The 1,500 MW Nathpa Jhakri, 1,000 MW Karcham-Wangtoo and 300 MW Chamera II hydro-power projects have been shut temporarily due to high silt levels in water, sources said.
Electricity generated in these three hydro-power plants is fed to Northern Grid, that caters to 28 per cent of the country's population.
A Power Grid Corp official said there is shortfall of around 3,000 MW supply to the Northern Grid due to non generation by the three hydro projects.
According to him, supply shortage in the grid was noticed at around 1000 hrs, when the demand was about 33,000 MW.
However, the situation could not be termed as grid disturbance, he added.
Meanwhile, an Uttar Pradesh government official said the state averted collapse of the Northern Grid at around 1000hrs.
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The latest incident comes within three weeks of failure of Northern, Eastern and North Eastern grids on July 31 that led one of the world's biggest power outages.
The Northern Grid, that covers nine regions, itself had tripped for two consecutive days on July 30 and July 31.
When contacted, an official of SJVN, that operates the Nathpa Jhakri project, said the plant was shut today due to high silt content in water from Sutlej river.
"The plant has to be closed if the silt level in water goes up beyond the benchmark level... We are closely analysing the situation and expect to restart the plant tomorrow morning," Nathpa Jhakri's Executive Director R K Bansal said.