Abstract
It is known that the occurrence and existence of ferroresonant oscillations at the subharmonic frequency (SHC) in power transmission lines (TL) and in power supply systems is extremely undesirable, since they cause ferroresonant overvoltages at different frequencies. At the same time, there is a wide class of nonlinear electrical circuits, in which the excitation of autoparametric oscillations (AIC) at the frequency of the SHC forms the basis of frequency converting devices serving as secondary power sources. It is shown that three-phase nonlinear systems are in one way or another equivalent circuits for power transmission lines, the main elements of which are: longitudinal compensation capacitors, transverse compensation reactors, and transformers with a nonlinear characteristic. To study the regularities of the excitation and maintenance of SHC at a frequency in three-phase electro-ferromagnetic circuits (EFMC), theoretical and experimental studies of an equivalent model of a three-phase circuit with nonlinear inductance were carried out. For the analysis of the steady-state mode of the SHC at the frequency, the method of a small parameter (averaging) was applied. A shortened differential equation of motion for a three-phase nonlinear circuit is obtained. By solving them, the regions of existence of the SHC and the critical parameters of the chain were determined. The obtained results of theoretical research are confirmed by experimental studies.
Highlights
Electrical systems contain a large number of elements with significant inductance
subharmonic frequency (SHC) in three-phase nonlinear circuits and systems are excited at certain ratios of circuit parameters, input voltage and nonlinearities of ferromagnetic elements, both in “soft” and “hard” modes and is limited to a certain region of existence
2.In a three-phase ferroresonant circuit, the excitation of SHC and the nature of the transient process depend on the structure and methods of connecting the circuit elements and on the initial conditions, as well as the amplitude-phase interactions of frequencies and nonlinear interactions of individual phases
Summary
Electrical systems contain a large number of elements with significant inductance (generators, transformers, reactors, etc.). Analysis of the conditions for the excitation of subharmonic modes of three-phase nonlinear systems, depending on the parameters of the circuit, and the applied impact, allows us to identify the main patterns of overvoltage in power lines and possible measures to prevent or reduce them to permissible values. Analysis of the conditions for the excitation of subgamonic oscillations in three-phase nonlinear systems, taking into account the parameters of the circuit and the applied voltage, makes it possible to identify the main patterns of overvoltage in power lines and, if possible, take measures to prevent such anomalous modes or mitigate their negative consequences.
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