Efficient operations and maintenance (O&M) and robust asset management are essential for ensuring the reliability, safety and long-term performance of hydroelectric power plants (HEPs). Given the long asset life of hydro stations, effective O&M practices not only maximise generation but also minimise forced outages, extend equipment life and ensure compliance with regulatory requirements. NHPC has developed a comprehensive O&M framework that combines operational monitoring, preventive maintenance, condition assessment, dam safety measures and advanced technologies to improve plant availability and operational efficiency.
Maintenance strategies for hydropower plants are increasingly shifting from reactive, breakdown-based approaches to preventive, condition-based and predictive maintenance. Enabled by advanced sensors, continuous monitoring and data analytics, these strategies help identify equipment deterioration at an early stage, minimise unplanned outages, optimise maintenance schedules, reduce costs and enhance asset reliability and longevity.
O&M best practices for HEPs
A proactive maintenance philosophy helps maintain high plant availability while extending the service life of critical equipment. One of the key recommendations of the Central Electricity Authority (CEA) is to investigate every equipment failure or unit trip by identifying why it occurred, how it occurred and measures needed to prevent its recurrence. Utilities are advised to maintain comprehensive maintenance schedules on a daily, weekly, monthly, quarterly and annual basis, covering all major equipment. During replacement of worn-out components, improved and technologically advanced equipment is preferred to enhance reliability and extend operational life. Continuous monitoring of operating parameters and proper record-keeping enable utilities to identify abnormal trends, diagnose faults and estimate residual life of the equipment. Historical performance data, combined with original equipment manufacturer (OEM) recommendations, can be used to establish maintenance intervals and operating limits that reflect site-specific conditions. The CEA also recommends minimising unnecessary start-stop cycles, optimising spare inventory, improving manpower utilisation, providing regular technical training and adopting online condition monitoring systems for generators, turbines and transformers. Catchment area afforestation is also encouraged to reduce silt inflow and improve plant performance.
Maintenance of the water intake and water conductor system is important because these components are subjected to high hydraulic stresses. Regular inspection of intake gates, tunnels, surge shafts, penstocks and valves helps detect erosion, corrosion, silt deposition and structural deterioration. Hydraulic testing, ultrasonic thickness measurements and stress analysis are carried out wherever abnormalities are observed. Protective coatings, timely replacement of valve seals, maintenance of hydraulic systems, inspection of cranes and hoists, upkeep of trash racks and reliable communication and emergency systems are also critical for ensuring safe operation.
Additionally, the turbine and its auxiliaries require periodic inspection to minimise efficiency losses caused by cavitation and erosion. Monitoring silt concentration in water enables operators to initiate corrective measures before severe damage occurs. Routine maintenance includes inspection of runners, annual polishing of underwater components, non-destructive testing, anti-erosion coating application, hydraulic oil purification and maintenance of governors, servo valves and associated control systems.
Generators and associated auxiliary systems also require systematic maintenance. Regular insulation resistance, tan delta and impedance testing help assess the health of stator and rotor windings, while proper cooling and periodic inspections improve winding life. Generator bearings, vibration levels, shaft alignment, protection systems, cooling equipment and fire protection arrangements require regular inspection to ensure reliable operation. Similarly, transformers and switchyards require continuous monitoring of oil and winding temperatures, oil filtration, dissolved gas analysis, insulation testing, breaker timing tests, protection system checks and periodic cleaning of bushings and insulators. Emergency diesel generator sets, station batteries, auxiliary transformers and cable ducts also require regular inspection and maintenance to ensure uninterrupted plant operation during contingencies. Together, these best practices strengthen plant reliability, improve operational efficiency and support the long-term sustainability of HEP stations.
NHPC’s O&M practices
A key element of NHPC’s O&M strategy is continuous operational analysis of all power stations. Generation performance is reviewed daily by analysing factors such as water inflows, reservoir levels, spillage and grid requirements. Plant operation is optimised in accordance with applicable operational guidelines, while ensuring compliance with regulations issued by the Central Electricity Regulatory Commission, the CEA and the Indian Electricity Grid Code. Critical operating parameters, including vibration, temperature and other condition-monitoring indicators, are continuously monitored to detect abnormalities at an early stage and facilitate timely corrective action.
Hydropower plants also play an important role in maintaining grid stability. NHPC closely monitors peaking availability factor (PAF) to ensure adequate peaking support for the grid. Automatic generation control (AGC) performance of generating units is regularly reviewed to comply with grid despatch requirements, while reactive power (MVAR) injection profiles are monitored to support voltage regulation. Real-time operational data from plant supervisory control and data acquisition systems are integrated with remote terminal monitoring (RTM) and SAP platforms at hourly, daily and 15-minute intervals, enabling continuous performance tracking and informed operational decision-making.
Another important focus area is reducing forced outages. Every tripping or breakdown event undergoes detailed analysis to identify its root cause and enable faster restoration. A dedicated corporate O&M team provides technical guidance and logistical support to power stations during restoration activities. Detailed tripping analysis reports include event chronology, system conditions, protection system operation, root cause assessment and restoration details. These reports are shared across all power stations through the NHPC intranet, allowing other stations to identify similar vulnerabilities and implement preventive measures.
Regular technical inspections and dam safety assessments are also an important component of NHPC’s asset management strategy. Corporate O&M teams conduct technical inspections of all power stations twice a year, preferably before and after the monsoon season. Simultaneously, design and engineering teams carry out dam safety inspections to assess the health of civil structures and hydromechanical systems.
Sediment management is a major operational challenge for hydro stations, particularly those located on the Himalayan rivers, which carry significant quantities of silt during the monsoon season. Excessive sediment accumulation reduces reservoir storage capacity and accelerates wear of hydromechanical equipment. NHPC employs several internationally accepted sediment management techniques to address this challenge. Drawdown flushing is carried out periodically in smaller run-of-the-river reservoirs during the monsoon to remove deposited sediment through spillways. Drawdown sluicing involves maintaining reservoir levels close to the minimum drawdown level to allow incoming sediment to pass through the reservoir rather than settle. In addition, desilting chambers are installed wherever required in water conductor systems to remove coarse sediment particles before water enters the turbines.
Further, silt-induced erosion of underwater turbine components remains a persistent issue in several Himalayan hydro stations. Rivers carrying hard mineral particles such as quartz, mica and feldspar cause hydro-abrasive wear of runners, guide vanes and other submerged components. To mitigate these effects, NHPC has adopted high-pressure high-velocity oxyfuel coating technology for critical underwater components, significantly improving their resistance to abrasion and extending service life.
Moreover, preventive and capital maintenance programmes are implemented according to detailed schedules developed from operational experience, equipment history, technical inspections and OEM recommendations. Timely implementation of these maintenance plans helps minimise breakdowns and improve equipment reliability. However, hydropower stations continue to face several environmental challenges, including flash floods, excessive silt inflows, reservoir sedimentation, high tailrace levels, floating debris at intake structures and choking of cooling water systems.
NHPC is modernising hydropower plant operations through digital technologies that enhance reliability, efficiency and asset management. A digitally integrated O&M platform based on real-time monitoring (RTM) system and SAP enables automated data capture, maintenance planning and real-time performance monitoring. QR code tagging allows operators to report defects and generate maintenance notifications using mobile devices, while digital dashboards provide continuous insights into generation, outages and equipment performance.
The company is also exploring artificial intelligence applications for predictive maintenance, reservoir optimisation, water flow forecasting, turbine performance monitoring and fault detection. These technologies are expected to improve water utilisation, minimise unplanned outages and support better operational decision-making.
To strengthen grid reliability, NHPC is implementing a remote access system and automated fault analysis system, enabling secure remote access to numerical relays and faster fault analysis. Additionally, its 24×7 master control room, supported by the eAABHAS early warning system, provides RTM and alerts for hydropower stations, enhancing operational readiness and emergency response.
To conclude, a combination of preventive maintenance, condition-based monitoring, digital technologies and skilled manpower can significantly enhance plant reliability, operational efficiency and asset life. NHPC’s adoption of advanced monitoring systems, AI-enabled solutions and systematic maintenance practices demonstrates how utilities can improve performance while addressing operational and environmental challenges, ensuring the long-term sustainability of India’s hydropower sector.