Gas Turbine Monitoring Solutions

Consistent with our culture and heritage of innovation, we are today developing a next-generation portfolio of dynamic pressure sensors that utilise optical technology, resulting in extended frequency response for even better combustion control. You can register to receive periodic updates as this exciting technology nears commercial release.

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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.

These services verify the operation of your already installed protection system, whether VM600, VM600^Mk2, or VibroSmart. They address the monitoring system, its connected sensors, and its communications with associated automation platforms such as the plant’s distributed control system.

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These services are similar to System Verification Services, but are 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.

Click here to find out more about our Commissioning services.

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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 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.

Click here to find out more about our FAT and IFAT services.

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Field engineers with machinery expertise are available to collect data from your machinery using portable data acquisition equipment or your installed condition monitoring systems. The collected data is reviewed and diagnostic reports are produced regarding machinery health such as the likely malfunction, its severity, and recommended corrected actions along with any corresponding urgency.

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These services are designed to address a wide range of a la carte or bundled activities such as generating project specifications, site surveys to assess machinery and corresponding recommended monitoring, ongoing predictive maintenance services, recurring audits of machinery condition at specified intervals and after major events, and many others that can be custom-tailored to your unique needs.

Click here to find out more about our advisory and consultancy services.

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• Sensor Calibration Services – Verification that your sensors are performing within published specifications and calibration as required; can be performed at site or in the factory.
• Condition and Combustion Monitoring System Upgrade Services – Site services to upgrade your installed condition and/or combustion 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.
• Long Term Service Agreements (LTSAs) – Tailored commercial agreements to maintain your vibro-meter instrumentation.
• Training – Tailored to cover the topics of your choosing at our facilities, your facilities, or other facilities – or even via video conferencing.

• Shaft-Relative Vibration
• Shaft Axial (Thrust) Position
• Bearing Temperature^*
• Phase Reference
• Speed/Overspeed
• Shaft Absolute/Bearing Absolute/Casing Absolute^†
• Dynamic Pressure/Pulsation Measurements

^* Although Meggitt vibro-meter® does not provide temperature, pressure or valve position sensors, our protection and condition monitoring systems can integrate these readings.

^† These sensors can also be used in conjunction with shaft relative vibration sensors to obtain absolute measurements if orientated to coincide with shaft relative measurement planes.

This measurement is made by means of a proximity probe, 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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This is the axial movement of the shaft at the thrust bearing, relative to the thrust bearing housing. It may be made at the end of the shaft or at the thrust collar. 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). Axial thrust movement in excess 2mm (80 mils) is rare and a probe with a 2mm range is usually sufficient. However, due to mounting constraints, the sensor must sometimes be installed further away from the shaft. In such cases, larger diameter probes are available with longer measurement ranges.

Many thrust bearings are designed to have a total range of 1–0–1 mm where the thrust collar can move in the normal or counter direction against the normally active or inactive thrust bearing pads. Excessive movement corresponds to damage of the thrust bearing and an axial rub between rotating and stationary parts such as blades contacting vanes on a gas turbine. As such, this measurement is extremely important for machinery protection, and also has diagnostic value for condition monitoring purposes.

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 measurement can also be done by means of a single probe but will have not voting. The thrust bearings on gas turbines are generally large enough to easily accommodate two probes – either to observe the thrust collar directly or to observe the end of the shaft near the thrust bearing.

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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 an RTD or thermocouple into the bearing pad(s) carrying the shaft load or on the outer race for rolling element bearings. When excessive temperatures are observed, the machine must be shut down because bearing failure may be imminent, resulting in damage far beyond an easily replaceable component.

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Each independent shaft in a machine is usually fitted with a once-per-turn mark, such as a key or keyway at a coupling, allowing a proximity probe to observe the passing of this mark with each shaft revolution. This provides a precise reference in time against which all other measurements along the shaft can be synchronized. This mark can also be used for basic speed indication, but cannot update fast enough for overspeed measurements.

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As noted above, a phase reference measurement is made using a proximity probe observing a once-per-turn shaft discontinuity such as a key or keyway. However, this will rarely update at a rate suitable for accurate speed indication, much less overspeed protection.

As such, a multi-tooth surface will be used – often a gearwheel made specifically for speed measurement purposes. Also, overspeed should never be measured by a single (non-redundant) sensor. Instead, there are usually three redundant sensors observing the same multi-tooth surface and then monitored in a 2-out-of-3 voting arrangement that represents an optimal balance of missed trips versus false (spurious) trips.

On aeroderivative gas turbines, there are normally 2 (and sometimes 3) separate spools that are aerodynamically rather than mechanically coupled, thus necessitating separate speed measurements for each spool.

Speed and overspeed sensors can include magnetic pickups (i.e., variable reluctance sensors), Hall-effect sensors, and conventional eddy-current proximity probes as used for vibration and position measurements.

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Aero-derivative gas turbines use rolling element bearings and mounting accelerometers at or near the bearings is impractical. Consequently, the accelerometers are mounted on the engine frame (often part of the support structure). However, such mounting locations are too far from the bearings to extract detailed bearing information (it is not only small in amplitude, but often swamped by other higher-amplitude signals such as blade passage).

The ability to monitor discrete bearing-related components is thus very limited and is instead primarily focused on identifying filtered vibration present at the various shaft (spool) speeds, indicative of gross problems such as loss-of-blading or catastrophic bearing failure that manifests at spool rotative speed.

In contrast, industrial and heavy-duty gas turbines use fluid-film bearings and proximity probes can almost always be fitted to the bearings. Many OEMs, however, mandate bearing cap seismic velocity measurements for protection, and proximity probes only for condition monitoring. Because the preferred engineering units are velocity rather than acceleration, signal integration (acceleration to velocity) must be used if the sensor does not provide a native velocity signal. Also, because these sensors are fitted to the bearing cap where temperatures are considerably cooler than elsewhere on the turbine, our CE-series models with integrated electronics can sometimes be used, or our CV-213 velocity sensor. In contrast, measurements on the frame rather than on bearing caps usually represent considerably higher temperatures (up to 700° C) at the mounting locations and must use our CA-series sensors with external conditioning electronics.

In addition to measurements at bearing locations, it is common practice to monitor the absolute vibration of the turbine casing – often near the combustion section. The primary reason for this is not to detect bearing, blading, or other rotor dynamic problems but combustion problems. During combustion, flame instability may trigger pressure pulsations (see dynamic pressure section below), resulting in casing vibration. Monitoring the casing to detect combustion issues is thus important for two reasons:

1. It provides a backup measurement in case the dynamic pressure sensors have malfunctioned or do not otherwise detect the pulsations for some reason. This level of redundancy afforded by two different measurement types is warranted because if left unchecked, pressure pulsations can quickly destroy the affected combustor(s).
2. On some machines (often older type designs), there are either no dynamic pressure sensors at all, or if present, only mounted on some combustors rather than all combustors. In such situations, the casing measurements allow visibility of combustor issues that would otherwise be undetected.

When monitoring casing vibration, it is imperative that the sensors are installed directly on the turbine casing, below the turbine insulation. However, this means they are subject to extremely high temperatures (up to 700°C) and therefore require our CA-series sensors. The CA series decouples the sensor from the signal conditioner and thus keeps the signal conditioning electronics from being exposed to the extreme temperature at the sensor mounting location.

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A dynamic pressure sensor is fitted to each combustor on most modern gas turbines to measure pressure pulsations and combustion dynamics. This is because the turbines burn fuel as lean as possible to reduce emissions to environmentally acceptable levels, but in so doing create metastable flame conditions and corresponding pressure pulsations that will damage and even destroy combustors if left unchecked.

The characteristic frequencies associated with these metastable conditions vary according to manufacturer and combustor. By tuning the monitoring system to these characteristic frequencies, the damaging pulsations can be detected and the fuel/air mixture adjusted to an operating point where the combustor will not be damaged.

The dynamic pressure sensors are thus used as part of a closed-loop control system that keeps combustion from persisting in a state that will damage the combustors. Highly sophisticated filtering and detection is used, as provided by the monitoring system. The dynamic pressure sensors are mounted in extreme environments where temperatures of up to 650° C and billions of pressure cycles must be endured.

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