Geomagnetically induced current model for the Namibian High Voltage Network
Geomagnetically Induced Currents (GICs) are low-frequency currents that enter power transmission networks through the grounded-neutral points of the transformer windings. The paper presents a model to emulate the flow of this current. As early as in 1998, GICs studies within the Southern African region focused on demonstrating the existence of GIC in this mid-middle latitude region. Recent literature has amply argued, proved and demonstrated the presence of GICs in the Namibian Transmission Network during a Geomagnetic Disturbance (GMD). Geomagnetic disturbances are perturbations in the magnetosphere which produce variations in the Earth's geomagnetic field, hence leading to flow of GIC in the transmission networks. Since the GICs are DC-like currents they are also essentially referred to as “quasi-DC” currents. Consequently, conventional AC models used in power system studies cannot be used directly to analyse the GIC flow in the electric transmission system, and hence there is need for the development of a working DC model to carry out GMD impact studies on the Namibia Power Network. In this paper, a working quasi-DC model for the Namibia High Voltage (HV) Transmission network is presented. The model is tested via modelling and simulation of GIC flows in the network using the EPRI OpenDSS (Open Distribution Simulation Software). The partial results seem to suggest that the magnitudes of GICs in the network are increasing with the expansion and development of the network since early 2002. The effects of probable network contingencies, based on N-1 Criterion, on the flow of GICs are also presented.
Surface electric fields for North America during historical geomagnetic storms
To better understand the impact of geomagnetic disturbances on the electric grid, we recreate surface electric fields from two historical geomagnetic storms—the 1989 “Quebec” storm and the 2003 “Halloween” storms. Using the Spherical Elementary Current Systems method, we interpolate sparsely distributed magnetometer data across North America. We find good agreement between the measured and interpolated data, with larger RMS deviations at higher latitudes corresponding to larger magnetic field variations. The interpolated magnetic field data are combined with surface impedances for 25 unique physiographic regions from the United States Geological Survey and literature to estimate the horizontal, orthogonal surface electric fields in 1 min time steps. The induced horizontal electric field strongly depends on the local surface impedance, resulting in surprisingly strong electric field amplitudes along the Atlantic and Gulf Coast. The relative peak electric field amplitude of each physiographic region, normalized to the value in the Interior Plains region, varies by a factor of 2 for different input magnetic field time series. The order of peak electric field amplitudes (largest to smallest), however, does not depend much on the input. These results suggest that regions at lower magnetic latitudes with high ground resistivities are also at risk from the effect of geomagnetically induced currents. The historical electric field time series are useful for estimating the flow of the induced currents through long transmission lines to study power flow and grid stability during geomagnetic disturbances.
Geologic transect across the Grenville orogen of Ontario and New York
Revised cross sections of the western Grenville Province incorporate new geologic results and reprocessed seismic reflection data. The geology is presented in terms of three tectonic elements: (1) "pre-Grenvillian Laurentia and its margin" with ca. 1740 and 1450 Ma continental arc plutons and associated supracrustal rocks; (2) "Composite Arc Belt" of allochthonous ~1300-1250 Ma volcanic arcs and sedimentary rocks; and (3) "Frontenac-Adirondack Belt" characterized by supracrustal and granitoid rocks, and anorthosites, of uncertain affinity, that may represent a distinctive part of the Composite Arc Belt or an offshore (micro)continent. Rocks of the Composite Arc and Frontenac-Adirondack belts were amalgamated with each other by ca. 1160 Ma, were then thrust over Laurentia during ca. 1080-1035 Ma and ca. 1010-980 Ma phases of convergence, and were dissected and exhumed by <1040 Ma normal faults. Penetrative deformation was restricted to that part of the pre-Grenvillian Laurentian margin that lies to the southeast of the Grenville front and parts of the accreted Composite Arc and Frontenac-Adirondack belts. The Laurentian rocks in the Grenville Province are bounded to the northwest and southeast by southeast-dipping ductile thrust and (or) normal shear zones. The Composite Arc and Frontenac-Adirondack belts to the southeast are bounded by ductile and brittle- ductile thrust and (or) normal faults that separate domains with contrasting cooling histories. Despite a long pre- Grenvillian tectonic and plutonic history, the present crustal architecture and much of the seismic reflectivity were acquired during 1080-980 Ma phases of compression and extension.