Almost one million people in England and Wales were without electricity on Friday after issues with two generators.
It resulted in traffic lights not working, Newcastle Airport fell into darkness and Ipswich Airport was affected by the power loss.
Thousands of passengers were left facing huge delays as a result of the electricity supply problems, causing chaos in the middle of the Friday night rush-hour.
Duncan Burt, operations director at National Grid, said the power cut was an "incredibly rare event".
He said the two power stations disconnected from the grid "near simultaneously".
Mr Burt said: "What happened then is our normal automatic response mechanisms came in to help manage the event, but the loss of power was so significant that it fell back to a set of secondary backup systems which resulted in a proportion of electrical demand across the country being disconnected for a short period to help keep the rest of the system safe."
He added: "Those events happened very, very quickly, in a matter of a few seconds, maybe a couple of minutes maximum.
"That sequence of events is entirely automatic, we think that worked well, we think the safety protection systems across the industry on generators and on the network work well to secure and keep the grid safe."
The country's railways suffered severe disruption during the busy Friday night commute with many passengers left stranded for hours and services at London's Kings Cross station were still not operating fully on Saturday.
Other train services in and out of London, including Thameslink, Southern and Gatwick Express, faced delays and cancellations because of the disruption.
London North Eastern Railway (LNER) said a number of its trains had broken down between London and Stevenage, suspected to be because of the electrical supply problem.
Newcastle Airport was plunged into darkness for about 15 minutes.
About 300,000 UK Power Networks customers were affected in London and the South East and Western Power Distribution said around 500,000 people were affected in the Midlands, South West and Wales, with power restored to them all shortly after 6pm.
Northern Powergrid, which serves Yorkshire and the North East, said 110,000 of its customers lost power, while Electricity North West said at least 26,000 people were without power in the North West of England.
Professor Tim Green, co-director of the Energy Futures Laboratory, Imperial College London, previously said that he believed the two disconnected generators were at Little Barford and Hornsea.
He said: "This event does not appear to be due to wind generation reducing owing to reduced wind speed.
"If that were the case there'd be reduction across many wind farms in [the] same area.
"The first generator to disconnect was a gas fired plant at Little Barford at 16:58. Two minutes later Hornsea Offshore wind farm seems to have disconnected."
Mr Burt said the loss of power had "nothing" to do with changes in wind speed or the variability of wind.
He said National Grid was "very confident" there was "no malicious intent or cyber attack involved" in the incident.
Energy watchdog Ofgem has demanded an urgent report from National Grid
Mr Burt said National Grid would provide a "a detailed technical report" to Ofgem, which has already urgently demanded information as to what went wrong.
He added: "This will require careful study to make sure that we do learn any lessons that come out of it and that the next time this happens disruption is minimised and hopefully a lot less than it was last night."
Labour and the trade unions criticised the scale of outage and the disruption it caused.
Shadow business and energy secretary Rebecca Long Bailey said: "Disruption on this scale is unacceptable.
"National Grid - which in May posted £1.8bn in profits and increased dividend payouts to shareholders - must urgently provide a full account of what went wrong, and why."
Rail Minister Chris Heaton-Harris praised the rail industry for how it handled the disruption and thanked passengers for their "incredible patience".
He added: "I have spoken to Network Rail and operators today and agreed we must now focus on learning the lessons, including how we can improve our resilience, capability, and in particular, ensure all passengers get the very best, up-to-date information during such extreme events."