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.
A Review of Geomagnetically Induced Current Effects on Electrical Power System: Principles and Theory
Geomagnetically induced current (GIC) has been a significant concern for the electrical power grid in high latitudes for decades. Its origin starts in the Sun; during extreme space weather, the magnetic field of the Earth varies rapidly. This variation induces electric fields at the Earth’s surface and leads to GICs in manmade technologies. Power systems are the most affected by this induced current, which causes half-cycle saturation of power transformers and other issues. Understanding the behaviours and chain effects of this phenomenon is the key consideration in modelling the hazards to technological systems from space weather. In this paper, a comprehensive review of space weather, geomagnetic disturbances (GMDs) and GICs and their impacts on the power systems in both high and mid-low latitude regions is presented. Additionally, we highlight the most commonly used methods to model and calculate geoelectric fields at the Earth’s surface and GIC in the power systems with respect to DC and AC analysis. In addition, we have classified the GIC effects on the different power system components. Moreover, the possible solutions and mitigation techniques to eliminate or reduce these effects based on different GIC blocking devices are reviewed in this work. This work provides researchers and power system operators a shortcut road path to understanding GIC phenomena, modelling and calculations, effects, and mitigation of these effects.
Ionospheric Elementary Current Systems in Spherical Coordinates and Their Application
Two sets of basis functions in spherical coordinates are presented, in terms of which any given ionospheric current system, consisting of horizontal sheet currents and their accompanying field-aligned currents, can be expanded, regardless of any considerations on the ionospheric conductances or the electric field. The single basis functions are called elementary current systems. One basis function set is curl-free and poloidal, and causes a toroidal magnetic field that is restricted to the area above the ionosphere. The other one is divergence-free and toroidal, and causes a poloidal magnetic field which is solely responsible for the magnetic effect of ionospheric currents below the ionosphere. The field-aligned currents are assumed to flow radially. The expansion presented is used on a model of a Cowling channel to decompose its Hall and Pedersen currents into their total divergence-free and curl-free parts. This application example shows how the analysis technique based on the elementary current expansion resolves the physically relevant primary and secondary currents inside the Cowling channel.