If a large solar flare strikes Earth, it will cause catastrophic damage by generating thousands or millions of volts across very long power lines. By using a transformer, one can short common-mode voltage (generated by the flare) to ground without also shorting out the differential voltage (which is how the power is transmitted). On the left is a two-phase 60Hz power source of 10kV plus a 10Hz 100V common mode power source representing a solar flare. As you can see the transformer in the middle presents a very low impedance to the common mode signal but doesn’t affect the differential signal where the power is transmitted. By employing such a transformer, one can provide passive protection against solar flares without impacting the grid’s performance or drawing unnecessary power. Of course, because the transformer has a non-infinite inductance it will draw some current, but that’s what power factor correction capacitors are for. If the appropriate value of capacitor is placed between the two lines it will cancel out the inductive current of the transformer leading to virtually zero current except to account for losses in the transformer, but that should be very small.
