Discussion on the application of speed regulation

2022-08-20
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Discussion on the application of pump speed regulation technology in sprinkler irrigation engineering

1. Overview

generally, the pressure water distribution in sprinkler irrigation engineering is mostly completed by motor pumps, and the power consumption of pumps accounts for a large proportion of sprinkler irrigation operation costs, so the operating efficiency of pumps has a great impact on the operating costs of sprinkler irrigation

sprinkler irrigation projects with large area usually adopt the working mode of segmented rotation irrigation. The terrain of each area, the distance from the pump room and the number of nozzles are different, so the requirements for water pumps are also different. In order to make all nozzles work normally, the water pump is usually selected according to the working condition that can meet the most unfavorable pressure point. This working point is also the normal working point of the water pump, that is, the rated point. For low places and areas close to the pump, close the valve and throttle to adjust the working pressure of the nozzle. In this way, there will be excess head loss on the valve, which will make the water pump deviate from the high-efficiency working area, resulting in a large waste of energy. For the following information, Jinan new era Gold Testing Instrument Co., Ltd. reminds you of the heavy uneconomical operation for reference only. Therefore, the speed regulation technology is adopted, so that the pump can adjust the output characteristics according to the working conditions of different areas, adapt to the working requirements of the nozzle, and can operate efficiently under various working conditions, so as to achieve the effect of power saving and pressure stabilization

this paper discusses the application of pump speed regulation technology in sprinkler irrigation engineering only from the performance and speed regulation principle of water pump

2. Pump house working condition analysis and pump speed regulation and power saving principle

the pumps in sprinkler irrigation projects are generally vane pumps, and the characteristics of vane pumps are Q ~ h, q ~ n, q ~, respectively η The curve shows the relationship between head, shaft power, efficiency and flow, as shown in Figure 1

Figure 1 working condition diagram of different flow regulation modes of water pump

in addition, the characteristics of the working system of water pump are often represented by Q ~ g curve

where h = HN + HF, HF = CQ2, HN = h net +h spray

c - hydraulic coefficient of pipeline from water pump to nozzle

h net head -- the net head from the water pump to the nozzle

h spray - nozzle working pressure

h = HH + CQ2 is a quadratic curve passing through the HH point. The intersection a of Q ~ h and Q ~ g curves is the normal working point of the pump. Generally, it is the point where the pressure is the most unfavorable, and it is usually the rated point of the pump

when the zone that is not in the normal working point is enabled, 7 When there are obstacles in the lifting process of the pendulum, the water pump will work under the following conditions

in the low-lying area, the net h decreases, the pump lift is higher than the rated working pressure of the nozzle, and the nozzle flow is also greater than the rated flow. The working point of the pump is lower than the normal working point, that is, the lowest point of the Q ~ g curve is to the point a 'of the intersection of Q' ~ g 'and Q ~ H. If the net h decreases significantly, the water pump will work in the non efficient area

when the terrain in the area is low and the number of nozzles is small, the net h decreases and the pump head is higher than the rated working pressure of the nozzle. At the same time, the number of nozzles is small, the flow required in the area is reduced, the system pressure will be higher, and the working pressure of the nozzle will be greater than the rated pressure. In this way, the working flow of the nozzle is much larger than the rated flow, and the working point of the water pump is lower than the normal working point, that is, the lowest point of the Q-G curve is at the intersection of Q ″ - G ″ and Q-H at point a ″

the terrain elevation is the same as that of the normal working point area, but when the number of sprinklers is small, the system pressure will be high due to the reduced flow required in the area, so that the working pressure and flow of the sprinklers are greater than the rated value, and the working point of the water pump is higher than the normal point. That is, the highest point of Q ~ g curve is Q ″ ~ g ", and the intersection with Q ~ h is at point a '

obviously, under the above working conditions, the nozzle works under non rated value, which affects the use effect and even damages the nozzle seriously. Therefore, measures must be taken to make the nozzle work within the allowable pressure range. The following methods are commonly used in engineering

(1) turn down the inlet gate valve of the working area or all relevant units: the outlet gate valve of the small water pump will increase the pipeline resistance coefficient, make the Q ~ g curve rise, intersect with the required flow point of the area on the pump Q ~ h, and waste the excess head on the valve

(2) select several water pump combinations with different lift and flow, and select the operation water pump or water pump combination according to the lift and flow in different areas. This method has no pressure loss of valves, but in projects with complex terrain and uneven nozzle distribution, it will increase the number of water pumps more

(3) speed regulation of water pump: after the speed regulation of water pump, the efficiency is basically unchanged, so the speed can be reduced to make the flow required for the intersection of its characteristic curve and the system characteristic curve be at points B ', B "and B". At this time, its corresponding speed is meeting the required flow, there is no waste of water head, and its work efficiency is also high

although water pump speed regulation is a power-saving measure, its investment is large, and it is not economical and reasonable in any case. In order to prevent blindness in work, power-saving calculation and economic comparison should be carried out before application

3. Selection of speed regulating equipment

(1) the characteristic selection of speed regulating pump should make each design combination of speed regulating pump on the basis of meeting the maximum design water volume, and try to make the speed regulating efficient characteristic curve close to the system characteristic curve of each area

(2) selection of speed regulating equipment: there are many kinds of speed regulating equipment, and their performances are also different. In the speed regulation of sprinkler pump station, the reasonable design should choose frequency conversion or electromagnetic slip clutch. Variable frequency speed regulation technology is relatively new, with high efficiency and good maintenance conditions, but it requires high management technology and large investment. The electromagnetic slip clutch has simple control part, low price and simple maintenance, but the transmission efficiency is low at low speed. It is suitable for high speed, high speed change rate, tight capital and low management technical conditions

(3) pressure regulation during pump room operation: after starting the water pump, start each area respectively, adjust the speed of the water pump to make the outlet pressure of the pump room suitable for the sprinkler work, and this pressure is the corresponding control pressure of each area. In operation, as long as the outlet pressure of the pump room is the corresponding control pressure according to the activated area

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