ГРАФОАНАЛИТИЧЕСКОЕ ИССЛЕДОВАНИЕ РЕЖИМОВ ОДНОФАЗНОГО ЗАМЫКАНИЯ НА ЗЕМЛЮ

Abstract

Relevance To determine the damaged phase in single-phase earth faults (SPEF), as well as for the purposes of relay protection and signaling of earth faults, it is important to know the phase voltages and the zero sequence voltage. Phase voltages are used to determine the damaged phase and determine the location of the damage. The zero sequence voltage is used to perform nonselective signaling of the SPEF and to determine the completeness coefficient of the fault in adaptive earth fault protections in networks with low earth fault currents. Single-phase short circuits in 6–35 kV networks occur as a rule through a fault resistance, the value of which can reach 5–7 kOhm or more. The fault resistance at the point of damage changes the values of both the zero sequence current and all phase voltages, and the zero sequence voltage. Therefore, the study of single-phase earth fault modes and the assessment of the effect of fault resistance on phase voltages and voltage. Aim of research The main aim of the research is to develop graphoanalytic methods for studying modes for SPEF through fault resistance in networks with an isolated neutral. Research methods Graphoanalytic methods are used to study the effect of fault resistance on phase voltages. The construction of phase voltage graphs directly in the fault resistance function may performe only for a specific electrical network. In the article, to perform the analysis in a generalized form, the equations of phase voltages are used as a function of intermediate variables, which depend on the value of the fault resistance, but do not depend on the parameters of the electrical network. As intermediate variables, the damage completeness coefficient, the relative fault resistance, as well as the angle by which the vector of zero sequence voltage, taken with the reverse sign, lags behind the vector of the pre-emergency voltage of the damaged phase. The main advantage of the phase voltage equations in the function of intermediate variables is that such equations have the same form for any electrical network. At the same time, voltage graphs and superimposed graphs of other parameters of the SPEF mode in relative units can be used as nomograms and allow us to study SPEF modes in a wide range of changes in fault resistances. Results Equations are obtained for the relative values of phase voltages and zero sequence voltages as a function of the damage completeness coefficient and the relative values of the fault resistance. Graphs of phase voltages and zero sequence voltages are constructed. Graphs of changes in the damage completeness coefficient and relative fault resistance are combined with voltage graphs. The obtained equations and constructed graphs are universal in nature, valid for any electrical network with an isolated neutral and can be used as nomograms for determining and analyzing all parameters of the SPEF mode in relative units. Formulas and examples of transition to named units are given.