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

Location of compensating devices is determined by various factors: configuration of power supply system, enterprise load schedule, type and length of power lines, parameters of capacitor banks, value of supply voltage. We consider the influence of the above factors on the creation of a mathematical model to determine the location of compensating devices, taking into account the minimum economic costs.

Keywords: compensating devices, reactive power compensation, power system, power grids of industrial enterprises, load schedule, mathematical model, reduced costs

The article discusses the production and use of environmentally friendly fuel - pellets. A review of the designs of mobile pellet production plants was carried out, the advantages and disadvantages of these designs were identified. Potential consumers of pellets and equipment (heating boilers for which pellets are the fuel) are considered. A mobile complex for the production of pellets on the chassis of the MSN-10-004-03 . The technology of pellet production using a mobile mobile installation is described.

Keywords: pellets, mobile plant, design, biofuels, production technology

Pipeline networks today are the main and one of the safest ways to transport all kinds of media. This engineering system consists of various elements, one of which is pipeline fittings that regulate the parameters of working media and protect pipelines from overpressure. In order to control the operability of pipeline fittings, it must be subjected to comprehensive tests, one of which is a leak test. The presented study describes the developed design of a technological hydraulic installation intended for use as part of process equipment for conducting in-plant testing of pipeline valves. The results of modeling the stress-strain states of the main units, as well as the hydraulic calculation of the test circuit of the installation are presented.

Keywords: rotary check valve, pipeline fittings, pipeline system, mathematical modeling, finite element method, strength analysis, stress-strain state, computational fluid dynamics, hydraulic tests, technological hydraulic installation