Sky TV News reports that:
More than 140 million people - up to 80% of the population - lost electricity after militants attacked a transmission tower and caused a massive power surge.....two nuclear power plants remain offline.

A spokesman added: "The blowing up of two power pylons in Naseerabad last night created a backward surge which affected the system. It was an act of sabotage."

A Pakistani account has more details, notably on a drammatic drop in power generation as fuel oil supplies have not arrived, but nothing on the power grid being attacked:

THis is in addition to a petrol shortage after a massive consumer switch from LPG to petrol added to debts to the state-owned oil provider: