Do you remember about 2 years ago , a sniper shot at transformers at a sub-station that supplied electricity to the Silicon Valley ?
They shot .556 rounds at selected transformers in a secluded area, and were never found. Area of fire was selectively choozen, and marked with rock piles, and they were effective.
They took out that one sub-station, but the grid was able to cover the loss, and the electrical grid stayed up.
A fluke - maybe so
But it was well planned and executed, and showed exactly how vulnerable the rural locations of the electrical infrastructure of this country really are.
Any break along the transmission lines would take down the area being served. The geographic area of transmission lines versus substations is a relative consideration of grid vulnerability. Power lines in an EMP would be an enormous collector of energy to be dissipated; but, could be recovered more quickly than damages to substation equipment. Widespread disruption of the grid would require substantial time to incrementally load the generation gear; and, maintain stability upon a reset after a major disruption.