The paper presents results of analysis of disadvantages of contactless automatic voltage regulation (CAVR) system with a reactor switching device (RSD) that is used on direct current electrified railways. It also shows direction of its improvement. The authors have considered a functional scheme of the closed CAVR system of a converter unit with a thyristor-reactor switching device (TRSD) and a TRSNP-12500/10 converter transformer. They have also carried out an engineering and economical comparison of two modes of traction power supply system (TPSS) operation: without application of voltage regulation devices on traction substations with no-load voltage of 3500 V and with application of voltage regulation devices by the CAVR system at stabilization of voltage on levels of 3500, 3600 and 3700 V with various variants of switching devices. As a result, the authors have determined that the use of the CAVR system with the TRSD is economically efficient.

The paper presents a refined method for calculation of critical currents flowing through thyristors of a thyristor-reactor switching device aimed at voltage regulation at traction substations on railways electrified with direct current. The method considers overcurrent of thyristors in a dynamic mode of operation that occur in result of discharge of accumulated energy in inductive elements of the device. The authors have calculated critical currents flowing through thyristors of the switch being a part of the perspective converter transformer TRSNP-12500/10 that has a 14 % range of voltage regulation.

The paper presents a short description of electric traction systems used on electrified railways in the world. For the proposed three-phase system of electric traction the authors consider features of operation of 6-pulse bridge rectifiers in full-phase and open-phase modes. The paper also demonstrates principal schemes and time diagrams that explain operation of 6-pulse bridge rectifiers in the open-phase mode at connection of valveside windings of a transformer «star» / «star» and «star» / «delta». On the basis of executed research the authors present relations that connect voltages, currents and power of 6-pulse bridge rectifiers in the open-phase mode for controlled and uncontrolled transformers.

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The article discusses the problem of increasing the energy efficiency of the 3 kV DC traction power supply system on the railways of the Russian Federation. As one of the ways to amplify it, the authors consider a system of contactless automatic voltage regulation under load of converting units of traction substations, where reactor controlled devices serve as the regulatory body. As one of the directions for improving the system, the use of thyristors in the design of a controlled device is proposed. The article presents the functional diagrams of contactless automatic voltage control systems with thyristor-reactor and thyristor controlled devices, shows the external characteristics of the converter unit with these systems. To calculate the economic efficiency when introducing contactless automatic voltage control systems with reactor, thyristor-reactor and thyristor controlled devices, a methodology has been developed based on calculating the savings in reduced costs, as well as the payback period when replacing a contactless automatic voltage control system under load with a reactor controlled device by a system with thyristor-reactor and system with thyristor.