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Planning and design of rural low-voltage irrigation and drainage lines?

What is the specific content of the planning and design of rural low-pressure irrigation and drainage lines? Zhong Da Consulting will answer your questions below.

The first and second reconstruction projects of rural power grid have realized the same price of domestic electricity for urban and rural residents, and the quality of rural power grid has been significantly improved, providing a good environment for rural residents to use electricity. However, rural irrigation and drainage power lines have been in disrepair for a long time, aging seriously, and underground climbing lines, broken skin lines and privately pulled wires have been repeatedly banned, which has serious security risks. Recently, State Grid Corporation put forward the call of "new countryside, new power and new service" and the strategic goal of "one strong and three excellent" modern company. Power supply enterprises should follow the working idea of "three stresses and one innovation", take serving "agriculture, countryside and farmers" as the starting point, take the management of "four households" of agricultural irrigation and drainage and "electrifying wells and holding cards for households" as the current key work, and increase capital investment. The design scheme of rural irrigation and drainage distribution radio station area and low-voltage line is as follows.

1 Selection of distribution transformer

Distribution transformers should be located reasonably according to the principle of "small capacity, dense point and short radius". Generally, each station provides 3-5 wells with electricity, and the transformer should be placed in the load center as far as possible, extending radially from the low-voltage outlet of the distribution transformer to each well point as far as possible, and the power supply radius should not exceed 500 m. The location of the distribution transformer should be away from inflammable, explosive, polluted and low-lying areas, and should be chosen in a place with high terrain, no sundries around and convenient access lines for high and low voltage. When selecting the capacity of distribution transformer, it should be selected according to the actual load and the rural power development plan in recent 5 ~ 10 years. Considering that rural areas have their own electricity consumption characteristics, which are easily affected by seasonality and timeliness, the electricity load fluctuates greatly, and lighting and irrigation are mixed. The distribution transformer can adopt mother-child transformer or capacity regulating transformer to meet the needs of different seasons and different times. The capacity of the special distribution transformer for agricultural irrigation and drainage can be determined according to the load size and the capacity-load ratio of 1.3 ~ 1.8, and the capacity of the newly added distribution transformer for agricultural irrigation and drainage should not exceed 100 kVA. Distribution transformers should choose S9 and above energy-saving products. In order to reduce the floor space, the distribution transformer should be installed on double columns, and its base should not be less than 2.5 m from the ground.

2 Selection of line path, conductor and power supply mode

Route design must be combined with rural economic development planning, consistent with rural construction planning, avoiding circuitous power supply and blocking lines, and at the same time, it should be convenient for machine farming and occupy less farmland, with the shortest lines, fewer bends and spans, and convenient for construction, operation and maintenance. In addition, it is necessary to stay away from places where flammable and explosive materials are used, and try to avoid places that are vulnerable to flash floods, rain erosion and afforestation. The conductor section of the line should be determined according to the power load transmitted, and the load growth in 5 ~ 10 years should be considered. At the same time, the heating conditions, voltage loss, economic current density and mechanical strength must be met. For the low-voltage power grid of special distribution transformer for irrigation and drainage, IT system should be adopted in new lines, and all safety technical indexes meet the standard requirements, which not only saves investment, but also ensures the reliability of power supply. The neutral point on the low voltage side of transformer should be equipped with high voltage breakdown fuse and protective grounding.

3 Low-voltage overhead line design

The three-phase load of irrigation and drainage electricity is relatively balanced, and the low-voltage overhead line can be powered by three-phase three-wire system; Pole adopts 10 m pole, low-voltage outgoing line adopts insulated wire not less than 35 mm2, and low-voltage trunk line adopts steel-core aluminum stranded wire or insulated wire not less than 25 mm2; Low-voltage lines are erected in strict accordance with the relevant requirements of low-voltage power technical regulations.

4 Low-voltage cable line design

Low-voltage overhead lines have many disadvantages, such as occupying more land, high cost and being easily damaged by external forces. Buried lines have the advantages of less investment, land saving, safe operation and less maintenance. It is suggested that buried cable lines be used for irrigation and drainage lines. It is suggested to implement one well and one line, and each well can be wired separately to reduce intermediate joints and accident points. Low-voltage power cable can generally choose three-core cable. Using PVC or XLPE insulated cables and using moisture-proof, insulated and shielded armored cables in special places or places where conditions permit requires high quality and technical standards. The cable section should be selected according to the allowable continuous current carrying capacity. Generally, the cable should be selected not less than 16 mm2. The route should be chosen as far as possible on the edge of the ground, along the road and by the canal, avoiding places that are easily washed away by flash floods and rain, places where compost and compost are concentrated, and buildings or construction sites. Before and after cable laying, insulation resistance must be measured by 1000 V megohmmeter, generally not less than 10 MW. Low-voltage cables are laid directly underground. Cable laying shall be carried out in strict accordance with the relevant requirements of Technical Specification for Rural Low-voltage Power. Before directly buried cables are backfilled, concealed works shall be accepted. After burial, the circuit diagram in line with the actual situation should be drawn, and the corresponding technical files should be established.

5 Design of low-voltage power distribution device

Distribution box can be set on the low voltage side of distribution transformer, which is not suitable because the distribution room occupies a large area. Over-current and residual current protection devices should be installed in the distribution box, and the residual current protector should be voltage type. The power distribution device of Dajing can be installed next to the machine well. The incoming and outgoing lines of the distribution box should be insulated wires or cables with insulated sheaths, and should be protected by sleeves when passing through the box shell. The bottom of the distribution box should be1.2m higher than the ground. Electricity for agricultural irrigation and drainage is measured by one well and one meter, and the metering box is installed beside each well platform or on the terminal pole. In order to avoid being affected by harsh environments such as high temperature, high humidity and high ultraviolet rays, as well as being damaged and stolen by external forces, the shaft platform with a height of not less than 1.2 m can adopt brick-concrete or concrete structure beside the shaft, in which cables are embedded and metering boxes are placed, which is convenient to disassemble when not in use. Promote the use of IC card prepaid watt-hour meter metering box. The metering box of prepaid watt-hour meter should have the functions of metering, phase failure protection, overload protection, residual current protection and overvoltage protection. IC card watt-hour meter should choose a fixed manufacturer with strong technical force and high reputation, and should be waterproof, anti-magnetic, anti-attack, anti-wear, anti-stealing, and increase the card pulling delay function to solve the problem of motor damage caused by frequent start and stop of deep well pumps.

6 reactive power compensation

The load of irrigation and drainage is mainly three-phase asynchronous motor, and the local reactive power compensation is implemented. The capacitor is connected in parallel with the motor and switched synchronously. The compensation capacity of the motor shall be 1.0 ~ 1.5 times of no-load reactive power. The construction and transformation of rural irrigation and drainage lines should follow the principle of "safety, reliability, economy, taking into account local conditions and the future", focusing on solving the problems of aging, high line loss and poor safety of rural irrigation and drainage lines. First, solve the problem of no power well, take the power supply area as the rectification unit, and simultaneously carry out 10 kV and low-voltage lines in one step. The reconstruction project of rural irrigation and drainage lines should carefully investigate the existing power grid, queue up in different categories, make full use of the original equipment, and cannot be reinvented. It is necessary to reduce the project cost and improve the technical standards.

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