Assessment of the geomagnetically induced currents impact on the power transformers cores of the Altai Republic 110 kV power grid

Abstract

Based on the Baigazan magnetic station data located in Altai, geomagnetically induced currents (GIC) in primary windings of transformers in the southern part of the Altai Republic power system were calculated during a strong magnetic storm on April 24, 2023 (geomagnetic activity index Kp=8). It is shown that the calculated currents in the primary windings of 110 kV power transformers can reach values of more than 0.4 A. At the same time, magnetizing fields are formed in the transformers cores. They make up to 70% of the working field created by the no-load current, that should negatively affect the efficiency of their operation. To assess the GIC effect on the transformer core, a GIC core magnetization coefficient is used. It represents the ratio of the magnetic field strength generated by GIС at the transformer core to the no-load current magnetic field strength. The greatest effect is observed in 2.5 MVA installed capacity transformers at the Ininskaya substation. The GIC effect decreases with an increase of transformer power. To increase the Altai Republic power system stability to GIC, it is proposed to shift the grounding point from the Ininskaya substation to the Ongudayskaya substation. The core magnetization coefficients in this case do not exceed 0.4.