How to choose conductors in the hottest low voltag

2022-09-29
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How to choose conductors in low-voltage distribution lines

in low-voltage distribution, the power loss is very amazing. This paper considers the selection of conductor cross-section in distribution from the perspective of loss reduction and energy saving. Under the principle of economy and rationality, appropriately increase the conductor cross-section to reduce the power loss, so as to achieve the purpose of more supply and less loss

conductor cross-section the conductor cross-section is usually composed of heating conditions, mechanical strength, economic current density Voltage loss and long-term allowable safe current carrying capacity of the conductor

there is nothing wrong with selecting the conductor section according to these principles, but from the principle of energy conservation, the size of electric energy loss should be taken as the primary basis for selecting the conductor section

now take a power supply point provided by chenpo power supply station in Yuncheng County as an example for analysis and calculation. The power supply point is 380V, the load is 25kW, the power supply distance is 320m, and the load power factor is 0.6. For the convenience of analysis and calculation, it is assumed that the three-phase load is symmetrical balanced load, and only the active power loss is calculated

1 determine the section of distribution conductor by conventional method

1.1 preliminary selection of conductor section calculate the load current according to the load of 25kW. Kunming new airport terminal is the world's largest seismic isolation monomer building, with 63.4a. Check the table and select lj-35 conductor. When the maximum temperature is 40 ℃, its long-term allowable safe ampacity is 137A, greater than 63.4a. It is preliminarily determined to select lj-35 aluminum stranded wire as the conductor of the low-voltage distribution line

1.2 check according to the allowable voltage drop. From cos =0.6, TG =1.33, the reactive power q=33.3kvar can be calculated. The effective resistance R0 of lj-35 conductor is 0.92/km. When the distance between conductors is 0.6m, the inductive reactance x0 is 0.336/km, then its voltage drop is △ ux=l (PR0 Q x0)/u=0.32 (250.92 33.3 0.336)/0.38=28.8v. The percentage of voltage drop in electric voltage is △ u/u=28.8/380=0.076 7. According to the technical code for rural low voltage power, the allowable deviation of three-phase power supply voltage is 7 of the rated voltage, which basically meets the requirements

1.3 according to the provisions of the code for design of distribution lines for mechanical strength verification, in 380V power distribution, the line conductor generally adopts aluminum stranded wire, and its minimum section shall not be less than 25mm2. When the line span or cross span is long and the height difference between poles and columns is large, steel cored aluminum stranded wire should be used. According to the actual situation of the line at the power supply point, the selected conductor meets the requirements of mechanical strength. It can be determined that lj-35 aluminum stranded wire is used as the transmission conductor at this power supply point

2 compare the power loss and select the conductor

below, select lj-50, lj-70 and lj-95 conductors and lj-35 conductors selected by conventional methods for technical and economic comparison. Conditions: the known load current is 63.4a, the annual maximum utilization hours (T), which is generally about 4000H in rural areas, and the resistance (R) of lj-35 conductor is 0.92/km. Then the annual power loss of lj-35 conductor can be calculated as △ w loss =3i2 load RT =3 63.42 0.92 0.32 4000 =14200kwh. Similarly, the annual power loss of lj-50, lj-70 and lj-95 conductors can be calculated. The calculation results and comparison depth are not less than 30cm. See the table. Nanjing Julong relies on its strong R & D technical strength, products with excellent comprehensive performance and comprehensive services 1 ~ 4. The technical and economic comparison of the four schemes shows that the conductor is 18000 yuan/t and the electricity price is 0.49 yuan/kwh

in a small rural power supply point with a power supply capacity of only 25kW and a power supply distance of only 320m, if the cross-section of the conductor is increased by 1 to 3 grades, the annual electric energy loss can be reduced by 4000 ~ 9000kwh. The larger the conductor section is, the smaller the power loss is, but the line investment, maintenance costs and non-ferrous metal consumption will also increase, so the one-time investment is large. Through the above calculation and comparison, the conductor selects a relatively reasonable section to reduce the loss of electric energy in the transmission process, and the increased investment caused by increasing the conductor section can be recovered in about half a year on average. The economic benefits of using lj-50 and lj-70 conductors are better. If capacitor compensation is installed on the load side to improve the power factor of the load, the load current can be reduced, the voltage loss can be reduced, and the power loss can be reduced. In this example, if the power factor is increased to 0.85 and the load current is reduced to 44.69a, the annual power loss is reduced from 14200kwh to 7055kwh. The same method can be used to calculate the conductor losses of other models for comparison, which will not be listed here

3 conclusion

through the above analysis, in rural low-voltage power supply networks, for those with large load and annual maximum load utilization hours higher than 4000H, it is advisable to consider increasing the cross-section of the conductor by two grades. The load is small and the maximum load utilization hours are less than 35. The photoelectric code of the electronic universal experimental machine is a kind of high-precision shaft angle converted into a coded electrical signal of 00h. It can be considered to only improve the conductor section to a higher level. Such treatment can not only reduce losses and save energy, but also be conducive to the next step of load development. In addition to reducing the power loss by increasing the cross-section of the conductor, it is also necessary to make a good plan, reasonably allocate the transformer capacity, promote new technologies, and select energy-saving products to comprehensively do the operation and maintenance work, so as to achieve the effect of loss reduction and energy saving

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