KEYWORDS: Transformers, Temperature sensors, Optical fibers, Thermal modeling, Fiber optics sensors, Thermography, Temperature metrology, Magnetism, Finite element methods, Thin films
Reliable, secure, and resilient electricity distribution requires continuous health monitoring of electrical assets including power transformers. Among all sensing parameters, temperature is of utmost importance. Using optical fiber sensors for temperature monitoring has various advantages over traditional methods as they are inherently immune to electromagnetic interference, are good insulators at high-voltage levels, and are easy to install due to their small size and flexibility. Measuring the temperature of different parts of a power transformer core can help to detect hotspots and predict imminent device health issues. In this paper, a low-cost temperature sensor based on plasmonic-enabled optical fiber is demonstrated in multiple arrangements. The simplest arrangement would cost ~ $100 with potential for further cost reductions through reductions in the cost of the detection and excitation circuitry and optical components. By functionalizing an optical fiber with Au-Silica thin-films, the sensor was also demonstrated to measure the temperature of an energized transformer core in real-time. Repeatability and reliability of the proposed sensor were confirmed by running multiple cycles.
Monitoring carbon dioxide (CO2) for carbon capture, gas pipelines, and storage as well as early detection of CO2 leakage is important to mitigate greenhouse gas emissions and have a high atmospheric concentration for a long lifetime. Moreover, the main cause of the corrosion in natural gas pipelines is owed by CO2. Therefore, real-time and effective CO2 monitoring is essential to improve efficiency, reduce pipeline emissions, and improve the economics of the natural gas industry. In this paper, we propose and experimentally demonstrate a distributed CO2 sensor based on the measurement of evanescent wave absorption by using optical frequency domain reflectometry (OFDR). A coreless fiber is re-coated with tetraethyl orthosilicate (TEOS) through a dip-coating process with well-defined fabrication conditions. Rayleigh scattering OFDR system is optimized to provide high spatial resolution and large dynamic range to trace gas detection. The proposed distributed fiber gas sensor exhibits continuous real-time measurement of CO2 gas concentrations from 5% to 100% calibrated with nitrogen (N2) as a background gas. The results provide confidence that the proposed sensing technology represents a novel paradigm and holds a potential tool for the early detection of CO2 leaks with high sensitivity in a distributed fashion.
A distributed fiber optic chemical sensor with a temperature compensation mechanism is revealed using optical frequency domain reflectometry (OFDR). Distributed chemical sensing has already been achieved through chemical sensitive films deposited on the multimode fiber. However, chemical sensing signal interfered by the temperature where the fiber under test locates. In this paper, a new configuration of the fiber sensing is developed using a double cladding fiber. The sensor is feasible for multi-parameter sensing including temperature and another chemical of interest (pH value in this paper) at the same location. In this way, a temperature compensated distributed sensing algorithm can be developed and have both fundamental mode and multimode propagation in the same measure and field. The possibility to adjust the specifications of the fiber and OFDR configuration provides ample opportunity to satisfy requirements of temperature compensation from different chemical sensing applications.
The presence of water can provide aqueous electrolytes for corrosion to occur inside the pipelines. The capability of monitoring water vapor condensation enables in-situ monitoring of internal corrosion in natural gas transmission pipelines. Previously, a fully distributed optical fiber sensor for water and humidity monitoring has been demonstrated, consisting of an unmodified off-the-shelf single mode (SM) optical fiber connected to an optical backscatter reflectometer. The intrinsic polymer jacket of the SM fiber is hygroscopic and can serve as a water sensing layer due to expansion/swelling from water absorption. In this work, strain changes were measured and calibrated in jacketed and unjacketed sections at different relative humidity levels (RH, 0% to 100%) and different temperatures (T, 21 to 50°C). In the jacketed section, the sensitivity to humidity decreased from 1.2 to 0.6 με/%RH and then diminished as T increased from 21 to 50 °C, which could be due to the intrinsic absorption property of polymer at higher T or the wet gas flow at room temperature being absorbed in the polymer jacket. The unjacketed section demonstrated a minimal sensitivity to humidity (<0.2 με/%RH) at 21-50 °C and a relatively consistent sensitivity to temperature.
Condition monitoring of power transformers is of great importance for the timely detection of incipient faults to avoid potential malfunctioning. Transformer insulating oil contains about 70% of diagnostic information, and a dramatic rise in oil temperature may drastically reduce the lifetime of power transformers, and thus the temperature of the oil is considered the most crucial parameter that has to be monitored continuously in real-time. Compared to traditional temperature measurement methods used in transformer condition monitoring, distributed optical fiber sensors have inherent advantages of immunity to electromagnetic interference and insulation at high-voltage levels, and they offer spatially resolved temperature monitoring with high accuracy and sensitivity. In this study, optical fiber-based distributed temperature measurement of a fully energized 100 kVA distribution transformer is demonstrated by using two different techniques: Optical Frequency Domain Reflectometry (OFDR) and Fiber Bragg Grating (FBG) sensor array. The fiber sensors are robust for a safe long-term installation into oil-filled distribution transformers during manufacturing, and they can withstand heat runs, long-term hot oil immersion, and transformer vibration. The internal transformer temperature is monitored during standard thermal tests prior to installation on the distribution system. The test results show very good agreement between the standard thermocouple and proposed distributed fiber temperature sensors, providing transformer manufacturers with new insights into the distribution of temperatures internal to their commercial products.
KEYWORDS: Interferometers, Signal detection, Nonlinear optics, Optical fibers, Spatial resolution, Photodetectors, Temperature metrology, Signal processing
Swept Wavelength Interferometry (SWI) based on Tunable Laser Source (TLS) has various applications in optical measurement and imaging. Nonlinear tuning of the TLS is always a problem in SWI and require proper correction to enhance the spatial resolution and SNR of the signal. Typically, nonlinear tuning correction requires an extra (auxiliary) interferometer. A new type of Optical Frequency Domain Reflectometry (OFDR) arrangement was proposed in which auxiliary interferometer was integrated with the main interferometer and only a single detection channel was used instead of two. This new hardware design eliminated the need for an extra photodetector and an acquisition channel for the auxiliary interferometer. Single trace having beating signal from auxiliary and Rayleigh backscattering from the main interferometer was acquired in a single detection channel. Then the beating signal of the auxiliary interferometer was used to correct nonlinear tuning effects from Rayleigh backscattered signal of the main interferometer. The feasibility of new hardware design is demonstrated by correcting nonlinear tuning effects in a 50 meters long optical fiber and performing distributed strain and temperature sensing in the OFDR technique. Furthermore, an extension of the proposed new design is also described in this paper in which the auxiliary interferometer is replaced by a high reflection event inside the Fiber Under Test (FUT) created by femtosecond laser which makes the overall system design more compact and simpler.
Methane is a major composition of natural gas and considered as a primary greenhouse gas of high global warming potential. In addition, it is also a hazardous flammable gas turns out to be highly explosive if its concentration level reaches 5 to 15 percent by volume. Carbon dioxide is another significant gas since CO2 corrosion is the most common cause of corrosion in natural gas pipelines. Long distance cost-effective CH4 and CO2 distributed sensing technologies for monitoring natural gas infrastructure are not yet readily available, and early corrosion on-set and low-level methane leak detection is highly desirable that can strengthen the integrity and operational reliability, improve the efficiency, and reduce pipeline emissions, which all advance the economics of natural gas delivery. In this work, two types of gas sensing materials, porous silica and hybrid polymer/metal-organic framework (MOF), are investigated based on evanescent wave absorption sensors consisting of a coreless fiber spliced between two single-mode fibers. The low-loss, low refractive index porous silica and the polymer/MOF material with an improved gas adsorption capability and CH4/CO2 selectivity prepared by the sol-gel dip-coating method are respectively used as coating applied to the surface of the coreless fiber. The effects of optical and morphological properties on the repeatability and sensitivity of fiber-optic evanescent wave sensors are studied from transmittance and reflectance measurements by utilizing laser diodes operating at CH4 and CO2 absorption lines. Distributed fiber gas sensing can benefit from the enhanced evanescent wave light scattering in the porous materials.
Internal corrosion can occur when aqueous electrolytes are present inside natural gas transmission pipelines. Despite upstream gas dehydration treatments, liquid water can form through condensation of water vapor or may be introduced from plant upsets. With dissolved salts and acidic gases such as CO2 and H2S, aqueous electrolytes become very corrosive with increased conductivity and lower pH. Since water provides the electrolytes that initiate and sustain corrosion, detection of water can locate the spots for potential internal corrosion inside the pipelines. In this work, a simple optical fiber-based sensor for fully distributed water monitoring has been demonstrated and studied. The system consists of an unmodified off-the-shelf single mode (SM) optical fiber and an optical backscatter reflectometer (OBR) capable of measuring the spatial profile of strain changes along the fiber. The polymer jacket coating of the SM fiber is hydroscopic and serves as the water sensing layer due to expansion/swelling from water absorption. The swelling induced strain change is interrogated with the OBR to enable fully distributed water monitoring. This strain-based H2O sensor is sensitive to H2O molecules regardless of the phase (liquid or vapor) or the surrounding media. Strain changes were measured at different relative humidity levels from 0% to 100% to demonstrate reversibility and linear correlation between humidity and strain. This sensor has the advantages of fully distributed sensing, low cost, simple preparation, easy operation, and good sensitivity.
Nonlinear laser wavelength tuning effects appear as phase noise in wavelength swept interferometry. A new method is proposed to compensate tuning nonlinear effects in optical frequency domain reflectometry (OFDR). The proposed method is simpler in configuration, and unlike conventional nonlinear compensation methods, it does not require separate auxiliary interferometer detection, which eliminates the need for an extra photo detector and an acquisition channel for the auxiliary interferometer. In the proposed method, an intentional beating signal is introduced in the beginning of the OFDR spectrum which is treated as an auxiliary interferometer to acquire tunable laser phase information for post signal processing. The proposed method can reduce overall OFDR system cost, reduce the data acquisition time and computational load by half, and make system configuration simpler by eliminating the need for extra components. Feasibility of the proposed method was demonstrated by compensating for tuning nonlinearity effects in an optical fiber approximately 35 m long with a measured spatial resolution of ~30 μm. To confirm performance of the proposed method, a comparison was carried out with a conventional nonlinear tuning compensation method, which requires the separate auxiliary interferometer. Moreover, distributed sensing using the proposed method was also demonstrated in an optical fiber approximately 35 m in length by performing strain sensing with 3 cm sensing resolution.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.