PMU-Based System State Estimation for Multigrounded Distribution Systems

Linear network modeling and phasor measurement units (PMUs) simplify the traditional system state estimation (SSE) problem. The existing multiphase SSE-PMU-based models are linear including earthing resistances as a fixed and invariable parameter. However, earthing resistances strongly depend on moisture and temperature changes over time. Thus, under unbalanced operation time-varying Neutral-Earth Voltages (NEV) could be higher than admisible touch and step voltages in urban areas. Earthing resistances can be now monitored using specialized meters and therefore duly incorporated as measured and state variables in a multigrounded SSE problem. Thus, the SSE problem becomes non-linear and the standard linear solution approach is no longer suitable. This fact has been overlooked in the literature. To fulfill the research gap, a new multi-grounded SSE-PMU-based formulation is presented. As a key contribution, the normal-equation structure used in linear SSE approaches was extended to a non-linear one in order to allow the estimation of grounding resistances, neutral-to-earth voltages, and neutral currents. The proposal was applied in a 2-bus example for illustration purposes and successfully applied and compared with existing methods under large-scale conditions.