The Requirement and Formulation of a Gic-Inclusive State Estimator for Geomagnetic Disturbance Events
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It is widely known that solar Coronal Mass Ejections (CMEs) emanating from the sun’s surface have the capacity to disturb the earth’s magnetic field. This leads to an event called a Geomagnetic Disturbance (GMD). The varying magnetic field caused due to this disturbance could result in an electric field over the earth’s surface. This electric field has the potential to eventually cause quasidc currents called Geomagnetically Induced Currents (GICs) circulating through the grid. When these quasi-dc currents flow through high-voltage transformers, they produce additional reactive power losses in them. Myriad research efforts have been taken to address the issue of circulating GICs from different perspectives. Improved GIC modelling, electric field estimation, GIC monitoring, stability analysis, and voltage study to list a few. But, none of the efforts have addressed the GMD problem from a Power System State Estimator (PSSE) perspective. PSSE is a tool employed by utilities in Energy Management Systems (EMS) and hence, is an important tool for making decisions pertaining to the grid. The additional reactive losses caused by GICs, being unaccounted for, could result in large deviations in the system states estimated. Therefore, my research is motivated by the lack of an accurate PSSE available for the utilities to be used during GMD events. A GIC-inclusive PSSE could greatly assist the utilities and system operators in taking operational decisions and hence, help in better management of the grid. The power grid is modelled as a dc system for GIC analysis and study. This is because GICs are quasi-dc and hence the system can be modelled as dc. Various studies that need to be carried out for GMD analysis require computation of transformer neutral GICs as well as other system parameters. A considerable portion of these studies are usually performed on MATLABR . But, there is no tool or package available on MATLAB that can provide easy and seamless calculations of these necessary parameters. One direct example, relevant to my thesis, of an application of such a tool, would be in the modified PSSE itself. The modified PSSE would require the calculation of transformer neutral GICs. Therefore, another research motivation is the construction of an efficient tool for the calculation of such system values that could be utilized for various GMD studies. For my research, the accuracy of the traditional state estimator was checked for GMD events. This state estimator failed to produce accurate results during the GMD events and accumulated noticeable results. To solve this problem, the GIC-Inclusive state estimator was constructed using the GMD tool, MATGMD. This modified state estimator was successful in obtaining accurate results for the EPRI 20 bus case and the UIUC bus case with the error in the voltage magnitude states in the range of 10^-5 and for the neutral current states in the range of 10^-4. The results for the EPRI 20 bus case using the GIC-Inclusive state estimator have been depicted and comparisons with the traditional state estimator have been made. The GIC-Inclusive state estimator, though computationally heavy, is very effective and the advantages of its applications outweighs the ease of using the traditional state estimator during GMD events.
Juvekar, Gandhali Prakash (2019). The Requirement and Formulation of a Gic-Inclusive State Estimator for Geomagnetic Disturbance Events. Master's thesis, Texas A&M University. Available electronically from