Dhaka, Jan. 27 -- Pakistan's generators produced more power than was required on Monday, causing voltage fluctuations that culminated in a system collapse that plunged 220 million people into darkness, an internal government document reviewed showed.

Complete grid failures are rare, and operators of modern grids count local shocks from integration of renewable energy as their primary challenge. But the blackout in Pakistan on Monday was its second near-complete grid failure and the third in south Asia in three months, reports Reuters.

The grid's failure plunged 220 million people into darkness for a whole day and disrupted commercial activity as outages also hit internet and mobile services.

The blackout was triggered by the power grid...