How strong of a magnetic pulse would a 1-kiloton blast create? And what and how would it damage the power grid? Not assuming you know or should know the answer...just wondering. It seems to me that the pulse would be of the transverse type. If so, would not the radiation decay at a rate inversely proportional to the radius? In which case a pulse high up in the atmosphere would decay immensely before it hit the earth...unless it was somehow guided to vulnerable infrastructure.
50,000 V/m is the unclassified field strength. Using simulation codes (from memory) a 1kT calculates out to around 40,000 V/m.
The impact to the power grid is projected to be to communications, controls, relays, generation plants. Below 100kV damage to infrastructure is possible. Above it’s not likely for a variety of reasons.
An EMP will not decay as you might expect, but a localized emitter would decay.
Damage predictions are statistical. Not everything will be destroyed but many things are expected to be damaged, destroyed, or upset.