The use of frequency conversion speed regulation system has obvious energy-saving effect, and this transformation scheme is feasible. As we all know, the power consumption of fans and pumps driven by AC motors accounts for about 50% of the entire industrial electricity consumption. If AC frequency conversion speed regulation technology is used for transformation, it can save 20% 50% of electricity, and the energy saving effect is very considerable. Among them, the electrical transformation of tap water, industrial water and other water supply pump pressure control is a very obvious example. Compared with the traditional constant speed pump water supply system, water tower high-level tank water supply system and air pressure tank water supply system, the frequency conversion speed regulation constant pressure water supply system has high water supply quality, strong flexibility, power consumption, motor braking balance, no water hammer effect , It takes up less area and saves the consumption of raw materials. Recently, our factory has transformed the water supply system of the living area by frequency conversion, speed regulation and constant pressure water supply, and achieved good economic and social benefits.
The composition of the original water supply system The original water supply system consists of 5 motor pumps, gate valves and some necessary pipelines. 5 motors are 45kW. Normally, 3 pumps are turned on. When the water pressure is low, turn on another one, and the other one is used as a backup pump. Previously, the system's on-off pump and pressure regulation were all done by manual operation. Due to the intervention of human factors, the water pressure is often high or low, which has undesirable consequences. When the water pressure is low, people's domestic water is affected; At that time, wasting electrical energy in vain, and even causing serious consequences of water pipe burst. In view of this, we decided to carry out electrical transformation of the system, which not only can solve many of the above problems, but also does not require manual operation, but also extends the mechanical life of the equipment and greatly improves the quality of water supply.
The composition of the variable frequency speed regulation constant pressure water supply system, constant pressure water supply technology The constant pressure water supply technology uses AC frequency conversion speed regulation (VVVF) device, PID adjustment system, pressure sensor. PLC programmable controller, etc., constitute an automatic tracking pipeline water pressure, automatically adjust the number of running pumps, complete the closed-loop control of the water supply system. The structure diagram is shown in Figure 1: 2.2 The control target of the system The control target of the system is the water pressure of the pipeline. The water supply pressure value can be arbitrarily changed. The value and the actual value fed back by the pressure sensor can be adjusted by PID to control the variable frequency speed regulation device Adjust the running state of the pump. PLC can complete the start and stop of the water pump, the monitoring of various parameters and control points in the system, realize the optimal control of the system, and achieve the best power saving effect.
Frequency conversion speed regulation constant pressure water supply system The system is mainly composed of 1 inverter (ATV), 1 programmable controller (PLC), 1 pressure sensor, 1 PID regulator and necessary related electrical appliances (air switch, AC contact Device, control cabinet, instrument, button, indicator light, etc.), 1 water pump. The inverter drives the 45kW motor pump. When the 45kW motor pump has been operated at power frequency, if the water pressure is still lower than the given value, the PLC will start another 45kW motor pump for power frequency operation and another 45kW motor. As a power frequency backup.
Frequency conversion speed regulation constant pressure water supply system, closed-loop control system adjustment principle In this closed-loop control system, when the water consumption changes, that is, the pipeline pressure changes, the pressure inverter monitors the pipeline water pressure and the given water pressure has an error. At this time, the output of the PID regulator will be adjusted according to the change of water pressure. Under the unified management of the PLC, the output frequency and voltage of the inverter are adjusted to increase and decrease the speed of the motor pump, thereby making the pipeline water pressure Consistent with the given water pressure. When the inverter has run to the power frequency, if the water pressure is still lower than the given value, the PLC will issue a pumping instruction according to the PID and the inverter operating status, it will automatically start the 3 pumps to do the power frequency operation, and immediately adjust the frequency of the inverter Make the actual pipeline water pressure and the given water pressure tend to be consistent. When the water consumption decreases, the inverter has run to the lower limit frequency, the actual pipeline water pressure is still higher than the given water pressure, at this time the system automatically stops the operation of the 3 pumps, and adjusts the frequency of the inverter at any time to make the water pressure and the given water pressure be consistent.
The system is provided with two kinds of manual working state and automatic working state. If the transfer switch is turned to the manual position, the manual indicator light will be on. At this time, each motor pump can be manually operated by its own start and stop buttons to determine which pump is operated by frequency. Turn the transfer switch to the automatic position, then the automatic indicator light is on. At this time, press the 1 pump button, the 45kW motor pump is driven by the frequency converter to run with frequency conversion. The system also has stop and emergency stop buttons. In the automatic state, if the inverter needs to stop running, you can press this button and the inverter will gradually decelerate to stop. If an unexpected situation occurs, you can press the emergency stop button to stop the entire system. Using the frequency converter to change the speed of the motor to achieve the method of adjusting the flow rate, its head characteristic curve H) Q (as shown in Figure 4) and power characteristic curve P) Q (as shown in Figure 5) for the change in speed: for a specific pipeline, when When the flow rate is Q1 and the head is required to be H, the operating point A can be found on the pump characteristic curve. It is assumed that the pump speed at this time is the rated speed N to meet the requirements. The corresponding power is P but the flow rate decreases from Q to Q. Because the pipeline requires the head to be B at this time, the operating point B at Q appears, and the corresponding power is; if there is a frequency converter to achieve speed control. It can be seen from Figure 4 that the power saving effect of AB size can be obtained.
In short, the variable frequency speed regulation constant pressure water supply control system has the obvious advantages of high water supply quality, strong flexibility, and low power consumption. This technology is worthy of popularization and application, and will bring considerable economic and social benefits.
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