Geomagnetic disturbances monitoring, modelling and mitigation

Electric power utilities in the United States are working with the North American Electrical Reliability Corporation (NERC) to develop Transmission Planning reliability standard TPL-007 – “Transmission System Planned Performance during Geomagnetic Disturbances”, addressing power systems’ reliable operation and control during these events. The Standard establishes two stages in which power systems should address Geomagnetic Disturbances (GMD). In the first stage, owners and operators of the Bulk-Power System (BPS) shall develop and implement operational procedures to mitigate the effects of GMD’s consistent with the reliable operation of the BPS. The second stage requires owners and operators of the BPS to conduct initial and on-going assessments of the potential impact of a benchmark GMD event. Operational response to GMD starts after receiving GMD forecasts or alerts from one of the NERC Reliability Coordinators (RC) – in this case the New York Independent System Operator (NYISO) - for storms rated K6 or higher on the K1 to K9 scale, and includes various actions, depending on the level of Geomagnetically Induced Currents (GIC). To help system operators monitor GIC flows, harmonics and transformer overheating, a special GIC monitoring system was designed and installed on transformers determined to be either vulnerable or exposed to high levels of GIC. Calculation of geomagnetically induced currents is a necessary and critical component of evaluating potential system vulnerabilities to severe geomagnetic disturbances. A GIC network model was developed including refinements to the existing system model, and the neighboring system models. During this effort, a number of existing modeling gaps were identified and resolved – such as inclusion of phase-angle regulators and shunt reactors in the GIC network model. The derived models are expected to be incorporated in the subsequent versions of the standard GMD vulnerability analysis tools being developed by NERC along with the industry and academia. Finally, the developed model of the BPS and surrounding systems was analyzed to identify the key drivers and sensitivities for the calculated GIC flows in response to a select number of system conditions. Three types of network changes were examined – switching of shunt reactors, the potential application of neutral blocking devices, and system reconfiguration through transmission system components switching.