One method of reducing the impact of sediments could be design optimisation of turbine components and application of coating. For a country like Nepal, which relies heavily on research outcomes of the developed countries for introducing new technologies, it is crucial to conduct independent research in the sector of minimising sediment erosion
The annual report 2020/2021 of Nepal Electricity Authority (NEA) specifies an annual peak demand of 1,482 MW in the country. The total installed capacity of Nepal is around 1,450 MW. Hydropower projects of around 943 MW are under construction, and 3,200 MW are in the planning stage. Despite the seasonal variation of flow and the fact that most of the hydropower plants in Nepal are run-of-river type, electricity consumption during most times of the day is going to be a major issue in the near future. Recently, some emphasis has been given by the government for cross-border power trade and increasing the domestic demand by promoting the use of electrical appliances. However, it is unlikely that the turbines in the hydropower plants will operate at maximum available capacity continuously.
On the other hand, operation and maintenance (O&M) issues of the turbines are a problem in Nepal, which is primarily posed by excessive sediment content in the rivers, with a quartz (a hard mineral found in sand) content of more than 50 per cent.
De-silting basins available in the power plants screen more than 80 per cent of the sediments contained in the flow, but small particles still remain suspended and are carried into the power house.
When the turbines operate at maximum capacity during the monsoon, maximum energy can be extracted.
However, turbines also strike the hard sediment particles, causing wear, technically termed as sediment erosion. Yearly, millions of rupees are spent for the repair and maintenance of the turbines.
Apart from these expenses, the loss of production during overhauling and due to efficiency loss after erosion makes up the indirect costs that are usually not accounted for.
When production is higher than demand, optimum use of the machines can be a key to reducing the maintenance cost and increasing the life-span of the turbines. Strategic operation of the turbines can be carried out, when they are operated mostly at designed (Best Efficiency Point) conditions. In these conditions, the turbines run at the highest efficiency with minimum impact of the sediment particles.
During low electricity demand, only a few turbines are operated at the designed conditions, while the rest of the turbines are kept closed.
Other methods of reducing the impact of sediments could be design optimisation of turbine components and application of coating. For a country like Nepal, which relies heavily on research outcomes of the developed countries for introducing new technologies, it is crucial to conduct independent research in the sector of minimising sediment erosion.
Academically, bachelor's level engineering studies in Nepali universities are to some extent inclined towards hydropower. Some dedicated programmes in hydropower engineering at the undergraduate level have also been introduced in some universities. This is probably due to the satisfactory job opportunities in this sector. The School of Engineering (Kathmandu University) has introduced specialised courses in hydropower under Civil and Mechanical Engineering programmes. KU also has a research-oriented Turbine Testing Lab that addresses the operation/maintenance challenges of the turbines in hydropower plants through state-of-the-art technologies and international collaborations for minimising erosion.
A key to academic success of any university focsing on hydropower study in Nepal is the connection with industries in terms of applied knowledge/research, problem-oriented students' projects and hands on skills on fabrication, operation/ maintenance and other aspects of the industry.
At present, every industry is seeking to promote digitalisation of the machines to minimise the cost of O&M. In the context of Nepal, or places where the O&M challenges in hydropower are predominant, digitalisation of the turbines and other components could enable detection of faults in the machines, or erosion in the turbines in the early stages.
This will help to carry out preventive maintenance, decreasing the overall operating costs and increasing the turbine's lifespan.
A lot of new power plants in Nepal, or those that were recently refurbished, have started using several sensors for real-time condition monitoring of the power plants. By integrating general fault signals with machine learning techniques, a proper fault detection and diagnosis, that is, origin of the faults can be investigated.
Universities are crucial for bringing these technological breakthroughs in the hydropower industry.
In a matter of just a few years, Nepal has transformed from an era of severe energy crisis to an era of surplus energy. Investment in the industrial sector is more convenient today because of the reliability of electricity. Electrical appliances, including EVs, are becoming more common and, in fact, more preferable. We can more assertively discuss exporting electricity through cross-border trade and even converting the surplus energy into hydrogen fuel cells. There was a time when the operation of turbines was governed merely by the intent to extract maximum energy from water.
However, we have reached a stage where we can develop best practices for design, fabrication, testing, O&M of the power plants for making the turbines more durable. Those practices will also be very relevant when more storage projects are developed in the future.
These are possible only through substantial investments in research activities.
Moreover, research and the university labs and the needs of industries must be aligned together.
This will provide a new direction for achieving flexibility in the power plants affected by sediment during times of energy surplus.
Chitrakar is assistant professor, faculty-in-charge, Turbine Testing Lab, KU and Lama is coordinator, academia-industry collaboration, KU
A version of this article appears in the print on March 30, 2022, of The Himalayan Times.
