Grid Impedance

[wwhitney]

Say I had a test device that could do the following measurements fairly quickly, so that the rest of the grid including other loads on the premises could be considered to be in a steady state: apply a series of test loads, of various currents and phase angles (or if you prefer, a series of test impedances of varying resistive and reactive components), and measure for each the resulting supply voltage, both magnitude and phase (relative to the unloaded supply voltage).

How well would the resulting data match the idealized model of a fixed voltage source in series with a fixed impedance? And what would the typical impedance be, both the resistance and the reactance, or if you prefer total impedance and X/R ratio?

Then if we repeat the data acquisition at different times, when the rest of the grid is in different states (e.g. more or less load elsewhere on the premises), we would get an unloaded voltage and an impedance each time. The unloaded voltage would vary depending on the rest of the grid's loads/sources. Would the impedance generally be the same each time? Seems like it should just be the composite impedance of all the premises equipment, along with the service drop and however many transformers back far enough into the grid that the further impedance contribution of upstream equipment becomes very small.

Just wanted to check that this is a reasonable model.

Thanks, Wayne

 

[JoeStillman]

Sounds like you want to quantify the system's "stiffness" (or it's reciprocal, the "softness") at various points. In my experience, you don't have to go too far upstream before source impedances are negligible. Your mileage may vary, especially if you are quantifying impedances in miles.

 

[wwhitney]

Sounds like you want to quantify the system's "stiffness" (or it's reciprocal, the "softness") at various points.

Mostly my question is to confirm that that "stiffness" for any given steady state will look like a fixed impedance, rather than some non-linear behavior.

Cheers, Wayne