Nonsinusoidal power caused by measurements of grid impedances at unbalanced grid voltages

Abstract

At low-voltage level there is already a commercial measurement device that is able to identify the grid impedance in dependency of time and frequency. Since at the low-voltage level a four-wire system and at the medium-and high-voltage level a three-wire system is installed, the method to identify the grid impedance has to be varied. This paper proposes a method that could be applied for the identification of the time and frequency dependent grid impedance at the medium- and high-voltage level. Another aspect that has to be considered is how to dimension the variable switched resistive load, which is necessary to stimulate the grid. The power-range of this load is limited by the maximum allowable voltage drop in the grid. Furthermore it is important to investigate what kind of power terms are caused by the nonsinusoidal stimulation of the grid in balanced and unbalanced configurations. For this purpose the power theory of Fryze is applied.