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 use of high-power thermistors as part of the control gear facilitates a smooth start-up of powerful motors with simultaneous temperature control. When calculating the starting processes, there are a number of limitations on which the nature of starting electric motors with the use of thermistor rheostats depends. The calculated relations describing the mathematical model of the influence of the temperature of overheating of semiconductor thermistors on the process of starting motors with a start-up rheostat are presented in the form of graphic dependences. As a result of modeling the layout of thermistor rheostats, it was determined that it is necessary to pay special attention to the material heating temperature.

Keywords: semiconductor thermistor, starting rheostat, boundary conditions, heating, specific heat, induction motor, starting current, overheating temperature

The problem of creating semiconductor thermoresistors (PTR) capable of dissipating large amounts of heat is an urgent problem of semiconductor technology. The article presents a brief analysis of the possibilities of using high-power ATGM, the picture of the distribution of thermal fields in the mass of the thermistor under certain boundary and initial conditions. It is shown that when selecting a thermistor material, special attention should be paid to the specific thermal conductivity of the material.

Keywords: High power thermistors, current density, thermal conductivity, energy balance, similarity criteria

In this article, problems of safety of the exploited structures of the contact network are examined. The types of contact network supports used in the construction of these structures are considered. The features of the centrifuged concrete structure formation, the reasons for the heterogeneity of the structure along the thickness of the annular section and the appearance of cracks are analyzed. There is a physical model, the use of which will allow to modify the structure along the thickness of the annular section due to directed structure formation in the process of concrete with a combined aggregate and fibrous components centrifugal compaction.

Keywords: safety of structures, contact network supports, centrifuged structures, annular cross-section, physical model of the process of compaction of concrete mixture during centrifugation, concrete with combined aggregate and fibrous component

In this article authors examine integrated method of ring cross-section concrete constructions diagnostics after the example of overhead contact system pylons. Complex physical-mechanical process of carcass and concrete working needs to take into consideration the state of these components. Authors suggest modern device of magnetic-particle method making for carcass state rating and its location in a pylon body. Concrete jacket defectoscopy may be done with modified device population of ultrasonic diagnostics. Examination zones of constructions are found depending on pylons workload scheme. The authors give correlations which let determine parameters of destructions (cracks) that lead to degradation of load-carrying capability. In the article there are graphic materials got as a result of ultrasonic inspection and mathematical expressions for estimating of residual load-carrying capability with a glance of carcass and concrete destructions.

Keywords: overhead contact system pylons, residual load-carrying capability, ultrasonic diagnostics, hodograph, cracks, carcass corrosion, technical state