Methods, devices and systems for detecting an isolation fault in an electrical installation

A method for detecting an isolation fault in an electrical installation by means of a detecting device associated with an electrical load supplied by the electrical installation, the electrical installation comprising an isolation monitor configured to inject a measurement signal into the electrical installation, said injected signal comprising a first component oscillating periodically at a predefined first frequency and a second component oscillating periodically at a predefined second frequency, the electrical phases of the installation being normally isolated from ground, the method comprising:

• measuring an AC electrical voltage between phase conductors of the electrical load to be monitored and ground, and an electric fault current flowing between said electrical load and ground;
• identifying, in the measured electrical voltage, at least one first component oscillating at the predefined first frequency and one second component oscillating at the predefined second frequency;
• calculating an impedance of the electrical fault from the fault current measurements and from the measured electrical voltage;
• calculating an impedance of the electrical installation from the first and second components identified in the measured electrical voltage;
• selecting a predetermined case from a predefined list, depending on the calculated impedances, on the measured electrical voltage and on the measured fault current;
• and
• identifying an operating condition of the electrical installation on the basis of the selected predetermined case.