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.
We have recently found that a long length of fiber of up to 1 km terminated with an in-fiber cavity structure can detect
vibrations over a frequency range from 5 Hz to 2 kHz. We want to determine whether the sensor (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 maintenance cost. The sensor may also
help detect in-slot vibrations which cause intermittent contact leading to sparking under high voltages inside air-cooled
generators. However, that requires the sensor to detect frequencies associated with vibration sparking, ranging from 6
kHz to 15 kHz. Acoustic vibration monitoring may need sensing at even higher frequencies (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 longgauge
vibration sensor depends on packaging.
Recently, we found that by terminating a long length of fiber of up to 1 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 reenforced 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.
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.
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 (<1kHz) in the vibration signal is compared with that of a commercial piezoelectric based solution. The potential and limitations of the prototype wide band FBG accelerometer are evaluated for use in vibration 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
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.
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.
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.
A wavelength conversion experiment based on Bragg grating fiber external cavity laser at 2.5 Gb/s rate is introduced. The primary result of 5 nm up-conversion and clear eye diagram is obtained. The laser is sealed in common DIP-14 package. This method shows advantages of simplicity and stable converted wavelength.
The rigorous coupled-wave analysis and our experimental measurements show optimal values of the phase retardation and duty cycle of the phase mask to minimize zero and even diffracted orders, that are more precise than that usually used according to the scalar theory of diffraction. Under an oblique incidence, we optimize the phase mask with three parameters: phase retardation, duty cycle, and refractive index, that results in a perfect sinusoidal interference field with high diffraction efficiency for writing the fiber Bragg grating.
The effects and characteristics of group delay ripple of chirped fiber gratings on the performance of a 10 Gb/s NRZ transmission system has been experimentally investigated. For the power penalty less than 1 dB at bit-error-rate of 10-9, our experiment results show that the ripple magnitude of dispersion compensating gratings should be less than +/- 20 ps within its pass-band for 10 Gb/s systems.
The advent of phase mask technique has made it possible to fabricate Bragg gratings to tight tolerances in a repeatable, reliable and cost effective manner. These gratings are in turn making it possible to manufacture a wide variety of high performance guided wave devices for lightwave communication and sensor applications. This paper will review the phase mask fabrication technology and the commercially available products. the paper will then discuss a few successful applications of grating based devices currently entering the market, in particular, wavelength demultiplexing devices, gain flattening filters for EDFA and dispersion compensators, all of which are critical elements in high data rate lightwave systems.
The paper is a description of a dedicated software for performing the mask layout of diffractive optical elements (DOE). This computer-aided design (CAD) tool is a high productivity tool developed to speed-up the layout process of DOE masks. This utility designs the mask layout, starting from the phase diffraction pattern of DOE expressed as re-usable objects, which are generated by different computing methods and optimization algorithms. The diffraction phase pattern of some frequently used diffraction structures (gratings, lenses), can be computed from the optical parameters entered as input data. The mask layout design can be made for any number of phase levels between 2 and 64, resulting in a set of binary encoding masks. Many DOE functions with the same number of levels can be combined on the same substrate. The mask layout, containing not only the diffractive pattern, but also all the process control patterns needed for manufacturing, is generated in GDS format. The capabilities of this design software are illustrated in an example containing many 4-phase level elements on the same substrate. This CAD mask design software was designed to run on PCs and on SUN Sparc workstations.
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