Empirical substantiation of the advantage of using the modified method of symmetrical components to estimate the value of zero-sequence current in distribution grids

Introduction. The tendency of growth in the number and increase in the installed capacity of single-phase nonlinear electric consumers leads to the deterioration of power quality. One of the criteria for assessing the quality of electric power is the zero-sequence and reverse sequence asymmetry indices. And the zero-sequence asymmetry coefficient is conditioned by the zero-sequence current strength. Goal. To empirically substantiate the advantages of using the method based on the measurement of instantaneous values of current strength synchronously on three phases for one period to estimate the zero-sequence asymmetry coefficient, as compared to the method of symmetrical components, implemented using the turnaround operator, for a more accurate assessment of current strength asymmetry in distribution networks.

Materials and methods. To achieve the set goal, an experimental stand of the power supply system was designed and assembled. The developed stand allowed to obtain a set of synchronously measured instantaneous values of current and voltage in each phase, as well as in the zero working conductor, when the magnitude, nature and non-sinusoidality of the load changes independently in each phase. In this case, the criterion for assessing the accuracy of calculation of the zero-sequence asymmetry coefficient was the value of current measured in the neutral working conductor.

Results and discussion. The use of the basic method of symmetrical components to determine the zero sequence current in the case of amplitude-phase asymmetry under active-inductive non-sinusoidal load leads to an unacceptable error, the median value of which is 21.25%. In order to reduce this error it is recommended to use in these modes the method based on the measurement of instantaneous values of current synchronously on three phases for one period, in this case the median value of the error does not exceed 0.16 %.

Conclusion. To reduce the zero-sequence current calculation errors, it is recommended to use a method based on the measurement of instantaneous current values synchronously on three phases for one period.

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