Power System State Estimation: Modeling Error Effects and Impact on System Operation

State estimation has been introduced to power systems and implemented in the 60s, using a single frequency, balanced and symmetric power system model under steady state conditions. This implementation is still prevalent today. The single frequency, balanced and symmetric system assumptions have simplified the implementation but have generated practical problems. This paper examines these simplified assumptions and their impact on the state estimation performance. It provides a theoretical basis for the well known fact that the reliability of the state estimator algorithms has been below expectations. Specifically, sensitivity analysis methods are used to quantify the impact of modeling simplifications and measurement schemes on the performance of state estimation. The results clearly illustrate that the traditional state estimation algorithm is biased. These biases affect the accuracy of state estimation and its convergence characteristics. The paper also reviews the traditional state estimation approach against recent technological advances that have enabled synchronized measurements. The implications and possibilities of this new technology are discussed in this paper. Specifically, an example application of the new technology for a Three Phase State Estimator is described. A power system state estimation based on a) multiphase model, b) voltage and current waveform measurements, and c) synchronized measurements is formulated. The paper focuses on the following: a) modeling, b) implementation, c) observability and d) performance. The overall performance of the system is described in terms of confidence level versus error. These concepts are illustrated with simple systems. In addition, we demonstrate the performance of the proposed methods on an actual system (New York Power Authority system) using actual synchronized measurements. The paper concludes with a commentary on the implications of improved state estimation methods on the security/reliability monitoring and control of an electric power system.