Maintenance of motor by frequency converter mainly includes the following aspects: overvoltage maintenance, undervoltage maintenance, overcurrent maintenance, phase-gap maintenance, reverse phase maintenance, overload maintenance, grounding maintenance, short circuit maintenance, overfrequency maintenance and stall maintenance. The following is a brief introduction to the maintenance methods of these types of converters for motors.
1. Overvoltage maintenance:
The output of the frequency converter has the function of voltage detection. The frequency converter can automatically adjust the output voltage so that the motor can not withstand the overvoltage. Even if the output voltage adjustment fails and the output voltage exceeds 110% of the normal voltage, the frequency converter will play a maintenance role to the motor through the shutdown.
2. Undervoltage Maintenance:
When the voltage of the motor is lower than 90% of the normal voltage, the frequency converter maintains shutdown.
3. Overcurrent maintenance:
When the current of the motor exceeds 150%/3 seconds of the rated value, or 200%/10 microseconds of the rated current, the frequency converter maintains the motor through shutdown.
4. Phase-missing maintenance:
Monitor the output voltage. When the output is out of phase, the converter alarms. After a period of time, the converter maintains the motor through shutdown.
5. Reverse maintenance:
Frequency converter can only rotate the motor in one direction, so it is impossible to set the direction of rotation. There is no possibility of inversion unless the user changes the phase sequence of connection A, B and C of the motor.
6. Overload maintenance:
Inverter monitors motor current. When motor current exceeds 120%/1 minute of rated current, the converter maintains the motor through shutdown.
7. Grounding Maintenance:
Frequency converter is equipped with a special grounding maintenance circuit, which is generally composed of grounding maintenance transformer and relay. When one or two phases of grounding occurs, the frequency converter alarms. Of course, assuming that the user pleads, we can also design to maintain the downtime immediately after grounding.
8. Short circuit maintenance:
After the short circuit of the converter output, it will inevitably cause overcurrent, and the converter will be shut down in 10 microseconds to maintain the motor.
9. Over-frequency maintenance:
The frequency converter has the function of maximum and minimum frequency limit, so that the output frequency can only be within the range of rules, thus completing the function of overfrequency maintenance.
10. Stall maintenance:
Stall maintenance is usually for synchronous motors. As for the asynchronous motor, the stall in the process of acceleration is bound to be overcurrent. The frequency converter completes this maintenance function through overcurrent and overload maintenance. The stall in the deceleration process can be avoided by setting a safe deceleration time in the debugging process to avoid the selection of the brake resistance of the converter. In the variable frequency speed control system, the motor's deceleration and shutdown are accomplished by gradually reducing the frequency. At the moment of the frequency decreasing, the synchronous speed of the motor decreases accordingly, while the speed of the motor's rotor remains unchanged due to the mechanical inertia. When the synchronous speed is less than the rotor speed, the phase of the rotor current changes almost 180 degrees, and the motor changes from the electric state to the power generation state. At the same time, the torque on the motor shaft becomes the braking torque, which makes the motor speed drop rapidly and the motor is in the regenerative braking state. The regenerated power of the motor is reverberated to the DC circuit after full-wave rectification by a continuous-current diode. Because the DC circuit can not be fed back to the grid through the rectifier bridge, it only depends on the capacitance of the converter itself to absorb, although other parts can consume electricity, but the capacitance still has a short time of charge accumulation, constituting a "pump-up voltage", which makes the DC voltage rise. Excessive DC voltage will damage parts of devices. Therefore, it is necessary to take necessary measures to dispose of this part of regenerative energy when the load is in the power generation braking state. Method of disposing regenerative energy: energy consumption braking and feedback braking.