0-7803-8560-8/04/$20.00©2004 IEEE MATLAB/PSB BASED MODELING AND SIMULATION OF 25 KV AC RAILWAY TRACTION SYSTEM- A PARTICULAR REFERENCE TO LOADING AND FAULT CONDITIONS U. J. Shenoy, Senior Member, IEEE, K. G. Sheshadri, K. Parthasarathy, Senior Member, IEEE, H. P. Khincha, Senior Member, IEEE, D. Thukaram, Senior Member, IEEE Abstract --This paper presents the modeling and simulation of a 25 kV 50 Hz AC traction system using Power System Block set (PSB) / SIMULINK software package. The three-phase system with substations, track section with rectifier-fed DC locomotives and a detailed traction load are included in the model. 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. A brief summary of the hardware set-up used to implement and test the relay characteristic using a Texas Instruments TMS320C50 digital signal processor (DSP) has also been presented. Keywords—Traction system, PSB/SIMULINK, Wrong phase coupling, TMS320C50 DSP, Quadrilateral relay characteristic 1. INTRODUCTION The function of an AC traction system is to deliver power to the locomotives as efficiently and economically as possible. Problems involved in providing protection to traction systems are different from those faced in protecting other transmission lines or distribution systems working at the same voltage level. This is due to the continuous movement of locomotive load, change in the length of the line during operation, nature of loading, voltage drop due to the flow of the lagging reactive current in inductive components of the overhead system and the high levels of harmonic distortion [1]. The situation is further aggravated due to the use of DC series motors in electric locomotives, which draw large current on starting. It may happen at times that several locomotives run in the same section of the overhead equipment (OHE), leading to large increase in load. The impedance seen by the relay on such heavy loads may be even smaller than that on distant earth faults. Fig. 1 shows the typical feeding arrangement of a 25 kV electrified railway system. The load current drawn by locomotives is rich in odd harmonic components [2]. The adjacent traction substations are fed from different U.J.Shenoy, corresponding author (e-mail: ujs@ee.iisc.ernet.in ) is Principal Research Scientist, K.G. Sheshadri (e-mail: kg_sheshadri@yahoo.com) is the Project Assistant, H.P. Khincha (e-mail: hpk@ee.iisc.ernet.in) and D. Thukaram (e-mail: dtram@ee.iisc.ernet.in) are Professors in the Electrical Engg. Department, Indian Institute of Science, Bangalore- 560 012. K. Parthasarathy (e-mail: prdc@vsnl.com) is with the Power Research & Development Company, Bangalore. phases of the three-phase supply in rotation having a phase difference of 120 o . The supply to the OHE can be switched ON/OFF through interruptors. Normally power supply from the traction substation extends upto the sectioning post (SP) on either side of the substation, but in case of an emergency necessitating total shut down of the substation, it can be extended upto the failed substation by closing the bridging interruptors at the two SPs. Fig. 1. Typical feeding arrangement of 25 kV traction system of Indian Railways Fault on the OHE can be of two types (i) Earth faults (ii) Phase-to-phase faults. The second fault can occur by accidental closure of the bridging interruptor at the SP during normal feeding condition or by a short circuit at the insulated overlap opposite a traction substation at times of emergency feed conditions. This is termed as Wrong phase coupling (WPC) fault. The harmonic currents drawn by the dc motor locomotives degrade the power quality of the traction supply [3]. The excessive voltage drop due to the flow of lagging reactive current makes the performance of the system even worse. Voltage regulation with shunt compensation allows overcoming these drawbacks. Static VAR Compensators (SVCs), Thyristor controlled reactors (TCRs) and Thyristor Switched Capacitors (TSCs) can be used to provide such compensation. This paper presents the modeling, simulation, implementation and testing of a quadrilateral characteristic single-phase digital distance relay for 25 kV AC traction applications. A Texas Instruments TMS320C50 digital processor (DSP) has been used to support the high-speed numeric processing capabilities required for transmission line protection. 508