Investigation the Influence of the Active Resistance Value in the Neutral and the Transient Resistance of Earth Faults in Medium Voltage Electrical Grids

The neutral of the medium voltage power transformer on the medium voltage side in medium voltage grids is most often earthed through an active resistance or through a combination from a reactor and an active resistance. The determining factors for choosing the grounding method are the value of the single phase to earth fault current, the transient overvoltages, the selectivity and sensitivity of the earth relay protection, the electrical safety and more. The paper researches the influence of the value of the active resistance included in the neutral of the power transformer and the transient resistance in the fault place on the regime parameters for single phase to earth faults in medium voltage electrical grid.