Four-Wire Three-Phase State Estimation for Multi-Grounded Distribution Systems

Abstract

Due to the lack of research papers considering four-wire three-phase distribution systems state estimation (SE), this paper presents a novel approach for SE in multi-grounded distribution networks. In the proposed methodology, the state variables vector is composed of branch currents in rectangular coordinates and measurements are obtained using PMUs (Phasor Measurement Units). A four-wire three-phase modeling is considered for the network elements assuming the representation of the neutral conductor and the earth grounding impedances. An optimization problem is formulated to determine the system state based on an objective function defined by the weighted least squares concept. Load pseudomeasurements are treated as inequality constraints to overcome the scarcity of real time measurements. As important contribution of the article, the power dissipation in the neutral-to-earth connection is also handled as an additional inequality constraint yielding reduced estimation errors for all the phases allowing to estimate NEV (Neutral-to-Earth Voltage) magnitudes. In order to demonstrate the effectiveness of the proposed method, simulations are conducted using the Kersting’s 21-bus test feeder and a modified 33-bus system.