Loads from ice and frost formations on the wires of the contact network worsen the quality of current carrying and contribute to the emergency situation. The article presents the analysis of methods and sets of equipment for diagnostics of ice and frost formations on the wires of the contact network. Elements of diagnostic equipment form an information system, the end point of which is the energy dispatcher's console. It is shown that the composition of the diagnostic equipment is determined by the type of contact suspension and its place of installation. The variety of methods used for diagnostics of ice on wires of the contact suspension shows the complexity of the problem to be solved.

Keywords: contact network, ice formation, loads, diagnostic methods, operation, current collector, working conditions, emergency situation, refinement of methods

The article presents a method for calculating short-circuit currents in a DC traction network. The system of group grounding of supports, considered in the article, is equipped with an additional conductor that improves the working conditions of the entire section of the electrified railway by reducing the resistance of the short circuit loop.

Keywords: group grounding of supports, short-circuit current, electrified railway, traction network, fiber-optic communication line.group grounding of supports, short-circuit current, electrified railway, traction network, fiber-optic communication line

The paper proposes a model of a circuit with a pulsating circulation of a liquid coolant for cooling an oil transformer and investigates the dependence of the heat transfer coefficient on the frequency of the liquid pulsation in the heated circuit. As a result of the experiments, it was found that the pressure amplitude remains practically unchanged up to a frequency of 0.45 Hz, then sharply decreases and at a frequency of 0.9 Hz it is approximately 12.5 kPa. It was also found that in the heated circuit (circuit 1) the temperature difference exceeds the temperature difference in the heating circuit (circuit 2), which is due to the fact that the fluid flow rate in the heating circuit exceeds the flow rate in the heated circuit. The theoretical calculation carried out showed that in the proposed model the heat transfer coefficient reaches its maximum at a pulsation frequency of 0.6 Hz and is 133.675 W/m2K.

Keywords: energy efficiency, oil transformer, heat recovery, heat exchanger, transformer cooling

The article provides a brief analysis of the processes that occur when starting an electric motor. Mathematical relations modeling the process of starting a direct current motor are presented. Graphical dependences allowing to determine parameters of a thermistor providing an optimum start-up of a direct current machine have been obtained.

Keywords: starting current, thermistor, starting rheostat, thermal characteristic, DC motor, boundary conditions, torque resistance, idealized rheostat, heat loss, economical starting

The article gives a brief analysis of thermal processes occurring during the start-up of an electric motor. Mathematical relations modeling the distribution of thermal energy in the thermistor during the process of starting the DC motor are presented. Graphic dependences are presented, which allow to make arrangement of thermoresistors for the starting rheostat and to determine parameters of the starting rheostat obtained in this way. Application of the starting rheostat made on the basis of thermistors, provide an optimal starting of a DC motor.

Keywords: control gears, thermistor, starting rheostat, DC motor, temperature, dynamic characteristic, form of starting current