Causes and implications of elevated neutral-to-earth voltages in residential areas near power substations

The increased use of non-linear loads in residential neighborhoods can lead to elevated current values in distribution feeder neutral conductors even under normal operating conditions. This increased current, can subsequently lead to undesirable neutral-to-earth voltages (NEVs) including shock sensation of individuals inside or around structures near power substations. In this thesis, a radial distribution system including non-linear loads is modeled. The MATLAB/Simulink application is used to perform a detailed balanced and unbalanced power flows and utilized to explore various effects of these non-linear and unbalanced loads on the NEV. The various grounding methods of primary distribution systems are evaluated in relation to their effects on both the NEV levels and safety considerations. The feasibility of modifying existing distributions systems and its economical impact are also addressed. A case study of elevated NEV level in a residential neighborhood is presented in details. Quantitative measurements of the effects of NEV are made before and after modification of the existing system. The analysis conducted in this thesis showed that the primary factors affecting NEV near the substation were largely dependant on the steady state unbalanced return current, the circuit grounding, and ground grid resistance. The analysis conducted also revealed that one of the most effective ways to reduce the effective ground grid resistance was achieved through bonding the primary and secondary neutral conductors. Additionally, it was shown that additional ground rods in excess of NESC standards do not appreciably effect the effective ground grid resistance. Lastly, recommendations for preferred configurations in general for both existing and new installations are given from the Author's view point.