Lin Yang

Bio: Lin Yang is an academic researcher from ABB Ltd. The author has contributed to research in topics: Fiber optic sensor & Optical fiber. The author has an hindex of 8, co-authored 25 publications receiving 156 citations.

Temperature Compensation of Interferometric and Polarimetric Fiber-Optic Current Sensors With Spun Highly Birefringent Fiber

Abstract: We theoretically and experimentally investigate intrinsic temperature compensation of interferometric and polarimetric fiber-optic current sensors with a coil of spun highly birefringent fiber operated in reflection mode. The interferometric sensor recovers the differential magneto-optic phase shift of the left- and right-handed circular (or slightly elliptical) polarization states in the fiber by means of non-reciprocal phase modulation, whereas the polarimetric sensor employs a simple passive polarization analyzer. We show that the two sensor types exhibit substantial differences in their response to temperature changes. The main parameters that determine the sensors’ sensitivity to temperature are, besides the fiber's Verdet constant, the intrinsic birefringence of the spun fiber, the retardation of the fiber retarder at the coil entrance that generates the elliptical polarization states, and the angle α between the principal axes of the retarder and spun fiber. In particular, fringe contrast changes at varying fiber birefringence make the polarimetric sensor version significantly more sensitive to temperature. Furthermore, whereas in the interferometric sensor, the contribution of the fiber birefringence to the temperature dependence disappears for special fiber orientations ( α = 0°, 90°), such an arrangement is not possible for the polarimetric sensor. Also, the response to changes in the retardation of the retarder shows different patterns for the two sensor types. In spite of the differences, we achieve intrinsic temperature compensation well within ±0.2% between –40 °C and 85 °C for both sensors by using the retarder contribution to balance the contributions from the Verdet constant, the fiber birefringence, and potential further effects of temperature.

Inherent temperature compensation of fiber-optic current sensors employing spun highly birefringent fiber

Abstract: We investigate the various contributions to the temperature dependence of an interferometric fiber-optic current sensor employing spun highly-birefringent sensing fiber, in particular, the contributions from the fiber retarder at the fiber coil entrance, the spun fiber's birefringence, and the Faraday effect. We theoretically and experimentally demonstrate that an appropriately designed retarder inherently compensates the temperature dependence of the fiber birefringence and the Faraday effect. We demonstrate insensitivity to temperature to within ± 0.2% between -40 and + 85 °C. Furthermore, we analyze the influence of the retarder parameters on the linearity of the recovered magneto-optic phase shift vs. current and determine a set of parameters that results in a perfectly linear relationship.

Long-Term Reliability of Fiber-Optic Current Sensors

Abstract: We present studies on the long-term reliability of interferometric fiber-optic current sensors (FOCS) for use in electric power transmission systems. Accelerated ageing tests are performed on crucial optical sensor components and a three-phase sensor system is subjected to an extended field trial. The sensor components under test include the sensor’s superluminescent light emitting diode light source, the integrated-optic phase modulator and various passive components such as fiber couplers, fiber polarizers, polarization-maintaining fiber connectors, and fiber coatings. The components are exposed to accelerated ageing conditions for extended periods of time, i.e., temperature cycling (between −25 °C and 65 °C for up to 15000 cycles), constant high temperature at dry conditions (up to 115 °C for up to 20000 h), and damp heat (85 % relative humidity at 85 °C for up to 7900 h). Crucial component parameters such as the source wavelength and polarization extinction ratios are repeatedly measured as a function of temperature at defined intervals during the ageing periods and examined for potential drift of component failures. The field trial is carried out for a three-phase FOCS system integrated into 420 kV double-chamber circuit breakers over a period of more than three years. The sensor signals are compared to the signals of conventional current transformers. In addition, the evolution of various operational parameters such as the light source power is continuously recorded. The results prove a high degree of reliability of modern FOCS systems.

Fiber-Optic Current Sensor Tolerant to Imperfections of Polarization-Maintaining Fiber Connectors

Abstract: We investigate the effect of polarization cross-coupling at polarization-maintaining (PM) fiber connectors on the accuracy of an interferometric fiber-optic current sensor. The sensor uses the Faraday effect in a fiber coil operated in reflection mode and an interrogator based on nonreciprocal phase modulation. PM connectors in the fiber link between the sensor's opto-electronic module and the fiber coil give rise to signal instability due to a limited and insufficiently stable polarization extinction ratio (typically <;25-30 dB). As a result the accuracy of the sensor can be well outside the allowed tolerances of applications in the electric power industry which often demands accuracy to within ±0.2%. We demonstrate that by means of a modified optical circuit the disturbing effects of polarization cross-coupling can be largely eliminated. The modified circuit introduces group delays for the cross-coupled light waves relative to the undisturbed waves much larger than the coherence length of the broadband light source. We theoretically and experimentally show that connector extinction ratios well below 20 dB are still uncritical. Furthermore, we verify the superiority of the modified circuit at changing connector temperature (and hence changing temperature-induced stress in the connector ferrules) and at repeated connector open-close operations.

Polarimetric Fiber-Optic Current Sensor With Integrated-Optic Polarization Splitter

Abstract: We report on a simple, metering class polarimetric fiber-optic current sensor (FOCS) for electric power transmission systems. The sensor uses a fiber coil operated in reflection mode and an integrated-optic polarization splitter (IOPS) for interrogation. At alternating currents, the sensor performs comparably to high-end interferometric FOCS that work with an integrated-optic phase modulator in a closed-loop detection circuit. Besides the passive interrogation scheme, a particular advantage of the sensor is the use of standard single-mode fiber leads to the sensor head instead of polarization maintaining fiber. The IOPS introduces a 90° phase bias between the interfering light waves and generates two anti-phase sensor signals. By various measures, we obtain repeatable splitter performance between −40 °C and 85 °C. Like for interferometric FOCS, we employ the fiber retarder that generates the left and right circular or elliptical polarization states in the coil to compensate for the temperature dependence of the Faraday effect. We show that there are substantial differences, however, between interferometric and polarimetric FOCS in this regard. Finally, we demonstrate sensor accuracy well within ±0.1% during more than 200 hours of temperature cycling between −45 °C and 85 °C, which is unprecedented for polarimetric sensors.

Temperature and vibration insensitive fiber-optic current sensor

Abstract: We present a robust, temperature and vibration insensitive fiber-optic current sensor. The sensor has been integrated into a high-voltage circuit breaker. One year field experience has been gained in two substations of the Italian railways.

Temperature Compensation of Interferometric and Polarimetric Fiber-Optic Current Sensors With Spun Highly Birefringent Fiber

Abstract: We theoretically and experimentally investigate intrinsic temperature compensation of interferometric and polarimetric fiber-optic current sensors with a coil of spun highly birefringent fiber operated in reflection mode. The interferometric sensor recovers the differential magneto-optic phase shift of the left- and right-handed circular (or slightly elliptical) polarization states in the fiber by means of non-reciprocal phase modulation, whereas the polarimetric sensor employs a simple passive polarization analyzer. We show that the two sensor types exhibit substantial differences in their response to temperature changes. The main parameters that determine the sensors’ sensitivity to temperature are, besides the fiber's Verdet constant, the intrinsic birefringence of the spun fiber, the retardation of the fiber retarder at the coil entrance that generates the elliptical polarization states, and the angle α between the principal axes of the retarder and spun fiber. In particular, fringe contrast changes at varying fiber birefringence make the polarimetric sensor version significantly more sensitive to temperature. Furthermore, whereas in the interferometric sensor, the contribution of the fiber birefringence to the temperature dependence disappears for special fiber orientations ( α = 0°, 90°), such an arrangement is not possible for the polarimetric sensor. Also, the response to changes in the retardation of the retarder shows different patterns for the two sensor types. In spite of the differences, we achieve intrinsic temperature compensation well within ±0.2% between –40 °C and 85 °C for both sensors by using the retarder contribution to balance the contributions from the Verdet constant, the fiber birefringence, and potential further effects of temperature.

Optical fiber current sensor research: review and outlook

Abstract: Optical fiber current sensor (OFCS) based on Faraday magneto-optic effect has many advantages of immunity against electromagnetic interference, high sensitivity and wide dynamic range. Thus, OFCS has extensive application prospects. In this paper, the authors present a review on OFCS. The basic principle of OFCS is firstly discussed. And then the main advantages and disadvantages of several common types of OFCS are compared. On this basis, the effect of the linear birefringence on OFCS is discussed emphatically. Moreover, the research results about the linear birefringence measurement and suppression methods are summarized. In the end, the future research direction of OFCS is presented, which will provide ideas for subsequent research work.

Cyber-enabled grids: Shaping future energy systems

Abstract: As the penetration of distributed energy resources based on renewable sources increases, several technical challenges are introduced into energy grids. These include real-time power balance, control of bi-directional energy flow, power quality, distributed optimization, state estimation and topology estimation in distribution grids, and multi-level electricity trading. To overcome these challenges and to create situational awareness in energy grids, pervasive sensing becomes essential. To overcome hurdles such as implementation and cost of such pervasive sensing, in addition to traditional contact-sensing methods, contactless sensors that can measure key variables in the grid needs to be leveraged. Contactless sensing enables measurement of process variables that may be hard to measure due to technological limitations of contact sensing, large measurement delays, or high costs. In addition to contactless sensing, pervasive sensing proves advantageous as it can leverage ongoing technological advances in Internet of Things (IoT), as they can lead to enhanced network connectivity between sensors as well as between the edge and the cloud. Finally, pervasive sensing proves even more attractive by integrating contactless sensing not only with wireless communication but also with shielding and energy harvesting. This paper reviews pervasive sensing techniques in power grids that encompass contactless sensing technologies, IoT connectivity, energy harvesting and shielding. In addition, we also explore how pervasive sensing in a Cyber-Enabled Grid (CEG) can contribute to the development roadmap of Autonomous Energy Grids (AEGs), a futuristic concept where the grid will be making automated operational decisions. The potential challenges and research opportunities in this pioneering research field such as data deluge, cybersecurity, and sensor fusion will be discussed. This review article, which addresses the role of pervasive sensing in CEGs, is a first of its kind. It will help engineers and scientists to understand its significant potential to shape future energy systems.

Review of Fiber Optic Diagnostic Techniques for Power Transformers

Abstract: Diagnostic and condition monitoring of power transformers are key actions to guarantee their safe operation. The subsequent benefits include reduced service interruptions and economic losses associated with their unavailability. Conventional test methods developed for the condition assessment of power transformers have certain limitations. To overcome such problems, fiber optic-based sensors for monitoring the condition of transformers have been developed. Flawlessly built-up fiber optic-based sensors provide online and offline assessment of various parameters like temperature, moisture, partial discharges, gas analyses, vibration, winding deformation, and oil levels, which are based on different sensing principles. In this paper a variety and assessment of different fiber optic-based diagnostic techniques for monitoring power transformers are discussed. It includes significant tutorial elements as well as some analyses.