Patent ID: 7772857
Filing Date: 2010-08-10
Classification: G01R,H02H

Abstract:
1. A system to determine an impedance of an electrical facility being disconnected from its high or medium voltage power supply, comprising: a signal injection unit arranged to inject a test signal at a first main frequency between a reference point of an electric circuit and ground and to inject another test signal at a second main frequency between a reference point of the electric circuit and ground, where the electric circuit is connected with the facility; a signal conversion unit arranged to measure a first response voltage and a first response current in the electric circuit, where the first response voltage and the first response current result from the test signal and to measure a second response voltage and a second response current as a result to the other test signal; and a processing device arranged to determine an impedance to ground of the facility from the first response voltage and the first response current and to determine another impedance to ground from the second response voltage and second response current to analyse impedances to ground of the facility, said analysing including comparing each determined impedance to ground with a predetermined value, and to determine a safety state of the disconnected electrical facility based on the analysed impedances to ground.