Why do the measured values for mains/loop impedance on generators fluctuate so much?

The measuring method basically works like this:
1. The voltage is measured without a load.
2. The "mains" is loaded with a test current. During the professional test, 3-4 amps are "burned", so to speak. Meanwhile, the voltage is measured again.
3. The load results in a voltage drop ΔU. The impedance is calculated using the formula R = ΔU / I, which in turn is used to calculate the short-circuit current.

Where does a problem arise in connection with generators?
A generator is not a power grid with a fixed transformer, but has a voltage regulator.
The voltage is therefore regulated under load. This makes the measurement of grid impedance and loop impedance on all regulated voltage sources (including USB systems or vehicle inverters) virtually meaningless - even if sometimes halfway correct-looking measured values appear on the display.
Depending on the "flywheel mass" or speed of the regulation, the measured values can also fluctuate extremely.

Example: With a 4 kVA generator, measured values for the short-circuit current can be displayed between 30 A and 1500 A - simply by repeatedly starting the measurement.

The above applies to all measuring devices - regardless of type, price or brand.