Condition monitoring in hydroelectric generators is crucial to ensure efficient, safe, and reliable operation. With large and complex machinery at play, failures can lead to costly repairs, operational downtime, and potential safety hazards. By monitoring parameters such as vibration, axial position, temperature, shaft speed, rotor-to-stator air gap, pressure, and water flow, operators can detect early signs of mechanical or electrical issues and take preventive action. Here’s an in-depth look at key monitoring techniques for hydroelectric generators.
Purpose: Absolute vibration monitoring of the generator casing is essential to detect mechanical issues that affect structural integrity, such as misalignment, unbalanced rotors, or loose components.
Method: Typically, accelerometers are used to measure head cover/draft tube vibration and velocity vibration transducers to measure stator frame vibration, capturing both amplitude and frequency data. These sensors provide insights into the overall health of turbine and generator by detecting abnormal frequencies that indicate issues such as rotor imbalance, misalignment, or structural looseness as well as cavitation.
Analysis: Collected data is analysed in both time and frequency domains to identify any anomalies. Established vibration thresholds help determine normal operating conditions, and any deviation can signal potential faults.
Purpose: Monitoring the shaft’s vibration relative to its bearings provides insights into rotor stability and helps detect mechanical issues such as imbalance, misalignment, or bearing wear.
Method: Non-contact eddy current probes (also known as proximity probes) are placed near the shaft, measuring the displacement of the rotating shaft in relation to the bearing housing. These probes detect minute movements and changes in shaft position.
Analysis: Shaft vibration data allows operators to observe shifts in rotor stability. High relative vibration amplitudes could indicate rotor imbalance, shaft misalignment, or bearing deterioration, helping operators take timely corrective action.
Purpose: The axial position of the rotor shaft is closely monitored to prevent excessive axial movement that could overload the thrust bearing, ensuring the correct thrust bearing oil pad thickness is maintained, otherwise potentially leading to catastrophic failure if unaddressed.
Method: Axial position probes (typically eddy current proximity probe systems) are installed at the thrust bearing to measure the rotor’s axial position. This provides real-time data on any movement along the shaft’s longitudinal axis.
Analysis: Deviations from the normal axial position indicate problems such as bearing wear, excessive hydraulic thrust, or mechanical stress. Early detection prevents axial misalignment, preserving the generator’s structural integrity and ensuring operational stability.
Purpose: Temperature monitoring in hydroelectric generators helps prevent overheating of critical components, such as windings, radial and thrust bearings. Excessive temperatures can cause insulation failure, mechanical wear, and overall degradation.
Method: Temperature sensors, like thermocouples and Resistance Temperature Detectors (RTDs), are placed in critical areas, including stator windings and core. These sensors continuously record temperature levels to ensure components remain within safe operating ranges.
Analysis: Temperature trends help detect early signs of potential issues, such as insufficient lubrication, cooling system inefficiency, or insulation degradation. By setting upper temperature thresholds, operators can receive alerts to intervene before overheating causes damage.
Purpose: Shaft speed monitoring ensures the generator operates within a stable speed range, maintaining power output stability. Deviations in shaft speed can indicate load imbalances, mechanical issues, or control system faults.
Method: An eddy current proximity probe system is aimed at a 1/rev target on the shaft provide real-time speed data, usually in revolutions per minute (RPM) as well as being used as a phase reference input for the vibration analysis channels.
Analysis: Speed data is continuously monitored for fluctuations. Any significant deviation from normal speed ranges can suggest mechanical imbalances, load changes, or other operational issues that require attention to maintain generator efficiency and protect against structural wear.
Purpose: Maintaining an optimal air gap between the rotor and stator is critical to prevent mechanical contact and ensure the generator operates with a stable magnetic field, avoiding electrical imbalances, mechanical wear, and catastrophic failure.
Method: Capacitive air gap sensors are positioned at multiple points around the rotor and stator, measuring the air gap as the rotor spins. The number of sensors required will depend upon the size of the generator but typically 4, 8 or 12.
Analysis: Air gap readings are examined for uniformity. Irregular gaps may indicate rotor eccentricity, misalignment, or sagging, which can lead to contact between the rotor and stator. Real-time monitoring ensures that any deviations are addressed promptly to prevent costly mechanical damage.
Purpose: Monitoring water flow pressure in turbines is crucial for maintaining hydraulic performance, maximising energy conversion efficiency, and preventing cavitation or structural stress on the turbine blades.
Method: Pressure sensors are installed at strategic points along the water flow path:
Inlet Pressure: Measures pressure upstream at the penstock or intake, confirming sufficient water flow for turbine operation.
Outlet Pressure: Measures pressure at the tailrace, ensuring adequate pressure differential across the turbine.
Turbine Housing Pressure: Measures local pressures to detect cavitation zones or excessive turbulence.
Analysis: Data from these sensors helps maintain an optimal pressure differential across the turbine. Fluctuations in inlet or outlet pressures can indicate flow restrictions, cavitation, or backpressure issues. Cavitation, a condition where vapor bubbles form in low-pressure zones and cause blade erosion, is detected through specific pressure fluctuations. Early detection allows operators to adjust the flow rate or turbine settings, avoiding turbine blade damage and enhancing performance.
| Parameter | Sensor Type | Purpose | Primary Analysis Indicators |
| Casing Absolute Vibration | Accelerometers & Velocity Transducers | Detects structural issues and external forces | Vibration amplitude, frequency spectrum |
| Relative Shaft Vibration | Eddy Current Proximity Probe Systems | Tracks rotor stability and bearing health | Displacement, frequency spectrum |
| Shaft Axial Position | Eddy Current Proximity Probe Systems | Monitors thrust bearing load and rotor centering | Axial displacement from center |
| Temperature | Thermocouples, RTDs | Prevents overheating in critical components | Temperature trend, threshold alarms |
| Shaft Speed | Tachometers, optical sensors | Ensures operational stability | RPM, speed fluctuation trends |
| Rotor-to-Stator Air Gap | Capacitive air gap sensors | Prevents mechanical rubs, ensures alignment | Air gap uniformity, eccentricity trends |
| Pressure Sensing | Pressure transducers | Optimises hydraulic flow and detects cavitation | Pressure differentials, fluctuations, cavitation indicators |
A comprehensive condition monitoring strategy incorporating casing absolute vibration, relative shaft vibration, shaft axial position, temperature, shaft speed, rotor-to-stator air gap, pressure sensing, and water flow pressure sensing provides a holistic view of a hydroelectric generator's health. Each parameter reveals different aspects of operational integrity and potential faults. Integrated, real-time monitoring systems allow operators to detect abnormalities early, enabling proactive maintenance and extending the equipment’s lifespan. Through precise, continuous monitoring, hydroelectric facilities can maintain high efficiency, minimise downtime, and ensure safe, reliable power generation.
Sensonics Ltd Condition Monitoring Systems: Sensonics is a UK manufacturer of sensors and machine protection instrumentation for hydrogenerators. We also offer a CMS (vibration analysis) add-on to our Sentry G3 machine protection system.
For more information visit our website: https://www.sensonics.co.uk/hydroelectrics or contact our sales team on Tel: +44 (0)1442 876833 or email sales@sensonics.co.uk.