This could happen at any time due to a solar flare.
Actually, no. If you want to read what happens in such an event, see section 3.8.2 of the PJM Emergency Procedures Manual.[1] You get DC current to ground in AC transformers, which results in saturation of the magnetic elements and transformer heating. It's a heat problem; it has to be dealt with in minutes, not milliseconds.
That document is addressed to the people in the grid control room. There used to be a training course on line which explained this in simpler terms.
Actually, no. If you want to read what happens in such an event, see section 3.8.2 of the PJM Emergency Procedures Manual.[1] You get DC current to ground in AC transformers, which results in saturation of the magnetic elements and transformer heating. It's a heat problem; it has to be dealt with in minutes, not milliseconds.
That document is addressed to the people in the grid control room. There used to be a training course on line which explained this in simpler terms.
[1] https://www.pjm.com/~/media/documents/manuals/m13.ashx