Fiber Optic Current Sensor Research Articles

Characteristic Analysis and Experiment of Adaptive Fiber Optic Current Sensor Technology

The straight-through magneto-optical glass current sensor has desirable temperature properties, but it is vulnerable to magnetic interference. In contrast, a polarization-type fiber optic current sensor has poor temperature performance, but the magnetic anti-interference characteristic is very good. Aiming at the problem that the accuracy of a fiber optic current sensor is susceptible to external disturbances and temperature fluctuations, we present an adaptive technology of a fiber optic current sensor that uses the magneto-optical output signal to correct the fiber output signal. The working principle of the improved method is introduced in this paper. The structure of the specific optical system and the signal processing system are presented. Temperature fluctuation and magnetic change detection units are included in the design in order to provide signal selection under different environmental fluctuations, thus stabilizing the output current data. The signal processing system was proved to be effective by building an experimental platform.

Structure Design and Simulation Study on the Symmetric Optical Path Reflection Current Sensor

Optical current sensor is received much attention by its good performance on safety and anti-interference. It displaces the traditional electromagnetic current transformer in power grid. However the optical current sensor is limited by its shortcoming in stability and reliability. It is result in big linear birefringence and low sensitivity. In this paper a new structure of optical current sensor is designed to achieve higher sensitivity about 580 times than traditional structure. The system transmission field has been obtained by simulating the transmittance of light propagating through optical sensing head by COMSOL software. The result obtained from the present work is useful for further research on the optical fiber current sensor.

Effect of Faraday mirror imperfections in a fiber optic current sensor dedicated to ITER

Plasma current measurements in ITER are safety-related and must therefore satisfy a very demanding specification. In this paper, the use of the Fiber Optics Current Sensor (FOCS) operating in the reflection mode with a Faraday mirror to perform plasma current measurements is analyzed. Based on the Jones matrix formalism, we performed numerical simulations to investigate the impact of the Faraday mirror detuning on the measurement accuracy. We show that the use of standard commercial components does not allow to satisfy the ITER requirements for the whole plasma current range. A simple solution to the problem is proposed, which consists in taking into account a mirror calibration in the current estimator. We show that the achievable mirror calibration accuracy is sufficient to fulfill the ITER requirements.

Insulating properties of optical fiber current sensor with external conversion

Insulating properties of optical fiber current sensor with external conversion

Simulation of the sensitivity of a fiber-optic magneto-optical electric current sensor with a strictly nonuniform distribution of the magnetic field around the loop

Using an asymmetric arrangement of current-carrying conductors with respect to the fiber measurement loop of a magneto-optical electric current sensor, the effect of magnetic field nonuniformity on the accuracy of the sensor characteristics is estimated.

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

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.

Status and future developments of R&D on fiber optics current sensor for ITER

Successful operation of ITER will rely on the use of a large set of magnetic diagnostics. Fundamental parameters such as plasma position, shape, and current are required for real-time plasma control and machine protection. For operating tokamaks such measurements are successfully performed using inductive sensors. In ITER and later in DEMO, the presence of strong radiations combined with steady-state operation creates a difficult problem: the useful signal is affected by the integration of radiation-induced noise. An attractive alternative for plasma current measurement consists in using Fiber Optic Current Sensor (FOCS). However, combined effects of radiation, elevated temperatures, vibrations together with the requirement of vacuum compatibility and installation constrains present a significant challenge for the ITER FOCS system. This paper describes recent results of the ITER FOCS R&D intended to demonstrate that the system can be installed on the tokamak and its performance can satisfy the required criteria. We emphasize that the choice of appropriate fibers is critical. Our simulations show that the spun fibers allow satisfying the target performance provided that the fiber beat length over spun period ratio is above a given value. This conclusion is confirmed by the experimental results obtained on JET.

Temperature evolution of interferometer visibility in a small radius fibre coil current sensor

We have experimentally demonstrated periodic oscillations of interferometer visibility in a current sensor in response to changes in the temperature of a small-radius spun fibre sensing coil. The observed effect has been shown to depend on the magnitude of the bend-induced linear birefringence in the spun fibre in the magnetically sensitive coil and the temperature behaviour of the built-in linear birefringence in the fibre. Using a model that considers a helical structure of the built-in linear birefringence axes in spun fibre, we have shown that the above factors result in periodic oscillations of the ellipticity of polarised light at the ends of the sensing coil and that this underlies the temperature oscillations of interferometer visibility in the current sensor. The effect may cause errors in the response of a fibre-optic current sensor with a small sensing coil.

全光纤电流传感器中传感光纤的温度特性研究

全光纤电流传感器中传感光纤的温度特性研究

Detection of electric current pulses by a fibre-optic sensor using spun fibre

We have studied distinctive features of the response of a fibre-optic current sensor with a spun-fibre sensing loop to short current pulses. It has been shown theoretically that, in a reflective interferometer, the polarisation mode dispersion (PMD) in the sensing spun fibre has no effect on the pulsed output signal of the sensor, in contrast to the PMD in a connecting fibre line. The response of the current sensor to a rectangular pulse has linear edges and its duration is determined by the relationship between the current pulse duration and the light propagation time in the spun fibre. The transition from a linear edge to the maximum sensor response is not accompanied by any transient process. The maximum response amplitude corresponds to the response to an equivalent direct current at a current pulse duration exceeding the light propagation time in the spun fibre. The present calculation results and experimental data agree well for current pulses longer than 300 ns at a light propagation time in the spun fibre of ~1 μs.

Experiment and Simulation Study on A New Structure of Full Optical Fiber Current Sensor

Optical fiber sensor offers an advantage of non-contact method to measure electric current. The optical fiber current sensor is based on the Faraday rotation effect and is immune from electromagnetic disturbance. In this paper a new structure of full-optical current sensor is designed. Firstly, experimental system has been set up in the laboratory to study the feasibility of the new design. Secondly, the system transmission field could be achieved by simulating the transmittance of light propagating through optical fiber by using the software. Finally, the experimental results are compared with simulation results, and there are discussions around those results. The results obtained from the present work will be useful for further research on the optical fiber current sensor.

Accurate measurements of circular and residual linear birefringences of spun fibers using binary polarization rotators.

We present a method to accurately measure the birefringence properties of spun fibers using binary polarization rotators. By taking the advantages of binary polarization rotator in polarization analysis, we are able to simultaneously measure both the circular and linear birefringences in a spun fiber with high accuracy. We obtain the circular and the residual linear birefringences of the spun fiber as a function of temperature T to be 3.34 × 10-5-5.11 × 10-8T and 8.1 × 10-6-1.19 × 10-8T, respectively, with the residual linear birefringence about 4 times less than the circular birefringence. We find, for the first time with the best of authors' knowledge, that the circular and the residual linear birefringences in a spun fiber are highly linear with the temperature, with thermal coefficients of -5.11 × 10-8 °C-1 and -1.19 × 10-8°C-1, respectively, and that the relative changes per °C of the circular and residual linear birefringence are almost identical, with values of -0.152% and -0.147% respectively. We believe that the method and data presented in this paper will be beneficial for making high quality spun fibers, as well as high accuracy fiber optic current sensors.

Analysis and elimination of bias error in a fiber-optic current sensor.

Bias error, along with scale factor, is a key factor that affects the measurement accuracy of the fiber-optic current sensor. Because of polarization crosstalk, the coherence of parasitic interference signals could be rebuilt and form an output independent of the current to be measured, i.e., the bias error. The bias error is a variable of the birefringence optical path difference. Hence, when the temperature changes, the bias error shows a quasi-periodical tendency whose envelope curve reflects the coherence function of light source. By identifying the key factors of bias error and setting the propagation directions of a super-luminescent diode, polarization-maintaining coupler and polarizer to fast axis, it is possible to eliminate the coherence of parasitic interference signals. Experiments show that the maximum bias error decreases by one order of magnitude at temperatures between -40°C to 60°C.

Birefringence Variation Independent Fiber-Optic Current Sensor Using Real-Time SOP Measurement

We propose a birefringence variation independent fiber-optic current sensor based on polarization diversity and a real-time state of polarization measurement technique. We theoretically and experimentally demonstrate the compensation for the degradation of Faraday effect due to the variation in birefringence of the sensing fiber. In experiment, a maximally two times higher sensitivity was achieved compared with that of the conventional one. We investigated temperature dependence of proposed method and the observed maximal variation in sensitivity is as small as 6%. The proposed method exhibits good immunity to the random variation of birefringence and the real rotation angle due to the Faraday effect can be accurately detected.

A Linear Birefringence Measurement Method for an Optical Fiber Current Sensor.

In this work, a linear birefringence measurement method is proposed for an optical fiber current sensor (OFCS). First, the optical configuration of the measurement system is presented. Then, the elimination method of the effect of the azimuth angles between the sensing fiber and the two polarizers is demonstrated. Moreover, the relationship of the linear birefringence, the Faraday rotation angle and the final output is determined. On these bases, the multi-valued problem on the linear birefringence is simulated and its solution is illustrated when the linear birefringence is unknown. Finally, the experiments are conducted to prove the feasibility of the proposed method. When the numbers of turns of the sensing fiber in the OFCS are about 15, 19, 23, 27, 31, 35, and 39, the measured linear birefringence obtained by the proposed method are about 1.3577, 1.8425, 2.0983, 2.5914, 2.7891, 3.2003 and 3.5198 rad. Two typical methods provide the references for the proposed method. The proposed method is proven to be suitable for the linear birefringence measurement in the full range without the limitation that the linear birefringence must be smaller than π/2.

Single-Ended Differential Protection in MTDC Networks Using Optical Sensors

This paper presents a method for rapid detection of faults on voltage source converter multiterminal HVdc transmission networks using multipoint optical current sensing. The proposed method uses differential protection as a guiding principle, and is implemented using current measurements obtained from the optical current sensors distributed along the transmission line. Performance is assessed through detailed transient simulation using MATLAB/Simulink models, integrating inductive dc-line terminations, detailed dc circuit-breaker models, and a network of fiber-optic current sensors. Moreover, the feasibility and required performance of optical-based measurements is validated through laboratory testing. Simulation results demonstrate that the proposed protection algorithm can effectively, and within very short period of time, discriminate between faults on the protected line (internal faults), and those occurring on adjacent lines or busbars (external faults). Hardware tests prove that the scheme can be achieved with the existing, available sensing technology.

Plasma Current Measurement in Thermonuclear Fusion Reactors Using a Photon-Counting POTDR

In this letter, we present a fiber-optic current sensor for the measurement of plasma current in thermonuclear fusion reactors. The sensor includes a low-birefringence optical fiber placed around a section of the vacuum vessel that hosts the fusion reaction. The interrogating unit consists of a polarization-sensitive photon-counting optical time domain reflectometer that enables to determine the light polarization rotation induced by the plasma current. The measurement principle is demonstrated by means of the Jones formalism. The sensor has been experimentally validated on the Tore Supra tokamak fusion reactor for a plasma current range going from 0.6 to 1.5 MA. A maximum error of 13.50% has been observed for the lowest current.

Study of the properties and structure of binary tin silicate glasses with zero photoelastic constant

Sn-containing silicate glasses with zero photoelastic constant (PEC) can potentially substitute zero-PEC Pb-containing glasses as optical fiber current sensor components based on the Faraday effect. These compounds allow monitoring of the electric power by measuring the electric current in high-voltage conductors operated with a 1550-nm light. The toxicity of Pb in these glasses still remains an important issue. However, replacing Pb in the sensors while minimizing the PEC of the resulting device would represent a significant breakthrough. We report a 43.5SnO–56.5SiO2 glass in molar% with zero PEC of + 0.01 × 10−12 Pa−1 observed with a wavelength of 632.8 nm.

Development and Application of Fiber-Optic Current Sensors Using Low Birefringence Faraday Sensing Glass Fiber

Development and Application of Fiber-Optic Current Sensors Using Low Birefringence Faraday Sensing Glass Fiber

Surface crystallization behavior during thermal processing of low-photoelastic ZnO–SnO–P2O5 glasses

Pb-containing glasses such as the PbO–SiO2 series are useful in optical devices because of their low-photoelastic constants (PECs); however, the toxic Pb component in these glasses is problematic. Transparent ternary ZnO–SnO–P2O5 glasses are potential substitutes for low-PEC Pb-containing glasses, but their thermal behavior is not well understood, which inhibits their ability to be drawn into fibers. Herein, we report the surface crystallization behavior of transparent ternary ZnO–SnO–P2O5 glasses, including those with low-PEC compositions, heated under isothermal conditions to temperatures above their glass-transition temperatures. The crystallization conditions for low-PEC phosphate glasses during their thermal processing into shapes of optical modules were deduced. The crystalline compounds precipitated on the surfaces were investigated via X-ray diffraction analysis, micro-Raman spectroscopy, and microscopic observations. A time–temperature–transformation diagram was constructed on the basis of the thermal stability of the glasses. We expect that this enhanced understanding of the crystallization behavior induced by the reshaping process will enable fabrication of precise polarization control devices with low PECs, such as optical-fiber current sensors, optical lenses, and filters.