Vol 90, No 7 (2019)

The article considers the methods of increasing the stability of high-power synchronous machines when stabilizing the torque angle in the structure of the automatic excitation control system. A mathematical model of an electric machine in open and closed automatic control systems is obtained, studies of electromagnetic processes and analysis of existing and proposed optimal control systems are carried out. A contactless sensor of torque angle of the synchronous motor based on measuring the available parameters of the synchronous machine and allowing us to calculate the torque angle in static and dynamic modes of operation of synchronous generator and compatible with the new control system was developed. The presented excitation control system of synchronous machine with a measuring sensor of torque angle that provides higher performance in dynamic modes, as well as allowing to stabilize the reactive power, the power factor and the voltage on the stator of the synchronous machine.

The characteristics, the design, and the principles of space-vector control of an induction electric drive based on a matrix frequency converter are considered. The output voltage and the current of the matrix frequency converter–induction motor with a squirrel-cage rotor system with a unitary power factor were studied. Using such a system in ac drives makes it possible to ensure the high energy efficiency and two-sided exchange of energy between the supply network and the load without additional energy conversion.

The article explores the possibility of using synchronous motors excited from permanent magnets (PMs) for electric starting of gas turbine powerplants (GTPPs) in gas transport systems. The two analyzed versions of the starter are one with radially magnetized inductor-surface-mounted permanent magnets (SPMs) and one with V-shaped inductor-core-interior-mounted permanent magnets (IPMs). The performance specifications entail that the starter has a multimode operation (hot start, dry run, gas–air flow duct flushing) in a short period of time and repeated short-time modes with target torque characteristics. The analyzed parameters of the compared rotor designs are magnetic flux distribution, harmonic composition of the field and counter-EMF, torque values and ripple, PM energy efficiency, and resistance to irreversible demagnetization. It is established that the SPM starter has a better torque density and overload capacity and weaker torque ripple and can be recommended for the electric startup of GTPPs with an increased inertia torque. The starter with an IPM rotor is preferable in terms of energy efficiency and ability to counteract the demagnetizing action of armature response. The technological difficulties of producing rotors with external magnets make it more complicated to use them in motors with high rotation frequencies.

A method is proposed for supplying backup power to power-supply systems with induction and synchronous motors that uses in-phase connection of the voltage of backup power source upon group spinning down of motors after emergency loss of the main power supply. Based on the results of mathematical simulation of switching modes of power supply, the permissible regions of phase-shift angles are determined in terms of voltages. In the proposed method, the instantaneous voltages of the main and backup power sources are controlled and the phase-shift angle between the vectors of these voltages is determined. By recording data on the times when the phase-shift angle reaches three predetermined values, a parabolic approximation of the time dependence of the change in the angle is carried out, with the help of which the time that it takes to reach a 360° angle is predicted and, then, taking into account the proper time of activation of the backup power switch, the time to issue the command that it switch on is determined. The results of mathematical simulation and a full-scale test of power switching modes are presented, which confirm the viability of in-phase voltage supply when using the method and a device based on it, making it possible to recommend the method for use in microprocessor-based devices of high-speed automatic power-supply switching.

The provision of scheduled freight and passenger rail transportation is carried out according to the train schedule, for successful fulfillment of which it is necessary to maintain the desired voltage level at locomotive pantographs. The voltage depends on the position of switching devices of distributing equipment and voltage regulation facilities. To increase operating efficiency, it is proposed to carry out the opposing interval regulation of performance factors of the traction power-supply system. The predictive sequence of discrete values of performance factors is determined by fulfilled train schedules and consumer loads. The discrete values are the initial data to determining the time intervals. The number of time intervals for 24 h is chosen taking into account the switching service life of devices and equipment. The time intervals and the predictive average values in intervals are the main criteria to choosing the proper power-supply circuits of traction loads.

It was revealed that one of the main reasons for erroneous operation of relay protection devices (RPs) is it being set in a way that does not correspond with the real operating conditions, which in turn is determined by the design procedures of the RP settings. An analysis of modern methodologies of RP adjustment revealed that there are no significant changes as compared with the guidelines of the past decades and, accordingly, there are the same disadvantages. The development of new adjustment techniques using detailed mathematical models taking into account the features of specific RPs and the processes in the measuring converters are considered in the work. Within the framework of solving this problem, mathematical models of measuring part of digital relay protection for various types of intermediate current transformers (ICTs) (active and passive) and filters (of Butterworth and Chebyshev types) are synthesized and a comparative analysis is done of their influence on the output signal waveform in the MATLAB software package, including taking into account the magnetization of measuring current transformers. It is revealed that the simplest (explicit and implicit Euler methods) numerical methods are not suitable to solving the created mathematical models. A comparative analysis of calculation results by these methods and by the more advanced Runge–Kutta method is conducted. The presented theoretical and practical studies made it possible to reliably formulate the requirements for detailed mathematical models of RPs.