Geomagnetically induced currents (GICs) can contribute to long-term
degradation of components of power networks and to corrosion of pipelines
and other buried infrastructure. The major power outage in March 1989 in
Québec in 1989, which left six million people without power for
nine hours, occurred when GICs caused a trip out of the lines from James
Bay and a collapse of the power system. The ability to model GICs more
accurately will assist utilities in planning and mitigation of these effects.
Modelling of powerline GICs requires information of the form of the earth
electric fields induced by different geomagnetic sources and therefore
a knowledge of the large-scale earth resistivity structure. In addition,
modelling of GICs on pipelines requires information on the local earth
resistivity structure near the pipelines. Present GIC predictions for the
Canadian power networks are based on research involving considerably simplified
models of Earth resistivity structure and simplified models of geomagnetic
source-fields. POLARIS EM infrastructure will allow refinement of GIC prediction
in Canada through improved definition of the large-scale resistivity structure
of the provinces and through correlation of measured GICs with realistic
source-fields and resistivity structures. This work is designed to yield
improved GIC predictions for specific power systems and may also lead to
an improved understanding of the GIC induction process.
The objective of the POLARIS Manitoba GIC project is to provide an improved knowledge of the large-scale electric fields induced in the province during geomagnetic field variations of varying frequency, intensity, and spatial wavelength. The primary focus is on powerline GICs. The study will be based on magnetotelluric (MT) array surveys. Simultaneous measurements of magnetic field variations and associated electric field variations will allow the earth impedance to be defined as a function of frequency and wavelength. Whenever possible the field measurements will be correlated with actual GIC recordings on powerlines. A secondary objective of the study is to examine the influence of smaller-scale resistivity variations on induction of GICs in pipelines. The results of the POLARIS study will also contribute to the overall mapping of the large-scale resistivity structure of the province and will provide useful tectonic results. The POLARIS Manitoba project will involve MT measurements at approximately 10 sites in Fall or Winter of each of the next four years. This science plan outlines the preliminary plans for the work. It will be amended as input is received from other parties including the POLARIS Steering Committee, the GSC Geomagnetic Laboratory, Manitoba Hydro, and possibly additional utilities concerned with GICs. The plan will form a basis for developing a joint project with the Manitoba utilities and the basis of an NSERC Collaborative Research and Development (CRD) or Earth Science Sector (ESS) proposal submitted to fund the operational aspects of the project.
Importance and Modelling of Geomagnetically Induced Currents
GICs have major impact on electrical and pipeline infrastructure. Extraneous currents entering power systems can cause misoperation of protective devices such as relays and circuit breakers resulting in system shut-down. In extreme situations GICs can cause the collapse of a power system, e.g., the power outage in March 1989 in Québec and the collapse of the Québec-New England DC link in March 1991. The total cost of the Québec blackout was $13.2 million which included about $6.5 million associated with damaged equipment (Geological Survey of Canada 2000). GICs are also thought to cause half-cycle saturation of magnetic devices.
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