The following geomagnetic storms damaged the electrical power grid (summarized by James Marusek from a paper published in 2007 (http://www.leif.org/EOS/SSTA.pdf):
August 2, 1972 – A solar storm caused a 230,000 volt transformer located at the British Columbia Hydro and Power Authority to explode
December 19, 1980 – A very expensive 735 kV transformer failed 8 days after the Great Red Aurora of 19 December at St. James Bay, Canada.
April 13, 1981 – A replacement 735 kV transformer at St. James Bay, Canada also failed the next year during another geomagnetic storm.
March 13, 1989 – At 02:45 EST on March 13, geomagnetically induced currents (GIC) inundated the transformers of the Hydro-Quebec power system and overloaded them with current. The voltage fluctuations that resulted prompted the tripping, or deactivation, of reactive power compensators at the Chibougamau, la Verendrye, Nemiscau and Albanel substations. A severe voltage drop resulted; the power lines from James Bay malfunctioned and the system collapsed. It was later determined that the power lines were substantially vulnerable due to their great length and the number of static compensators that ran along their distance. The Hydro Quebec outage resulted from the linked malfunction of more than 15 discrete
protective-system operations. From the initial event to complete blackout, only one-and-a-half minutes elapsed—hardly enough time to assess what was occurring, let alone to intervene.15 The blackout resulted in the loss of 21,500 megawatts of electricity generation. It took nine hours to restore 83% of that electrical load. The blackout affected 6 million people. The physical damage included a 1,200-ton capacitor failure at a Static VAR Compensator (SVC), overvoltage damage to two step-up transformers at the La Grande 4 generating station, surge arresters at the La Grande 2 and Churchill Falls generating stations, and to a shunt Figure 2. Earth ground resistivity based on underlying rock strata. Conductivity measurements from the Geomagnetic
Laboratory of the Geological Survey of Canada in Ottawa with Extension to the United States Completed by Electric Power Research Institute – Sunburst Project. Units – siemens per meter.
(regions in red are very non-conductive). reactor at the Nemiscau substation, and damage to the SVCs themselves.
March 13, 1989 – The solar storm destroyed a $12 million generator step-up transformer owned by the Public Service Electric and Gas Company of New Jersey. The transformer was a linchpin in converting electricity from the Salem Nuclear Generating Plant. The 288.8/24-kV single-phase shell-form transformers, which are rated at 406 MVA, are connected grounded-wye. The damage to the transformers included damage to the low-voltage windings, overheating, thermal degradation of the insulation of all three phases, and conductor melting.12 The utility asked the supplier for a replacement and was told thatthe order would receive top priority, but it would still take almost two years to fill. Fortunately a spare transformer was made available, but it still took 6 weeks to install.
October 30, 2003 – A power grid in southern Sweden located in Malmo experienced a 20-50 minute electrical blackout affecting 50,000 customers due to a strong solar storm. The same storm caused significant transformer damage in South Africa. Over 15 transformers in South Africa were damaged, some beyond repair.
Just as sunspot 1105 was turning away from Earth on Sept. 8th, the active region erupted, producing a C3-class solar flare (peak @ 2330 UT) and a fantastic prominence. Here is a snapshot from the Solar Dynamics Observatory:
