10 ohm Neutral grounding resistance in 30kV western Libyan network and effects

Abstract

Direct Grounding of the transformer neutral point leads to single line to ground fault current with a high-value, which may reach the value of the three-phase fault current or more. This high fault current causes destruction of fault locations (equipments and operators), and raises the ground voltage that increases the high step and touch voltages, which is dangerous to humans and animals, causes destruction of communications equipment and can be of great danger to the users. Those high fault currents can be reduced by inserting resistance to the neutral point of injection feeding transformer. In this research, the importance and effect of neutral grounding resistance in 30kV system network and its impact in the determining and limiting of the single line to ground fault currents for a network fed by a single or multi sources will be addressed. Also, the characteristics of the neutral grounding resistance installed in 220/30 kV transformer will be determined and discussed. According to the historical data, two events of tripping happened in 30kV transformer substation in Tripoli area network, due to high single line to ground fault. The behavior of single line to ground fault current for the above mentioned tripping events in Tripoli area were measured, and this will be compared to the simulated results of the same cases and discussed. The ATP (Alternative Transient Program) and Neplan software programs are used for simulation of such events [5] [6]. Finally, the effect of the Temporary Over Voltage (TOV), which is also called Power Frequency Over Voltage, on the healthy phases during the single line to ground fault current occurs will be discussed, as well as the effect of the neutral grounding point.