Economic analysis of variable-frequency motors

Variable frequency design is utilized in situations where frequent adjustment of flow rate is required and the load varies significantly, as this is when the advantages of variable frequency pumps become apparent. For example, if a pump is used for water supply and the maximum flow rate required is 50 m3/h while the minimum flow rate is only 10 m3/h, then a pump with a high flow capacity should be used; when a lower flow rate is needed, the speed of the pump can be reduced accordingly. This thus offers an energy-saving advantage over regulating flow by closing the outlet valve. The energy-saving advantages of variable frequency drive are not evident in terms of maintaining a stable supply and demand balance; however, variable frequency drives can be used to stabilize certain parameters in subsequent stages. For example, in the case of ion-exchange membrane brine supply pumps, their operation can be stabilized by controlling the level of the brine reservoir (in the Asahi Kasei process) or the ultra-pure brine tank (in the chlorine production process). This approach is much more reliable than regulating flow rates by adjusting the valves at the pump outlet, and it also results in significant cost savings. Another use of variable frequency is for precise control; for example, in situations where strict flow control is required, this can be achieved by controlling the speed of the pump. The moderator’s choice has only one parameter; it seems that variable frequency speed control isn’t necessary.

This post was last edited by huawei on 2010-4-29 at 16:10. Haha, the post has been edited again? There is a minimum value of 20 m3 for this parameter; I need to know the medium and operating conditions of this pump. The operating conditions include: maximum flow rate, time at which the maximum flow rate is reached, minimum flow rate, time at which the minimum flow rate is reached, normal flow rate, time at which the normal flow rate occurs, pressure at the maximum flow rate, pressure at the minimum flow rate, the maximum head that the pump can handle, and whether the pump is installed at a high position (with suction capability) or at a low position (without suction capability)

First of all, thanks to Brother Tiger for his help! Motor operating condition: Installed at a low position; 3 kilograms of pressure is required under normal conditions. If the flow rate increases, the pressure can be reduced appropriately. Flow rate (m³/h), hours (%): 20, 20, 30, 25, 40, 50, 50, 5. For any items not specified, please analyze them based on the simplest scenario. Thank you!

With a pressure of three kilograms, the hydrostatic pressure of the liquid column in the tank resulting from installation at a low level can be ignored. For pump selection, a flow rate of around 60 cubic meters and a head of around 50 meters are sufficient. If the pipeline is very long, i.e., over 50 meters, then a higher head is required. The selection of a pump should be discussed with the manufacturer based on the medium temperature, flow rate, and head. Since the accompanying motor does not operate for long periods under its rated conditions, a smaller margin can be chosen – as long as it is sufficient. The motor speed is 2900 revolutions per minute, while the synchronous speed is 3000 revolutions per minute. Equipped with an inverter for stepless speed control. Variable frequency speed control for pumps does not involve increasing the speed; the maximum speed is 50 Hz at the power frequency. When the flow rate is low, the operating speed can be reduced, thereby lowering the motor’s shaft power and operating current, and achieving energy savings and reduced consumption.