A real-time DSP based quadrilateral relay for distance protection of 25 kV AC traction overhead equipment

This paper presents the design, implementation and testing of a single-phase distance relaying scheme for 25 kV 50 Hz AC traction system using a Texas instruments TMS320C50 digital signal processor (DSP). The three-phase system with substations, track section with rectifier-fed DC locomotives and a detailed traction load are modeled using power system block set (PSB)/SIMULINK software package. The model has been used to study the effect of loading and fault conditions in 25 kV AC traction. The relay characteristic proposed is a combination of two quadrilaterals in the X-R plane in which resistance and reactance reaches are independently controllable. The algorithms, hardware and software are also briefly described.