Electrical Maintenance and Reliability

Maintenance of a hydropower plant is the systematic set of activities carried out on civil, mechanical, and electrical components to keep the plant available, efficient, and safe throughout its design life. The maintenance works are broadly classified into the following types:

1. Preventive (Routine) Maintenance This is planned maintenance carried out at fixed intervals (daily, weekly, monthly, annually) before any fault occurs, based on the manufacturer's schedule and operating experience. It includes:

• Daily inspection of the powerhouse, penstock, intake, and switchyard; checking oil levels, temperatures, vibration, and abnormal noise of turbines and generators.
• Periodic cleaning of trash racks and intake screens, greasing/lubrication of bearings and gates, tightening of terminals, and checking of relay settings.
• Annual shutdown (overhaul) maintenance: inspection of runner, guide vanes, seals, turbine bearings, generator windings, excitation system, transformer oil testing, and calibration of protection relays.

2. Corrective (Breakdown) Maintenance Maintenance carried out after a fault or failure has occurred, to restore the plant to working condition. Examples: repair/replacement of a burnt generator winding, damaged turbine runner due to cavitation or silt erosion, leaking penstock joints, failed transformer bushing, or a defective circuit breaker. It is unscheduled and often costly, so it is minimized by good preventive maintenance.

3. Predictive (Condition-Based) Maintenance Maintenance based on the actual condition of equipment monitored through measurements and tests, rather than on a fixed time schedule. Tools used include vibration analysis, thermography (infrared scanning of joints and bearings), dissolved gas analysis (DGA) of transformer oil, partial discharge measurement, and oil contamination tests. Action is taken only when a parameter crosses a threshold, thus avoiding unnecessary shutdowns.

4. Planned/Scheduled (Preventive) Shutdown Maintenance Distinct from routine work, this is a planned outage of a unit or the whole plant for major works — e.g., major overhaul of the turbine, rewinding of the generator, repair of the headrace tunnel or desilting basin, and painting of penstock. It is scheduled during low-flow (dry) season to minimize generation loss.

5. Emergency Maintenance Immediate, urgent work required to prevent damage or restore supply after an unforeseen event such as a flash flood blocking the intake, a landslide damaging the canal/penstock, a fire in the powerhouse, or a grid disturbance. It is carried out on a priority basis, often with the unit kept isolated.

6. Shutdown and Startup (Operating) Maintenance Routine checks performed during every start-up and shutdown of a unit — checking for abnormal sound, vibration, oil leakage, brake operation, and synchronizing conditions — to ensure the unit is healthy before it is put on load.

7. Overhauling / Major Maintenance A comprehensive periodic overhaul (typically every 4–8 years or as per Original Equipment Manufacturer (OEM) recommendation) in which the machine is fully dismantled, worn parts are measured against tolerances, and components such as bearings, guide-vane bushes, and wearing rings are replaced. This restores original efficiency and reliability.

8. Civil Structure Maintenance Inspection and repair of dams, weirs, intake, desilting basins, headrace and tailrace canals/tunnels, forebay, penstock supports, and powerhouse buildings — including removal of silt, repair of cracks, grouting, and slope protection works.

9. Electrical and Auxiliary Maintenance Maintenance of generators, transformers, switchgear, protection and control systems, batteries, station auxiliaries (cooling water, compressed air, drainage pumps), and Supervisory Control and Data Acquisition (SCADA)/communication equipment.

Conclusion A well-run hydropower plant follows a balanced maintenance strategy — preventive and predictive maintenance as the backbone, planned shutdown maintenance during the dry season, and corrective/emergency maintenance only when unavoidable. This ensures high plant availability factor, longer equipment life, safe operation, and maximum energy generation.