Effect of neutral earthing in LV distribution system.

Abstract

In any power system, a neutral point is a common point between the three single phase voltages used to close the circuit and it is a current return path to the transformer point. This neutral point may or may not be accessible, distributed and earthed. During the investigation, it was learnt that an unearthed system leads to dangerous touch and step voltages and unstable voltages in the interconnected installation. However, the values of the fault current touch voltage and overvoltage and the extent of damage is associated to the kind of neutral earthing employed in that particular network. The earthing system in low voltage is more concerned about the combination of earthing at the source side and also at the installation (consumer/customer’ premises). This research focuses on the detailed comparative study of the following neutral earthing in low voltage power systems namely: earthing where the source and load are earthed independently, earthing where the supply is not earthed or is earthed through the impedance and the load is independently earthed), earthing that is further broken down into earthing where the source is earthed and the neutral is combined with earth to form protective earth neutral conductor and earthing that starts from the source (such as a utility company) with a combined protective earth neutral conductor until the customer installation service entry point, e.g. a residential unit, is reached, where the neutral and earth conductors are split throughout. The research was conducted by a simulation method of single phase and three phases to ground fault whereupon the behavior of various earthing methods was studied. The focus was on following aspects including but not limited to the detailed study of the various types of neutral earthing, the study of the unearthed system comparative to study between the neutral earthing systems. The study went about simulating the behavior of the unearthed system as a base case and the other other neutral earthing system in order to determine the effect of earthing the neutral. It was learnt that the selection criteria for the best neutral earthing method depends on the governing requirements, the supply continuity, operating condition and the typical system loading. The main hazard that was identified in the study was that of the challenges associated with the loss or detection of the neutral, protective earth (PE) and protective earth neutral (PEN) and these pose a serious risk on all these low voltage networks in a form of damage to equipment and endangering the lives of the people.