A hydroelectric project (HEP) typically requires renovation and modernisation (R&M) after 30-35 years of operation. R&M is a cost-effective option for maintaining operational capacity after an old HEP reaches the end of its useful life. It prolongs the useful life and augments project capacity through appropriate technological interventions that result in enhanced operational efficiency, dependability and security. Besides, from the point of view of an optimal economy, achieving a higher energy yield by renovating and uprating existing operational power plants is substantially superior to building new power plants.
Progress and plans
Under the Central Electricity Authority’s (CEA) R&M programme for HEPs, R&M works at 118 HEPs with an aggregate installed capacity of 22,634.7 MW were completed by the end of 2017-22 and a total benefit of 4,016 MW was accrued through life extension, uprating and restoration. Of these, 26 plants belong to the centre and the remaining 92 to various states. During 2017-22, renovation, modernisation, uprating and life extension (RMU&LE) works at 14 HEPs (five central sector and nine states sector) with an aggregate capacity of 2,023.20 MW were completed, yielding a cumulative benefit of 848.68 MW. During 2021-22, RM&LE work was completed on Odisha Hydro Power Corporation Limited’s Hirakud HEP (2×37.5 MW), Gujarat State Electricity Corporation Limited’s Ukai HEP (3×75 MW), NHPC’s Baira Siul HEP (3×60 MW), the Bhakra Beas Management Board’s Dehar Power House (165 MW), the Jammu & Kashmir State Power Development Corporation’s Ganderbal HEP (4.5 MW) and the Chenani HEP (5×4.66 MW).
During 2022-27, RMU&LE work at 67 HEPs with an aggregate capacity of 11,935.6 MW is planned for completion, which is expected to yield a cumulative benefit of 9,623.3 MW. As such, the revised aggregate capacity after the RMU&LE works of these 67 projects would be 12,182.1 MW. Of these 67 projects, six projects in the state sector worth Rs 3.6 billion, with an aggregate installed capacity of 1,414.8 MW, have been completed as of December 2022. Meanwhile, during 2027-32, RMU&LE work at 21 HEPs (three central sector and 18 state sector) with an aggregate capacity of 2,879.2 MW at an estimated cost of Rs 6.83 billion is planned for completion.
CEA’s guidelines for R&M of HEPs
Recently, the CEA issued guidelines for R&M of HEPs, which provide a framework to ensure timely completion of R&M work without cost overruns, outline approaches and strategies for R&M and discuss the latest technologies to meet the requirements of HEP operators. These guidelines serve as a basis for utilities’ decisions over whether to upgrade existing plants or opt for R&M. The guidelines also address the challenges faced by utilities in deciding whether to go for refurbishment or part/complete replacement of equipment under the R&M programme.
Approaches to R&M: As per the guidelines, while performing R&M for life extension, the potential for uprating should be assessed. Installation of new power plants, rehabilitation/renovation of existing power stations and modernisation of operational power plants can increase the current hydro generating capacity. While renovating the machine, technological alternatives such as epoxy insulation instead of bitumen in the generator and SF6 switchgear over conventional switchgear should be utilised to replace old items. Even turbines can be renovated to produce higher outputs by modifying their flow passages and by using a modified runner profile design.
The utility should also have a close monitoring system in place for the physical and financial progress of various activities with well-defined delegation of powers to the project head executing the work, and an adequate dedicated term to ensure timely implementation of the RM&LE programme.
R&M of silt-affected and acidic water-affected hydro stations: Power stations facing extensive damage in the Himalayan belt due to high silt content require renovative maintenance of underwater parts every year. Silt measuring instruments with online monitoring/telemetering systems and radiographic equipment for video display of damage inside the machine could be considered for modernising a silt-affected power station.
Usually, particles sized 150 microns and below are difficult to arrest by normal desilting chambers. Due to recent developments in desilting chambers, particles up to 20 micron size can be arrested, which extends the life of underwater parts.
Power stations subjected to acidic water/environments may be handled separately by changing underwater parts, cooling water system, and drainage and dewatering system to stainless steel pipes valves/impellers, etc.
Strategy for R&M: Repair and maintenance efforts in some cases become so massive that they cannot be classified under normal O&M activity. Those power stations need resource support to implement challenging renovative measures. The imbalance between the requirements of such power stations and normal power stations can be taken care of by suggesting R&D-based measures such as application of advanced techniques, including plasma/high velocity oxy fuels/high velocity air fuel-based thermal spray coating (if suitable) on underwater parts of turbines, cupro nickel tubes to replace conventional admiralty brass tubes of coolers, incorporation of cyclone separators in the cooling water system, and adoption of modified runner profile designs suitable for silt-laden flows.
All components of the plant may be selected in such a way that they meet the main objective of R&M. Modern instruments, such as laser silt meters and photoelectric silt meters for measuring silt and video probes to evaluate the amount of damage inside the generating unit without dismantling it, should be used in combination with the uprating of silt-prone power stations to keep track of their status. Numerical relays, supervisory control and data acquisition, digital voltage regulators, digital governors, self-lubricating non-metallic bearings, shifting from servo valve-based governing system from a conventional one, digitalisation of signals using optical fibre and remote terminal units in place of hard wiring, must be introduced during R&M of a power plant.
Essential requirements/approach for successful implementation of RMU&LE: To ensure close monitoring, coordination, quality assurance and speedy implementation, and avoid administrative delays in the placement of orders, a dedicated R&M cell with an empowered committee committee (task force) at each power station could be created to deal exclusively in all matters relating to the implementation of R&M/LE schemes.
Further, R&M for life extension study may include a comparison of the best approaches suited for a given power station undertaking R&M/LE. One approach could be the complete shutdown of the power plant and unit-wise restoration after undertaking R&M/LE works, while another approach could be unit-wise shutdown for R&M/LE works and concurrent generation from other units. In both these approaches, analysis should deliberate regulatory provisions and benefit the power plant.
In addition, overhauls/shutdowns of the unit should be planned in such a way that the maximum amount of R&M works can be executed during the overhaul to avoid separate shutdowns for carrying out R&M works. Proper planning of resources (personnel and material) should be done to match the planned unit shutdown for the execution of R&M works and all LE works should be executed during a single shutdown of the unit undergoing annual/capital maintenance. In case R&M activity is planned at more than one power station of a utility, then a centralised action for procurement of equipment could be taken to reduce time and cost overruns as well as to avail concessional prices for bulk orders, since the centralised set-up is fully equipped to handle the engineering and coordination work. After implementation of the scheme, a feedback system needs to be introduced to analyse modifications carried out (that is, benefits achieved vs anticipated). Based on the feedback analysis, remedial steps must be taken during subsequent implementation.
Conclusion
With the large-scale integration of renewable energy sources expected in the future, hydropower is anticipated to play a crucial role in grid balancing owing to its distinctive qualities of fast ramping and black start. R&M of HEPs provides a time- and cost-efficient way to increase hydro capacity; therefore, this is expected to gain further traction. Overall, the successful implementation of R&M works at HEPs depends on good project management, careful planning, detailed project report preparation and financial support.