1. Introduction For power supply departments, energy loss management can be considered a systematic project. It involves not only various aspects of planning, design, operation, and maintenance, but also close connections with lines, substations, and power consumers. The magnitude of energy loss rate is related to various factors such as network structure, system operation mode, load size, maintenance quality, power consumption management, meter management, meter reading cycle, and reactive power compensation. Within our power supply area, there are 42 transformers, nearly 150,000 meters of high and low voltage transmission lines, and over 500 streetlights, with an annual power transfer volume of approximately 30 million kWh. Moreover, with the expansion of the region, the capacity of power distribution facilities is expected to increase. For the increasingly large power supply system, certain technical measures are needed to control energy loss. If we start from the power consumption organization design, under the premise of meeting safe use and actual investment benefits, through reasonable material selection, utilizing energy-saving technologies, and strengthening operation management, we can effectively control unnecessary energy loss during operation and grid construction. Therefore, the technical measures we consider to take mainly include the following three aspects: 1) Reasonable operation mode of transformers. 2) Improve power factor and reduce line loss. 3) Install energy-saving devices on streetlights along the same route. 2. Energy Saving of Transformers To transmit electrical energy from power plants to users, the power system must pass through at least 4 to 5 transformers to deliver the energy to low-voltage electrical equipment (380/220V). Although transformers themselves are highly efficient, their large number and capacity result in significant total losses. It is estimated that the total losses of transformers in China account for about 10% of the total power generation. Reducing losses by 1% can save tens of billions of kWh of electricity annually. Therefore, reducing transformer losses is imperative. Data analysis recorded by the automated monitoring system reveals that the peak load in summer in our region is more than three times higher than the peak load in winter, with a peak load to off-peak load ratio of 11:1. The load varies greatly with seasonality. Furthermore, most residential buildings in the region are first- or second-level loads. According to the principles for transformer configuration in substations (distribution stations) in the "Compilation and Application Guidelines of Electrical Regulations in Beijing," our substations typically use two or more transformers. Based on the existing number, capacity, and model parameters of transformers in the substation, we have taken the following measures to save power losses by adjusting the transformer operation mode: 1) Transformer model selection: Before the grid transformation, most of the transformers in operation were products from the 1960s and 70s. These products had poor materials and outdated structures, resulting in high energy consumption. Therefore, in the grid transformation, the selection of transformers first eliminated S7 or S9 model oil transformers, and most of them were replaced with SCB9 model type 10 transformers. 2) Economic operation of transformers: There are three operating modes for two transformers: transformer A operating alone, transformer B operating alone, and transformers A and B operating simultaneously. In actual use, from the perspective of energy saving, the operating mode with the lowest loss is prioritized. Through detailed calculations, the switching point for economical operation of transformers is found, and appropriate transformers are put into operation according to seasonal changes. (1) Determination of operating mode, using the comprehensive power loss calculation method For example, a substation has two SCB9/6.3 kV dry-type transformers, and the parameter values ​​are shown in the attached table. [ALIGN=CENTER] Attachment [/ALIGN] 1) Excitation power (reactive power) on the power supply side when the transformer is unloaded Leakage magnetic power (reactive power) consumed by the transformer under rated load 2) Comprehensive power loss of the transformer under no-load (kW) Since our area is a user of transformers of level three or above, KQ=0.08～0.15, take 0.1. Comprehensive power loss of the transformer under rated load (kW) 3) Comprehensive power critical load power of transformer A and transformer B 4) Critical power between transformer A and transformers A and B 5) Critical power between transformer B and transformers A and B The data obtained from the above calculations are used to determine when 0 At 533 kVA, it is more economical to put two transformers into operation. However, in actual operation, the summer load within the power supply range of these two transformers often exceeds 533 kVA, so two transformers are put into operation, and one is taken out when the winter load decreases, with one transformer operating alone. Other substations can follow the above method to determine the operation mode of the transformer, thereby improving the utilization efficiency of the transformer and reducing losses. (2) Energy-saving effect of the economical operation mode of transformers Taking the two transformers of a certain substation mentioned above as an example, assuming that the peak summer load is 800 kW, compare the transformer losses when one transformer is operating with the full load and when two transformers are operating with the load separately. When 800 kW is driven by one transformer, I = 0.8 × 91.65 = 73.32 A. When the full load is driven by two transformers, according to the load distribution of transformers in parallel operation, it is proportional to the rated capacity and inversely proportional to the short-circuit voltage. It can be seen that when the load is distributed as follows: when the loss of transformer A is 355KW, I=355/800×73.32=32.53A. When the loss of transformer B is 445KW, I=445/1000×91.65=40.78A. The total loss of transformer copper is 1.4+1.7=3.1 kW. The loss is reduced by 5.6-3.1=2.5 kW. The annual electricity saving is 2.5x30x5x24=9000 kW.h. There are 13 power stations in the residential area. The method of changing the operation mode can be used to save electricity. Therefore, the annual electricity saving in the entire power supply range is roughly estimated to be 13x9000=11.7x104 kW.h. 3. Improve the power factor (1) Methods to improve the power factor According to the relevant provisions in the "Electricity Business Rules": reactive power should be balanced locally. Users should design and install reactive power compensation devices according to relevant standards, based on improving the natural power factor of electricity consumption. Within our power supply area, we use centralized reactive power compensation devices installed on the secondary side of transformers to improve the power factor and meet the specified requirements. 1) Compensating for reactive power can increase the proportional constant of active power in the power grid. This reduces the design capacity of power generation and supply equipment, thus reducing investment. For example, when the power factor COSφ=0.8 increases to COSφ=0.95, installing a 1kvar capacitor can save 0.52 kW of equipment capacity; conversely, it increases by 0.52 kW. For existing equipment, this is equivalent to increasing the capacity of power generation and supply equipment. Therefore, for new and renovated projects, reactive power compensation should be fully considered to reduce design capacity and thus reduce investment. 2) Reducing line loss is derived from the formula △P％=[1-（COSφ[SUB]1[/SUB]/cosφ[SUB]2[/SUB]）[SUP]2[/SUP]]x100%. Where COSφ[SUB]2[/SUB] is the power factor after compensation, and COSφ[SUB]1[/SUB] is the power factor before compensation, then COSφ[SUB]2[/SUB]>cosφ[SUB]1[/SUB], so improving the power factor also reduces the line loss rate. Reducing design capacity, reducing investment, increasing the proportion of active power transmitted in the power grid, and reducing line losses all directly determine and affect the economic benefits of power supply companies. Therefore, the power factor is an important indicator for evaluating economic benefits, and planning and implementing reactive power compensation is imperative. There are two ways to improve the power factor: one is to improve the natural power factor of the electrical equipment, that is, the power factor without any compensation device; the other is to improve the total power factor through artificial compensation. The following method is used to improve the natural power factor. 1) Choose the appropriate motor model and specifications. First, select a motor with a high power factor while meeting usage requirements. Second, ensure the selected motor maintains a high load rate and avoids prolonged light-load operation. Third, minimize the motor's no-load running time; for equipment with repetitive short-time operation, consider using a no-load cut-off device. 2) Improving the power factor through artificial compensation is a common method. The calculation method is as follows: For artificial compensation to improve the power factor, the reactive power capacity to be compensated can be calculated. For example, a power station has a calculated load of 800 kW and an average power factor of 0.85. If it is increased to 0.95, the reactive power capacity to be compensated is TanA=tan(arccos0.85)=0.62 TanB=tan(arccos0.95)=0.33 Compensation capacity Q[sub]cc[/sub]=0.75x800x(0.62-0.33)=174kvar (2) Energy saving effect after power factor improvement The total power loss in the area is 3000xO.ll=3.3 million kWh; the power loss includes the losses caused by various links: lines, transformers, metering devices, and metering asynchrony caused by manual meter reading, etc. After the grid renovation, D&D compensation devices were added to substations and box transformers, and the power factor was increased from 0.76 to more than 0.93, and some were increased to 0.96 or higher. Before the renovation, this part of the power loss accounted for about 40%, that is, about 1.3 million kWh. For ease of calculation, the power factor is uniformly increased from 0.8 to 0.93. Since I=P/U×xcosφ, P (active load) and U remain unchanged, i only changes with cosφ: when the power factor is φ1, the loss is P1; when the power factor is φ2, the loss is P2. P₂/P₁ = (cosφ₁/cosφ₂)² The saved electricity is P₁-P₂ = [1-(cosφ₁/cosφ₂)²]P₁ The annual electricity saving in the residential area is 130 x [1-(0.8/0.93)²] = 338,000 kWh . 4. Installing energy-saving devices in the street lighting system In our power supply area, there are 13 street lighting circuits with approximately 500 sets of lights of various types, consuming approximately 700,000 kWh annually. Market research indicates that a certain energy-saving product, applied to street lighting systems, can achieve annual energy savings of up to 20%. The system operates as follows: The device starts at full voltage of 220V (t0-t1), then gradually reaches the set voltage of 210V within a few minutes (t1-t2), and then runs stably (t2-t3). After 4 hours (midnight), it gradually (t3-t4) reduces to the energy-saving voltage of 200V, continuing operation until dawn. (See Figure 1.) After the street light energy-saving system was fully operational, we conducted data tracking and monitoring of the street lights in our jurisdiction for two months (June 12th to August 14th). The system was put into operation and taken out of service at intervals, i.e., put into operation in the first week, taken out in the second week, and so on. The operational data was recorded accordingly. The monitoring results for the electricity consumption (kWh) of the Dongli street lights are shown in Figure 2. [ALIGN=CENTER] Figure 2 Comparison of electricity consumption during the energy-saving system's operation (June 12th to August 14th) [/ALIGN] The monitoring current and voltage data for the Xili street lights are shown in Figure 3. [ALIGN=CENTER] Figure 3 Comparison of voltage and current before and after the energy-saving system's operation [/ALIGN] Through analysis and summary of the two months of monitoring data, the following information can be obtained: 1) The electricity consumption during the 28 days the energy-saving system was taken out of operation (June 12th to August 14th) was 1880 kWh. 2) The electricity consumption during the 28 days the energy-saving system was put into operation (June 12th to August 14th) was 1520 kWh. 3) When the energy-saving system was deactivated, the average operating voltage was 223 V and the current was 28 A. In the four hours prior to activation, the average voltage was 210 V and the current was 20.7 A. The energy-saving rate was (1880 kW.h - 1520 kW.h) / 1880 kW.h = 360 kW.h / 1880 kW.h = 19.1%. Based on the annual electricity consumption of 700,000 kW.h for streetlights, the annual energy saving is 700,000 x 19.1% = 133,700 kW.h. The energy-saving system has been operating stably since its activation in June of this year, without any abnormalities. 5. Other Measures In constructing the power supply system within our jurisdiction, we also adopted a series of other measures to reduce network losses. These include: optimizing the busy status of medium-voltage substations; using new cross-linked cables for medium-voltage transmission lines whenever possible; locating newly built low-voltage substations near load centers; selecting energy-efficient new transformers; using energy-efficient new switchgear for distribution equipment; employing centralized or decentralized automatic capacitor compensation devices for centralized or local compensation of low-voltage lines; minimizing the distance between low-voltage power supply lines and loads; using advanced and standardized connection methods for all joints from medium to low voltage to reduce joint losses; prioritizing card-type metering devices in the upgrading of electricity metering devices; and encouraging residents to use energy-saving electrical appliances. (Article excerpted from "Energy Saving Innovation 2006—Proceedings of the First National Electrical Energy Saving Competition")