Power Systems Engineering Research Center ACCURACY IMPROVEMENT STRATEGIES FOR PROBLEMATIC POWER SYSTEM MEASUREMENTS AND THEIR EFFECT ON STATE ESTIMATION

This is a project report from the Power Systems Engineering Research Center (PSERC). PSERC is a multi-university Center conducting research on challenges facing a restructuring electric power industry and educating the next generation of power engineers. More information about PSERC can be found at the Center's website: Notice Concerning Copyright Material PSERC members are given permission to copy without fee all or part of this publication for internal use if appropriate attribution is given to this document as the source material. This report is available for downloading from the PSERC website. This research discuses several power system measurement pre-processing techniques , which may improve calculations like state estimation (SE). SE is a proven technology , but operates under assumptions which may be inappropriate. The concept of non-collocated power measurement error is introduced, where reactance between current and voltage instruments creates power calculation error. A calculation-based method for correcting these measurements is presented and shown to slightly improve state estimates. SE may assume balanced operation. However, unbalance is common in power systems. Under certain assumptions, single-phase power measurements and complex current unbalance factor (CCUF) can calculate three-phase power. This yields better measurements, but is shown to have little effect improving traditional SE. Methods for estimating or calculating CCUF are also presented. SE often assumes all measurements are simultaneous. A simple linear prediction method used to identify late measurements is studied and shown to work in systems with low measurement noise and low system dynamics. The main elements of this research are: • It is possible to correct the measurement error associated with reactance in-between the CT and PT component of a power measurement from knowing the non-collocated power measurement, a local voltage magnitude, and the reactance. This is a software solution that avoids hardware reinstallation and may have a positive effect of state estimation results by lowering estimate error and, more iv dramatically, lowering state estimate variance. The practical significance of this is that a software patch can be used to correct for non-collocated power measurements , thereby avoiding a hardware fix. • State estimators that incorporate three-phase power flow may operate under a balanced system assumption when unbalanced conditions. A more accurate three-phase power calculation may be calculated from single-phase measurements and the complex current unbalance factor, resulting in improved state estimation output. Methods for estimating or directly calculating the complex current unbalance factor are also presented. The practical significance …