General comparison of the electrical transportation systems that are fed with 1/spl times/25 kV or 2/spl times/25 kV and expectations from these systems

In electrical transportation systems which are fed from interconnected AC networks, the voltage of the conductor is 25 kV, frequency is 50 Hz or 60 Hz. Power need depends on the number of the cars and the density of traffic. In modem fast trains it can be seen that the power is 12-15 MW per car. Beside technical needs, all system's economy is an important concept. Two scenarios for providing of energy of high power traffic are considered: (a) with returning conductor in 1/spl times/25 kV systems, and (b) with autotransformer in 2/spl times/25 kV systems. If there is no added returning conductor in 1/spl times/25 kV systems, there will be some unwanted effects between transportation system conductor and signalization conductor. The current which passes over earth to substation causes these effects. There is a conductor that is serially connected with transformers, in order to limit this returning current so this current passes over this conductor. When the line current increases, the voltage drop increases. We assume that the phase disconnection place which is necessary for interconnected network feeding is next to the substation for comparison of both basic systems. In this condition, substation transformers are connected with the three phase network, so asymmetrical load of interconnected AC networks can be decreased. Neutral areas usually are placed between two wired stations in a free way.