Method and detection device for detecting a high-impedance ground fault in an electrical energy supply network with a grounded neutral point

A detection device assembly for detecting a high-impedance fault having a presence of a fault current in a three-phase electrical energy supply network with a grounded neutral point, the detection device assembly comprising:

• a detection device configured to:
• connect to phase conductors of the three-phase electrical energy supply network;
• inject a test signal into the three-phase electrical energy supply network, the test signal having a frequency which differs from a network frequency of the three-phase electrical energy supply network, said detection device configured to inject the test signal as a three-phrase test signal into phase conductors of the three-phase electrical energy supply network;
• and
• generate a measuring signal which indicates a residual voltage, the residual voltage is vector sum of the voltages to ground of the several phrase wires of an electrical supply circuit, of the test signal induced in three-phases of the three-phase electrical energy supply network;
• said detection device having a testing device configured to compare the residual voltage with a threshold value;
• and
• said testing device is configured to detect a presence of a high-impedance ground fault if the residual voltage exceeds the threshold value.