We examine the use of state-of-the-art distributed sensing systems to extract temperature information from the optical fibre infrastructure already of the Electricity Authority of Cyprus power distribution network (~25-year old installation); as a means of optical fibre distributed sensing in the underground cables. The optical fibres are collocated with existing power distribution cables, for the purpose of power line monitoring cable joints that are prone to failure, along with general monitoring for unusual behaviour and potential cable fault conditions. Detection is achieved using DTS: Distributed Temperature Sensors (Silixa Ltd) that use RAMAN-based measurements in combination with BOTDR (Brillouin Optical Time-domain Reflectometry) for high-precision temperature detection. We examine the correlation between the temperature of the power cable with the power consumption provided by the EAC and the weather conditions. Furthermore, our data will give an indication of how important is uniform spacing between power and optical cables. The real-time and continuous monitoring of the temperature of the optical cables through the distributed sensing systems may help identifying abnormal cable behavior (hot spots) and possible future network failures in the power network.
In this work we utilize multimode optical fibers for the detection of simulated errors or failures in underground power cables. It is known that in cases of failure the underground transmission cables overheat locally, they become a hot-spot, and it is extremely difficult to detect and locate the problem. The proposed methodology is as follows, having an underground electric cable we simulate various temperature profiles whilst the optical fiber was placed in selected distances away from our simulated fault to examine the detection performance of our fiber. In this way we aim to stabilize the operation of the underground cable damage detection system that is placed by the Electricity Authority of Cyprus. The EAC has certain locations where the existing single-mode optical fibres are collocated with the underground power cables, although relative spacing may not be constant. Our data will give an indication of how important is uniform spacing between power and optical cables. We examine if any change in the temperature of the power cable is also reflected in the optical fibre cable. The real-time and continuous monitoring of the temperature of the optical cables through the distributed sensing systems may help identifying abnormal cable behaviour (hot spots) and possible future network failures in the power network.
We present a study on the use of state-of-the-art distributed sensing systems to extract temperature and vibration information from existing single-mode, optical fibre infrastructure in Cyprus (~25-year-old installation); as a means of optical fibre distributed sensing. In this study, we have focused on the underground optical fibres of the Electricity Authority Cyprus (EAC). The optical fibres have been selected to be collocated with existing underground power distribution cables that are sited in and around Nicosia, for the purpose of monitoring power cable joints that are prone to failure, along with general monitoring for unusual behaviour and potential cable fault conditions. Three state-of-the-art distributed sensing systems have been deployed to run in parallel, on the same optical cable branch and all optimised for use with single-mode fibre. The underground power cables were monitored using a fast Brillouin optical time-domain reflectometer (BOTDR, with temperature and vibration measurement capability), a Distributed Temperature Sensor (Silixa, single-mode DTS) and an intelligent Distributed Acoustic Sensor (Silixa, iDAS). The results include calibration methods performed under controlled laboratory conditions for the fibres under test, prior to field deployment. The field data, recovers both temperature and vibration measurements over a 3-month period the results of which will be presented.
Fiber optic distributed temperature sensing based on Raman scattering of light in optical fibers has become a very attractive solution for distributed temperature sensing (DTS) applications. The Raman scattered signal is independent of strain within the fiber, enabling simple packaging solutions for fiber optic temperature sensors while simultaneously improving accuracy and robustness of temperature measurements due to the lack of strain-induced errors in these measurements. Furthermore, the Raman scattered signal increases in magnitude at higher fiber temperatures, resulting in an improved SNR for high temperature measurements. Most Raman DTS instruments and fiber sensors are designed for operation up to approximately 300˚C. We will present our work in demonstrating high temperature calibration of a Raman DTS system using both Ge doped and pure silica core multi-mode optical fiber. We will demonstrate the tradeoffs involved in using each type of fiber for high temperature measurements. In addition, we will describe the challenges of measuring large temperature ranges (0 – 600˚C) with a single DTS interrogator and will demonstrate the need to customize the interrogator electronics and detector response in order to achieve reliable and repeatable high temperature measurements across a wide temperature range.
Advances in opto-electronics and associated signal processing have enabled the development of Distributed Acoustic and Temperature Sensors. Unlike systems relying on discrete optical sensors a distributed system does not rely upon manufactured sensors but utilises passive custom optical fibre cables resistant to harsh environments, including high temperature applications (600°C). The principle of distributed sensing is well known from the distributed temperature sensor (DTS) which uses the interaction of the source light with thermal vibrations (Raman scattering) to determine the temperature at all points along the fibre. Distributed Acoustic Sensing (DAS) uses a novel digital optical detection technique to precisely capture the true full acoustic field (amplitude, frequency and phase) over a wide dynamic range at every point simultaneously. A number of signal processing techniques have been developed to process a large array of acoustic signals to quantify the coherent temporal and spatial characteristics of the acoustic waves. Predominantly these systems have been developed for the oil and gas industry to assist reservoir engineers in optimising the well lifetime. Nowadays these systems find a wide variety of applications as integrity monitoring tools in process vessels, storage tanks and piping systems offering the operator tools to schedule maintenance programs and maximize service life.
Complex optical networks demand high levels of functionality from optical components requiring high density integration in low cost, compact, plug and play format. Technologies at the forefront of this move to higher integration are MEMs and planar waveguide options. In all cases the components are interfaced with the transmission medium, generally through precision alignment to individual fibres. All-fibre technologies offer good performance but are not in general appropriate for multi-functional integration. One all-fibre approach that offers the potential for integration is the fibre evanescent field technology. This technology creates a waveguide substrate from the transmission optical fibre onto which the optical circuit can be built. This paper describes a VOA-power monitor device formed using evanescent field approach, to assess its performance and the potential for full integration.
KEYWORDS: Sensors, Temperature metrology, Signal attenuation, Polarimetry, Polarization, Modulation, Polarizers, Transmitters, Temperature sensors, Fiber optics
This paper describes a remote polarimetric low coherence temperature sensing system employing intensity and wavelength compensation mechanisms. Possible interconnection interference effects and system polarisation dependent losses are minimized using a broadband (low coherence) optical source followed by a fibre Lyot-type depolariser. The sensor was optimized to operate over a temperature range of 160° C corresponding to the linear region of the interferometric response. A high extinction broadband fibre polariser (>40 dB) was fabricated to achieve maximum modulation depth. The intensity referencing scheme employed allows the remote operation of the sensor and can compensate up to 90% attenuation along the fibre line without any loss of resolution. The wavelength referencing scheme discriminates against temperature dependent shift of the source spectra and minimizes possible measurement errors. The modular structure of the system can be expanded to accommodate a number of sensors.
A distributed optical fibre detection system has been developed for damage detection in composite structures. Low coherence interferometry was used to identify damage locations due to coupling of power between the two orthogonal polarisation modes in an embedded fibre.
Composite materials are vulnerable to damage, and this can result in conservatism in design and increased maintenance costs. One way of reducing these costs is by integrating a system into the composite material which can sense the damage condition and provide an assessment of its size, location and significance. This is a difficult task, and one of the main challenges is to develop sensor systems that can detect damage reliably while not compromising the material properties of the composite or significantly increasing its weight. A sensor system will be described which fulfills some of these requirements. It is based on the use of a highly birefringent optical fiber. The whole length of the fiber is used as the sensor, which minimizes additional weight. It also enables information to be obtained on the position of the damage along its length. The mechanical properties of the composite material are not degraded when the fiber is embedded, as long as some simple precautions are taken. The sensor utilizes the propagation of low coherence polarized light in highly birefringent optical fiber. Light is launched into one of the polarization states of the fiber and is coupled into the orthogonal state in the presence of damage. The sensor is interrogated interferometrically. Its operation will be described in detail and results will be presented which illustrate its perforce in detecting impact induced damage in a number of different composite material systems. Benefits of the system will be described together with areas which need further development.
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