Hydropower Monitoring Solutions

The sensors in this section are supplied by third parties, but are generally compatible with our monitoring platforms. Consult vibro-meter for additional information on these sensors for new or retrofit applications, or if you have existing sensors of the types mentioned here and want to explore compatibility. In some cases, vibro-meter may be able to source these sensors, size them to the particulars of the application, install and/or provide installation guidance depending on the project requirements, and assume full system responsibility.

• Magnetic Flux Sensors
  Monitors non-homogeneity in a generator’s magnetic field, often caused by shorted poles.
• Dynamic Pressure Sensors
  Used primarily for cavitation.
• Load Cells
  Used in spillway gates and other non-rotating hydro assets.
• RTDs and Thermocouples
  Used primarily for bearing pad temperatures.
• Partial Discharge Sensors
  Used to detect degradation of insulation on generator windings.
• Magnetic Pickups (Variable Reluctance Sensors)
  Used for speed sensing, primarily for governor control.
• Fiber Optic Accelerometers
  Often used for monitoring stator end winding vibration.
• Hall-Effect Sensors
  Used for speed sensing.

Contact your vibro-meter sales professional for additional assistance.

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These services performed at time of initial system deployment and include the installation activities – not just the verification activities. These services also include training so that operators and others will be proficient in using the newly installed systems.

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Training can be delivered at our facilities, your facilities, or other facilities such as hotels or conference centers. We can also provide training via video conferencing if required. Training is delivered by certified professionals and is assembled based on your specific needs to cover sensors, monitors, software, vibration diagnostics, measurement fundamentals, system maintenance, system operation, and other specialized topics pertaining to machinery monitoring and protection such as cybersecurity and hydro-specific monitoring. We maintain dozens of standard training modules that can be mixed, matched, and customized to meet your needs, and modules to address new topics can be developed as required.

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These services allow robust functional testing of new systems before they leave the factory, and typically occur once the systems are mounted in cabinets and pre-wired to terminations, ready to accept field wiring at site. Signals are simulated during FATs to ensure point-to-point wiring is correctly installed and labeled, alarms and signal processing are configured and working properly, relays are configured and wired properly, and digital communications such as Modbus, GOOSE, or Profibus are mapped and working properly. When condition monitoring is included with the machinery protection, this functionality is tested as well. This testing can also be carried out at locations other than vibro-meter premises when full integration with other systems, such as the plant DCS, must be exercised and verified.

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These services verify that your sensors are performing within published specifications and calibrate them where required. Sensors can be returned to the factory for calibration or can be calibrated in the field. Factory as well as field calibration services are performed using equipment calibrated to NIST-traceable references.

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Remote connection to installed condition monitoring systems for periodic or on-demand machinery health assessment.

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• Machinery Protection System Verification Services
  Site services to verify your protection system and connected sensors are performing within published specifications.
• Condition and Monitoring System Upgrade Services
  Site services to upgrade your installed condition monitoring systems, whether vibro-meter or other, to our state-of-the-art VibroSight platform.
• Project Engineering/Management/Planning Services
  Turnkey site services to manage the entirety of your protection and/or condition monitoring project.
• Instrument Rentals
  Portable data acquisition and condition monitoring systems.
• Advisory/Consultancy Services
  Specification writing, reliability assessment, condition monitoring strategies, specialized measurements and applications, and more.
• Long Term Service Agreements (LTSAs)
  Tailored commercial agreements to maintain your vibro-meter instrumentation.

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• 1Shaft-Relative Vibration
• 2Bearing Seismic Vibration
• 3Air Gap
• 4Thrust Position
• 5Speed/Overspeed/Phase
• 6Stator Expansion
• 7CasingSeismic Vibration
• 8Magnetic Flux
• 9Partial Discharge
• 10Temperatures¹
• 11Pressure
• 12Level
• 13Guide Vane² Position

¹ Windings, bearings, etc.

² Also called wicket gates; used only with Kaplan- and Francis-type runners.

These measurements are made by means of proximity probes, usually affixed to the bearing housing and observing the vibratory motion of the shaft within its bearing clearance. The probe can return both AC and DC signal components, corresponding to dynamic motion (vibration) toward and away from the probe, as well as the average position (DC component of signal). The average position shows the location within the bearing clearance where the shaft rides on its film of lubricating oil. It is about this point that dynamic motion occurs.

Although this can be a single-channel measurement with a probe mounted in only a single vibration plane, it is more common – particularly on critical machinery – to mount a second probe in an orthogonal axis so that position and vibration in both an X- and Y-plane can be observed, ensuring that any motion within the bearing clearance is detected.

These measurements are routinely used for both protection and condition monitoring. The amplitude of the signal corresponds to the amount of vibration and can be related to bearing clearances. It is made in units of displacement, either micrometers or mils.

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The massive size of hydropower turbine-generators means that there will be appreciable vibration of the bearing housing – not just the relative motion between the shaft and the bearing. Consequently, it is common to measure the seismic vibration of the bearing relative to free space and to do so in the same planes as X and Y shaft-relative probes for ease of comparison. These measurements are sometimes also made in the axial direction on hydro turbine-generators. Moving-coil velocity sensors or accelerometers are used for this measurement.

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Rotor-to-stator air gap is an extremely important measurement on many hydroelectric generators as the relative air gap between the two can become unacceptably non-uniform due to a variety of causes including:

• vibration of the rotor (or components thereof)
• vibration of the stator (or components thereof)
• misalignment
• non circularity
• thermal and/or centrifugal expansion of the rotor
• thermal expansion of the stator
• foundation movement (concrete growth, concrete deterioration, seismic activity, etc)
• rotor rim deformation
• looseness (soleplate, frame-to-foundation, pole-to-rim, rotor spider welds, etc.)

By use of a phase reference probe, and a sufficient number of air gap sensors (usually 4 to 16 depending on stator diameter), a complete air gap profile can be mapped with each rotation, and problems can be detected and isolated before they progress.

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These measurements are made by means of proximity probes, and reflect the axial movement of the shaft at the thrust bearing, relative to the thrust bearing mounting. On hydro turbine-generators (unlike the depiction in the animation at right) the measurement is made by observing the collar because the end of the shaft is not accessible.

A similar measurement is called rotor position and is when the axial position is made relative to the machine casing rather than the thrust bearing. Like shaft-relative vibration measurements, shaft axial position is made via a proximity probe. Unlike shaft-relative vibration, it is generally the DC component of the signal (position) that is of interest rather than axial vibration (AC component of signal).

Some machines have axial thrust movement in excess 2mm (80 mils), or have geometries that entail a large static gap, and probes with a range longer than 2mm are required. In such cases, vibro-meter offers larger diameter probes with longer measurement ranges.

Because the shaft axial (thrust) position measurement is so important, it is usually made by means of two (or even three) redundant probes that compare their readings and use logical AND voting. The thrust bearings on hydro turbines are generally large enough to easily accommodate two or three probes.

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Shaft rotative speed is fixed on hydro turbine-generators as they are synchronous machines. However, speed is useful during runup and rundown to collect transient data under changing speed conditions.

By use of a once-per-turn discontinuity in the shaft, a phase reference can also be established. A proximity probe observes the passage of this mark with each shaft revolution and thus provides a precise reference in time against which all other measurements along the shaft can be synchronized, whether vibration, flux, or air gap. Fundamentally, a phase reference measurement is a timing measurement, but it is usually expressed in degrees of shaft rotation after the timing mark occurs.

This mark can also be used for basic speed indication, but cannot update fast enough for overspeed measurements. For this reason, a toothed wheel is used for overspeed rather than a once-per-turn mark. Also, because overspeed events can happen so quickly and can be so catastrophic, redundant sensors are a necessity.

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Air gap measurements will usually suffice as a means of assessing the relative thermal expansion of the stator. However, air gap measurements are, by their nature, relative measurements because the sensors are affixed to the stator and will measure a change in gap produced by stator motion, rotor motion, or both. In instances where the stator expansion must be isolated, the air gap measurement alone is insufficient and proximity probes can be installed to more directly measure the thermal expansion. The probes can be mounted to observe the stator soleplate directly, or they can be mounted at locations near the air gap sensors. This allows the absolute position of the stator relative to the foundation to be known, as well as the rotor relative to the foundation, and augments the rotor-to-stator relative measurements provided by air gap sensors.

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Analogous in concept to bearing seismic vibration measurements, and using the same sensors, these are measurements made on machine elements other than the bearing housing or bearing supports such as a headcover or stator.

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The magnetic flux in a generator’s rotor should be uniform and consistent as it rotates. By monitoring magnetic flux, non-homogeneities can be detected, indicative of rotor winding insulation degradation and problems such as turn-to-turn shorts. By use of a phase reference sensor in conjunction with magnetic flux sensors, the precise location of the flux anomalies can be known, allowing isolation to a specific pole piece and more targeted inspections during outages.

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As the winding insulation in a generator’s stator deteriorates, it will begin to exhibit electrical arcing in the locations of compromised resistance. These are known as partial discharges (PDs) and although present on all types of generators as they age, hydro turbine-generators are the machines where such measurements are most common. Many customers use portable PD instruments to periodically assess stator winding health, while a small number instead prefer continuous PD monitoring. Vibro-meter has extensive experience in both portable and continuous PD monitoring and is able to assist you in sourcing the hardware when required as well as integrating the measurements into VibroSight software.

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To ensure radial and axial (thrust) bearings are not too heavily loaded, or starved of necessary lubrication, it is customary to embed RTDs or thermocouples into the bearing pads. Other temperature measurements are also important on hydroturbines such as stator and rotor windings.

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Dynamic pressure sensors are useful for detecting cavitation and rough load zone. The measurements are typically made on the draft tube or headcover near the runner, where the hydraulic disturbances can be most easily detected. Because hydro units are subject to more variable conditions than in the past, and many now use air injection, the ability to directly detect cavitation and rought load zone has become even more important.

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Level is a straightforward measurement and often relates to reservoir level. Such measurements are generally made by means of a process transmitter that provides a quasi-static value.

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Like level, guide vane position will often be measured by means of a process transmitter and available in the control system. However, there are instances where it is useful to bring the signal directly into a machinery monitoring system, such as for state-based monitoring. The quasi-static signals associated with such measurements are easily brought into the VibroSmart and VM600^Mk2 platforms. When they are not needed as part of the monitoring system, they can be imported to VibroSight software as the information is almost always useful for diagnostic purposes to correlate with vibration and other measurements.

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