The operations and maintenance (O&M) of hydropower plants is essential for asset management of plant equipment. These practices should aim to reduce the rate of failure and optimise the utilisation of power. A preventive maintenance schedule can play a key role through comprehensive documentation and periodic checks and inspections. Continuous vigilance of day-to-day operations, along with periodic inspections, is essential to proactively address potential issues. The O&M of hydropower plants should aim to minimise downtime and increase reliability, ensuring a good life cycle for the facility.
Operational analysis: The operational assessment of generation units can be determined by evaluating factors such as inflow, water utilisation, reservoir level, spillage and operational parameters, as well as by ensuring compliance with the Indian Electricity Grid Code. The methods of carrying out operational analysis of generation units include examining the injection or drawal of megavolt-ampere reactive as per the generator capability curve or grid requirement, implementing the restricted governor mode of operation (RGMO) and automatic generation control (AGC), and conducting mock black starts. The implementation of RGMO involves establishing specific operational constraints or limitations in the governor control system of a hydroelectric power plant. This is typically done to address certain operational, environmental, or regulatory requirements and is a non-standard solution that compensates for changes in frequency by changing generation levels. On the other hand, AGC is a crucial component of power system management that ensures balance between generation and load. It is responsible for adjusting the power output of generating units to maintain system frequency within acceptable limits. Implementing AGC in hydropower plants involves integrating control systems to automatically respond to changes in system frequency and generation demand.
Tripping and breakdown analysis: Tripping and breakdown analysis is carried out to identify the root cause of a fault and promptly address it. To minimise instances of tripping or breakdown, corrective measures are implemented. Forced breakdowns or outages in power stations are being monitored, accompanied by technical inputs, logistics support and restoration efforts led by NHPC Limited’s corporate O&M division. Its efforts have resulted in 0.93 per cent in 2017-18 to 0.46 per cent in 2021-22.
Silt/Sediment management: Hydropower plants in the Himalayan region face a primary concern related to sediments in the inflow, especially during the monsoon season. Silt erosion can adversely impact reservoir capacity and underwater components, which necessitates mitigation measures such as reservoir flushing or maintaining it at a minimum draw-down level during the high inflow season.
Desilting the chambers, applying high velocity oxygen fuel (HPVF) coating to the runner and guide vanes, and installing a closed-loop water system can be useful for addressing this issue. Rivers carrying hard particles such as quartz, mica and feldspar can damage turbine components due to their high velocity. NHPC’s efforts to mitigate these damages include using hard materials to resist quartz particles or applying HPVF coating on runners, guide vanes, cheek plates, etc., to reduce abrasion.
Critical spares and inventory management: Critical spares are of high value for power station inventory and their non-availability can highly impact the station’s performance. The remote locations of hydropower plants make it essential for operators to maintain a minimum level of inventory. The procurement/contract processes, encompassing the purchase, award and delivery phases, are closely monitored to guarantee the availability of essential spare parts. This enables timely execution of annual and capital maintenance, as well as prompt response to any emergencies. NHPC has identified critical spares, along with minimum and maximum reorder levels for each power station. This requires power stations to maintain minimum critical inventory levels.
Preventive and annual maintenance: The maintenance schedule is determined based on recommendations from original equipment manufacturers, technical inspections, and operational considerations in order to reduce outages and breakdowns. The replacement of crucial underwater parts has become less time-consuming compared to the repair and reuse method, increasing the operational availability of the plant.
Dam instrumentation: Dam instrumentation, encompassing the water conductor system, powerhouse cavern and electrical machines, is crucial for measuring parameters to assess the health and performance of the plant. Contingency plans and protocols are also vital in cases of emergencies and disasters, and mock drills should be conducted at regular intervals for better preparedness. Measuring pressures, the inclination of the dam, seepage and water stress are important to ensure its proper functioning, which can now be done through remote technology without the need for manual interference.
Repair and rehabilitation: Repairing damaged structures can be a costly process. The materials to be used while repairing should meet the standards set by the authorities. They should be efficient and durable, as shutting down the plant can be an expensive procedure. Steel liners are one among most efficient and durable materials for these plants, ensuring optimal results and minimising the need for shutting down plants. Further, spillways during water release should be carefully regulated to prevent damage in downstream areas, energy dissipation systems and stilling basins.
Early warning system: Cloud bursts and flash floods are common occurrences in hilly areas, making hydropower plants vulnerable. Due to this, it is necessary to install early warning systems to alert nearby residents, providing them with sufficient time to evacuate, and allowing the local administration to arrange for shelter before floods. So far, 47 hydropower projects have been identified as vulnerable. The Ministry of Power has entrusted NHPC with setting up the control master room for all the hydropower generation companies. It has established a master control room in Faridabad that operates 24×7, facilitating an alert mechanism and real-time monitoring.
Scada, digital governors and excitation systems: Digital systems offer reduced wiring, flexibility in design and stability of fixed values. With the introduction of microprocessors, digital control systems can now achieve machine responsiveness at a higher sampling rate while providing a plethora of user-friendly functions. Additionally, digital technologies have aided in the enhanced application of power system stabiliser tuning, data telemetry, RGMO/free governor mode of operation and other grid requirements. Supervisory control and data acquisition (SCADA) is an essential tool for establishing connectivity in a plant and communicating with plant hardware and software.
Conclusion
Asset management is a crucial component in enhancing the efficiency of hydropower plants, especially in a market driven by rising costs and strict regulatory structures. Adopting cutting-edge O&M technology and methods enhances performance, ensures a constant supply of electricity, and reduces future maintenance costs, thereby increasing reliability.
Based on a presentation by Sandeep Batra, General Manager (Planning), and Suraj Dhiman, General Manager (O&M), NHPC Limited, at a Power Line conference