Earlier quoted context omitted.
Terrorism has a specific meaning. All these are what one would call sabotage. It would be terrorism if the saboteurs disabled the substations in support of an attack terrorizing civilians. Example, they shoot up a substation so that police are unable to respond to a siege on some government agency or a hostage situation at a bank.
The attack on infrastructure itself could constitute terrorism, if the infrastructure attack was intended to scare or intimidate the public to achieve some political objective. Wiktionary's definition of terrorism includes attacks against property: "The use of unlawful violence against people or property to achieve political objectives." https://en.wiktionary.org/wiki/terrorism
Terrorism is so overused it has lost pretty much any meaning. Being called a terrorist just means you’ve annoyed someone in authority.