Stationary load accounting in modelling of traction power supply system of alternating current railroad

摘要

Asynchronous load accounting in calculation of asymmetry factor is especially important at calculations of the electrical power systems feeding the traction substations of alternating current railroads. In the adjoining networks considerable asymmetry can take place, for which elimination it is necessary to use expensive symmetrizing devices. The cost of these devices is defined by asymmetry levels which at a stage of design are defined by calculations. Without accounting of asynchronous load’s symmetrizing effect this levels will be overestimated, that will lead to overpriced cost of asymmetry elimination.Asynchronous engine is more difficult object for modeling then static element. Difficulties are connected with existence of two rotating magnetic fields (in direct and in backhanded directions). At asymmetry of the feeding voltages in the asynchronous engine sinusoidal processes at three frequencies proceed: at a frequency of 50 Hz, frequency of sliding and at a frequency about 100 Hz.It may be two variants of calculating algorithm for electric system with asynchronous load steady states. The first assumes calculation of the beginning of transient process at rather fast change of voltages, when mechanical power and speed of rotation didn't change yet because of rather big mechanical inertia. Frequency of rotation of the engine is defined by the initial approach of voltages. Therefore these basic data of voltages have to be carefully verified. Basic data are initial approximations of voltages and mechanical capacity on the engine shaft, corresponding to these voltages. The second variant assumes calculation of operating mode at the end of the engine transient process with new frequency of the rotation, with new moment and new mechanical power according to its static characteristic. The calculating model of the asynchronous engine is represented by three current sources connected by a star with the isolated neutral.Modeling results of one of Eastern Siberia railroad power supply system showed that not accounting of asynchronous load can lead to overestimate of the maximum values of negative sequence asymmetry factor to 30% or more.