Analysis of transformer transient saturation process characteristics under geomagnetically induced current pulses

• Transformer saturation lags behind GIC pulse variations, revealing an asynchronous electromagnetic response. • A single-pulse discharge method enables continuous and accurate measurement of deep saturation magnetization curves. • Saturation time decreases sharply with higher GIC amplitudes, validated by analytical fitting. • A corrected π-model shows strong agreement with EMTP simulations, enabling precise GIC transient analysis. The extreme geomagnetically induced current (GIC) pulse can lead to transformer iron core saturation, affecting normal power system operation. While numerous experimental studies have focused on DC steady-state GIC conditions, the transient excitation characteristics under extreme pulse GIC still remain largely unexplored. This paper investigates the dynamic saturation process of transformer cores under extreme GIC events. A specialized GIC simulation source was developed to generate high-amplitude, long-duration pulse current waveforms for experimental purposes. Tests were conducted on small-scale single-phase transformers to obtain nonlinear deep-saturation parameters using an improved π-model topology. Furthermore, the DC magnetization curve of the scaled transformer was accurately derived through this novel methodology. Finally, extreme GIC injection tests were performed, and the experimental results were validated against an EMTP-based electromagnetic transient model. Parameter correction was carried out through comparison with measured deep saturate experimental data, yielding a highly accurate transformer model for GIC transient studies.