Abstract
Abstract. Assessing the geomagnetic hazard to power systems requires reliable modelling of the geomagnetically induced currents (GIC) produced in the power network. This paper compares the Nodal Admittance Matrix method with the Lehtinen–Pirjola method and shows them to be mathematically equivalent. GIC calculation using the Nodal Admittance Matrix method involves three steps: (1) using the voltage sources in the lines representing the induced geoelectric field to calculate equivalent current sources and summing these to obtain the nodal current sources, (2) performing the inversion of the admittance matrix and multiplying by the nodal current sources to obtain the nodal voltages, (3) using the nodal voltages to determine the currents in the lines and in the ground connections. In the Lehtinen–Pirjola method, steps 2 and 3 of the Nodal Admittance Matrix calculation are combined into one matrix expression. This involves inversion of a more complicated matrix but yields the currents to ground directly from the nodal current sources. To calculate GIC in multiple voltage levels of a power system, it is necessary to model the connections between voltage levels, not just the transmission lines and ground connections considered in traditional GIC modelling. Where GIC flow to ground through both the high-voltage and low-voltage windings of a transformer, they share a common path through the substation grounding resistance. This has been modelled previously by including non-zero, off-diagonal elements in the earthing impedance matrix of the Lehtinen–Pirjola method. However, this situation is more easily handled in both the Nodal Admittance Matrix method and the Lehtinen–Pirjola method by introducing a node at the neutral point.
Highlights
Geomagnetic disturbances can have a detrimental influence on the operation of the electric power transmission systems
There are three steps involved in calculating geomagnetically induced currents (GIC) using the Nodal Admittance Matrix method
The third step is to use the nodal voltages to determine the currents in the lines and in the ground connections
Summary
Geomagnetic disturbances can have a detrimental influence on the operation of the electric power transmission systems. Problems arise because the variations of the magnetic field induce electric currents in the power transmission lines These geomagnetically induced currents (GIC) flow to ground at substations of the power system, where they cause partial saturation of the power transformers (Molinski, 2002; Kappenman, 2007). There is increased concern that a repeat of such an extreme magnetic storm could cause widespread problems for the supply of electricity This has prompted renewed efforts to precisely understand the geomagnetic effects on power systems so as to make accurate risk assessments and plans for mitigation. Inclusion of multiple voltage levels introduces nodes into the network model that do not have a direct connection to the ground It is shown how this can be handled in each modelling technique and used to calculate the GIC in different types of transformers
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