Analysis on energy saving and consumption reductio

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Analysis on energy saving and consumption reduction of frequency converter in water supply engineering

0 introduction

in traditional water supply engineering, various system parameters change continuously with the change of working conditions. In order to achieve accurate control, only the method of controlling the opening of valve or baffle can be used to increase or decrease the resistance artificially, so that a large amount of energy is lost on the valve and baffle. With the maturing of variable frequency speed regulation technology, the speed, starting time and other parameters can be adjusted according to the load characteristics of the motor, so it has obvious energy-saving characteristics

at present, the frequency conversion speed regulation technology is adopted in the water supply pump station to realize the closed-loop control of the pump, which has achieved the purpose of energy saving and stable operation. This paper will give a specific analysis of the variable frequency speed control of the water supply system of a secondary pump station. 1 energy saving and consumption reduction principle of variable frequency speed regulation of water pump

centrifugal water pumps are widely used in industrial and domestic water supply systems. Its output characteristics depend on the type of pump and the resistance characteristics of water supply pipe system. The characteristic curve of the centrifugal pump and the resistance curve of the water supply pipe are shown in Figure 1 and Figure 2

in Figure 1: Q - flow, H - head curve of water pump at a certain speed, P - power curve of water pump, I - efficiency curve of water pump; Figure 2: resistance curve of de water supply pipe

from the perspective of energy saving, for the occasion of operating conditions, the frequency conversion motor is usually used to change the pump speed to meet the performance requirements when the operating conditions change. Therefore, the H-Q curve during pump speed regulation is shown in Figure 3. The intersection A0 of the pump characteristic curve n and the pipeline performance curve De is the working point of the pump during normal use

the energy-saving principle of variable frequency speed regulation is explained by the comparison between throttling control and variable frequency speed regulation

throttling control is to increase the friction resistance of the valve to the water supply by changing the opening of the valve or baffle installed on the pipeline. Therefore, as reflected in the above figure, the resistance curve moves from De to De', the lift rises from H0 to H1, the flow decreases from Q0 to Q1, and the operating condition point moves from A0 to A1

variable frequency speed regulation control is to change the performance curve of the pump by changing the working speed of the pump under the condition that the pipe performance curve remains unchanged, so as to change the operating point to achieve regulation. The characteristic curve of the pump depends on the speed of the motor. If the common Lego building block of the speed is ABS product from n to n', the operating point will be moved from A0 to A2, and the lift will be changed from H. When it is reduced to H2, the flow will be reduced from Q0 to QL, which is the same as the output flow when throttling control is used

when the two methods are adopted for operation, the pump shaft power of point A1 and A2 are respectively:

that is to say, using throttling to control flow wastes more △ P power than using variable frequency speed regulation, and the consumption increases with the decrease of valve opening. On the other hand, when variable frequency speed regulation is used, according to the similarity law of the impeller of the water pump, when the speed changes from N0 to N2, the approximate change relationship of Q, h and P is:

when the speed of the water pump decreases, the power consumed also decreases greatly. Therefore, China has made great breakthroughs in the external wall insulation technology. Therefore, the most effective energy-saving measure is to use variable frequency governor to regulate the flow. Generally, the power saving rate of frequency converter is 20% ~ 50%, and the benefit is remarkable. 2 variable frequency speed regulation system of water supply system

the composition of the variable frequency speed regulation system of the water supply system of a secondary pump station is shown in Figure 4. The pump station is composed of two iosap-6b pumps, and the power of each motor driving the pump is 180kW. According to the statistical data, the peak water consumption can reach 1200 ~ 1400t/h, while the lowest peak water consumption at night is only 400t/h. The flow of the pump changes greatly, so it has great energy saving potential. 2.1 at this time, the jaw system composition should be replaced.

Figure 4 shows the composition of the variable frequency speed regulation system. The system is mainly composed of the following parts:

(1) control object: two 180kW water pump motors MI, M2

(2) frequency converter and PID regulator: in order to save investment, the scheme of "one control and one" control of two motors is adopted. The two frequency converters are controlled synchronously, with intelligent protection of water pump and frequency conversion host, time adjustable soft start, soft stop and other advanced functions, which can ensure that the equipment is in a stable, efficient, safe and low consumption operation state

(3) power frequency controller: the original motor starting system

(4) pressure transmitter

(5) power frequency/frequency conversion switcher: conventional double head knife switch is selected to ensure that the two systems do not affect each other and the switching is reliable. 2.2 working principle of the system

the regulation means of the system adopts constant pressure control at the most unfavorable point of the pipe. After the pressure transmitter sends the signal to the PID regulator through the shielded cable, it controls the frequency of two motors at the same time. When controlling guoshunxi, Secretary of the Party committee of Shanxi Aluminum Plant, when the water consumption is 400t/h, only one variable-frequency speed regulating motor can meet the whole water supply requirements. The other pump motor can be started until the water consumption rises. The head h after speed regulation should be consistent with the pipeline resistance characteristic curve to obtain the best energy-saving effect. The frequency setting of the frequency converter can be set manually or a closed-loop control system can be formed according to the pressure at the most unfavorable point at the end of the pipe to adjust the motor speed in real time

in the above systems, the scheme of one set of constant speed and the other set of speed regulation is not adopted, and the drive motors of the two water pumps all adopt variable frequency speed regulation. Although the one-time investment is a little large, it will

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