Preliminary Analysis on the Interplanetary Cause of Geomagnetically Induced Current and Its Effect on Power Systems

Using the detected events of geomagnetically induced current (GIC) in the Ling’ao nuclear power plant from 2004 to 2005, and focusing on the interplanetary cause of GIC and its effect on power systems, we have analyzed the corresponding solar driving sources and interplanetary solar wind structures, and performed spectral analysis on the most intense GIC event by means of wavelet transform. The results of this study show that: (1) Most GIC events were driven mainly by the halo coronal mass ejections, the interplanetary cause of GIC events includes the shock sheath, magnetic cloud, and multiplex interplanetary solar wind structure. (2) Based on the strongest GIC event on 2001 November 9, we find that the fluctuation of GIC in the earlier stage was related to the magnetic cloud boundary layer, and the variation of GIC intensity in the later stage was caused by magnetic cloud itself. (3) Compared to the frequency of the power system (50 Hz), the GIC can be equivalent to a quasi direct current. The energy of the GIC is embodied in the two time intervals in the wavelet power spectrum: the first interval is shown as an impulsive type and with a weaker intensity, and the second one is stronger. Regarding to the cumulative time of the transformer temperature rise caused by GIC, the second interval has a longer duration than the first one. Hence, during the second interval, it is more harmful to the power systems and devices. (4) With a correlation analysis, the correlations of the SYM-H index and dBx/dt with the GIC are significantly stronger than those of other geomagnetic indices with the GIC.