The 1,000 MWe first unit was shut down on Tuesday, a top official of the plant said.
This is the second exercise undertaken by the authorities after it was synchronised with the southern grid last Friday.
"Yes. It has been suspended around 8.03 pm on Tuesday. I cannot tell the time till when it will be like this. But, so far we have generated 300 MWe. We stopped the turbine to undertake the mandatory tests", official sources told PTI.
It may be recalled that last week the power production was temporarily halted for tests as mandated by the Atomic Energy Regulatory Board.
Power at Kudankulam Nuclear Power Plant would be increased gradually towards the 1,000MWe benchmark by December this year once the unit attains operational stability.
Unit-1 had attained criticality on July 13 this year after much delay following protests against the project by anti-nuclear activists in areas around the complex, citing safety reasons.
Nuclear Power Corporation of India is constructing two 1,000MW units at KNPP jointly with Russia at Kudankulam in Tiruneveli district, about 650 km from Chennai.