Comprehensive, Trusted Nuclear Asset Monitoring Solutions
From sensors to machinery protection to condition monitoring to turnkey services, our solutions cover every type of asset found in PWR, EPR, SMR, CANDU, ABWR, and BWR nuclear power generating plants*. Whether an 1800 MW steam turbine generator, a reactor coolant pump, a containment air recirculation fan, or huge circulating water pumps, we have thousands of monitored points in service at nuclear plants around the world delivering the reliable information you need to protect, monitor, and manage your machinery assets.
* EPR and CANDU reactors are variants / evolutions of PWR technology. ABWRs are evolutions of BWR technology. SMRs may employ underlying BWR or PWR technologies and are so-called due to their size and modularity – not their underlying technology.
Dynamic Pressure Sensors
Accelerometers with integral electronics*
Housing Expansion LVDTs
Additional Nuclear Machinery Sensors
Valve Position Transducers
RTDs and Thermocouples
Magnetic Pickups (Variable Reluctance Sensors)
A hallmark of vibro-meter’s expertise with sensors is that they are robust – able to endure the harshest conditions. We are also the only manufacturer with the ability to support either voltage-mode or current-mode signal transmission in most of our sensors, affording you more flexibility to address noisy environments and long cable runs. And, our sensor solutions provide the flexibility of industry-standard outputs that allow them to be used with our own monitoring systems as well as others. Because most nuclear plants utilize PWR processes*, a majority of the machinery is not in containment conditions and standard sensors can be used. For BWR** and applications where the sensors will be exposed to elevated radiation levels, consult the vibro-meter factory for assistance.
* EPR, CANDU, and many SMRs
** BWR, ABWR, and some SMRs
Vibro-meter is the only supplier that provides an option for either current-mode or voltage-mode outputs on proximity measurements, allowing more flexibility and the ability to transmit signals over longer distances without interference. We are also one of the few suppliers to offer all of the proximity probes needed for large steam turbines found in nuclear plants, covering the full spectrum of applications from conventional measurement ranges for vibration to the extended ranges needed for differential expansion.
Used on most of the large, rotating machinery found in nuclear plants such as turbine generators, large pumps, motors, standby gas turbines, and mechanical drive steam turbines. These machines have fluid-film bearings and proximity probes are the right choice for radial vibration, shaft axial (thrust) position, differential expansion, rotor expansion, rotor position, speed, zero speed, rotor acceleration, and phase reference. Models with extended ranges and/or flange-mount form factors are available for applications such as differential expansion where the linear range of a conventional probe is insufficient and a right-angle cable exit is ideal.
Explore our extensive proximity probe offerings
Vibro-meter is recognized globally as a leader in dynamic sensors for harsh environments – and nowhere are environments more demanding than in nuclear containment.
These sensors are used primarily on the reactor vessel itself to monitor the dynamic pressure pulsations therein. They are designed to survive in particularly harsh environments where elevated temperatures are present and models such as the CP 103 and CP 104 are also able to withstand elevated radiation levels.
Explore our extensive dynamic pressure sensors offerings
Vibro-meter is the only supplier that provides an option for either current-mode or voltage-mode outputs on many of our velocity sensors, allowing more flexibility and the ability to transmit signals over longer distances without interference. Our velocity sensors also provide a much stronger voltage output than most other commercially available sensors, ensuring better signal-to-noise ratio while remaining compatible with our own monitoring systems as well as those of most other suppliers.
Used on machines where casing velocity measurements are valuable and particularly useful on large steam turbine generators where both casing absolute and shaft absolute measurements are required. A variety of models are available with or without integral cable for different temperature ranges and with different frequency responses. In addition to moving-coil designs, piezoelectric models are also available with a conventional voltage output or with a proportional 4-20ma “transmitter” output – ideal for general-purpose assets. These designs do not have moving parts that can wear out over time and are thus preferred for many applications.
Explore our extensive velocity sensor offerings
Vibro-meter is world-renowned for our accelerometer technology. For machinery vibration applications, very few can match the breadth of our portfolio or rival our quality. We are also the only supplier to offer the option for voltage-mode or current-mode transmission, providing superior immunity to noise and signal degradation over long wiring distances.
Accelerometers can be useful when high-frequency vibrations must be examined, beyond those available from the 1 kHz upper limit of our velocity sensor offerings. They are particular useful on machines with rolling element bearings were the bearing geometry generates characteristic frequencies indicative of problems. Accelerometers are also useful for measurements directly on the reactor vessel and models such as the CA 901 are thus available that can withstand elevated radiation levels.
Explore our extensive accelerometer offerings
Vibro-meter offers accelerometers with or without integral electronics. Those with integral electronics are preferred when possible because they are easier to install and do not require a junction box for separate electronics, lowering installation costs. Those with separate electronics are generally reserved only for applications where the mounting surface temperatures would damage integral electronics and a segregated design must be used instead. Models with Integral electronics are available for applications up to 350°C. Models with non-integral electronics are also available and specifically intended for high-temperature applications up to 700°C.
Vibro-meter is committed to providing a complete portfolio of transducers for steam turbine measurements. Our housing expansion LVDTs have been field-proven over decades to provide accurate, trouble-free measurement of this critical parameter.
These transducers are used for measuring housing expansion on the high-pressure case of large steam turbines. They allow operators to ensure that the sliding feet on such cases have not become stuck, resulting in a warped or cracked case. The measurements are made via a DC LVDT in a special IP54 housing that is suitable for the temperature and humidity conditions routinely encountered at the high-pressure casing of a steam turbine.
Explore ordering information and specifications for our housing expansion LVDTs
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.
Generally involve very close proximity to a steam turbine’s valves and thus elevated temperature and humidity levels compared to those incurred with housing expansion measurements.
Contact your vibro-meter sales professional for additional assistance.
Used for bearing temperatures as well as other machinery-related relevant process temperatures.
Contact your vibro-meter sales professional for additional assistance.
These sensors are typically used for overspeed measurements and are often the default sensor type provided by the OEM with steam turbines and some other machines. Although magnetic pickups can be used for phase-reference measurements, proximity probes are generally advocated instead.
Passive-type magnetic pickups are usually not designed to work at rotative speeds below 200 rpm and are thus not suitable for zero speed measurements. Although active-type magnetic pickups are available for such applications, a proximity probe or Hall-Effect sensor will usually be a better choice. However, we can supply magnetic pickups upon request.
Contact your vibro-meter sales professional for additional assistance.
Often used for overspeed applications and our SpeedSys300 overspeed system is consequently designed to be universally compatible with a very broad range of third-party Hall-effect sensors.
Contact your vibro-meter sales professional for additional assistance.
VM600Mk2 – rack-based monitoring
VibroSmart – distributed monitoring
Vibration transmitters and single-channel monitors
SpeedSys300 – overspeed protection
Vibro-meter is unique in the industry by offering both distributed and centralized platforms with very similar channel types between the two, allowing you to choose the platform that fits your field wiring and topology preferences rather than forcing you to choose between “full capability” and “limited capability” platforms. Each platform provides the flexibility of stand-alone condition monitoring, stand-alone machinery protection, or seamless integration of the two in a “zero footprint” fashion that requires no additional modules. And, consistent with industry best practices and standards, we offer a completely independent platform for overspeed protection of steam turbines – our SpeedSys300.
Our “one card does it all” approach revolutionized the industry more than two decades ago and our 2nd generation of this popular platform provides new levels of value, power, cyber security, and flexibility.
The VM600Mk2 is our centralized monitoring platform in a conventional 19” EIA rack-mounted form factor. It provides integrated protection and condition monitoring capabilities for all critical machinery (including TSI measurements), and builds on the enormous success of our original VM600 platform by providing numerous second-generation improvements while maintaining backward compatibility with the substantial installed base of first-generation racks (more than 240,000 protection and 88,000 condition monitoring channels).
Released in 2000, the original VM600 introduced the concept of “one module does it all” – a feature many others have since emulated but which was pioneered by vibro-meter.
You can learn more in our all-new whitepaper or explore the full capabilities, specifications, and ordering options of our VM600Mk2 offering.
Developed in conjunction with one of the world’s leading turbine OEMs, the VibroSmart architecture can reduce wiring costs without sacrificing functionality – employing our “one card does it all” philosophy pioneered in the VM600.
The VibroSmart System is our distributed monitoring platform in a 35mm DIN-rail mounted form factor. It provides integrated protection and condition monitoring capabilities for all steam turbine measurements, including TSI, and is ideal for new installations where wiring costs can be dramatically reduced by mounting the monitoring modules near the machine and using single or redundant network cables to bring necessary status and current values back to the control room.
The VibroSmart platform is often an excellent solution for smaller assets that do not warrant a larger, rack-based solution like the VM600Mk2.
Explore the full capabilities, specifications, and ordering options of our VibroSmart offering
Vibro-meter is committed to helping you address all classes of machinery with affordable yet robust online monitoring solutions, and this includes the smaller steam turbines that often comprise balance-of-plant mechanical drive applications.
For “Balance of Plant” (BoP) assets that do not warrant a more full-featured approach of VM600 or VibroSmart that includes condition monitoring, a very basic protection solution can often suffice. Our portfolio of vibration and position transmitters and single-channel monitors represents an economical “right sized” solution.
Multiple devices can be used in tandem to monitor not only the prime mover – such as a motor – but also the driven machine – such as a pump or fan.
Explore the full capabilities, specifications, and ordering options of our transmitter and single-channel monitor offerings
Designed from the ground up for SIL-certified, stand-alone overspeed protection, this platform reflects innovative design features that set it apart in the industry while ensuring it can evolve with enhanced functionality while maintaining its SIL ratings.
The SpeedSys300 platform is an innovative overspeed protection solution design for stand-alone operation and independence from all other systems in accordance with API Standard 670 and industry best practices. It can be used in simplex, duplex, or triple-modular-redundant configurations for 1oo1, 1oo2, 2oo2, or 2oo3 voting and is certified for SIL 2 and SIL 3 applications.
Overspeed is a critical protection measurement on steam turbines and other prime movers. The SpeedSys300’s adaptability means it can be used economically on your smallest machines while scaling to fit your largest machines – such as main steam turbine generators.
Explore the full capabilities, specifications, and ordering options of our SpeedSys300 offering
VibroSight software suite
Our condition monitoring software is designed to provide a seamless, unified environment for your machinery information regardless of what underlying hardware you may be using. Our configuration environments are designed for exceptional ease of use, allowing you to accomplish in minutes what formerly took hours, establishing an industry leading benchmark for power, flexibility, and intuitiveness with a highly graphical approach. And, our expert system environment is designed to automate your machinery diagnostic and anomaly detection tasks while providing a highly intuitive dashboard of machinery status suitable for operators – not just machinery specialists.
Full-featured condition monitoring and configuration software that allows you to unify your underlying protection, condition monitoring, and other data sources into a single, powerful environment for maximizing machinery availability, reliability, profitability, and safety.
VibroSight is a suite of powerful applications used for not just condition monitoring but also communications, data import/export, and configuration of our monitoring hardware platforms. When using VibroSight for condition monitoring, all of the plot types required for deep analysis of rotating machinery in nuclear plants available, under steady-state and transient operating conditions. For an extensive overview, visit the VibroSight landing page.
Explore the full capabilities, specifications, and ordering options of our VibroSight offering
Configure and test your SpeedSys300 overspeed hardware in an intuitive, convenient, and powerful environment.
Our SpeedSys300 software is used for the configuration and maintenance of our SpeedSys300 overspeed systems. It is a stand-alone software package that, like our VibroSight suite of tools, is designed for highly intuitive ease-of-use.
Explore the full capabilities, specifications, and ordering options of our SpeedSys300 system
Machinery Protection System Verification Services
Factory Acceptance Testing (FAT) and Integrated Factory Acceptance Testing (IFAT) Services
Machinery Diagnostic Services
Advisory and Consultancy Services
Vibro-meter provides comprehensive services that extend beyond just our nuclear machinery monitoring and protection instrumentation to encompass your broader needs such as machinery diagnostics, training, system integration, product rental, and project management. Some of our customers have a high degree of self-sufficiency and need little more than occasional technical support, while others prefer to outsource the installation, maintenance, and even operation of their systems.
Wherever you fall within this spectrum of needs, we have both standard and tailored service offerings to fit. In addition to the short descriptions below, you can read more in our Services Brochure.
These services verify the operation of your already installed protection system, whether VM600, VM600Mk2, or VibroSmart. Although our monitoring systems do not require calibration, periodic functional testing to verify that the system working within published specifications is recommended at 2-year intervals. These services cover the monitoring system, its connected sensors, and its communications with associated automation platforms such as the plant’s distributed control system.
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.
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. 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.
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.
Our machinery diagnostic services can also be used to generate customized algorithms within your installed VibroSight Rulebox software, allowing it to perform automated diagnostics by embedding the same analytical processes and domain expertise utilized by our own engineers.
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.
Every measurement customarily made on the rotating machinery found in nuclear plants for both protection and condition monitoring is available in our monitoring system platforms. Pumps, motors, blowers, fans, large steam-turbine generators, mechanical drive steam turbines, standby gas turbines, and even the reactor vessels themselves. In addition, we provide most of the sensors you will need either directly or via partnerships. In instances where we do not provide sensors (such as temperature), we can provide guidance to assist you in sourcing them yourself or we can source and install them for you as part of turnkey installation and project management capabilities. You can also download our publication A Practical Guide for Understanding Turbine Supervisory Instrumentation. For details on measurements used on standby gas turbines, visit our gas turbine monitoring pages. For details on monitoring mechanical drive steam turbines as well as driven machinery such as pumps, blowers, and fans, see our diagrams here and here.
* 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 used on all machines with fluid-film radial bearings. It 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.
This measurement is made on all machines with a fluid-film thrust bearing. It 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. In such cases, larger diameter probes are available with longer measurement ranges.
Because the shaft axial (thrust) position measurement is so important, it is usually made by means of two redundant probes that compare their readings and use logical AND voting. The thrust bearings on steam 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.
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. When excessive temperatures are observed, the machine must be shut down because the bearing babbitt material can melt, resulting in damage far beyond a replaceable bearing pad – such as a scored shaft or an axial rub.
Often, sudden catastrophic changes in a machine will result in instantaneous changes in shaft position or vibration, and the thermal inertia of the bearing materials will cause temperature to rise more slowly than vibration levels, but still relatively fast.
For this reason, it is not always advisable to vote temperature and vibration using AND logic. By the time both measurements indicate a problem, it may be too late to trip the machine and prevent damage.
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. It is particularly important for diagnostics where vibration phase is extensively.
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 usually used for speed measurements instead of a once-per-turn mark.
While a phase reference measurement is made using a proximity probe observing a once-per-turn shaft discontinuity such as a key or keyway, 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. While such a surface is recommended for greater accuracy in speed indication purposes, it is absolutely essential for overspeed protection measurements for the reasons discussed in the phase reference section.
Also, overspeed is almost never 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.
1-out-of-2 arrangements are also used (sometimes on gas turbines), but are less common on steam turbines where 2-out-of-3 is routinely used instead as part of a SIL 3 protection loop. 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. Proximity probes are generally recommended due to their superior self-checking capabilities and the ability to measure speeds as low as 0 rpm and as high as 120,000 rpm.
For machines with rolling element bearings, it is customary to measure vibration on the bearing cap. The geometries of the rolling elements within the bearing give rise to characteristic frequencies and these can be used to detect defects and wear.
Casing measurements are also useful on machines with fluid-film bearings where the casing is quite compliant and can vibrate independently of shaft motion. The casing and shaft-relative measurements can be vectorially combined to give a shaft absolute measurement in addition to casing absolute and shaft relative. The shaft absolute measurement requires both the bearing absolute and shaft-relative measurement to be made in the same measurement plane. Examples of compliant foundations would be in plants where the turbine is mounted on the top floor of a building, many stories above ground with steam piping and auxiliary machinery beneath the turbine.
Lastly, casing vibration measurements are useful on reactor vessels as well as gearboxes and gas turbines.
Casing vibration is made by means of a seismic sensor such as a moving-coil velocity pickup or a piezoelectric accelerometer.
Dynamic pressure measurements can be particularly useful on reactor vessels (steam generators) to observe flow oscillations. Given the high-temperature, high-radiation environment, case must be taken to select a sensor that will survive these rigors.
These measurements are also useful on gas turbine combustors – and these machines are sometimes found in nuclear plants as stand-by units to bring the plant up during a “black” start.
Dynamic pressure measurements are made with special dynamic pressure sensors, similar in principle to a piezoelectric accelerometer but measuring changes in pressure. Wide frequency responses are available from below 5Hz to 10 kHz or higher. High-temperature environments are typical and require sensors that can endure surface temperatures of up to 650 C.
Control valves on main steam turbine generators are critical and experience has shown that monitoring valve condition is warranted on large machines – particularly those in nuclear service. For example, a 1990 study documented that more than 1.5 million MWh were lost in nuclear plants each year due to valve issues. Although it is common to include valve position on large steam turbine generators as part of a TSI suite of measurements, it is less common to monitor valve condition. Vibro-meter can do both.
Working with major OEMs, vibro-meter has developed a comprehensive solution to monitor valve condition by using strategically placed accelerometers as well as using process signals to trigger data collection at appropriate times and conditions for correlation with valve vibration. The vibration is monitored in multiple frequency bands to detect various types of problems and the success of the system has resulted in a solution that is standard and preferred on many steam turbine generators in nuclear service. Because these same issues can affect valves in non-nuclear plants, they can also be used in conventional fossil-fuel plants.
Contact vibro-meter to learn more about our valve condition monitoring solution
The differences in materials and also mass between a turbine case and its rotor means that they expand at different rates. As they grown or shrink relative to one another, the differential between the two must be monitored very carefully, to prevent axial rubs from occurring between stationary and rotating blading.
These measurements are most often made with extended-range proximity probes observing a collar or other surface. To allow smaller-diameter probes with shorter linear ranges, the probes can be arranged back-to-back in a complementary arrangement that effectively doubles the linear observable measurement range.
Another common technique by some turbine manufacturers is to create a ramped surface on the rotor such that a trigonometric relationship exists between movement observed by the probe and actual relative motion between the probe’s mounting (turbine case) and the rotor. This arrangement allows a small change in the radial direction observed by the probe to correspond to a large change in the axial direction through differential expansion. Still another arrangement is by means of a magnetic collar and a probe observing a swinging pendulum that also exhibits a trigonometric relationship, similar in principle to that of the ramp approach.
The exact method used typically depends on that adopted by the turbine OEM. vibro-meter monitoring systems are designed to be adaptable to all of these.
The steam admitted into the high-pressure case of a large turbine is not only at high pressures, it is at high temperatures. This causes the HP turbine case to expand during start up and to accommodate this expansion, the case is generally designed with fixed feet on one end and sliding feet on the other end.
When one or both of these sliding feet stick, it can warp the case and the expansion must thus be monitored. This is normally done with LVDTs and can be accomplished by either a single- or dual-channel measurement. Dual-channel is normally recommended as it can display not only the absolute expansion, but also the differential between each side to ensure both feet are sliding properly – not just one. When only one foot slides and the other is stuck, it can result in a so-called “cocked case”.
When both feet are stuck, this can likewise create problems.
The rotor on a large turbine generator can have extremely long unsupported spans between its bearings and can thus sag if not kept constantly turning. For this reason, when a turbine is brought offline, its rotor will generally continue to slowly rotate by means of a turning gear mechanism. As the machine is again brought on line and back to speed, the amount of residual bow must be carefully monitored by means of a probe to observe the shaft “wobble” (called eccentricity).
Excessive eccentricity corresponds to excessive bow and if the machine is further accelerated in speed with excessive bow, the bow can exceed the elastic limits of the shaft and become a permanent bend. Eccentricity is measured by means of a proximity probe mounted some distance away from a bearing. This allows the bow to be more pronounced and thus more easily observable than if attempted at a bearing location by a radial vibration probe.
Valves are used to control steam admission into the turbine and thus to control its speed. For larger machines, there are often a series of valves that work together to admit the steam rather than a single large valve. These valves are frequently arranged in a so-called “valve rack” that mechanically lifts the valve stems by means of a cam and levers.
The linear travel is usually measured by means of LVDTs attached to the rack mechanisms. In some cases, the valve adjustments are measured using rotary position rather than linear, in which case a sensor measuring degrees of rotation is used such as a rotary potentiometers, RVDT, or rotary Hall-effect sensor.
At one time, these measurements were always made in the same system as the vibration and other TSI measurements. However, today the valve position measurements are often moved into the turbine control system because they are fundamentally not just for indication, but for actual control purposes.
Thus, during an instrumentation upgrade, the measurement may be migrated from the TSI environment to the control environment. In other instances, the user may wish to leave the measurement within the TSI system. vibro-meter monitoring systems are designed to accommodate any of these sensors, allowing inclusion of valve position measurements when required.
As noted in the description of eccentricity measurements, to prevent excessive shaft bow or even a bent shaft, the rotor of a large steam turbine must be kept constantly turning when the turbine in use. This is done my means of a special turning gear that keeps the rotor slowly turning – often at speeds below 5 rpm. When the rotor decelerates toward a standstill, this turning gear must be engaged at the right speed to keep the rotor turning. This is done by means of a zero-speed tachometer.
To ensure very low speeds can be measured with acceptable update rates, a multi-tooth gear is used and it is observed by a speed probe (usually proximity, but Hall-effect of active magnetic pickups can also be used).
If a simple once-per-turn discontinuity was used instead of a multi-tooth wheel, the rotational speeds would result in unacceptably slow update rates.
Boiling Water Reactor (BWR)
Pressurized Water Reactor (PWR)
Open full-sized image in a new tab
In a boiling water reactor, the steam for the turbine is heated directly in the reactor and is radioactive. Most of the monitored machines (such as the main turbine generators and many of the pumps) in a BWR plant are thus in radioactive containment because they directly contact the steam/water in this loop.
Open full-sized image in a new tab
In a pressurized water reactor, the steam for the turbine is heated indirectly in a secondary loop and thus never comes into direct contact with the reactor’s high-radiation environment. Most of the machines in a PWR plant are thus not in radioactive containment and in many respects can be treated much like a conventional thermal plant where no radiation is present.
|A Practical Guide for Understanding Turbine Supervisory Instrumentation|
|Speedometer – a vibro-meter publication on overspeed|