Water supply companies transport tap water using pumps, completing the energy conversion process from electrical energy to mechanical energy to potential energy. They are major electricity consumers in cities. An investigation of a water company revealed that electricity costs accounted for 24.5%, 17.7%, and 21.4% of the total water production cost in the past three years, respectively, averaging 40.6 million yuan annually. At the same time, water supply companies have significant energy-saving potential. Taking this company as an example, every percentage point reduction in energy consumption can save over 400,000 yuan in costs. Based on years of experience in electrical technology management and energy conservation, this paper summarizes the main energy-saving technologies and methods for water supply companies and analyzes their energy-saving effects to discuss energy conservation and economic operation management in water supply companies. 1. Transformer Energy Saving Transformer energy saving refers to the continuous production of transformers with lower losses through equipment upgrades, achieved by improving transformer design technology and manufacturing processes. Specifically, this is reflected in the reduction of transformer no-load losses and load losses, i.e., increased efficiency. The transformer efficiency η is the percentage of the output active power to the input active power, that is: η=βS2Ncosψ2／βS2Ncosψ2+P0+β2Pf×100% (1) Where: S2N——rated capacity of the secondary side; cosψ2——power factor of the secondary side, generally taken as 0.8; β——load factor, β=I2/I2N; P0——no-load loss; Pf——load loss. As can be seen from formula (1), when the transformer is running under load, the no-load loss is independent of β and is a constant value, while the load loss is proportional to β2. When β=√P0/Pf, the value of η is the largest, which is also the most economical operating point. Taking three types of 800kVA transformers commonly used in a water plant as examples, the energy-saving effect is compared, and the η～β curves of the three transformers are drawn, as shown in Figure 1. Transformer loss reduction is the percentage reduction in losses when a new transformer replaces an old transformer under the same load, i.e.: △η=[（βS2Ncosψ2/η2-βS2Ncosψ2/η1）／（βS2Ncosψ2/η2）>×100% =（1-η2/η1）×100% （2） Where η1——new transformer efficiency; η2——old transformer efficiency. If a new transformer S9 is used to replace old transformers S7 and SL7, and the annual average load rate β=0.5 is taken, then according to formulas (1) and (2), the efficiency and loss reduction rate of each transformer are shown in Table 1. Table 1. Transformer Efficiency and Energy Saving Rate. As shown in Figure 1 and Table 1, S7 and S9 transformers have better energy-saving effects compared to SL7 transformers, and the higher the load rate, the greater the energy saving rate. However, the losses between S9 and S7 transformers are not significantly different; in fact, when β>0.6, the S9 transformer has slightly higher losses than the S7 transformer. Based on the above analysis, transformer energy saving is achieved by using transformers with lower losses. 2. Energy Saving of High-Voltage Motors Currently, most urban power distribution networks in China are 10kV and 6kV. In the design, selection, or technical renovation of large and medium-sized urban water plants, high-voltage motors have been widely and rapidly applied due to their significant advantages in technical and economic analysis. Their advantages are as follows: ① Reduced investment in equipping 10kV and 6kV to 0.4kV level transformers and their low-voltage distribution systems (due to the use of low-voltage motors). ② Reduced need for a larger number of pumps due to the smaller capacity of low-voltage motors. ③ Reduced land and building occupation and corresponding investment required for transformers, low-voltage distribution systems, and more pumps as mentioned in points ① and ②. ④ Reduces power supply links, improves electrical safety and reliability, and reduces maintenance workload. In terms of energy saving, it also has the following effects: ① Avoids transformer losses (e.g., when β=0.5, the S7-800/10 loss reaches 1%). ② Reduces increased line losses caused by using low-voltage motors. ③ Large and medium-sized high-voltage motors have high efficiency; low-capacity motors have comparable efficiency to low-voltage motors of the same capacity, while large and medium-capacity motors have even higher efficiency, especially as the efficiency increases, breaking through the dual limits of low-voltage motor capacity and efficiency. For example, using a high-voltage motor Y6303-61400kW has an efficiency of 96.5%, while to achieve the same capacity, five JS2-400M3-6280kW low-voltage motors are needed, each with an efficiency of only 93.4%, a difference of 3.1%. ④ Reduces efficiency drops caused by multiple low-voltage motors operating in parallel. 3. Reactive Power Compensation Energy Saving When current passes through a line or transformer, it will generate line resistance loss or transformer load loss, and its active power loss is: △P=3·P2R/U2cos2ψ (3) Where P——active power, kW; U——rated voltage, kV; R——total resistance of line or transformer, Ω; cosψ——power factor From formula (3), it can be seen that when the active power of the load is constant, △P is inversely proportional to cos2ψ. If the power factor increases from cosψ1 to cosψ2, the percentage decrease in active power loss is: (△P%)=[(3·P2R/U2cos2ψ1-3·P2R/U2cos2ψ2)／3·P2R/U2cos2ψ1>×100% =（1-cos2ψ1/cos2ψ2）×100% (4) If the power factor is compensated from 0.8 to 0.9, according to formula (4), (△P%) = 21%, that is, the line or transformer loss decreases by 21%. From the above analysis, it can be seen that reactive power compensation reduces the loss in the line or transformer by improving the power factor and reducing the operating current, thereby achieving energy saving. 4. Water pump energy saving The load of water supply enterprises is mainly mechanical pumps, and the water pumps have lower operating efficiency. Water pump energy saving is the main way for water plants to save energy, which is specifically manifested in two aspects. 4.1 Water pump modification and upgrading energy saving In recent years, urban development and pipeline network transformation have been rapid. The pipeline resistance characteristic curve has been continuously shifted downward and the water supply has been continuously increasing. However, the water plant pumps cannot be modified in sync, which has caused the working head of many water plant pumps to decrease and move them away from the high-efficiency zone, greatly reducing the pump efficiency and causing a lot of electricity waste. By modifying and upgrading the water pumps, the pumps can be made to operate in the high-efficiency zone, which can greatly improve the pump efficiency and thus achieve the purpose of energy saving. Effective power of water pump N = HQ/102 (kW) (5) Power of water pump shaft P_shaft = HQ/102η_pump (kW) (6) Where H is the water pump head, m; Q is the water pump flow rate, L/s; η_pump is the water pump efficiency, %. The following is an example of a pump in a water plant to calculate and analyze the energy saving effect. Figure 2 shows the Q1~H1, Q1~η1 curves and Q2~H2, Q2~η2 curves of the original Type I pump and the newly modified Type II pump. The rated head of the original Type I pump is 55m, the head in the high-efficiency zone is 59m~47.5m, and the actual average head in operation is 42m, which is far from the high-efficiency zone. At this point, from Figure 2, we can obtain that the flow rate Q1 = 360 L/s and the efficiency η1 = 72%. Substituting these values ​​into formulas (5) and (6), we can calculate that the effective power N1 = 148.2 kW and the shaft power P1 = 205.9 kW. If a new type II pump is used, with the same flow rate Q2 = Q1 = 360 L/s, from Figure 2, we can obtain that the head H2 = 41 m and the efficiency η2 = 82%. Substituting these values ​​into formulas (5) and (6), we can calculate that the effective power N2 = 144.7 kW and the shaft power P2 = 176.5 kW. If we approximate the effective power of the pumps using a linear relationship, the type II pump saves energy compared to the type I pump (shaft power): △P_shaft = P1 - N1/N2·P2 = 25.1 (kW). Energy saving effect: (△P_shaft%) = △P_shaft/P1 × 100% = 12.2%. In other words, if a Type I pump is upgraded to a Type II pump, the actual operating condition of the pump can be operated in the high-efficiency zone, and energy consumption can be reduced by 12.2%. From the above analysis, it can be seen that the energy saving of pump upgrade is actually achieved by improving the efficiency of the pump operating point. The further the actual operating condition is from the high-efficiency zone, the greater the energy saving effect after the pump upgrade. 4.2 Pump speed regulation for energy saving The selection of pumps in water plants is generally determined according to the highest daily and hourly water demand in the city. Therefore, the pumps are in low-load operation for most of the time, and it is necessary to reduce the speed to change the operating condition. When the pump speed n changes, the performance parameters of the pump change. The formula is as follows: [align=center]Q'/Q=n'/n (7) H'/H=(n'/n)2 (8) P'/P=(n'/n)3 (9)[/align] Where Q (Q'), H (H'), and P (P') represent the flow rate, head, and power of the pump at speed n (n'), respectively. Using the Q-H(n) curve (see Figure 3), we can draw a set of Q-H curves and a set of equivalent lines at various speeds. Taking any point A (Q,H), when the speed n decreases to n', we can calculate point A' (Q',H') according to formulas (7) and (8). Similarly, taking points B, C, and D on the Q-H(n) curve in sequence, when n decreases to n', we can calculate the corresponding points B', C', and D'. Connecting these points A', B', C', and D' gives us the Q'-H'(n') curve. Therefore, as the speed decreases, we can obtain a set of downward-shifting Q-H curves. Connecting the corresponding A, A', B, B', ... on this set of curves gives us a set of equivalent lines AA', BB', CC', DD', ... Water pump speed regulation in water plants is generally carried out using constant pressure. The following is an example of a water pump (see Figure 3) to analyze the energy-saving effect of speed regulation. In Figure 3, point A is the design operating point, at which time the speed is the rated speed, the flow rate QA=550L/s, the head HA=35m, and the efficiency ηa=88%. Substituting into formula (6), the shaft power PA=214kW is calculated. If the water volume is reduced to 80%, the pump operating point moves to point E, that is, QE=440L/s. From Figure 3, the head HE=39m and the efficiency ηe=82%. Substituting into formula (6), the shaft power PE=205kW is calculated. If constant pressure speed regulation is adopted, when the flow rate is 440L/s, the head remains unchanged, and the operating point moves to point F (the horizontal line FA is the constant pressure line). Flow rate QF=QE=440L/s, head HF=HA=35m, the equivalent line passing through point F intersects Q～H at point G, the corresponding efficiency ηg=84%, substituting into formula (6) to calculate, shaft power PF=179kW, energy saving △Pshaft=PE-PF=26kW, energy saving effect: (△Pshaft%)＝△Pshaft/PE×100%＝12.6% Similarly, the energy saving effect at each flow rate value can be calculated, see Table 2. From the above calculation and analysis, it can be seen that constant pressure speed regulation achieves energy saving through two factors: first, improving pump efficiency (taking 80% flow rate adjustment as an example, ηg>ηe), and second, reducing the pressure loss caused by valve throttling (HE-HF). It can be seen that constant pressure speed regulation has a dual energy saving effect. From Table 2, it can also be concluded that for a certain pump, the smaller the flow rate, the greater the energy saving effect of constant pressure speed regulation. 5. Economical and Energy-Saving Water Supply Operation Based on the adjustment of the urban water supply network, several basic pressure measurement points and pressure standard values ​​should be determined. Ensuring that the pressure values ​​at these measurement points are not less than the standard values ​​will meet the city's water supply needs. On this basis, the control range of the outlet water pressure of each urban water treatment plant should be formulated and optimized to correspond to the city's water demand. Each water plant should operate with the basic pressure measurement point standard values ​​as the control target, ensuring urban water supply while reducing unnecessary pressure waste. This will minimize the water consumption per 1000m³ of the entire water company, thereby achieving economical water supply operation. The energy-saving effect of this method can be analyzed from the unit power consumption to head curve of a single pump. Taking the Q-H curve of the pump in Figure 3 as an example, according to the pump flow rate Q, the corresponding head H and efficiency η can be found from Figure 3. Substitute them into formula (6) to obtain the shaft power P_shaft, and then calculate the unit power consumption F = P_shaft / [Q> (here, the unit power consumption only includes the power consumption of the pump in the outlet pump room. The unit of "[Q>" in the unit power consumption calculation is 1000m3/h). As shown in Table 3, the percentage decrease in unit power consumption for each unit head reduction is: △Fi+1 = [Fi-Fi+1/Hi-Hi+1／Fi>×100%] In the formula, Fi represents the unit power consumption corresponding to the head Hi. Plotting the data in the table as F~H and ΔF~H curves, Figure 4 shows that the unit power consumption decreases as the head decreases. This means that if the pump's operating head is reduced, the unit power consumption per 1000m³ of water also decreases. Table 3 shows that at the rated head (H=35m), a 1m decrease in head reduces unit power consumption by 3.3%, with higher heads resulting in greater energy savings. This can also be verified through speed regulation energy saving. In Figure 3, if the constant pressure speed regulation HF=35m is changed to HH=30m when the flow rate Q=440L/s, the pressure loss HF-HH=5m can be reduced, and the pump efficiency ηg=0.84 can be increased from ηi=0.86, achieving further energy savings. Similarly, reducing the operating head (or pressure) of the water plant or the entire company's outflow water can reduce the unit power consumption per 1000m³ of water for the entire water plant or company, achieving comprehensive energy savings. 6. Conclusion Energy conservation (mainly electricity conservation) in water supply enterprises is a comprehensive issue that requires integrated approaches. Transformer energy conservation, high-voltage motor energy conservation, and reactive power compensation energy conservation can be considered in conjunction with water supply development plans or enterprise equipment upgrade plans during water plant design or equipment upgrades. Those with significant energy-saving effects can also be considered separately. Furthermore, energy conservation can be achieved through economical equipment operation, especially in transformer energy conservation, where economical operation often yields better results than replacement. Pump modification and replacement have significant energy-saving potential, good energy-saving effects, and fast investment recovery; replacement can be implemented for pumps whose operating conditions deviate from the high-efficiency zone based on calculations. Pump speed regulation has excellent energy-saving effects, but the initial investment is large; implementation should be determined after technical and economic analysis for pumps with large water volume fluctuations or significantly insufficient water supply. Energy conservation through economical water supply operation is achieved through management-based energy conservation, with a holistic effect, but this requires network adjustment and further research.