Electricity supply stopped around 1.00 PM and was restored after 5.00 PM, an Electricity Board spokesman said.
The breakdown was not due to local fault, but was triggered by the failure of Northern Grid and as soon as the fault was rectified, power supply was restored, he said.
"Now there is normal power supply in the entire state and power generation in all our hydropower projects have resumed," he said.
"All six units of 1500 MW Nathpa Jhakri Power Station have restarted power generation," V K Verma, Deputy General Manager of Satluj Jal Vidyut Nigam (SJVN), said.
The state-run Himachal Pradesh State Electricity Board Limited has 21 hydropower projects across the state with a combined optimum generation capacity of 8.5 million energy units a day.