Given the increasing renewable energy integration into the grid, hydropower is set to play a major role in addressing the intermittency and grid balancing requirements. Well-maintained hydropower assets offer significant benefits for a long period of time as compared to other energy sources. In this regard, regular operations and maintenance (O&M) and asset management strategies are needed to prevent plant outages and maintain optimal power generation.
Asset management can be broadly identified as a strategic, long-term approach for carrying out the O&M of power stations to derive the maximum benefits following all safety procedures and requirements. Asset management helps in improving power generation efficiency, services, output, risk management, sustainability and compliance with the various statutory requirements. An integrated approach to asset management requires proper documentation, O&M, repair and rehabilitation, and renovation and modernisation, so as to extend the life of the power plant.
Documentation would include a data inventory like a detailed project report, construction stage drawings, design memos (including design calculations, software analysis and finite element modelling), model study report, test report, site-specific seismic studies, environmental impact assessment and EMP studies, report by a panel of experts, databook and completion report. Further, it can include operation manuals like a reservoir operation manual, a hydromechanical works manual and an instrumentation manual. These reports are submitted to the concerned authority on a yearly basis. Guidelines have also been formulated in the corporation so that repair and rehabilitation works can be standardised.
In line with the international agreements and sustainable development goals, various safety procedures have been formulated by the National Disaster Management Authority, which have been customised by the Ministry of Power (MoP) for hydro, thermal, etc. These safety procedures include a disaster management plan, an emergency action plan (EAP) and a standard operating procedure for downstream releases.
The Disaster Management Act, 2005, aims to prevent the danger or threat of any disaster, mitigate risks, facilitate capacity building, improve preparedness, enable prompt response and assess severity. It also provides for evacuation, rescue and relief, rehabilitation and reconstruction. Meanwhile, the Disaster Management Plan for the Power Sector was launched in January 2021 to effectively deal with disaster situations in the sector. In this plan, the MoP has developed a four-tier structure of disaster management at the central, state, regional and plant levels.
Meanwhile, the EAP defines the unusual and unlikely conditions that may endanger dams. It aims to minimise damage and environmental impacts in the event of flood caused by large releases from dams, or dam failure. EAP is prepared as per the Central Water Commission (CWC) guidelines for developing an emergency action plan for dams.
Operations and maintenance
O&M is carried out to ensure that all standard operation procedures are being followed. Improvement in operation procedures is carried out as per the experience and subsequent updation of the existing documents. At hydroelectric plants, periodic dam safety inspections, both pre- and post-monsoon, are undertaken as per the CWC guidelines. Meanwhile, the Dam Safety Act, 2021, formulated in December 2021, provides for the surveillance, inspection and O&M of specified dams for the prevention of dam failure-related disasters. Overall, the act provides an institutional mechanism to ensure the safe functioning of dams.
As part of O&M works, the preparation of comprehensive reports along with an action plan for repair and rehabilitation is undertaken. It is followed by monthly monitoring of identified repair works, comprehensive dam safety review by an independent panel of experts, and submission of report and compliance.
The guidelines for safety inspection of dams include an overview of dam inspection, a dam safety inspection programme, inspection of embankment/concrete/masonry dams, inspection of spillway outlets and mechanical equipment, inspection of general areas, visual inspection and use of remotely operated vehicles and unmanned aerial vehicles, documentation, and a comprehensive dam safety review by a panel of experts.
Notably, NHPC is taking steps for the automation and remote operation of its hydroelectric projects through SCADA. This would enable the centralised operation of machines, and digitalise various operational parameters. During Covid, the company also resorted to online inspections so that preventive action can be taken at the power stations.
Repair and rehabilitation
Rehabilitation of a dam is the act of restoring the distressed dam to its original state and also improving it to meet the added requirements caused by changes in the safety criteria from time to time. The manual for rehabilitation of large dams released by CWC in January 2018 gives an overview of dam rehabilitation, planning, field investigation, material, concrete and masonry dams, embankment dams, and appurtenant works. NHPC is adopting the latest available
technologies while simultaneously ensuring the uniformity of practices. It has adopted standardised methodologies, and adheres to technical specifications as per the stipulated guidelines for repair and rehabilitation. The company has also adopted best practices for repair and rehabilitation in line with the national and international standards, and is undertaking innovations to improve the repair and rehabilitation procedures for optimal benefits and safety.
The quality tests are done to maintain the quality of work and assess the functional requirement of the various components of power stations. Moreover, the use of appropriate material with
standardised performance characteristics can optimise the cost and frequency of repair and enhance plant safety. Early repair and rehabilitation of civil structures is essential for continued and reliable operation of these valuable assets. Uniformity in processes adopted for repair and maintenance across locations will help in early detection and recognition of deviations and deficiencies.
Further, repair and rehabilitation is important to achieve structural integrity and address safety concerns. During monsoon, the Himalayan rivers carry a large quantity of sediment along with boulders over the spillway, causing frequent damages in dam spillways, stilling basin and other critical areas. Other components also get damaged due to ageing, hydraulic forces and various other reasons.
The regular periodic inspection of completed and operating hydraulic structures is extremely important. It helps in identifying structural cracking, spalling and surface irregularities, and determines the extent of damage. Further, the condition of concrete is assessed by non-destructive testing or core drilling and sampling if required. Existing and potential problems are identified and categorised as minor, major or potentially catastrophic. The scope of work and the repair methodologies should be identified beforehand in view of the limited time period for undertaking repair works. A quality assurance and monitoring system should be in place for the timely completion of work.
A number of construction materials including high performance concrete, standard concrete, cementitious mortar, epoxy compounds, crystalline material, and steel liner are available to repair the damages. Cementitious mortar is used for structural repair and for repair of cracks and voids while epoxy mortar is used for the repair of concrete and epoxy grout for repair of cracks. Meanwhile, crystalline material finds applications in repair and waterproofing with slurry or in sealing of cracks and construction joints with mortar.
For the rehabilitation of large dams, CWC launched the Dam Rehabilitation and Implementation Project with assistance from the World Bank in 2012 with an objective to improve the safety and operational performance of selected dams with an institutional support system-wide management approach. Dam Health and Rehabilitation Monitoring Application software is being developed for the effective collection and management of asset and health data for all large dams in India. The construction of a new dam is very challenging given the population density, intensive land use and other factors. The safe operation of dams and reservoirs through the latest safety concepts is the need of the hour for dam safety management.
The way ahead
The digitalisation of hydropower plants and control systems is an emerging industry trend that promises to optimise performance and asset management. Condition-based monitoring and predictive maintenance of hydropower systems are some of the other solutions that can yield immediate savings in maintenance costs. Since O&M and asset management strategies can optimise the performance of hydropower stations for longer durations, hydropower stations must adopt emerging technologies and undertake innovative approaches for the same. n
Based on a presentation by T. Venugopal, Senior Manager, Design and Engineering, NHPC Limited, at a recent Power Line conference