ANALYSIS OF APPLICABILITY OF EXTERNAL NETWORK SIMPLIFIED MODELS FOR DEFINITION OF SHORT CIRCUIT CURRENTS IN SYSTEMS OF RAILROAD TRACTION POWER SUPPLY

In practical methods of emergency operation in systems of tractive electric power supply systems the equivalent models of external network constructed on the basis of tractive substations short circuit (SC) reactances are used. Such modeling can give errors of definitions of SC mode parameters. The origin of errors consists of the fact that the offered estimated formulas are based on method of symmetric components with one asymmetry in three-phase circuit. Tractive network short circuit in case of double-sided supply of inter substation zone creates double asymmetry as it affects directly on two adjacent tractive substations, and in case of external network close coupling there is an interference of asymmetries at each other. For delimitation of simplified equivalent models applicability authors made comparative calculations of emergency operation by means of models constructed in phase coordinates and using external electric power supply equivalent reactances. Determination of SC currents in system of 27,5 kV tractive electric power supply of rather simple configuration is carried out in three options: on formulas of "Guide-line on relay protection of tractive electric supply ", on full-function estimated scheme of Fazonord complex considering wires capacity and inductive interferences and on specified analytical formula. The received results show rather small errors at SC power exceeding 1000 MV·A. At small values of SC power error can reach several tens percent and becomes inadmissible