Floodwater breached flood defences at Lancaster's main substation just before 23:00 on Saturday, cutting power to 55,000 properties.
Engineers have been working in the substation since 11:00 on Sunday when it was safe to enter and start repairing damage caused by the water.
Steve Cox, Electricity North West Incident Manager, said: "While we still have a significant amount of work to do to fully repair the substation, our teams have worked round the clock and done enough to restore power to a large number of customers earlier than expected.
"Rather than wait any longer for the full repair and restoration of the site, we have chosen to provide power at the earliest opportunity.
"I'd like to thank customers for their understanding and their goodwill to our teams during what continues to be an enormously challenging time for everyone involved. We are immensely proud of the area and the people we serve in the way they have dealt with this incident."
Engineers will remain on site at the substation to continue additional repair and restoration work to equipment affected by the floodwater until all supplies are restored.
2,657 properties remain without power in Cumbria, where floodwater is restricting access for Electricity North West teams.
Steve added: "We will continue to work with the emergency services and our other partners in Cumbria to gain access to our sites and restore power to those still waiting to be connected as soon as the waters have receeded."
Flood defences at Kendal and Carlisle substations have held, protecting supplies to 110,000 homes.
Electricity North West is posting regular updates on its social media channels and has drafted in extra support to its contact centre to handle customer calls.
Areas currently without power in Cumbria are:
Area | Properties off |
Fusehill area of Carlisle | 1734 |
Cockermouth | 218 |
James Street area of Carlisle | 204 |
Appleby | 161 |
Willowholme area of Carlisle | 159 |
Grizedale | 75 |
Mintsfeet area of Kendal | 72 |
Melling | 22 |
Ravenstone | 10 |
Braithwaite | 2 |