The company did not explain what triggered the outages but said it was working to "restore normalcy within shortest time possible".
It buys the bulk of its power from Kenya Electricity Generating Company.
The outages follow widespread blackouts this month in East Africa's economic powerhouse.
In January a high voltage transmission line connecting the capital broke causing a nationwide blackout.
Later that month, three senior managers Kenya Power were charged with sabotage and negligence.
(Reporting by Duncan Miriri; writing by Hereward Holland; editing by James Macharia Chege and Jason Neely)