Harmonic Distortions in 3ϕ Auto-Transformers Due to Geomagnetically Induced Currents

Geomagnetic disturbances can trigger large geomagnetically induced currents (GICs) to flow into power systems through grounded equipment. Several studies identify power transformers (with grounded windings) as the main path for GIC flows into power systems. The flow of a GIC (dominated by a dc component) through grounded windings of a power transformer can lead to severe impacts on its functionality, such as significant increases in its reactive power demands, high levels of current harmonic distortions, and possible thermal damages. This article presents case studies and analyses of harmonic distortions in 3ϕ power auto-transformers during GIC flows. Case studies and analyses are conducted using data collected from laboratory experiments. Analyzed data sets are collected from 3ϕ power auto-transformers with different power ratings, voltages ratings, and core types. Furthermore, analyzed sets of data are collected for various levels of GIC flows. Analysis results reveal that the dc component and 2
^nd
harmonic dominate the 3ϕ currents in grounded windings of tested 3ϕ power auto-transformers over a wide range of GIC flows. In addition, the 3
^rd
, 4
^th
, 5
^th
, 6
^th
, 7
^th
, and 8
^th
harmonic components are present with low magnitudes.