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The measurement of water inside a transformer is essential to maintain its reliable operation, as the water content can increase as the transformer ages. This measurement is frequently performed by a utility as a part of its periodic maintenance activities. In this paper, the application of optical fiber sensors as an online method to measure water content of paper inside an operating transformer is presented. There are several advantages of using these sensors, including their size, lightweight, flexibility, multiplexing, no-electromagnetic interference, etc. A unique benefit of fiber optic technology is that sensors can be embedded into the winding structure and operate in areas of high electric field strength. For this work, fiber optic water and temperature sensors are investigated by comparing their measurements to a commercial water activity probe immersed in oil. The study found that the determination of water content by fiber optic sensors compared closely with other techniques, which lead to the conclusion that they can be an effective technology for water measurement in an operational transformer. [ABSTRACT FROM AUTHOR]

We describe a low cost optical temperature sensor that is simple to manufacture. The sensor is constructed by simple soaking of paper in a solution of the temperature sensitive luminescent indicator Ru(phen) 3 and subsequent lamination of the dried paper. Lamination prevents O 2 diffusion to the indicator and thus eliminates O 2 cross-sensitivity. The temperature sensitivity was up to −2% change in luminescence lifetime per K, a t 90 response time of 10 s. Besides luminescence lifetime based measurements, the sensor is well suited for ratiometric imaging with simple RGB cameras, where the temperature dependent red luminescence can be referenced by the blue luminescence of the optical brightener in the paper. [ABSTRACT FROM AUTHOR]

Utility asset managers and engineers are concerned about the life and reliability of their power transformers which depends on the continued life of the paper insulation. The ageing rate of the paper is affected by water, oxygen and acids. Traditionally, the ageing rate of paper has been studied in sealed vessels however this approach does not allow the possibility to assess the affect of oxygen on paper with different water content. The ageing rate of paper has been studied for dry paper in air (excess oxygen). In these experiments we studied the ageing rate of Kraft and thermally upgraded Kraft paper in medium and high oxygen with varying water content. Furthermore, the oxygen content of the oil in sealed vessels is low which represents only sealed transformers. The ageing rate of the paper has not been determined for free breathing transformers with medium or high oxygen content and for different wetness of paper. In these ageing experiments the water and oxygen content was controlled using a special test rig to compare the ageing rate to previous work and to determine the ageing effect of paper by combining temperature, water content of paper and oxygen content of the oil. We found that the ageing rate of paper with the same water content increased with oxygen content in the oil. Hence, new life curves were developed based on the water content of the paper and the oxygen content of the oil. [ABSTRACT FROM PUBLISHER]

Abstract: This study explores the possibility of converting a self-supporting, randomly aligned, low impedance multi-wall carbon nanotube (MWCNT) paper into a resistive temperature measurement unit working at ambient pressure in air in the 25–70°C range. Thermosensitization was achieved by decorating the surface of the films with pyroelectric CsNO3 or LiNbO3 crystals. Assuming a linear temperature response, temperature coefficient of resistance values of −0.158%°C−1 and −0.246%°C−1 were calculated for CsNO3 and LiNbO3 doped films, respectively. The corresponding temperature measurement accuracies (2.2°C and 3.0°C) are acceptable for some applications but the precision of the temperature measurement needs to be improved. [Copyright &y& Elsevier]

The classical region of a Bose gas consists of all single particle modes that have a high average occupation and are well described by a classical field. Highly occupied modes only occur in massive Bose gases at ultra-cold temperatures, in contrast to the photon case where there are highly occupied modes at all temperatures. For the Bose gas the number of these modes is dependent on the temperature, the total number of particles and their interaction strength. In this paper, we characterize the classical region of a harmonically trapped Bose gas over a wide parameter regime. We use a Hartree-Fock approach to account for the effects of interactions, which we observe to significantly change the classical region as compared to the idealized case. We compare our results to full classical field calculations and show that the Hartree-Fock approach provides a qualitatively accurate description of a classical region for the interacting gas. [ABSTRACT FROM AUTHOR]

The narrow gap semiconductor TlBiTe2 undergoes a solid–solid phase transformation from the rhombohedral (D3d) to the cubic (Oh) phase. The present paper deals with the study of this phase transformation combining the results of Differential Scanning Calorimetry (DSC) and Transmission Electron Microscopy (TEM). It has been found that during heating the transformation is an athermal activated process, which can be described only by a combination of more than one processes while during cooling it exhibits an expectable thermal hysteresis due to the volume difference. The results of the kinetic analysis combined with the electron microscopy findings, supported also by the Fourier Transform Infrared (FTIR) spectroscopy ones, lead to the conclusion that TlBiTe2 undergoes a multiple-step, displacive, martensitic type transformation. [ABSTRACT FROM AUTHOR]