The Impact of Geomagnetically Produced Negative-Sequence Harmonics on Power Transformers

Ahmed Abuhussein,Mohammad Ashraf Hossain Sadi

doi:10.1109/access.2021.3054366

Abstract

Geomagnetically induced currents (GICs), although small in magnitude, can inflict detrimental effects on power systems. GICs damage transformers, generate unusual harmonics, trip reactive power support equipment, cause protective relays to malfunction, and may even collapse the entire power system if not mitigated. This paper studies the adverse effects of the negative-sequence harmonics produced by GICs flowing in power transformers. Our simulations show that a transformer's susceptibility to GIC depends on core type, voltage level, associated harmonics order, and GIC magnitude. High-voltage and extra-high-voltage tests were carried out in SIMULINK. GIC was also emulated experimentally to validate the simulated excitation current and harmonics produced by the GIC. The simulation and experimental results show that the 2nd and the 5th harmonics are the most prominent harmonics associated with GIC and dc saturation. Even if a transformer is ungrounded, the negative-sequence harmonics produced by the GIC can still propagate through a transformer and cause harmful effects on the isolated side.

Highlights

The main source of space weather is the interaction between the earth’s magnetic field and the sun, whose activity directly affects the earth’s magnetosphere; any significant variation in the sun’s emissions causes a corresponding geomagnetic disturbance (GMD)
A GMD is defined as a temporary disruption in the earth’s magnetosphere caused by the sun’s emissions that are directed at the earth, such as solar flares, radiation storms, and coronal mass ejections (CMEs)
HARDWARE TESTING AND RESULTS The purpose of the experimental testing is to confirm the simulated behavior of transformers during a geomagnetically induced currents (GICs) event

Summary

Introduction

The main source of space weather is the interaction between the earth’s magnetic field and the sun, whose activity directly affects the earth’s magnetosphere; any significant variation in the sun’s emissions causes a corresponding geomagnetic disturbance (GMD). A GMD is defined as a temporary disruption in the earth’s magnetosphere caused by the sun’s emissions that are directed at the earth, such as solar flares, radiation storms, and coronal mass ejections (CMEs). Fluctuations in electrojet intensity and direction produce an electric field at the ground level called a geoelectric field, which accumulates over distances, causing a ground-potential difference between distant locations. Earth’s surface in the direction of the field These currents are called geomagnetically induced currents (GICs). GICs can enter the power system through the grounded neutrals of wye-connected transformers

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