Ground fault monitoring device for an electrical power distribution system

A ground fault monitoring device for an electrical power distribution system comprising:

• ground fault voltage means for measuring, filtering, sampling and analog-to-digital conversion of the residual ground fault voltage of an electrical power distribution system to generate a digitized residual ground fault voltage signal,
• ground fault current means for measuring, filtering, sampling and analog-to-digital conversion of the residual ground fault current to generate a digitized residual ground fault current signal,
• means for synchronizing sampling of the digitized residual voltage and current signals,
• computing means for computing, at each sampling period, the fundamental components of the residual ground fault current and voltage observed on a window of a period equivalent to the period of the power distribution system, so as to supply a first quantity representative of the phase difference between said fundamental components of the current and voltage,
• first comparing means for comparing the first quantity and a first preset threshold,
• determining means for determining a second quantity in terms of the result of the comparison performed by the first comparing means, and
• second comparing means for comparing the second quantity with a second preset threshold,
• and fault signal means for producing at least one of a fault signal and a tripping signal when said second quantity exceeds said second preset threshold.