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This study presents a theoretical model that enables a fast and precise calculation of a sampled apodized fiber Bragg grating and the related sensor. Transfer matrix method was used since there is no analytical solution due to the complex refractive index profile. Errors brought by the uniform refractive index profile approximation were compensated, which allows a smaller number of divided segments and therefore a fast and memory efficient simulation. This compensation method realizes a high speed and high precision simulation. The theoretical spectra of both the grating and the sensor agrees well with those given by the experiments. According to the experiment, the sensitivity of the moisture sensor is −0.6165 pm/ppm in mineral oil. This theoretical model provides a new choice for the researchers and developers to design and optimize the sensing structure instead of a blind try and error process.

Simultaneous monitoring of moisture and temperature using advanced fiber gratings is a fairly new concept. This paper implements and characterizes an apodized, 24mm long, pi-PSFBG moisture and temperature sensor through Matlab. Testing and calibration of a similar fabricated sensor records the sensitivity of 7.5+/− 0.1 pm/RH% for moisture, 10 pm/°C for temperature at a response time of 20 minutes.

Fiber optic sensors based on fiber Bragg gratings (FBGs) find potential use in condition monitoring because their spectral properties change according to external environmental and/or physical factors. We propose and demonstrate a technique for interrogating multiple FBG-based sensors based on microwave photonic (MWP) filtering. In particular, we exploit the spectrum-slicing properties of two different FBG Fabry-Perot cavities to implement a double passband MWP filter. Each sensor spectrum results in a unique MWP filter passband. As temperature is applied to a sensor, the corresponding MWP filter passband will shift in frequency; we track such shifts by monitoring the detected power at a fixed radio frequency. We discuss the use of a ratiometric approach for enhancing the sensitivity and the impact of cross-talk from the MWP filter responses in terms of simultaneous multi-sensor operation. Results show that we can monitor local temperatures at two (or multiple) different locations simultaneously and independently using a single measurement system.

Moisture and temperature are the two most important factors controlling the life of the transformer. Together, they could accelerate the aging of the mineral oil and the insulating cellulose paper. For every 10 °C rise in temperature, the expected life of the transformer can be reduced by a half; moisture has a similar effect. A standard moisture transport model currently used by the industry assumed that the temperature of the recirculating oil stays the same at both the top and the bottom. This has been proven to be incorrect. Since the solubility of moisture in oil is temperature and load dependent; if we can measure the trace moisture directly on the cellulose paper and the pressboard, we might be able to understand the true picture and then perform measures to optimize transformer's life. This challenge is now solved by fiber optics moisture and temperature sensor. This type of sensor is immune to high voltages and strong electromagnetic field yet has a working life of 25 years. This paper will describe technology behind the sensor and how these sensors are packaged and installed inside the transformer. We will also discuss a successful field test with cooperation with a large transformer manufacturer.

A thin fiber optics sensor, VibroFibre, has been developed to fit into a 2 mm gap in transformer windings for directly measuring the winding vibration. The new innovation is aimed to help the transformer users to safely extend service lives of their assets and to mitigate risk of unscheduled shutdown due to premature equipment failure. The optic fiber based vibration sensor can be installed inside a transformer and the resulted vibration measurement is no longer affected by various noise sources from peripheral equipment. The vibration frequency spectrum measured inside an oil-filled transformer, shows a signature of wider band ranging between 20 Hz to 1000 Hz. The new sensor has shown superior performance, especially in its response to frequencies below 100 Hz. When combined with the new Long Gauge technology, the response goes as low as 5 Hz. The sensor’s small size makes it possible to install the sensors in the winding spacers with built-in cradle-like slots, which helps avoid possible disturbance to the cooling oil flow.

The philosophy literature is rife with thought experiments, and quite recherche thought experiments at that. Derek Parfit’s Reasons and Persons, arguably the most influential work on personal identity in the last 50 years, walks readers through cases of teletransportation, gradual matter reorganizers, brain transplants, fission, and so on. Other famous thought experiments ask us to imagine a man shuffling papers in a room to implement a Chinese-speaking computer program; or “people seeds” that float in past your window screens and lead to a person blooming on your sofa; or a neuroscientist confined to a black and white room who nonetheless learns the complete (and finished) neuroscience of color vision. But while these evocative, rich cases have spawned a huge literature, it is a recurring complaint that we should not settle debates in philosophy using such recherche thought experiments.

We review recent results on exploiting microwave photonics to enable simultaneous interrogation of multiple fiber Bragg grating (FBG)-based sensors. In particular, we describe the use of (1) microwave photonic filtering and (2) chirped microwave pulse generation and compression as a means to map the wavelength (spectral) changes in the response of FBG-based sensors (specifically, an in-fiber Fabry-Pérot cavity sensor based on FBGs, FBG sensors directly, and a linearly chirped FBG sensor) to applied temperature (or strain) to the power of a radio-frequency signal (i.e., a wavelength-to-power mapping) or to the correlation peak of the compressed microwave signal. The approaches support high-resolution and high-speed interrogation and can be suitable for large scale sensing networks.

Winding distortions can be mechanically induced during transportation, by large transient currents caused by lightning events or short-circuits, or as a result of gradual clamping looseness as the transformers age, after many loading and unloading cycles. Winding distortions lead to increased electromagnetic forces between the windings and the core, giving rise to changes in vibration signatures that could be useful as online condition monitoring tool. Unfortunately, this method is difficult when using electrical sensors mounted on the tank walls, i.e., vibration signals are highly dependent on mounting positions, and contaminated by noise from oil pumps, cooling fans, or the oil tank itself. For the first time, a thin fiber optics sensor has been developed to fit the 2 mm gap between the winding and the slot for direct winding vibration measurements. This sensor is an extension of the Fabry-Perot fiber optics vibration sensor — The VibroFibre — developed by QPS 5 years ago and already deployed around the world for monitoring Stator End Winding (SEW) vibration. The same hermetic junction plate developed to isolate the hydrogen cooled generator from the outside ambient is now conveniently adapted to become the feedthrough into the transformer tank, thus preventing any oil leaks to the environment. This paper discusses the successful showcase developed between QPS and Xian E-Sys Automation Engineering Co., Ltd in China. The proposed sensor, which is 2 mm thick, 50 mm long, and 20 mm wide, can measure vibration between 20 Hz to 1000 Hz. This work has been inspired by an extensive research program at University of Western Australia performing a rigorous finite element model simulating the magnetic forces interaction and vibration inside the transformer. We will validate all their simulation results showing how it is possible to detect significant winding distortions like buckling and bulging, open and short circuits, and clamp looseness. Missing inter-winding separation can also be identified as we trend the vibration amplitudes at twice the line signal frequency. The special sensor is also capable of measuring temperature to achieve a cost effective monitoring solution to extend the life of the transformers while providing good diagnostics.

We investigate the use of all-fiber distributed Bragg reflector (DBR) lasers for fiber optic sensing. We measure the steady-state strain response and show that it is very similar to that for a simple fiber Bragg grating (FBG). The lasers can be wavelength multiplexed and support multisensor operation without crosstalk. We also verify the principle of wavelength-to-power mapping, which can simplify sensor interrogation. Finally, we demonstrate that all-fiber DBR lasers can be used to detect acoustic waves.

A great many arguments in philosophy turn on claims about what is possible, and in fact it’s difficult to overstate how central modal claims are in all areas of philosophy. Making claims about what could be and what must be is the bread-and-butter of philosophy. In philosophy of mind, for example, it is contended that some of the best arguments for dualism hinge on a modal premise. In recent years there has been a resurgence of debate about the merits of modal arguments for dualism, and this has in turn sparked interest in modal arguments generally. What makes for a good modal argument? How do we know that the crucial modal premises of such arguments are true? Hume offers the traditional answer in the Treatise: “ ‘Tis an established maxim in metaphysics, That whatever the mind clearly conceives includes the idea of possible existence, or, in other words, that nothing we imagine is absolutely impossible” (I.ii.2, emphasis removed). Hume is certainly right about this much: many in philosophy presume this established maxim. We take ourselves to have some knowledge of what could be, or what could have been, and by this we mean knowledge of metaphysical possibility. Hume does not tell us, however, how this “established maxim” has been established. The more we consider the maxim, the more it cries out for explanation. What is it to conceive something? Why is it that conceiving, so understood, provides evidence for possibility? I think it is fair to say that we lack clear and satisfying positive answers to these questions; what we have instead is a general unease about the central philosophical practice of making claims about the possible and a particular dissatisfaction with “controversial” modal premises in arguments whose conclusions we don’t like. Part of the problem is that many candidate answers to the “what” question quite obviously lead nowhere. ‘Conceive’ is a word with many senses, and many of these senses are clearly unsuitable to play the role of evidence for possibility. Merely understanding, thinking, or entertaining a proposition is not sufficient, for it is easy enough to understand, think, or entertain thoughts about what is necessarily false. The same goes for assuming, supposing, and taking for granted. If the kind of conceiving that philosophers have in mind isn’t any of these, it is less obvious what the right kind is. (“Clear and distinct conception” anyone?)

Arthroscopic resection of the distal clavicle has been advocated as a surgical treatment option for acromioclavicular (AC) joint pathology. To our knowledge, iatrogenic fracture of the distal clavicle during distal clavicle resection has never been reported. This report describes distal clavicle fracture as a complication of misidentification of the AC joint and subsequent aggressive burring of the distal clavicle during shoulder arthroscopy. This case is further complicated by the development of symptomatic delayed union and adhesive capsulitis. Ultimately, a revision distal clavicle resection was performed, underscoring the fact that special care must be taken to properly identify the AC joint and rule out pre-existing distal clavicle stress fracture or osteolysis before performing the arthroscopic Mumford procedure.

Recently in epistemology a number of authors have mounted Bayesian objections to dogmatism. These objections depend on a Bayesian principle of evidential confirmation: Evidence E confirms hypothesis H just in case Pr(H|E) > Pr(H). I argue using Keynes’ and Knight’s distinction between risk and uncertainty that the Bayesian principle fails to accommodate the intuitive notion of having no reason to believe. Consider as an example an unfamiliar card game: at first, since you’re unfamiliar with the game, you assign credences based on the indifference principle. Later you learn how the game works and discover that the odds dictate you assign the very same credences. Examples like this show that if you initially have noreason to believe H, then intuitively E can give you reason to believe H even though Pr(H|E) ≤ Pr(H). I show that without the principle, the objections to dogmatism fail.

The biomechanics of the glenohumeral joint depend on the interaction of both static and dynamic-stabilizing structures. Static stabilizers include the bony anatomy, negative intra-articular pressure, the glenoid labrum, and the glenohumeral ligaments along with the joint capsule. The dynamic-stabilizing structures include the rotator cuff muscles and the other muscular structures surrounding the shoulder joint. The combined effect of these stabilizers is to support the multiple degrees of motion within the glenohumeral joint. The goal of this article is to review how these structures interact to provide optimal stability and how failure of some of these mechanisms can lead to shoulder joint pathology.

We propose using an optical fiber cable to monitor distributed vibration changes. The cable connects a vibration point sensor based on a twin fiber Bragg grating (FBG) interferometer operating in reflection to its interrogation unit that locks a narrowband DFB laser to the central interference fringe.

Recently, we found that by terminating a long length of fiber of up to 2 km with an in-fiber cavity structure, the entire structure can detect vibrations over a frequency range from 5 Hz to 100 Hz. We want to determine whether the structure (including packaging) can be optimized to detect vibrations at even higher frequencies. The structure can be used as a distributed vibration sensor mounted on large motors and other rotating machines to capture the entire frequency spectrum of the associated vibration signals, and therefore, replace the many accelerometers, which add to the maintenance cost. Similarly, it will help detect in-slot vibrations which cause intermittent contact leading to sparking under high voltages inside air-cooled generators. However, that will require the sensor to detect frequencies associated with vibration sparking, ranging from 6 kHz to 15 kHz. Then, at even higher frequencies, the structure can be useful to detect acoustic vibrations (30 kHz to 150 kHz) associated with partial discharge (PD) in generators and transformers. Detecting lower frequencies in the range 2 Hz to 200 Hz makes the sensor suitable for seismic studies and falls well into the vibrations associated with rotating machines. Another application of interest is corrosion detection in large re-enforced concrete structures by inserting the sensor along a long hole drilled around structures showing signs of corrosion. The frequency response for the proposed long-gauge vibration sensor depends on packaging.

This paper investigates the use of fiber Bragg grating (FBG) accelerometers for wide band vibration monitoring in a wound rotor induction generator. The sensor performance is assessed in a series of experiments on a laboratory test rig comprising a 30kW induction machine operating under steady state and variable speed regimes. Vibration measurements are investigated in the frequency domain for generator fault specific electromagnetically induced vibration components. The fiber optic sensor effectiveness in detection of wide band spectral effects (

This paper investigates the use of fibre Bragg grating (FBG) accelerometers for wide band vibration monitoring in wound rotor induction generators. The sensor performance is assessed in a series of experiments on a laboratory test rig comprising a 30kW induction machine operating in healthy conditions and with electrical or mechanical fault. Vibration measurements are processed and analyzed in the frequency domain for fault feature extraction. The fibre optic sensor effectiveness in measurement of wide band fault signatures in the vibration signal is compared with that of a commercial piezoelectric based solution. The potential and limitations of the investigated FBG accelerometer design are evaluated for use in condition monitoring applications.

Optical fiber is made of glass, an insulator, and thus it is immune to strong electromagnetic interference. Therefore, fiber optics is a technology ideally suitable for sensing of partial discharge (PD) both in transformers and generators. Extensive efforts have been used to develop a cost effective solution for detecting partial discharge, which generates acoustic emission, with signals ranging from 30 kHz to 200 kHz. The requirement is similar to fiber optics Hydro Phone, but at higher frequencies. There are several keys to success: there must be at least 60 dB signal-to-noise ratio (SNR) performance, which will ensure not only PD detection but later on provide diagnostics and also the ability to locate the origin of the events. Defects that are stationary would gradually degrade the insulation and result in total breakdown. Transformers currently need urgent attention: most of them are oil filled and are at least 30 to 50 years old, close to the end of life. In this context, an issue to be addressed is the safety of the personnel working close to the assets and collateral damage that could be caused by a tank explosion (with fire spilling over the whole facility). This paper will describe the latest achievement in fiber optics PD sensor technology: the use of phase shifted-fiber gratings with a very high speed interrogation method that uses the Pound-Drever-Hall technique. More importantly, this is based on a technology that could be automated, easy to install, and, eventually, available at affordable prices.

Many defects can cause deterioration and cracks in concrete; these are results of poor concrete mix, poor workmanship, inadequate design, shrinkage, chemical and environmental attack, physical or mechanical damage, and corrosion of reinforcing steel (RS). We want to develop a suite of sensors and systems that can detect that corrosion is taking place in RS and inform owners how serious the problem is. By understanding the stages of the corrosion process, we can develop special a sensor that detects each transition. First, moisture ingress can be monitored by a fiber optics humidity sensor, then ingress of Chloride, which acts as a catalyst and accelerates the corrosion process by converting iron into ferrous compounds. We need a fiber optics sensor which can quantify Chloride ingress over time. Converting ferric to ferrous causes large volume expansion and cracks. Such pressure build-up can be detected by a fiber optic pressure sensor. Finally, cracks emit acoustic waves, which can be detected by a high frequency sensor made with phase-shifted gratings. This paper will discuss the progress in our development of these special sensors and also our plan for a field test by the end of 2014. We recommend that we deploy these sensors by visually inspecting the affected area and by identifying locations of corrosion; then, work with the designers to identify spots that would compromise the integrity of the structure; finally, drill a small hole in the concrete and insert these sensors. Interrogation can be done at fixed intervals with a portable unit.

Recently, we found that by terminating a long length of fiber of up to 2 kilometers with an in-fiber cavity structure, the entire structure can detect vibrations over a frequency range from 5 Hz to 100 Hz. We want to determine whether the structure (including packaging) can be optimized to detect vibrations at even higher frequencies. The structure can be used as a distributed vibration sensor mounted on large motors and other rotating machines to capture the entire frequency spectrum of the associated vibration signals, and therefore, replace the many accelerometers, which add to the maintenance cost. Similarly, it will help detect in-slot vibrations inside an air-cooled generator which causes intermittent contact leading to sparking under high voltages. However, that will require the sensor to detect frequencies associated with vibration sparking, ranging from 6 kHz to 15 kHz. Then, at even higher frequencies, the structure can be useful to detect acoustic vibrations (30 kHz to 150 kHz) associated with partial discharge (PD) in generators and transformers. Detecting lower frequencies in the range 2 Hz to 200 Hz makes the sensor suitable for seismic studies and falls well into the vibrations associated with rotating machines. Another application of interest is corrosion detection in large re-enforced concrete structures by inserting the sensor along a long hole drilled around structures showing signs of corrosion. The frequency response for the proposed long-gauge vibration sensor depends on packaging.

The FBG cavity sensor was invented to measure and trend End Winding Vibrations (SEW) inside larger power generators. The sensor consists of a twin grating cavity which can be used to monitor vibration as well as temperature change by changing the center wavelength of the transmitting laser to track the movement of the interference fringes. This paper will discuss the adaptation of this FBG cavity structure to measure much higher frequency signals like those found in Partial Discharge (PD) events. Special package design is necessary to maintain the signal to noise ratio as the high frequency PD signal propagates along the conductor inside the stator slots to the end windings. The challenge would be the coupling of these signals to our PD sensors. They will be mounted at the same locations where SEW sensors would be installed for end winding vibration. We would select the windings with the highest induced voltage hence most susceptible to PD. By trending the vibration amplitude related to loading, we would be able to diagnose each winding structure has become loose. These sensing channels would be correlated with PD amplitudes as well as their signature; more work would be required to relate the signature to the degradation process of the insulation layer. By measuring time of arrival differences at both ends of the generator, we can estimate which slot is associated with the discharge event. The addition of the PD sensor to vibration and temperature capability makes TG Guard a comprehensive solution for safeguarding the generator; its diagnostic capability would also shorten maintenance time and reduced the required resources. Owner would know exactly what to do by integrating all the trending data.

Fiber optics vibration sensors have been extensively studied over the last ten years they have mainly been used to capture low frequency signals. One of these investigations has been commercialized to measure and trend End Winding Vibration (SEW) inside larger power generators. This sensor consists of a twin grating cavity and can be used to monitor temperature change as well as vibration. This paper will discuss the adaptation of the FBG cavity structure into a broad band sensor capable of measuring a range of higher frequencies previously identified as PD signals in the transformer from 30K to 300 KHz. Other work has been done to explore the possibility of developing a fiber optics acoustic sensor. The incentive is to overcome the limitation of the resonant based, acoustic, piezoelectric PD sensors previously used to analyze and locate PD. Working in resonance, they are unable to reveal the detailed spectrum or the signature of the PD events. We want to improve the packaging material and structure, then optimize the coupling methods to enhance its signal to noise ratio. All our work is still based on the fiber gratings cavity structure.

In most aging transformers, windings failures are caused by the deterioration of the insulation, leading to arcing and short circuits. Vibrations in a transformer are generated by different forces appearing in the core and winding during the operation. Winding vibrations result from the electromagnetic forces that are generated by the interaction of the current in a winding with leakage flux. These forces are proportional to the square of the load current, and therefore vibration is always there. VibroFibreTM technology was invented by QPS to monitor the vibration of the end windings. It works according to optical interference, i.e., when subjected to vibration, the signal reflected off the sensor is interpreted as intensity changes resulting from the change in the length of a fiber Bragg grating-based cavity. However, as temperature rises, the fringes also move making it necessary for other control measures to track this temperature rise. These counter measures effectively constitute indirect temperature measurement during this vibration monitoring. In other words, one single sensor can give two critical parameters The same technology is now adapted to be applied to diagnose transformers. The twin cavity sensor is packaged to measure trace moisture in oil. This moisture sensor has built in temperature compensation as well as direct temperature read out. This paper will describe the theoretical basis of this twin cavity sensor. In addition, we will also describe the fiber laser sensor for PD measurement. Because of the fact these PD sensors are to be mounted on the transformer wall. QPS continues to work on a miniature acoustic chamber. The paper will also discuss conceptually the algorithm behind the location of PD events in the context of a four wall transformer. Finally we will discuss in details the moisture sensor cable of reading moisture down to 1ppm with built in temperature compensation. Actually this moisture sensor is capable to give direct readout of the oil temperature which is the first in the world.

Partial discharge (PD) measurement has been deployed as a well established test method to monitoring the health of the insulation inside generators, transformers, gas insulated switch gear, and bus bars. There are different technologies to monitor the health of insulation by PD measurement, e.g., UHF high frequency capacitance measurement and acoustic emission using piezoelectric sensors. UHF technique has proven to be very sensitive but had troubles locating the sources of such PD activities. Piezoelectric acoustic sensors seem to be able to locate PDs, but their signal is weak and locating the sources using time of arrival method proves to be complicated: acoustics signal can travel through the insulation media such as oil or SF6, but they could also hit the metallic container and then travel to where the sensor is mounted. This paper will discuss a break through. First, a fiber laser can be formed by including a twin grating structure over an active fiber segment having Erbium and Ytterbium doping and pumped with 980 nm laser light. A DBR laser capable to follow very high frequency response is formed. Furthermore, this cavity can be made to be wavelength specific. A string of these can be installed over the walls of the transformer or a multi-segment GIS or Bus Bar. The signal from these laser sensors will become self identifying. These reflected signals can be demultiplexed with an array waveguide grating (AWG), which places the signal into buckets of various center wavelengths; therefore, each bucket can be related to where the sensor has been installed. The fiber laser sensor gives a higher signal to noise ratio than piezoelectric sensors, and these DBR lasers can be serially connected to diagnose the location of the PD events. There is no need for complicated software and algorithm to calculate and interpret the difference in time of arrival. Furthermore other fiber optics sensors such as temperature, moisture and loading can be installed to help to correlate PD with these operational and environment condition.

With the advent of devices such as smart phones and tablet computers, multi-touch applications are rapidly becoming commonplace. However, existing multi-touch sensors are not able to report which finger, or which hand, is responsible for each of the touches. To overcome this deficiency we introduce a multi-touch system that is capable of identifying the finger and hand corresponding to each touch. The system consists of a commercially available capacitive multi-touch display augmented with an infrared depth camera mounted above the surface of the display. We performed a user study to measure the accuracy of the system and found that our algorithm was correct on 92.7% of the trials.

The Vibrofiber sensor is a Fabry-Perot cavity formed between two broad band fiber gratings creating interference fringes. It was introduced three years ago to monitor the vibration and temperature rise of the stator end winding in a power generator.(1) This paper will discuss the use of Vibrofiber to monitor the deflection of the bridge under adverse conditions: wide temperature swings, excess load, strong winds, earth quake, etc. The fringes in these cavity sensors have features like peaks and valleys which are sensitive to temperature and strain. When the bridge becomes overloaded, we are interested in knowing the extent of the deflection. In addition, we might want to locate the cause of the overload. A simple Sagnac FBG interferometer has been invented to provide such diagnostics. A pair of long fibers with such cavity sensors can be installed on the underside of the target bridge segment between two supporting columns. The objective is to monitor the deflection together with any distortion of the bridge deck. Each of the 2 long fiber segments has a pair of cavity sensors, one measures the deflection as a result of the excess strain, and the other measures temperature and provides compensation for the deflection data. An array of cavity sensors with different center wavelengths will be used to support the typical multi-segment bridge structure. The interrogation unit is based on a tunable laser that can hop to different ITU grids. A separate DFB laser will run a grating based Sagnac interferometer, measuring weight in motion, identifying the speed and the make of vehicle in traffic and provide deflection diagnostics. Overloaded trucks and speeding vehicles can be captured and tagged for corrective actions. The interrogation unit is equipped with wireless Ethernet communication enabling the monitoring of many bridges from a central location and similarly warning can be initiated to alert the central traffic control ahead of any problems.

This paper will discuss a new distributed fiber optics sensing technology that uses an array of low reflectivity fiber gratings having the same center wavelength. Furthermore this array would be embedded in a military grade reinforced outdoor cable. Three of these gratings cables are to be stitched onto a meter high geo textile and used as a solution for landslides warning. The special cable is made with a material that prevents moisture penetration and provides extra pulling strength of up to 500 Newtons. The geo-textile provides the added restraining force of up to 1100 Newtons. The solution is therefore capable of not only measuring small earth movements but also provides added time delay in a pending crisis so that people can evacuate from danger.

We characterize the steady-state strain characteristics of an all-fiber distributed Bragg reflector (DBR) laser sensor interrogated using a wavelength-to-power mapping system. We also demonstrate that the system is capable measuring dynamic strain from four parallel DBR sensors without crosstalk.

In most aging transformers, windings failures are caused by the deterioration of the insulation, leading to arcing and short circuits. Vibrations in a transformer are generated by different forces appearing in the core and winding during the operation. Winding vibrations result from the electromagnetic forces that are generated by the interaction of the current in a winding with leakage flux. These forces are proportional to the square of the load current, and therefore vibration is always there. VibroFibre™ technology was invented to monitor the vibration of the end windings. It works according to optical interference, i.e., when subjected to vibration, the signal reflected off the sensor is interpreted as intensity changes resulting from the change in the length of a fiber Bragg grating-based cavity. However, as temperature rises, the fringes also move making it necessary for other control measures to track this temperature rise. These counter measures effectively constitute indirect temperature measurement during this vibration monitoring. The same technology is now adapted to be applied to diagnose transformers. The special sensors are based on the advanced fiber optic vibration sensing technology, where up to 50 vibration sensors can be connected in series along a single optical fiber. These sensors are made thinner so they can be embedded between the windings and are best installed by the manufacturer of the transformers. These vibration sensor arrays will generate temperature information concurrently and will work up to 250 degrees C.

In most turbine generators, excessive vibration and thermal cycling weaken the insulation on the windings causing stator bar to fracture and leading to partial discharge (PD), which ultimately results in fire. Therefore, PD becomes extremely dangerous for large hydrogen cooled turbines because it might lead to explosion in the plant. These risks can be mitigated by using VibroFibre™ fiber optic vibration sensors and the Integrated Signal Conditioning (ISC) system as condition monitoring solution. This solution prevents unplanned down time by obtaining a warning against arcing and fire resulting from the measurement and trending of vibration amplitudes in the stator end windings. The presence of an alarm stops the machine for repair before a disaster occurs, resulting in a life extension of critical power plant assets by at least 200%. Inside power generators, there are high voltages and strong electromagnetic fields, and such hostile environment makes the use of ordinary piezoelectric vibration sensors impossible. In this case, fiber optic vibration sensors are the most effective solution. Yet, until now, only single channel fiber optic sensors have been available. They are hard to manage and require one full week of down time to install. Using a bundle of fiber optic vibration sensors and an ISC unit, the architecture can be simplified. Moreover, one-day installation can be achieved by gluing the sensors onto the end cap with high temperature epoxy. This results in instantaneous return on investment.

We characterize the dynamic response of a fiber Bragg grating (FBG)-based laser sensor system. The sensor system comprises a laser based on a reflective semiconductor optical amplifier and an FBG; interrogation of the wavelength shift is performed using a wavelength-to-power mapping with an optical filter. We demonstrate that the system is capable of detecting dynamic strain over a wide range of frequencies.