Reactive power transformation using а passive electronic transducer

Transformation of reactive power into active power, which can be used to perform work for various purposes, is of practical use. Goal. The aim of the work is analysis of the processes of resonant conversion of reactive power into active power in the proposed converter circuit. Methodology. A practical solution to this problem can be real-ized using a converter circuit consisting of two in-ductively coupled parallel and series resonant circuits. The use of a parallel circuit with resonance currents minimizes the impact on the processes in the reactive power source. The use of a series circuit with a voltage resonance allows maximizing the original active power in the converter load. Results. The simplest scheme of a passive electronic converter of reactive power into active power is proposed. The conditions are determined, whose fulfillment minimizes the influence of the proposed scheme on the processes in the reactive power source at the maxi-mum current in the converter load. Originality. Efficiency of the device under test means maximum cur-rent and power in the load with minimum impact on the inductance of the reactive power source. Practical value. The parameters of a real circuit have been calculated, which allows for practically lossless conversion of reactive power into active power with a minimum effect on the current in the source.

On Developing the Theory of Resonant Processes in Power Transformer Windings. Part 2. Frequency Responses of a Circuit with Four PI Sections

In the first part of the article, the results from theoretical studies of frequency responses in a homogeneous chain circuit containing two PI sections were presented, and conclusions about the voltage resonance occurrence conditions were drawn. A circuit with two PI sections has a single independent node and one natural frequency, whereas transformer windings are more complex oscillatory circuits and have a much larger number of natural oscillation frequencies. The second part of the article presents the results from studies of frequency responses in a homogeneous chain circuit containing four PI sections, three independent nodes, and three natural oscillation frequencies. Analytical expressions for the admittances of the equivalent circuit individual parts and the voltages at the intermediate nodes, as well as expressions for the natural frequencies are obtained. Using an analysis of the frequency dependences of the admittances of the equivalent circuit parts, the conditions and frequency ranges under which voltage resonance may occur at the first, second, and third natural frequencies, are shown. It has been demonstrated that for the considered resonant circuits there is a critical frequency above which the conditions for voltage resonance are not satisfied. Formulas for impedances and voltages at intermediate nodes of a chain circuit with an arbitrary number of PI sections are given.

On Developing the Theory of Resonant Processes in Power Transformer Windings. Part 1. Frequency Responses of a Circuit with Two PI Sections

The windings of power transformers are complex oscillatory circuits. Their natural oscillation frequencies range from a few to hundreds of kHz, and under unfavorable conditions they can coincide with the frequencies of transient voltage oscillations in electrical networks caused by switching operations and short circuit faults in cable lines. The development of electrical networks and the technical solutions that have come in wide use in recent years give rise to a situation in which the cases of damage to the insulation of power transformer windings resulting from resonant overvoltages are increasingly more frequently encountered during operation. An attempt is made in the article to develop the theory of resonant processes in the windings of power transformers. The frequency responses of voltages and currents in a simplified equivalent circuit of the power transformer winding are considered. Analytical expressions are obtained for the admittances of individual parts of equivalent circuits and the voltages at intermediate nodes, as well as expressions for the natural frequencies of the equivalent circuits considered. It is shown that the resonant growth of voltage in the transformer windings results from the voltage resonance caused by the presence of the winding’s own inductance and capacitance with respect to ground. By analyzing the frequency dependences of the admittances of equivalent circuit individual parts, the conditions and frequency ranges in which voltage resonance may occur are shown.