Research On Influencing Factors Of Line Loss And Loss Reduction Strategy In Low Voltage Distribution Networks

Along with the increasing power consumption load and the constant enlargement of the power system,the energy loss during transmission is increasing,which causes serious waste of resources and brings great pressure to the ecological environment.The low voltage distribution network has large scale,large number of branches and three-phase unbalanced load.Therefore,the problem of high line loss is particularly prominent.This thesis takes line loss of low voltage distribution networks as the research object,focusing on the influence factors of line loss and loss reduction method used in low voltage distribution networks.The main research contents are as follows:(1)The three-phase flow algorithm which is suitable for line loss calculation of low voltage distribution networks has been researched.Three-phase mathematical models for main electrical components such as lines,distribution transformers and electric loads are established and the iterative correction formulas corresponding to different load characteristics and connection modes of loads are discussed.Then,two line loss calculation methods according to the power flow results are explained,which are based on calculating the net injection of active power and summing active power loss of branches respectively.(2)This thesis makes a deep analysis on the influencing factors of line loss in the low voltage distribution network.Through theoretical derivation,the quantitative relationships between influencing factors such as unbalance degree of three-phase load,load curve,load level and line loss are obtained.Then corresponding equivalent loss coefficients are presented to characterize the influence of different factors on the active power loss of branches or networks.In addition,probabilistic models are proposed for the stochastic simulation of three-phase load and load curve respectively,which introduces load deviation coefficient and variation coefficient to characterize the unbalance degree of three-phase load and the fluctuation degree of load curve.Based on this,the load simulation by applying Monte Carlo method is studied.(3)In consideration of the characteristics of unbalanced three-phase load in low voltage distribution network,this thesis proposes a loss reduction strategy based on optimization of load phase.Alternative access methods for three-phase load and single-phase load in the optimization model are analyzed.Then,the optimization results and run time of different objective functions are compared.Finally,improved genetic algorithm is used to solve the optimization model and it is verified through an example that the loss reduction method can effectively balance the three-phase load in single-period and multi-period,reducing the active power loss,and playing an important role in solving voltage imbalance and current imbalance problems.