Simulation study of DC transit systems with inverting substations

The increasing use of chopper-controlled regeneratively braked stock in rapid transit and suburban railways has brought into focus the problems of limited energy receptivity in the DC supply network. While the use of on-board rheostatic braking or mechanical braking are established methods of dealing with non-receptivity, an alternative arrangement using inverting equipment at the DC substation has been introduced at some locations in Japan, Germany and Brazil. This paper describes a simulation-based study of a rapid-transit system with substation inverters, which was undertaken to establish operating limits and optimum design criteria which could be generally applicable. The paper deals with the choice of installed inverter capacity, inverter location, current commutation limits and inverter control. In addition the energy-saving consequences of using inverter equipment are discussed in detail. The implications of fitting inverters, with respect to the bulk AC supply system, in terms of voltage distortion, voltage regulation and reactive power demand, are considered for a range of typical values of short-circuit level.