Impedance measurment in 3 phase curcuit.

Hi guys,

I made a "Grid connected wind turbine" scheme from standard Simscape library blocks and tried to measure summarized phase to ground impedance in "PCC" point with "Impedance Measurement block" for further Short circuit ratio calculations. As I know, the value should increase if we go from the WT to the grid, but the calculated values look random.

I suppose that the leftmost block measures the impedance to the left of itself, the rightmost to the right. What is wrong and how should i measure for getting the correct final impedance of the scheme?

Answer 1

[Joel Van Sickel]

The impedance measurement block is measure total impedance, so it is measuring the combination of the impedance to the wind turbine AND the grid from each point. This is similar to if you try to measure impedance in a real circuit, the upstream circuit effects the measurement as well as the downstream circuit as they are directly coupled. Also, note that the DFIG is modelled such that is has no path to ground, so it isn't being included in these impedance calculations, but the helped load is. As an example, you can add an extremely large resitance between the utility and PCC. Then you will only see the downstream impedance, not effected by the upstream impedance.