Patent ID: 6933714

Claim:
A method for measuring the impedance of a live energy supply system at a rated frequency by impressing a testing current into the system and measuring the resulting changes in the system current and the system voltage, comprising the steps of measuring said system current and said system voltage during a first time interval (T 1 ) without the impressing of said testing current and during a second time interval (T 2 ) with the impressing of said testing current, composing said testing current of at least one periodic signal with at least one testing frequency that deviates from said rated frequency and the harmonics of this rated frequency, using, based on said measured system currents and system voltages, a Fourier analysis in such a way that complex Fourier coefficients of system current and voltage are respectively determined for the two time intervals (T 1 , T 2 ) and all testing frequencies, complex differences between T 1 and T 2 of these coefficients are used to calculate the impedances at all testing frequencies, and deriving the impedance of the energy supply system at the rated frequency from said impedance or impedances obtained for all testing frequencies.