Search

Introduction. A significant proportion of earth faults in medium voltage networks represents a short-lived and transient process. Problem. In such cases, earth fault protection that responds to steady-state current and voltage is not able to operate properly. Purpose. To develop earth faults protection selective algorithm using transient components, that occur in zero-sequence currents and voltage in the fault process. Method. A mathematical model of the power supply system was applied to study the transient components of currents and voltage of zero sequence in compensated electrical networks with phase-to-earth faults, and a those model also is used to test the operation of the developed protection algorithm. The results showed that, the reactive power for transient components, of the frequency greater by 4-6 times, than fundamental frequency, which are extracted from the current and voltage of zero sequence by wavelet transform in compensated electrical networks on the damaged feeder, is positive regardless of the degree of compensation of the capacitive current. That may be the basis of the principle of directional protection. Originality. Phase-to-earth fault selective protection algorithm has been developed. In that algorithm, first derivatives of currents and voltages of zero sequence are found, to reduce the influence of aperiodic components. And then, by using of the wavelet transform with Morlet mother function, an orthogonal components are extracted from them. Reactive power is calculated for transient component. If that reactive power excess of threshold, the relay will make a decision. The reliability of the developed protection algorithm is confirmed by the results of mathematical modelling and verification of the test sample at the laboratory stand and by means of field signals that were recorded by digital loggers at the substations.

This article examines cooperation in the electric energy sector in the Baltic region. The author explores the existing undersea HVDC power exchange projects. It is emphasised that cooperation in the electric energy sector is concentrated largely in the EU member states despite earlier plans to establish the Baltic energy ring, which would also include Russia and Belarus. The author stresses that one of the most acute problems for the EU today is overcoming isolation of the energy systems of the Baltic States (Lithuania, Latvia, and Estonia) from that of the major part of the EU. This task has become especially relevant after the closing of the Ignalina NPP (Lithuania), which used to be the primary energy source for the three Baltic States. The article examines key projects of the construction of new international power transmission lines in the framework of the Baltic Energy Market Interconnection Plan (BEMIP) and the prospects of the Visaginas NPP (Lithuania) in solving energy problems of the Baltic States. The author analyses Russia’s role in the electric energy market and focuses on a possible increase of the country’s energy market share following the construction of the Baltic NPP and the export of generated electric energy to Poland, Lithuania, Germany, and Sweden. The author concludes that the prospects of Russia’s energy export to the Baltic Sea region will be determined not only by technological, economic and market factors, but rather by the general state of relations between Russia and the EU. Moreover, a lot depends on Lithuania’s decision on the construction of the Visaginas NPP, as well as the way the EU and the Baltic States solve the problem of energy supply in case the NPP project is terminated.