Concerns over possible damage to the turbines due to silt laden water at the Nathpa Jhakri project (NJP) has lead India's Ministry of Power to place limitations on the tolerable silt content.
Satluj Jal Vidyut Nigam (SJVN), the utility operating the project, has been asked to cease operation when the silt level exceeds 4000ppm (parts per million). The decision has been taken in light of the rupture of the labyrinth pipe, which led to the flooding of the underground power house last September.
Accordingly, the generation target for 2006-07 has been scaled down from 6950MkWh to 6400MkWh. NJP has been designed for a silt level of 5000ppm but the high velocity silt particles had been eroding parts of turbines such as guide vanes, labyrinth seat, cheek plates and runners. Besides this, the level of silt also crossed permissible limits frequently causing repeated shutdowns during the peak generation season last year.
The ministry has also asked SJVN to coat the vulnerable parts of all six generating units with erosion-resistant tungsten carbide-based protective material by 15 May. This will enable them to last the full generation season until 15 September, when the discharge in the river is generally high.