Probabilistic Load Flow Analysis Of Power System With Traction Power Load Of Electrified Railways

With the explosive development of China’s railway,the electrified railway traction power supply system brings great challenges to the power system because of its transformation from three-phase to two-phase,single-phase independent operation and the characteristics of randomness and shock load.Due to the unbalanced and random features of traction load,a single-phase probabilistic power flow algorithm based on Monte Carlo method is combined with a three-phase power flow algorithm based on phase-sequence hybrid modeling to extend the probabilistic power flow algorithms for the symmetric systems to the asymmetric systems to reveal the impact of the traction loads on the power system side.Major research works are as follow:(1)Construct the probabilistic load flow compute model of power system with traction load.Firstly,select the Point of Common Coupling(PCC)of traction load,then construct the whole system through hybrid modeling of symmetrical and phase components.Then divide system into two parts,one with only symmetrical components and loads and the other with at least one unsymmetrical component or load,and build the first one with positive-negative-zero sequence model and the second one with phase model.After that,transform system into probabilistic model through Monte-Carlo algorithm.At last,build the power probabilistic model of traction substation and convert the mode into three-phase form according to the connection of traction transformer.(2)Probabilistic load flow calculation of power system with traction load.On the basis of Monte-Carlo algorithm,take sample from traction load,common load and generator.To every certain sample,set initial voltage of boundary node and conduct the concurrent computation,in which symmetrical part using symmetrical component method and unsymmetrical part using phase component method,and then value of power deviation will be obtained.Check the value,if it did not meet the requirement,then compute the new voltage of boundary node through the value of power deviation and start the load flow calculation again.After all samples have their calculations completed,obtain the probability distributions of phase voltage of nodes and branch power flow of branches.(3)Study the influence of traction load bring to power system.Compare voltage amplitude of PQ nodes and active power of all branches in power system connecting common load with which connecting traction load.The results shows that,though the traction load is light,it brought huge influence to nodes and branches near PCC,and the fluctuation traction load bring to three phase are different due to unbalanced factor.Besides,according to national standards,the voltage deviation of all nodes meet the requirement while voltage fluctuation of PCC might exceed the limit,and over-limit probabilities of three phase are different.