Detection and Protection Against Geomagnetically Induced Current via Harmonic Signature Analysis

Geomagnetically induced current (GIC) manifests its effects in electric power systems with DC current flow and characteristic harmonic signatures in the AC current. The harmonics generated from GIC will overheat transformers and other iron core circuits and increase reactive power consumption. We identify the major power devices affected by GIC and determine the modeling requirements for realistic assessment of GIC effects including harmonic signature during these events. Low frequency broadband transmission line models, grounding models, and transformer models with nonlinear reluctance in the magnetic circuit are developed and used for high fidelity simulations of power systems subjected to GIC. In addition, the DC component generated by GIC would introduce DC flux in iron cores instrument current transformers, leading to distorted magnetizing current and distorted output. The non-sinusoidal magnetizing current will increase significantly as the DC flux increases, leading to distortion in measurements. To reduce this distortion, a state estimation based method for instrumentation channel error correction is implemented, derived from the detailed modeling of the instrumentation channel. The method reduces the error from this distortion and recreates the primary quantities with high fidelity. The risk of relay misoperation due to errors in measurements is drastically reduced. Based on the result of harmonic signature analysis, a detection and protection scheme for GIC is proposed and simulated. The detection is based on the characteristic harmonic signature consisting of odd- and evenorder harmonics; the control consists of the insertion of a grounding capacitor between transformer neutral and ground. The results show the proposed method is able to successfully detect the onset of GIC and protect the power system by drastically reducing the harmful harmonic components during GIC.