without encoder), motor rated power, rated voltage, and rated. The current, the speed or the number of poles, the rated frequency, the maximum operating frequency, the acceleration and deceleration time of the motor starting and stopping, the protection mode of the inverter control motor, the protection proportional coefficient, and the carrier frequency are all set. After these parameters are set, select whether it is vector control or V/F control. When vector control is selected, the motor needs to be paired with the inverter to dynamically self-learn or static self-learning with load. After self-learning, the motor can cooperate with the inverter to achieve the accuracy of vector control; when V/F control is selected, Self-learning is required, and the parameters are adjusted and then directly powered on.
3.The running direction of the inverter motor fan is inconsistent with the direction of rotation indicated on the fan. The fan can not function, causing the heat dissipation condition of the motor to deteriorate, and the heat generated by the motor can not be emitted, causing the motor to heat up or burn out.
4.Two or three of the above three cases occur for the above situation. It is recommended that the customer choose the inverter motor when controlling the motor. The inverter selects the manufacturer with good quality. Although the initial investment is a little higher, the quality is good. It is guaranteed that the fault-free running time is long, it is not easy to cause the production stoppage caused by the fault of the motor or the inverter, and the good quality after-sales service is guaranteed and the response time is fast.