VFD for hydroextractor
The hydroextractor is widely used in the dyeing, washing water and weaving in the textile industry as well as the dehydrating of the washing material in hotels. The modern hydroextractor must satisfy the requirements of different revolving speeds for different materials. Therefore, the revolving speed of the hydroextractor must be able to be regulated, so as to reach the technological requirements. In the past, most hydro extractors adopted the high and low motors. The low-speed acceleration and deceleration motor is used for feeding and discharging in low speed. The high speed revolving is driven by another motor. In deceleration, mechanical brake is used. The transmission system is rather complicated, with a high failure rate. Because the high-speed motor has a rather big capacity, combining the high inertia of the dewatering tank, the starting current is extremely high and the lasting time is rather long. Furthermore, it has a low operating efficiency. And the speed is unable to be regulated.
In recent years, VFD has been keeping on updating and developing as a kind of industrial controlling device. It has wide application in various industries. As the power electronic technology, frequency control theory, microcomputer control technology are becoming more and more matured, the performance of the VFD has been improved and the functions have also been intensified, such as: multi-stage speed, programmable automatic operation, communication function and so on. So VFD can be used in many situations.
According to the manufacturing technology of the hydroextractor, the multi-speed functional control of the VFD can be used. The hydroextractor with VFD control system belongs to the approximate constant torque load with big inertia. Therefore, the system requirements can be reached by configuring braking unit and braking resistor on the basis of selecting the AC converter. The built-in braking unit of the 30hp VFD and below power can not only save space, but also save the cost.
II. Control principle
High-speed dehydrating, low-speed cloth feeding and discharging.
- Cloth feeding: Led the wet cloth into the low-speed (1Hz) operating drum through the cropping shelf (controlled by a small motor) evenly.
- Dehydrating: Start the main motor and speed up to the maximum frequency slowly. The water will be spin-drying under the centrifugal force. Meanwhile, setting time on the timer as the requirements to stop the machine automatically (deceleration + DC braking).
- Cloth discharging: Led the dry cloth outside through the cropping shelf (controlled by a small motor).
III. Parameter setting of ATO VFD
Parameter setting of the 25hp VFD for the hydroextractor
|Function code||Name||Set value||Remark|
|P0.03||Operating command channel||1||Terminal operation|
|P0.04||Operating direction setting||0 0||Reversal is allowed|
|P0.17||Acceleration time 1||240||Set according to the field condition|
|P0.18||Deceleration time 1||420|
|P0.19||Upper limiting frequency||40|
|P0.22||V/F curve setting||4||Muti-stage V/F curve|
|P0.23||Frequency value F3||40||Set according to the field condition|
|P0.24||Voltage value v3||95|
|P0.25||Frequency value F2||25|
|P0.26||Voltage value v2||70|
|P0.27||Frequency value F1||15|
|P0.28||Voltage value v1||30|
|P2.05||Halt mode||2||Deceleration + DC braking|
|P2.06||DC braking starting frequency in halt||0.8||Set according to the field condition|
|P2.07||DC braking time in halt||8|
|P2.08||DC braking voltage in halt||10|
|P5.02||Overvoltage speed loss selection||1||Allowed|
|P5.06||Automatic current limiting||110%||Set according to the field condition|
|P5.09||Malfunction self-recovery times||10|
|P4.01||Function selection of input terminal X2||2||Multi-stage speed 2|
|P4.03||Function selection of input terminal X4||17||External fault reset|
|P3.14||Acceleration time 2||20||Set according to the field condition|
|P3.15||Deceleration time 2||20|
|P3.27||Multistage frequency 2||1|
|P4.12||Equipment (TA TB TC) output selection||15||Fault of VFD|
IV. Matters needing attention in ATO VFD debugging
- The starting of the hydroextractor in inertia load requires a rather big torque. It might cause the condition of big starting current. At this moment, the torque of the VFD can be lifted properly. The current of the VFD increases in the acceleration operation process. When it reaches a certain speed, the liquid will flow out of the hydroextractor under the centrifugal force. In such way, some liquids will be separated in the first. As the revolving speed of the motor further improves, the load will also decrease correspondingly. At this time, the multi-stage V/F curve and automatic current limiting can be set for adjustment as the practical condition on site.
- The function of preventing from over-voltage speed loss: In the deceleration process of the VFD, influenced by the load inertia, there might be condition that the practical descending rate of the revolving speed of the motor is lower than the descending rate of the output frequency, the motor will feed electricity to the VFD at this moment, thus increasing the voltage of the DC bus of the VFD. When it reaches the braking voltage, the braking unit takes action. Because the braking unit has a certain usage rate, if the influence of the high inertia continues, the DS bus voltage keeps on increasing. The application of the function of preventing from over-voltage speed loss will compare the over-voltage speed loss point and the practical DC bus voltage automatically in the deceleration process. If the later passes the former, the output power of the VFD will stop declining until it has inspected that the later is lower than the former again, the VFD can conduct decelerated operation.
- Acceleration and deceleration time: Influenced by the load inertia, the acceleration and deceleration time of the VFD must be set a proper value. If the time is too short, there might be overflow, overvoltage faults of the VFD. If the time is too long, the operation power of the device might be reduced greatly.