The planning of medium and low-voltage power grids should be changed or adjusted accordingly with the distribution of load, and the development and planning of low-voltage distribution networks should be scientifically standardized to meet the long-term electricity demand of users of low-voltage power grids.
I. Necessity and method of medium and low voltage distribution network planning
1. The necessity of medium and low voltage power grid planning
Since the period of building the power grid is relatively long, there is generally no major change after the completion of the construction. As the country develops and builds every day, and the load of electricity becomes an uncertain factor, and the medium and low voltage power grid is the most commonly used power grid, the medium and low voltage distribution network must be closely coordinated with urban construction. A certain degree of advance awareness and coordination with the urban landscape, the planning of the medium and low-voltage power grid should be changed or adjusted accordingly, and the development and planning of the low-voltage distribution network should be scientifically standardized to meet the long-term needs of users of the low-voltage power grid. Electricity demand. The medium and low voltage distribution network has a large amount of equipment, many users, and complicated equipment. In order to solve the problems of insufficient power supply or overload, it is far from enough to deal with these problems by experience alone. The equipment and grid structure of the network are optimally configured to maximize the power supply quality and power supply capacity of the medium and low voltage distribution network, so as to maximize the economic and social benefits. Therefore, the medium and low voltage grids are more adjusted than the high voltage grids. Frequent and complicated.
2. Method of medium and low voltage power grid planning
In general, the selected lines are different because of the voltage level, the structure of the line, and the load conditions. Also, the size of the load is changing at any time, so the total demand for electricity in an area is calculated and then the planning of the medium and low voltage grid is carried out. Generally speaking, there are three methods for predicting the total electricity demand in a region: the first one is the sector analysis method, which is based on the economic industry of a country, and then the power demand forecast by the industry, and finally the cumulative sum is obtained. Total demand for electricity. The second is to investigate and verify the users who use more electricity and then count the total number of users with less power consumption to get all the needs of the region. The third is to use electricity elasticity coefficient method, average growth rate method, load density method and other methods to evaluate the electricity consumption in an area. Then according to the data obtained, make the corresponding planning plan.
Second, the technical principle of medium and low voltage distribution network
1. General principles for planning medium and low voltage distribution networks
The medium voltage distribution network requires simplification and standardization, and the backbone poles are required to be clear and reliable, which is conducive to the development of the low-voltage power grid. In consideration of the load, etc., the power supply radius of 10 kW in the urban area should preferably not exceed 3,000 meters, and the power supply radius of the suburb should preferably not exceed 5,000 meters. It is necessary to make full use of highway resources and improve the utilization rate of power supply equipment. Where the conditions permit, cable lines should be the mainstay, and the construction of the cable lanes should be implemented in parallel with the planning and construction of the area. Try to require the medium and low voltage distribution network to achieve self-healing, interaction, and compatibility requirements.
The lines of the low-voltage line distribution network should have a clear power supply range. It is best not to supply power across the block. The low-voltage distribution network adopts a branch-like radiating structure, and when necessary, a communication switch can be installed between adjacent low-voltage power sources, thereby improving operational flexibility. Generally speaking, the radius of the low-voltage line power supply is no more than 150 meters in the city center and no more than 250 meters in the urban area. Residential electricity should be able to implement a one-meter metering method. The general residential electricity supply is powered by a single phase of 220 volts, and the villa can be powered by three phases.
2. Planning the line principle of medium and low voltage distribution network
In the medium voltage distribution line, the current carrying capacity of the components of the medium voltage power supply line should be matched with each other, and the load capacity of the medium voltage power supply line cannot be affected due to a certain component. When using two or more power supplies, the medium voltage power lines are preferably erected in different directions or different paths. Try to use equipment with high reliability and gradually eliminate those equipment that is backward in technology. It is necessary to gradually improve the automation function of the medium voltage distribution network so that it can be automatically isolated due to line faults. For those newly built medium voltage distribution networks, the lines should be fully insulated when they are overhead. It is necessary to continuously carry out anti-external damage and environmental remediation.
The principle of planning the low-voltage distribution network: low-voltage overhead lines are generally used for cottage residential areas; low-voltage cable lines are generally used for residential buildings. Insulated cables are generally used for the lines of the low-voltage distribution network, and the cross-section of the insulated cables should be 185 square millimeters and above in diameter in the urban main line. In a three-phase four-wire power supply system, the zero line and phase line sections are preferably the same. Generally speaking, it is generally not necessary to supply single-phase power in a street with pure lighting load. The radius of the power supply to the wires in the low-voltage distribution line should meet the voltage loss requirements. Generally, the power supply radius of the urban main line is less than 150 meters, and the branch line is generally less than 250 meters.
It is best to use a geographic line for the line of residents. The phase requirements of the low-voltage residential subscriber line in the same area are uniformly listed with obvious markings. At the end of the low-voltage line trunk and each branch, the neutral line is required to be repeatedly grounded, not less than three.
3. Other principles of planning for medium and low voltage distribution networks
1. Design principles of the power distribution room
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