The fire department was already on site.
The GT7 is a 110MegaWatt plant which was currently not being used due to its high cost.
Power was restored to the capital around 12.30 am on local time Wednesday.
Anti-aircraft fire lit up the night sky soon after power was cut to the capital when Tamil Tiger guerrilla aircraft were detected on the western coast of the island.
Military spokesman Udaya Nanayakkara said Tamil Tiger aircraft had dropped two bombs near the Mannar area police headquarters around 10.30 p.m in northeastern Sri Lanka in another raid.
Tamil Tigers had previously raided petroleum installations in the capital Colombo using low flying light aircraft.
They are using a 'Bed check Charlie' strategy successfully used in Korea by communist forces against the United States.
Some of the 'Charlies' were