Abstract: Based on the characteristics of residential community environment and equipment operation, this article focuses on analyzing the forms of power consumption of lines and main equipment in the power supply and distribution system, and discusses the reduction of line losses and the selection, economic operation and management of equipment such as transformers and motors. Several energy-saving technical measures and specific methods for reducing power consumption in residential communities are proposed, which are also of reference value to other property management companies. Keywords: Line loss, operating voltage, transformer, motor, frequency conversion speed regulation, reactive power compensation, lighting, energy-saving measures 1 Introduction With the rapid development of China's economic construction, the overall situation of real estate investment, development and sales is getting better and better, and new residential communities are springing up like mushrooms after rain. However, the energy utilization rate of residential communities is relatively low. Because electricity accounts for a considerable proportion of property management costs, how to save and effectively use precious electricity depends on the management level of the property management company. It is necessary to achieve the enjoyment brought by electricity consumption without excessive waste. In recent years, the heating period in residential communities has been longer than in the past, resulting in an increase in energy consumption of boiler heating power systems. The transformation of community street lighting from simply being bright to truly "beautiful" also involves energy conservation and consumption reduction. Therefore, energy conservation and consumption reduction in the power supply and distribution system of residential communities are even more important. 2. Reducing Power Supply and Distribution Line Losses Line loss is a crucial indicator of the economic operation of power supply and distribution lines. The power supply lines in residential communities are generally 10kV or 35kV, 380V/220V systems. Especially in older planned residential communities, overhead or cable power supply is used. With the increase in electrical load, the power supply and distribution lines have not undergone technical upgrades, resulting in uneconomical operation. A large amount of electrical energy is lost in the power supply and distribution lines, leading to a decline in power supply voltage quality. To solve the above problems, technical upgrades should be carried out using economic current density to determine conductor and cable cross-sections and reduce line loss. The economic current density stipulated in China is shown in Table 1. Years of design and operation experience show that for boiler heating power systems, with stable electrical loads, even in cold winters, the maximum electrical load remains within the original design calculation range when the standby boiler circulating pump is put into operation. In addition, the ambient temperature in winter is good for heat dissipation of conductors and cables, so selecting conductor and cable cross-sections according to the parameters in Table 1 is feasible. Table 1 shows the economic current density (A/MM2) of conductors and cables specified in my country. However, selecting conductors and cables for power supply to residential buildings based solely on the parameters in Table 1 has a relatively small margin. Factors such as the voltage level of the power supply line, initial investment, installation and construction, power factor of the load, and minimizing the total loss cost over the entire economic life of the cable should also be fully considered. With the improvement of people's living standards, household appliances are increasingly entering homes, leading to rapid growth in residential electricity load, especially during the summer when residential electricity load peaks. When selecting the current density of conductors and cables for power supply to residential buildings based on the parameters in Table 1, a margin of 1.5 times should be allowed (see the values ​​in parentheses in Table 1). According to statistical analysis of residential electricity consumption in Beijing from 1992 to 2000, the average annual growth rate of residential electricity consumption was 16%. This growth rate is far higher than that of other industries, indicating significant room for further growth. Currently, residential electricity consumption accounts for 12% of total social electricity consumption (Beijing area). The proportion of residential electricity consumption in the central and western regions is far lower than this, indicating that there is enormous potential for growth in residential electricity consumption. Based on the experience of developed countries, residential electricity consumption typically stabilizes at around 30% of total social electricity consumption, taking into account the important factor of an average annual growth rate of approximately 16% for residential electricity consumption. To reduce losses in power supply and distribution lines, additional parallel conductors and cables, or other technical means, can be used to reduce losses. For example, consider a residential building of 3200 m² with 48 households. Designed in 1988, it was calculated at 10W/m², with a calculated load Pjs = 19.2kW and a calculated current Ijs = Pjs/×Ue×cosφ = 19.2/×0.38×0.9 = 32A. In the summer of 1999, during the peak electricity load period, the average daily maximum load Pav.max = 48kW, and the average daily maximum load current Iav.max = 81A. Since the annual maximum load utilization hours were less than 3000 hours, an economical current density Jjil = 3A/mm.2 was chosen, and the conductor cross-section Sjil = Ijs/Jjil = 32/3 = 10.6mm². The selected overhead line was a neoprene rubber conductor BXF-3×16 + 1×6mm². During the power supply and distribution technology upgrade in 1999, an economical current density of 2A/mm² was selected, and the conductor cross-section Sji2 = Iav.max/Jji2 = 81/2 = 40.5mm². To allow for future growth in residential electricity load, a neoprene rubber conductor BXF-3×70 + 1×25mm² was chosen to replace the original overhead power supply line. Source: http://www.tede.cn The cable length is 102m. Neglecting the effect of inductive reactance, the resistances R16 = 0.136Ω and R70 = 0.032Ω. The active power loss ΔP16 = 3 × I²av.max × R16 × 10⁻³ = 3 × 8¹² × 0.136 × 10⁻³ = 2.676kW, ΔP70 = 3 × I²av.max × R70 × 10⁻³ = 3 × 8¹² × 0.032 × 10⁻³ = 0.629kW. The difference in active power loss between the two conductors with different cross-sections is ΔP = ΔP16 - ΔP70 = 2.676 - 0.629 = 2.047kW. During the peak load season of 100 days, with an average daily electricity consumption of 20 hours, totaling 2000 hours, the energy saving ΔW = ΔP × t = 2.047 × 2000 = 4094 (kWh). The calculations show that under the same electrical load conditions, the power loss varies greatly depending on the cross-section of the conductor or cable. In this example, replacing the original power supply trunk line with a 70mm² cross-section can save 4094 kWh of electricity in just one peak load season, equivalent to 1068 yuan. Using cables selected based on economic current density, the energy savings can be recovered in just 3 years. The value of electricity savings over the remaining lifespan of the cable is even easier to calculate – this is the profit for the property management company! A residential community has dozens to hundreds of power supply trunk lines, and the above phenomenon exists to varying degrees. Currently, the property management company I work for manages six residential communities, and a rough calculation shows that after all renovations, 160,000 kWh of electricity can be saved annually, equivalent to 63,000 yuan. The aforementioned active power loss occurs on the power supply trunk line between the user's electricity meter and the low-voltage distribution cabinet in the substation. However, in some companies, the power supply department only checks the high-voltage or low-voltage meters in the substation, leaving the property management company to bear the active power loss on the power supply trunk line. The above calculations cover active power losses, but also include the saved reactive power losses. The significant benefits of reducing reactive power losses improve the power factor of the residential power distribution network, reduce load current, and thus improve voltage quality for residents. These are all economic benefits! The relationship between active power loss and cross-section of cables is shown in Figure 1. 3. Appropriately Increasing the Operating Voltage and Power Factor of Power Distribution Lines Some earlier-planned residential power distribution lines are still operating under heavy load conditions, resulting in poor voltage quality at user terminals. Single-phase voltage drops to 170V, affecting the starting of fluorescent lamps and causing incandescent lamps to emit dim light. Starting boiler induced draft and blower motors is also very difficult, and property owners lack sufficient funds for technical upgrades. In this situation, by rationally selecting the transformer tap changer and appropriately increasing the operating voltage of the distribution lines, line losses can be significantly reduced. Under load conditions, it would be even more convenient to use on-load tap-changing transformers for automatic graded voltage regulation. Appropriately increasing the operating voltage can reduce line power losses. See Table 2. Improving the power factor of the power supply and distribution system is also an effective measure to reduce line loss. After the power factor is improved, the load current of the power supply trunk line decreases, and the line loss can be effectively reduced. The specific methods are: (1) Install intelligent reactive power factor compensation devices at the entrance of the main distribution box of the residential building. These devices can automatically put on and cut off capacitors according to the size of the power load and the power factor. (2) Use end compensation capacitors to improve the power factor next to the motors of the boiler heating power system with a power output of 22kW or more. End compensation can directly provide reactive power to the motor, reducing the reactive power loss on the power supply line. This is a relatively reasonable, low-investment, and quick-effect energy-saving measure. The voltage and current vector diagram of the installation location of the phase-shifting capacitor in the power supply and distribution system, low-voltage group compensation and decentralized compensation. See Figure 2. 4 Reasonable selection and economical operation of power transformer capacity In the design of the power supply and distribution system of residential areas, the transformer capacity is generally selected based on the calculated load. In actual operation, the operating load is not equal to the calculated load, but varies with the seasons, and even the load changes greatly within 24 hours. The load curve of the residential community is shown in Figure 3: As shown in the load curve in Figure 3, the load rate varies from 42% to 93% throughout the year. In the design and operation of the power supply and distribution system of the community, the reasonable selection of transformer capacity should be given great importance. When the building area of ​​the residential community is greater than 50,000 m2, two power transformers of 560kVA or more should be selected for parallel operation in the power supply and distribution system design to give full play to the advantages of parallel operation of transformers. Due to seasonal reasons, the operating load of the residential community changes. How to determine whether to operate one or two transformers in parallel? There are three methods: (1) When the load rate of the transformer is less than 0.6, it is more economical to cut off one transformer for operation; (2) When the load rate of the transformer is greater than 0.8, it is more economical to put the standby transformer into parallel operation; (3) Determine the value of the critical load by the critical load formula, and find the relevant parameters in the manual or product technical data to calculate the critical load Sj. When the operating load of the transformer is less than the critical load Sj, it is more economical to operate one transformer. Otherwise, it is more economical to operate in parallel. In the formula: Se——rated capacity (kVA) ΔPo——no-load loss (kW) ΔPd——short-circuit loss (kW) Qo——no-load reactive power loss (kVar) Qe——rated load reactive power loss (kVar) Kq——reactive power economic equivalent coefficient (kWh/kVarh) The reactive power economic equivalent parameter Kq in the formula ranges from 0.1 to 0.15. In summary, rationally arranging the number of transformers put into operation is a good measure to reduce active power loss and improve energy saving efficiency. In addition, special attention should be paid to the parallel operation conditions of transformers: (1) The rated voltage and the turns ratio are equal, otherwise eddy currents are easily generated, which leads to increased losses and higher temperatures; (2) The connection groups are the same. If the connection groups are different, the circulating current will increase, and its value is 5 times the rated current; (3) The impedance voltage Ud% is equal, so as to make equal use of the power supply capacity during parallel operation. 5. Electric Motor Saving Residential communities typically have a large number of motors, including hot water circulation pumps, induced draft fans, blower motors, grate drive motors, electric hoist motors, and conveyor belt motors in boiler heating systems, as well as elevator traction motors and high-pressure water pump motors. Special attention should be paid to saving energy in small and medium-sized motors. These motors are mostly fan and pump loads and should utilize variable frequency drive (VFD) technology. The property management company I work for currently manages six residential communities with a total installed motor capacity of 1200kW. The plan is to gradually upgrade these motors over 3-5 years, replacing them with VFD and high-efficiency motors. Currently, 335kW of motors have been equipped with VFDs, saving up to 33kWh per hour during operation, resulting in 80,000kWh savings per heating season, equivalent to 46,000 yuan. The investment can be recovered in just three heating seasons. Other energy-saving methods include selecting appropriate motor capacity for economical operation, reducing light-load and no-load operation time, and ensuring the motor's power supply voltage remains basically normal. 6. Energy Saving in Lighting Fixtures ** Select High-Efficiency Light Sources and Energy-Saving Fixtures.** Previously, most residential communities used incandescent or mercury lamps for streetlights and public areas. These should be replaced with compact fluorescent lamps, which can save approximately 50% of electricity. Old-style lamps in office and commercial buildings should be replaced with energy-saving fluorescent lamps with electronic ballasts and small-diameter tubes, saving over 15% of electricity, extending tube life by about 60%, increasing luminous efficacy to 50%, and eliminating flicker and noise. The investment can be recovered within two years of using energy-saving fluorescent lamps. **Optimize Lighting Design and Management.** In residential community lighting design, different illuminance standards should be applied to different areas such as roads, public areas, offices, and commercial buildings, in addition to residential lighting. Reasonable light distribution and energy-saving control methods should be adopted to maximize the use of natural light beams and reduce artificial lighting, allowing for flexible adjustment of illuminance levels based on time, location, weather changes, and work/life needs. The adoption of an intelligent lighting management system not only saves electricity but also transforms the community from bright to beautiful. This enhanced aesthetic appeal has a positive psychological and lifestyle impact on residents. 7 Conclusion Electricity saving in residential communities is a crucial component of property management. It requires minimal investment, yields quick results, has a short cycle, and offers high returns. Implementation can significantly reduce the operating costs of property management companies. In short, the potential for electricity saving in residential communities is enormous. If the more than 20,000 property management companies nationwide adopted just one or two electricity-saving measures, the resulting energy savings and economic benefits would be immense! Please visit: Power Transmission and Distribution Equipment Network for more information. References: 1. Yu Zhiyong. Analysis and Forecast of Residential Electricity Market in Beijing. Electrical Age Magazine, 2000; 9. 2. Building Electrical Design Manual Compilation Group. Building Electrical Design Manual, 1994.