A Three-Phase State Estimation Based on Alternating Optimization for Power Systems Including Conductor Temperatures

This article presents a temperature-dependent three-phase power system state estimation method in which the bus voltage phasor and line conductor temperature are considered as state variables. The heat-balance conditions of the overhead lines and underground cables are integrated into the state estimation problem. To improve the robustness of the estimation results, the objective function of the constrained optimization problem is based on the Schweppe-type Huber generalized maximum-likelihood (SHGM) estimator. A solution strategy based on an alternating optimization approach has been proposed. The method begins by estimating the voltage phasors of all buses while keeping the line conductor temperatures fixed to their present values. The optimization then uses the estimated voltage phasors and environmental information around all transmission lines to estimate the conductor temperature variables. These two optimization stages are alternatively repeated until the convergence conditions are satisfied. The effectiveness of the proposed state estimation has been demonstrated on IEEE 30-bus and 118-bus systems modified as three-phase systems containing both overhead lines and buried underground cables. The results show that the proposed method can provide good estimated state accuracy and reduce the computational burden.