High resistance ground fault protection

Protection device for high resistance ground faults in a threephase electric power distribution network, comprising:

• means for analog/digital conversion of analog signals representative of at least two phase currents and the zero sequence current of the network;
• means for analog/digital conversion of analog signals representative of each of the three phase voltages;
• means for estimation of the Fourier parameters of the converted phase current and phase voltage signals;
• means for estimation of the frequency of the electric power distribution network;
• means for the estimation of the Fourier parameters for the remaining phase current and the negative and positive sequence currents of the electric power distribution network;
• means for establishing the Fourier model of the electric power distribution network using the estimated Fourier phase currents, phase voltages, frequency and the negative and positive sequence currents;
• means for determining the instantaneous residuals of the electric power distribution network as the difference between the digitized values of said at least two phase currents and the Fourier model values;
• means for establishing the instaneous loss function;
• and
• means for generating a trip signal indicating the existence of a high resistance ground fault on any of the phases of the electric power distribution network when the zero sequence current is greater than a lower limit value and simultaneously therewith said loss function has a value greater than a second lower limit value for a time longer than a lower limit time value.