Power system damage in Ukraine
The damage being done to the power system in Ukraine is going to take years to make good.
Downing transmission lines, if the structures are being hit, is significant enough, but there are temporary measures that can be used to replace damaged towers. Damaged conductors are generally pretty easy to repair. But if transformers are being destroyed, that's a whole different game...large power transformers have a lead time measured in years, a price tag well into seven figures, and there is limited global capacity for manufacture. And in Europe, a very large proportion of the raw materials came from ... Ukraine. This war was already impacting the industry supply chain before Putin starting targeting the power system ... now, Ukraine will itself absorb manufacturing capacity to get itself back in shape post-war, whenever that is. And consider too that the rush to renewables had already stretched the supply chain before it all kicked off in Eastern Europe.
Getting mobile generation into damaged areas is important, but it will bring very local relief only. The authorities will have to decide who needs access to this generation, and it will only provide a small part of the lost supply. Someone above mentioned 1.5MVA generators as being the largest available on truck and that sounds about right...but they will only be suitable for the substation at the end of your street (in the UK, these typically operate at 11kV and up to around 1MVA). So good for local housing / schools / small industry, but not much more. A number of such machines would be needed to keep a hospital supplied, but that's before you then think about the diesel supply chain, and the operatives needed to keep it all running.
And one other big factor ... people. The power industry is currently crying out for people globally. Demand (from net zero projects) and lack of supply (power, unfairly, is not seen as a sexy career option) is causing even the big manufacturers to search far and wide for people. And locally in Ukraine, I guess many of the younger men have been moved to the front. As a power engineer, back in January I was imagining spending autumn in Kiev, helping Ukraine get back on its feet ... but there aren't that many of us to go around.
Putin knew exactly what he was doing hitting the grid, and it will take a long time to repair the damage.