Deep-well small-flow frequency conversion constant pressure and pressure water supply system

Deep-well small-flow frequency conversion constant pressure and pressure water supply system

Abstract: Currently, deep water wells are widely used in frequency conversion speed control. Due to the “fee-charge” problem during the low flow of domestic water, many villages and towns have higher energy consumption per kiloton of water after changing to variable-frequency water supply mode. In this paper, the small-flow frequency conversion constant pressure water supply system for deep wells in Dongdian Village, Chaohua Town, Xinmi City is introduced. The design and operation of the low-frequency variable frequency water supply system for deep wells are introduced.

Keywords: deep water well frequency conversion water supply small flow water supply energy saving rural drinking water

1 Introduction

At present, China has initially established the conditions for the construction of a new countryside: On the one hand, after the rapid development since the beginning of reform and opening up, the comprehensive national strength has been significantly enhanced, and there is an economic basis for supporting agriculture and increasing the investment in rural infrastructure; on the other hand, In recent years, on the basis of a relatively high starting point, the Party Central Committee and the State Council have issued a series of more direct and more powerful policies and measures to improve rural production and living conditions. In particular, the construction of rural "Six Small Projects" has progressed smoothly with remarkable results. Rural construction has accumulated useful experience. The implementation of the frequency conversion water supply project in Dongdian Village, Chaohua Town, Xinmi City is a bright spot in the construction of a new rural village.

Dongdian Village, Chaohua Town, Xinmi City is located 800 meters east of Chaohua Town Government and has a population of more than 900 households. The local coal resources are abundant, and it is also the country's production base for refractory materials. With the rapid economic development, especially the development of coal resources, it also has a certain impact on the drinking water problem of the local people, and the level of drinking water can be reduced. The government at all levels in Xinmi City attaches great importance to the drinking water problem in Dongdian Village. According to the actual problems in the village, the state allocates special funds, the village raises some of its own funds, and each household collects household water meter fees and house entrance fees. The total investment is about 1 million. Yuan, built the maximum daily water supply of 800 tons of deep water well frequency conversion speed water supply system.

2. Introduction of deepwater well frequency conversion water supply equipment

With the development of frequency control technology and people's requirements for the quality of drinking water continue to increase, frequency conversion water supply equipment has been widely used in urban residential residential secondary pressure water supply system. In recent years, deep-water well submersible pumps have adopted a wide range of frequency-variable speed control technology. Since there is no need to build water towers, the equipment occupies a small area and the construction period is short. In addition, the water quality is free from secondary pollution, and the soft-start soft-stop of the water pump has a low failure rate. The overhaul period of equipment is extended and the service life is improved.

However, in practice, if the frequency conversion and constant pressure water supply system is improperly selected and controlled, it will not only fail to achieve the purpose of energy saving, but will also result in “fee-for-charge”, especially the deep water well frequency conversion system. For this reason, after adopting the variable frequency water supply mode, many villages and towns did not feel that they “powered the use of variable frequency energy” as traditionally advocated, resulting in “suspicion” and “confidence crisis” of the frequency conversion model, and even some local drinking water projects Do not use variable frequency water supply mode. Is the country's promotion of frequency conversion power saving technology really problem? The fundamental reason lies in the low-flow energy consumption problem of variable frequency water supply systems.

3, the frequency of water supply equipment, the small flow of "fee" problem

According to the theory of fluid mechanics, when the water pump speeds, the relationship between the pump motor shaft power P and flow Q, pressure H and speed N is:

Q1/Q2= N1/N2 (1-1)

H1/H2=(N1/N2)2 (1-2)

P1/P2=(N1/N2)3 (1-3)

That is, the flow rate of the pump is proportional to its rotation speed, and the head (pressure) is proportional to the square of its rotation speed, and the shaft power is proportional to the cube of its rotation speed. According to the above relationship, under the condition that other operating conditions are not changed, by lowering the operating speed of the motor, the power consumption is reduced in relation to the speed setting party, and the power saving effect should be very significant. For example, if the operating conditions only require 50% of water, the motor speed can be adjusted to half of the rated speed. At this time, the motor consumes only 12.5% ​​of the rated power, which means that the theoretical energy saving can reach 87.5%.

However, the above conclusions are only theoretical analysis, and the prerequisite for the above relationship is that the total efficiency of the pump is constant. In fact, when the range of speed regulation is large, the total efficiency of the pump η changes (decreases), according to the pump motor shaft power P and flow Relationship between Q and lift (pressure) H:

P=K·H·Q/η (1-4)

Where K is a constant and η is the total efficiency of the pump. Generally, when the water pump speed is less than 70%, the pump efficiency η decreases sharply. Moreover, the actual water supply system is not an open-loop state, but a constant pressure closed-loop control system. The speed adjustment range cannot be large, otherwise it cannot meet the set pressure. The requirements, therefore, the actual frequency conversion constant pressure closed-loop water supply control system small flow even "zero flow" when the pump speed is not very low, the higher the pipeline pressure setting, the higher the "zero flow" frequency. According to experience, the “zero flow” frequency for multi-tier water supply systems is approximately 25 to 30 Hz, and the “zero flow” frequency for high-rise, deep-water well water supply systems is approximately 30 to 35 Hz. If the pump head (unproper selection) has a small amount of margin, "Zero flow" frequency will be greater.

Therefore, when the pump speed is adjusted below 70%, the power P of the motor shaft decreases slowly, and it is not completely reduced in relation to the speed setting party. This has been confirmed by practice. It can be said that the formulas (1-1) to (1-3) are only established when the speed adjustment range is not large, and therefore, when the pump speed adjustment range is large relative to the power frequency water supply mode such as the water tower and the high water tank, the frequency conversion water supply mode There is a problem of "cost of electricity" for small traffic.

With the improvement of people’s living standards, the general living water supply system requires 24 hours of uninterrupted water supply, and the village and town water supply system also has this requirement. For the pure water supply system, the water supply peak is mainly concentrated in about 8 hours in the morning, evening, and evening. The water supply in the rest of the time is small (even if the water supply is large). It is known from the above that the variable speed pump operates at a low flow rate with low efficiency, thus resulting in a large energy waste during the small flow rate of the water supply period. The power of the general submersible pump is relatively large, so the problem of the "low waste" of small flow in deep water well frequency conversion system is more prominent. If the deep-well submersible pump power is 30KW and the low-flow frequency is calculated as 30Hz, about 50~70KWh of electricity will be “wasted” in nearly 6 hours of nighttime every day, and there will be less water consumption in the actual daytime in nearly 8 hours. It is estimated that one year will consume 30000~40000KWh more! Therefore, many villages and towns feel that the use of variable frequency water supply mode is very expensive. Following the frequency conversion water supply system in conjunction with Dongdian Village, the use of a constant-voltage, variable-frequency water supply solution was introduced to solve the energy consumption problem of small-flow water supply.

4. Dongdian Village Deepwater Well Water Supply System Solution

Dongdian village committee attached great importance to the project construction, after many inspections, and several times with the Zhengzhou Kangda Frequency Inverter Technology Co., Ltd. technical personnel in-depth discussion, and finally determined the use of deepwater wells with frequency conversion and supporting small-flow capsule pressure tank Constant voltage regulator water supply program.

Deepwater wells are inspected and drilled by the Xinmi Water Conservancy Bureau. The well depth is 650 meters. The water level of the well is about 65 meters. The dynamic level is 81 meters. The model of the submersible pump is 200QJ40-204/16. The rated water output is 40m3/h. 204 meters, rated power 37KW, motor rated current 79A. Supporting PCS-BP-1R-45KW frequency conversion cabinet, the main device inverter adopts Toshiba original VF-P7-45KW type inverter, in order to ensure reliable water supply, a spare set of Xi'an Xipu STR soft starter is used as standby frequency start. Loop. In order to save power consumption, a small-flow water-saving plan was considered. A NZG1600-0.6MPa bladder pressure tank was installed on the main water supply pipe. The water pressure signal is provided by a shock-resistant remote transmission pressure gauge YZT-1.0MPa and a shock-proof electrical contact pressure gauge YX-1.0MPa installed on the main water supply pipe.

The frequency conversion cabinet control core is a Siemens programmable controller LOGO 230RCo. When it starts running, it first enters the constant pressure water supply mode. When the system water consumption is reduced and the operating frequency is reduced to a small flow frequency fL, the system enters a state of small flow frequency regulation. At the same time, the LOGO automatically calculates the submersible pump operating time Tb and stop pump holding time Tt. If Tb exceeds T0 (set to 6 minutes) or Tt exceeds Te (sets to 3 minutes), the system will return to the submersible pump constant pressure water supply mode . The program flow of the system is shown in Figure 1.

Fig. 1 Flow control of constant pressure and constant pressure water supply for small wells in deep wells

5, the frequency conversion control equipment debugging operation situation

The frequency conversion control equipment is debugged according to the following steps:

1) First check the insulation of the submersible motor. The result should meet the requirements of the manufacturer's instructions.

2) Connect the main incoming line of the frequency conversion cabinet power supply, run the inverter idly, check the inverter display and inverter parameter settings, and set the low flow frequency to 50Hz.

3) Connect the submersible motor cable. Turn off the main valve, turn the two-way knife to the power frequency side, start the pump, and use the clamp meter to check the three-phase running current. Observe whether the three-phase current is balanced, and gradually open the main valve to observe whether the current change and other conditions are normal.

4) After shutdown, check the connection of the pressure gauge sensor and adjust the upper and lower limits of the pressure gauge of the electrical node. Set according to the actual requirements. This project can be set to 0.24MPa~0.50MPa.

5) Turn off the main water outlet valve and operate the variable frequency control equipment with load. Use the up and down keys of the inverter panel to adjust the constant pressure setting value so that the water pressure at the outlet of the mains is constant at 0.3MPa (set according to actual needs). Adjust the main valve properly, observe the pressure changes and response conditions, and if necessary, adjust the internal PID parameters of the inverter (see related instructions).

6) Shut off the water outlet valve, test the system's "zero flow" frequency f0, according to the frequency value set a small flow frequency fL, generally 3 ~ 5Hz higher than the "zero flow" frequency.

7) Open the total water outlet valve slightly to simulate the small-flow water supply condition and observe the condition of entering the low-frequency variable-frequency regulator mode by the constant-voltage conversion mode. Gradually open the total water outlet valve and observe the switching operation of the low-frequency variable frequency mode to return to constant voltage mode.

8) Record relevant operating parameters, programmable settings and frequency converter parameters, and file for archiving. See Table 1 for inverter parameter settings.

The actual debugging process is smooth and meets the design requirements. It is not described in detail here. The equipment has been operating normally for nearly 2 months. The actual operation test shows that according to the current water supply scale, the average daily power consumption is 400KWh without small flow function, and the flow rate is small. The average daily power consumption is 200KWh.

Table 1 main parameters of the inverter setting table

6 Conclusion

In the current new rural construction, governments at all levels are paying great attention to and increasing investment in rural infrastructure construction, and in particular effectively solving the drinking water problems of the peasants. The implementation of the frequency conversion water supply project in Dongdian Village, Chaohua Town, Xinmi City is a new rural area. A bright spot of construction, through the formal operation in the past two months, proved the feasibility of deepwater wells and supporting a small-flow constant-frequency constant-voltage water supply program. The successful operation of the system has also accumulated useful experience for the construction of drinking water for people and livestock in the construction of new rural areas.

Author:

Li Yonggang: A teacher and associate professor at Zhengzhou University, mainly engaged in frequency conversion drive technology research and technical consultation. Feng Jinyong: Head of drinking water project of Dongdian Village, Director of Dongdian Village Water Supply Association. Li Xinyi, Yan Maowei: Engineer and project leader of Zhengzhou Kangda Variable Frequency Drive Technology Co., Ltd.