Event under the auspices of the Ministry of Economy of Slovak Republic

Relay protection designing as a solution to the problem of recognizing the regimes of the electrical grid

*Ivan Nagay
Platov South-Russian State Polytechnic University (NPI) ,«RE

Vladimir Nagay
Department "Electric stations and electric power systems" Platov South-Russian State Polytechnic University (NPI)

Pavel Kireev
Department "Electric stations and electric power systems" Platov South-Russian State Polytechnic University (NPI)

Sergei Sarry
Department "Electric stations and electric power systems" Platov South-Russian State Polytechnic University (NPI)


     Last modified: 2017-06-16

Abstract
Electric grids 6-110 kV are one of the most widespread and extended in Russia and provides power to both industrial and municipal consumers. The detection of faults in electrical distribution grids with branching substations is a complex task, especially if there is an effect of the arc resistance, starting currents on the currents of fault regimes that are comparable in level with the currents of the load regimes. In this case the presence of a arc resistance at the fault location leads to a decrease in current and an increase in the resistance of the short-circuited circuit, i.e. to displacement of the fault regime area towards the load mode area. It is possible to cross these areas, especially if there is a power motor on adjacent substations in relation to the protected substation, which leads to a practical impossibility of recognizing fault regimes by traditional methods.
Increasing use of microprocessor technology in the systems of relay protection and automation (RPA) of power systems allows to increase their technical perfection. The use of a programmable element base has a sense if not only well-proven algorithms of functioning are used, but also algorithms that increases the sensitivity, selectivity, speed and reliability of the relay protection devices. A purposeful definition of a strategy for recognizing normal, abnormal and fault regimes and making a decision based on the results of this recognition allows the designing of hardware and software relay protection complexes with better characteristics for the modern electric power systems.
In the paper are seen approaches to designing of relay protection of electric distribution grids with branching, intermediate substations and transformers of various power in view of pattern recognition task decision. The stages of designing a system for recognizing phase-to-phase short circuits, open-phase regimes and complicated faults against the background of loading and starting regimes of high-voltage electric motors. It are determined qualitative and quantitative criteria for recognizability of regimes. The technique of an estimation of the information signs characterizing redimes of operation of electric grids with use of linear and polynomial decision functions is offered.

 

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