High Voltage DC Active Current Injection to Simulate Geomagnetically Induced Currents in New Zealand

This study investigates the effects of geomagnetically induced currents (GIC) on New Zealand's electrical infrastructure via an intentional ground injection of direct current (DC) from a high voltage DC converter station. GIC manifests as quasi-DC currents within power systems, potentially causing transformer saturation, increased reactive power demand, elevated harmonics, and transformer overloading. In January 2023, with support from Transpower, we utilized New Zealand's high voltage DC link to inject current directly into the ground at Haywards substation in Wellington, North island. This allowed us to monitor the effects of half-cycle saturation of two 216 MVA, 220/110 kV autotransformers. Over 9 days, six injection tests were conducted, each lasting between one and 2 hours, with peak ground injection current reaching approximately 621 A, corresponding to 35 A measured to flow through one of the transformers on site. The saturation threshold of the transformer was measured to be around 20 A. Analysis of power quality measurements revealed a clear correlation between even total harmonic distortion and DC current, along with corresponding increases in acoustic sound and vibration levels. There was strong agreement between differential magnetometer (DMM) and transformer measurements of DC current. Variations in very low frequency radio harmonic observations were correlated with temporal variations in ground current. These findings provide valuable insights into the impact of GICs on in-service equipment and inform grid operators on potential mitigation strategies.