"We were unable to operate any of the lines for an hour from 6 am to 7 am due to tripping of power supply. At 7 am we restored 25 percent of the trains on all the lines, and now all the trains are plying as usual," the official added.
Train services on the 190 km Metro network connecting the length and breath of the national capital region (NCR) were affected due to power failure in the Northern Grid, the main power source for Delhi, Uttar Pradesh, Punjab, Haryana, Rajasthan, Himachal Pradesh and Jammu and Kashmir.
The Northern Grid failure also caused power cuts in most parts of Delhi.
Delhi Metro normally operates over 2,700 trips a day, covering about 70,000 km and carrying around 1.8 million passengers on week days.