Dozens of workers were airlifted ashore after the incident which shut down production and left the platform with only emergency power.
The blast happened in one of three generators on the Britannia platform, 130 miles north east of Aberdeen.
A spokeswoman for owner Britannia Operator Ltd said the explosion was contained within the generator, although some damage was done to the surrounding area.
None of the 150 staff on board was injured in the incident, which happened at about 1615 BST on Monday.
The company said 78 non-essential personnel were airlifted to Aberdeen or a nearby accommodation vessel.
A spokeswoman said the staff had been taken off the platform because the loss of power had led to reduced facilities - including hygiene and catering.
"We have to assess the situation and see what damage has been done before the generators can go back online," she added.
An investigation will be carried out by an on-board technical crew assisted by the Health and Safety Executive.
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