Research On Distribution And Calculation Of Electric Traction Load Harmonics And Negative Phase Sequence In Power Systems

With the increasing construction speed of electric railway and the development in the operation railway length, China is now having the world's second longest electric railways. The electric traction drive is put into ever increasingly wide use in modem rail transportation for its advantages of heavy load, high speed, primary energy conservation and less environment pollution. However, the electric railway traction load which is a violently fluctuating high power single-phase rectified one and can cause much harmonics and negative sequences in the power system would seriously threaten the power system' voltage quality and economic and safe operation if adequate measures are not taken. Under such circumstances, the distribution calculation of power system asymmetrical load, especially the electric traction load is becoming increasingly important.It is proposed that the three phase analysis method be used for the distribution calculation of asymmetrical load in the power system. Based on predecessor's experiences the distribution and calculation of harmonics and negative phase sequence created by electric power traction load is studied in this paper. The relationship of calculation of three-phase basic power flow and negative-sequence distribution in the power system with electric traction loads is presented. It is point out that mean effective value algorithm based on current injection method should be used. The three phase model and three phase harmonic model of elements in power system and electric power traction system are presented. Facing the fact that the traditional brand additional method can hardly calculate the three phase nodal admittance matrix, a new method based on the branch three phase model has been put forward to deal with this problem. The method to form the three phase system's jacobian matrix is also given in this paper. On the basis of former research, a program is developed to analyze the negative phase sequence and harmonic of electric traction loads. The function and structure of the program is given. Using this program, an actual electric power system with electric traction loads is studied, and the voltage of negative phase sequence and harmonic on point of common coupling (PCC) and electric traction substations in electric power system caused by electric traction loads are obtained. The results indicate that the models and the arithmetic in this paper are right and feasible.