Economic power supply radius under different distribution transformer installation in rural low-voltage network

Abstract: The distribution transformer is one of the most important pieces of equipment in rural distribution networks. In the construction and reconstruction of a rural power-distribution network, the power-supply radius of a low-voltage network is an important index for planning and design, which is of great significance for reasonable layout of low-voltage distribution power supply, ensuring the quality of power supply, reducing line losses and reducing investment costs. At present there are mainly the following several methods to calculate the power supply radius of a low-voltage power system. The power-supply radius is determined by setting power loss and voltage loss from main power lines as the constraint conditions. In different voltage levels, using the rural electric equipment capacity density and geographic features to divide economic power supply radius is another method. It is also common to calculate the power-supply radius based on the model of unconstrained optimization whose objective function is to minimize the annual cost of the power-supply area. The first two methods are simple and rough, without considering the investment, consumption and other economic factors. The third method involves a comprehensive consideration of the transformer and line investment, consumption and other economic factors, and the power-supply radius obtained is more reasonable and practical. However, this method is still insufficient because it does not consider the investment difference of different types of distribution transformers. Because the installation form of the actual distribution transformer (such as outdoor stage posture or box-type transformer) has a great influence on investment cost (several times or even more), so it is natural that we cannot ignore the influence on economic power-supply radius caused by different installation types. Therefore, this paper starts from the overall economic efficiency and builds the optimization model based on unit power-supply area by minimizing the cost to analyses and count economic radius of distribution transformers of different types in a rural low-voltage network. We can see that the economic power supply radius of a transformer differs by transformer type corresponding to the same load density and maximum load utilization time from the calculation results. So transformer type will affect the economics of power grid construction. Meanwhile, load density and maximum load utilization hour exhibit a similar trend. That is to say, when the density of load or peak load utilization increases, its economic power supply radius decreases. We can conclude that it is more convenient for practical engineering application to use power density to illustrate the changes of economic power supply radius. Power density is the product of load density and maximum load utilization time. The paper proposes to estimate economic radius judging by power density. Finally, the paper gives economic radius recommended value of transformers of different types. It is easy to use the recommended value to estimate the economic radius in a rural low-voltage network; the recommended value can provide technical support in the selecting of economic radius in the power grid construction. Finally, the recommended value of economic power supply radius is given in different power densities and transformer types.