Centrifugal fans are commonly used ventilation equipment, especially in many industrial production workshops. Centrifugal fans can effectively ventilate the workshop, and can even be used as induced draft fans for some equipment. It will not carry out continuous high-load production, so it is necessary to continuously adjust the rotational speed of the centrifugal fan, otherwise the energy consumption will be very high. At this time, a frequency converter that can fully meet the requirements is required to transform the motor of the centrifugal fan. How to choose inverter for fan?
1. Performance requirements of centrifugal fans for frequency converters
1. Let the centrifugal fan save electricity, reduce production costs and increase net profit;
2. Built-in PID, closed-loop operation, to achieve constant temperature and multi-speed air volume control;
3. Stepless speed regulation, reduce the starting current of the centrifugal fan, and make the grid voltage more stable;
4. Smooth start, reduce mechanical impact, reduce noise, and prolong the service life of equipment
5. Simple management, protection and automatic control.
2. the selection principle of centrifugal fan frequency converter
When selecting a frequency converter for a centrifugal fan, generally only need to choose a general-purpose frequency converter, and make the rated current of the frequency converter larger than the rated current of the matching motor. The power can only be used as a reference, and cannot be calculated based on the power only, because the power of the inverter is considered according to the four-stage motor, so the current should be compared. Motors below grade 4 can be selected according to the matching motor power.
In addition, correctly grasping the torque characteristics of the mechanical load object driven by the inverter is the basis for selecting the inverter capacity and determining its control method. The load of the centrifugal fan is generally a square torque load. With the decrease of the speed, the required torque decreases in a square proportion. At low frequency, the load current is small, and the motor overheating phenomenon will not occur. However, some loads have large inertia and must be set. Long acceleration time, or shock caused by high torque when restarting.
At the same time, it is necessary to fully consider the rich high-order harmonics contained in the output of the frequency converter, which will deteriorate the power factor and efficiency of the motor. Compared with using the frequency converter to supply power to the motor, the current of the motor will increase by 10%. %, while the temperature rise will increase by about 20%. In addition, when the motor runs at a speed higher than the base frequency speed, the power required by the load increases sharply with the increase of the speed, which easily exceeds the capacity of the motor and the inverter, which will lead to interruption of operation or serious motor heating. Therefore, it is necessary to consider the margin when selecting the frequency converter of the centrifugal fan to prevent the temperature rise from being too high and affecting the service life of the motor.
3. centrifugal fan frequency converter selection method
1. When the inverter is far away from the fan motor, you should choose to enlarge one or two gears, or install an output reactor at the output end of the inverter, otherwise the long cable will affect the ground coupling capacitance, resulting in insufficient output of the inverter.
2. When the frequency converter is used to control several centrifugal fans in parallel, it must be considered that the total length of the cables from the frequency converter to the motor is within the allowable range of the frequency converter. If it exceeds the specified value, it must be enlarged by one or two gears to select. In addition, in this case, the control mode of the inverter can only be the v/f control mode, and the inverter cannot realize the overcurrent and overload protection of the motor. It is necessary to add a fuse on the motor side of each centrifugal fan to achieve protection.
3. When the centrifugal fan is located in a special environment such as high temperature, high switching frequency, high altitude, etc., it may cause the derating of the inverter, so it is necessary to enlarge the first gear to select the inverter.
4. In the face of high-speed centrifugal fans, due to the small reactance of the motor, more high-order harmonics will be generated, which will lead to an increase in the output current value of the inverter, so the selection of the inverter should be larger than the ordinary case. Some.
5. When facing the wound rotor asynchronous motor, the winding resistance of the wound motor is smaller than that of the ordinary squirrel cage motor, so the phenomenon of overcurrent tripping caused by the ripple current is easy to occur, so the ratio should be selected. Usually the inverter with a slightly larger capacity.
4. centrifugal fan frequency converter selection precautions
1. The use environment of the inverter should be fully considered in the energy saving transformation of the centrifugal fan. When there is a lot of conductive dust and damp dust, the inverter with high protection level should be selected, such as a dust-proof and sealed inverter.
2. In terms of control, according to the different dust removal conditions, the dust removal speed on the centrifugal fan should be automatically controlled by an external detection unit and a frequency converter, so that the centrifugal fan runs in a good state, in order to meet the better energy saving effect.
3. When the number of poles is changed during the operation of the centrifugal fan, the motor should be stopped first, otherwise the motor will be idling, and the inverter will be damaged in severe cases.
4. When using the frequency converter to drive the explosion-proof motor, since the frequency converter has no explosion-proof structure, the frequency converter should be set outside the dangerous place.
5.the difference between the fan frequency converter and the water pump frequency converter
1. Fan inverter
The centrifugal fan frequency converter adopts the frequency conversion speed regulation control device. By changing the speed of the fan, the air volume of the fan can be changed to meet the needs of the production process, and the operating energy consumption is more economical and the comprehensive benefit is higher. It is a high-efficiency centrifugal fan speed regulation. It can realize the stepless speed regulation of the fan, and can easily form a closed-loop control system to achieve constant pressure or constant flow control.
2. Water pump inverter
The water pump is generally considered according to the upper limit of the working conditions when the water supply system is designed, and the actual use of the water system may not reach the upper limit of the water consumption for a lot of time. Generally, the valve adjustment is used to increase the system resistance to throttle, which will cause the motor to use. The use of frequency converter can make the working state of the system smooth and stable, change the speed to adjust the water supply, and reduce the speed to save energy and recover the investment, so it is not suitable for centrifugal fans.
