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A Brief Talk on Frequency Conversion of Fans and Pumps for Energy Saving

05 Mar 2022Email

The electricity consumption of electric motors in my country accounts for 60% to 70% of the country's electricity generation, and the annual electricity consumption of fans and water pumps accounts for 1/3 of the country's electricity consumption. The main reason for this situation is: the traditional speed regulation method of fans, water pumps and other equipment is to adjust the air supply and water supply by adjusting the baffles and valve openings at the inlet or outlet, and a large amount of energy is consumed in the baffle. , during the valve shut-off process. Since most of the fans and water pumps have square torque loads, the shaft power and the rotational speed have a cubic relationship. Therefore, when the rotational speed of the fans and water pumps decreases, the power consumption is also greatly reduced, so the energy saving potential is very large. The most effective energy saving measure is to use frequency conversion. The speed governor is used to adjust the flow and air volume. The power saving rate of the inverter is 20%~50%, and usually in the design, the designed capacity of the user's water pump motor is much higher than the actual need, and there is a phenomenon of "big horse-drawn trolley". , low efficiency, resulting in a lot of waste of electric energy. Therefore, the promotion of AC variable frequency speed control device has significant benefits.

The use of inverter drive has a high energy saving space. At present, many countries have specified that the flow and pressure control must be replaced by a frequency conversion speed control device. The second paragraph of Article 29 of China's National Energy Law also clearly stipulates that power electronic speed control should be used for fans and pumps.

Energy saving principle of frequency conversion speed regulation energy saving device

1. Frequency conversion energy saving

It can be known from fluid mechanics that P(power)=Q(flow)╳H(pressure), the flow Q is proportional to the power of the rotational speed N, the pressure H is proportional to the square of the rotational speed N, and the power P is proportional to the cube of the rotational speed N. , If the efficiency of the pump is constant, when the required flow rate decreases, the rotational speed N can decrease proportionally, and the shaft output power P decreases in a cubic relationship at this time. That is, the relationship between the power consumption of the pump motor and the rotational speed is approximately a cubic ratio. For example: the power of a water pump motor is 55KW. When the speed drops to 4/5 of the original speed, its power consumption is 28.16KW, saving 48.8% of power. When the speed drops to 1/2 of the original speed, its power consumption The power is 6.875KW, saving 87.5% of electricity.

2. Power factor compensation for energy saving

Reactive power not only increases line loss and equipment heating, but more importantly, the reduction of power factor leads to a reduction in the active power of the grid. A large amount of reactive power is consumed in the line, resulting in low equipment use efficiency and serious waste. The formula P=S ╳COSФ, Q=S╳SINФ, where S-apparent power, P-active power, Q-reactive power, COSФ-power factor, it can be seen that the larger the COSФ, the larger the active power P, and the power factor of the ordinary pump motor is Between 0.6 and 0.7, after using the variable frequency speed control device, due to the effect of the filter capacitor inside the inverter, COSФ≈1, thereby reducing the reactive power loss and increasing the active power of the grid.

3. Soft start energy saving

Since the motor is directly started or Y/D started, the starting current is equal to (4-7) times the rated current, which will cause a serious impact on the electromechanical equipment and the power supply grid, and will also require too much power grid capacity. High current and vibration will cause great damage to baffles and valves, and are extremely detrimental to the service life of equipment and pipelines. After using the frequency conversion energy-saving device, the soft start function of the frequency converter will make the starting current start from zero, and the maximum value will not exceed the rated current, which reduces the impact on the power grid and the requirements for power supply capacity, and prolongs the use of equipment and valves. life. Save equipment maintenance costs.

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