For what it's worth, a couple weeks ago someone (according to a manifesto, an anarchist group) did exactly that in Munich - they set about 50 10 kV electricity cables that were laid bare due to construction works ablaze to strike against a military supplier and cut off about 20.000 households for over 36 hours until the utility managed to restore service: https://www.br.de/nachrichten/bayern/stromausfall-in-muenche...
Sabotage or plain old theft against utilities is pretty common, but it's hard to do something physical that truly disrupts service for longer than a day or two - the networks are designed with reliability against all kinds of issues in mind. An IT-based attack leaves no traces if done well and can have a week to month long impact, simply because back when these networks were designed, IT threats were not existing.
It's impossible to prevent all attacks, physical or cyber, so at some point one needs to either submit to an order where attackers act with impunity, or otherwise invest in retribution.