Reliability evaluation of a bulk power system for the traction power supply system of a high-speed railway

5000 kM high-speed railways with speed of 350 km/h are being constructed in China in the next five years. A high-speed railway has many traction power substations (TPS) which convert the high voltage electricity of the public bulk power system to 25 kV single phase electricity and supply it to the high-speed locomotives through the catenary system. These substations and the catenary system form the traction power supply system (TPSS) of the high-speed railway and its Reliability, Availability, Maintenance and Safety (RAMS) evaluation become a critical issue in China now. A novel reliability evaluation approach using Monte Carlo simulation is discussed in this paper. This analysis approach is proposed for a bulk power system for the traction power supply system of a high-speed railway. The traction substations of a railway are taken as composite loads of the bulk power system. Different from the traditional generation and transmission reliability evaluation, these loads are not independent. The traction substations are designed to have section-crossing power supplying ability. When one substation is down the adjacent two substations can extend their power supplying sections to the blackout part and the railway can still operate as normal. Four reliability indices for the individual TPSs and five indices for the entire railway considering the section-crossing ability of the substations have been proposed. The analytical expressions of these reliability indices and their sensitivities with respect to power system component reliability parameters have been deduced. In order to calculate the practical shedding loads of each TPS, a heuristic load shedding strategy has also been suggested which simulates the actions of the grid operators. When the reliability of TPSS is evaluated at the first time, the Monte Carlo simulation approach is used. This procedure is somewhat time-consuming. After that, the analytical expressions of the reliability indices have been determined. W- hen the reliability performance of the power system changes all these reliability indices can be calculated directly through the analytical expressions without simulation so the evaluation is sped up. RBTS benchmark model[17] and IEEE RTS79[18] have been used and the results show that the proposed approach is correct and effective.