Development of a Method for Tuning Arc Suppression Reactors With Sub-Magnetization for a Network With Isolated Neutral Mode

Our country’s power industry uses different voltage classes from 0.38 kV up to 750 kV. At the same time, depending on the voltage class, several systems of neutral grounding of power transformer windings are used (blindly grounded neutral, isolated, compensated neutral, effectively grounded). It should be noted that the effective operation of electrical equipment, depending on the voltage class, depends directly on the selected neutral mode of the electrical network. In fact, electrical equipment of different voltage classes can operate in any of the above-mentioned neutral modes of power transformer windings. However, depending on the voltage class of the network, it is advantageous to apply the neutral mode that will give not only the greatest economic effect, but also electrical safety. The aim of the research is to develop a new method to improve the tuning accuracy of arc suppression reactors with sub-magnetization, as well as a device based on the proposed method. Materials and Methods. As initial data, the results of operation of 0,4–35 kV distribution power grids, including electrical complexes with arc-quenching reactors of JSC “Grid Company” of the Republic of Tatarstan in relation to their adjustment for compensation of capacitive currents were considered and analyzed. Research results. The paper considers the issues of compensation of capacitive currents in 6–35 kV power grids with isolated neutral with schemes with all their advantages and disadvantages. Special attention is paid to the new method and device to tune arc-quenching reactors with sub-magnetization, which increases the accuracy and speed of tuning the proposed device by pre-calculating the initial magnetization current based on calculating the current capacity of the network using the analysis of the difference in frequency spectra of signals before and after excitation of the zero sequence circuit of the network obtained using fast Fourier transform, with subsequent adjustment of the arc-extinguishing reactor. The reactor with sub-magnetization made using a new tuning method and a device for its implementation, is successfully operated at the 110 kV Buinsk substation of the Republic of Tatarstan. Conclusions. The problems of the tuning accuracy of arc suppression reactors with sub-magnetization have been proposed to be solved by measuring and comparing frequency spectra of neutral voltage with application of fast Fourier transform before and after perturbation of zero-sequence circuit by reference current acting briefly on neutral through signal winding of arc suppression reactor. Using the difference of the obtained frequency spectra, the natural frequency of the zero-sequence loop is determined by the maximum amplitude corresponding to the frequency of free oscillations. According to the found frequency at known inductance of the arc suppression reactor, the capacitance of the network and the necessary current of the reactor sub-magnetization to adjust it to resonance are determined.