Nathpa Jhakri achieves another first
Creates hard-coating facility
Rakesh Lohumi
Tribune News Service

Shimla, July 24
The country’s largest 1,500-MW Nathpa Jhakri project has achieved another first by creating in-house high-tech facility for hard coating of erosion-prone components of the turbines.

The sophisticated equipment with a programmable robotic arm to carry out tungsten carbide coating on machine parts has been imported from Germany at a cost of Rs 8 crore. It is the first hydroelectric project in the country to have such a facility to effectively deal with the problem of erosion of parts of the turbines caused due to excessive silt in the Sutlej. The Sutlej Jal Vidyut Nigam (SJVN), which manages the project, sent four engineers for training to Germany who are now operating the equipment.

Tungsten carbide powder is sprayed on the surface of components at supersonic velocities and high pressure to produce fine erosion-resistant layer. The robotic arm handles the high velocity gun, which bombards the surface with powder at the speed of 2,160 m per second. The high kinetic energy particles impinge on the surface and the impact produces a very good bond. There are six 250-MW generating units in all and the facility will enable the SJVN to save about Rs 2 crore annually.

Turbine parts like cheek plates, guide vanes and labyrinth seal were severely eroded by high velocity silt particles moving at 70 m sec, creating deep cavities and forcing authorities to shutdown the project for maintenance. The heavy parts affected by erosion were sent to distant places for hard coating, which was not of very good quality. However, with a sophisticated in-house facility both time and money will be saved, says NC Bansal, general manger of the project.

The problem had been acute in the Nathpa Jhakri project as the level of silt had been very high and it mainly comprised quark particles, the hardest rock, which caused extensive damage. The parts were being coated with layers of thickness ranging from 300 to 500 microns, which would make them last for at least two years. The raising of the height of the diversion dam at Nathpa by 10 m had also helped in bringing the level of silt at the intake to manageable levels.

The project had been witnessing frequent shutdowns due to excessive silt ever since it was commissioned in 2003, but this year it had been doing well and generated 3,000 mu till Thursday, 50 mu more than the enhanced target. There had not been a single shutdown and the target of generation was surpassed by 80 mu in June and 100 mu for July till date.