Fiber Optic Current Sensor Research Articles

Zastosowanie światłowodowego interferometru różnicowego w pomiarach natężenia prądu elektrycznego

The article presents an electric current sensor built of a fiber-optic differential interferometer using the Faraday effect in a single-mode fiber. It was applied to measure current waveforms with large amplitudes and mains frequency. The optical sensor does not introduce additional resistance and inductance into the measured circuit, which is a desirable phenomenon in this type of measurements. The magnetosensitive element is an optical fiber coil made of a quartz single-mode telecommunications fiber. The optical fiber, in which the core is twisted around its axis, is characterized by a small influence of disturbing quantities, i.e., mechanical vibrations and pressure changes, on the working of the differential interferometer by inducing linear birefringence in the glass fiber. The methods of elimination of the quantities influencing the operation of the optical fiber current sensor were proposed by reducing the linear birefringence induced in the optical fiber from these quantities. The dependence of the normalized light intensity was plotted. The results of experimental research on a design solution of a differential interferometer based on the Faraday effect, operating at a wavelength of 1550 nm, are presented. The sensor was used for measurements of sinusoidal current with a frequency of 50 Hz and amplitudes ranging 100–1500 A. The uncertainty of measurement of the electric current amplitude was determined in the range of the measured values, which was estimated at no more than 1.5 %.

Fiber Optic Voltage Sensor Based on Capacitance Current Measurement With Temperature and Wavelength Error Correction Capability

Traditional optical voltage transformers (OVTs) based on electro-optical and inverse piezoelectric effects are gradually exposing their accuracy and reliability issues. In contrast, fibers for measuring electricity have unique properties and significant advantages in the high-voltage power industry, especially fiber optic current sensor (FOCS), which has been widely used in the field of high-voltage measurement. As a result, a novel fiber optical voltage sensor (FOVS) is proposed, which uses FOCS to measure the current flowing through the capacitive voltage divider (CVD) and then calculates the primary voltage proportional to it. In order to solve the inherent temperature- and wavelength -dependent errors and achieve high accuracy, a novel closed-loop signal processing method, which aims to minimize the influence of temperature-sensitive components such as CVD, quarter waveplate, and sensing fiber on the measurement accuracy of the system, is presented. A 110-kV FOVS prototype with a rated voltage of 110/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$({3})^{1/2}$ </tex-math></inline-formula> kV and a rated frequency of 50 Hz is developed and tested. The results show that after temperature and wavelength correction, the accuracy reaches the metering class of 0.2% and protection class of 3P specified in GB/T20840.7-2007

Temperature-Monitored Fibre Optic Current Sensor Using Channelled-Spectrum Analysis

The fibre optic current sensor demonstrated here uses the intrinsic temperature and wavelength dependence of the Verdet constant of a terbium gallium garnet (TGG) magneto-optic material and the two micro-optic linear polarizers attached, to simultaneously extract the values of temperature and the optical Faraday rotation (induced by the presence of the magnetic field due an electric current on a conductor) without any extra optical component attached to the optical sensor head. The simultaneous measurement is achieved by illuminating the sensor head with a broadband optical source and by careful signal processing of the originated channelled-spectrum, compensate the sensor’s temperature dependence.

Simulation of the Limiting Parameters of Polarimetric Fiber-Optic Current Sensor on a Spun Fiber

Simulation of the Limiting Parameters of Polarimetric Fiber-Optic Current Sensor on a Spun Fiber

Relative error's quadratic dependence on the electric current and the methods for its compensation in fiber optic current sensor systems.

We find that the relative error of a fiber optic current sensor (FOCS) increases quadratically with the electric current to be measured, causing unacceptable inaccuracy for direct current (DC) measurements beyond 100 kA. We prove analytically and confirm experimentally that such a nonlinear relative error escalation (REE) mainly originates from the residual linear birefringence of the spun fiber used in the FOCS. We propose and demonstrate that by first measuring residual linear birefringence, together with the circular birefringence of the spun fiber, the REE of the FOCS can be significantly reduced from -1.22% to -0.15% at 200 kA DC by a compensation scheme using the measured birefringences in the quadratic expression we derived. Further reduction of the REE to -0.02% at 200 kA DC can be obtained if the quadratic relation between the REE and the current under test is experimentally obtained. Our work points to a new direction for drastically improving the accuracy of FOCS at large currents and shall prove beneficial for scientists and engineers working in the field of current sensing.

Optical Magnetostrictive Current Sensor Based on In-Fiber Fabry–Pérot Cavity

In this article, a compact fiber-optic current sensor (FOCS) based on an in-fiber Fabry–Pérot interferometer (FPI) and a magnetostrictive transducer is presented. The in-fiber FPI sensor employed in the proposed FOCS was fabricated with a 273- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> Section of a capillary fiber spliced between two pieces of a standard single-mode fiber (SMF). The in-fiber FPI sensor and a commercial fiber Bragg grating (FBG), which was used as a reference sensor for sensitivity comparison, were bonded to a small magnetostrictive actuator (Terfenol-D) and assembled in the proposed FOCS for electric current monitoring up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$800 {A}_{\text {rms}}$ </tex-math></inline-formula> using a commercial FBG interrogator. The in-fiber FPI sensor presented a sensitivity 84.4% higher than that of the FBG sensor. An alternative interrogation system based on an edge-filter technique with temperature compensation was also developed and employed for the characterization of the proposed FOCS under the same range of electric current. Using the edge-filter interrogation system developed, the in-fiber FPI sensor presented a sensitivity 169.8% higher than that shown by the FBG sensor. The results show that the proposed FOCS using an in-fiber FPI sensor presented high sensitivity to electric current sensing and, therefore, is a potential candidate for current monitoring in complement to conventional current transformers (CTs) as well as to conventional optical CTs (OCTs).

Compact Fiber-Optic Current Sensor With a Polarization Splitter and a 22.5$^\circ$ Faraday Rotator

In this letter, a novel implementation of a polarimetric fiber-optic current sensor scheme based on polarizing beam splitter and a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$22.5^{\circ }$</tex-math></inline-formula> Faraday rotator will be presented. The developed sensor employs a compact and pigtailed component realized by joining a polarizing beam splitter and a Faraday rotator, it does not require any external adjustment to work and shows very high immunity to external electromagnetic and mechanical interference. The experimental results prove good sensitivity of the sensor allowing for the measurement of small value of current down to 100 mA.

Unclosed fiber optic current sensor based on helically wound spun highly birefringent fiber half waveplate

• An unclosed fiber optic current sensor based on the helically wound spun highly birefringent fiber half waveplate on the tunnel boring machine is proposed and experimentally demonstrated. • The unclosed fiber optic current sensor is designed to coil the spun highly birefringent fiber around the measured current clockwise and counter clockwise alternately in order to be mounted on the measured object with large diameter easily. • The helically wound spun highly birefringent fiber half waveplate is proposed to accumulate the Faraday effect. • The good performance of the unclosed fiber optic current sensor is confirmed by the laboratory experiment. In the application of the fiber optic current sensor that is mounted on tunnel boring machine (TBM) for measuring the probe current in tunnel geological prediction, the field installation and the influence of the linear birefringence caused by external perturbations are problems needing to be solved. In this paper, an unclosed fiber optic current sensor (UFOCS) based on the helically wound spun highly birefringent (SHB) fiber half waveplate is proposed and demonstrated. The UFOCS is designed to coil the fiber around the measured current clockwise and counter clockwise alternately in order to be mounted on the measured object with large diameter easily. The all-fiber half waveplate made by the helically wound SHB fiber is used to accumulate the Faraday effect. The simulation is carried out based on the polarization model and a linear response is obtained. The laboratory experiment is conducted and the results confirm the good performance of the UFOCS.

A simple fiber optic magnetic field and current sensor with spectral interrogation

In this paper we present a simple fiber optic sensor for magnetic-field/electric current measurement in a BSO crystal. We make use of a simple polarimetric scheme based on a broadband white LED source and a spectral detection in combination with 200μm multimode fiber. A detailed Mueller–Stokes polarization analysis is presented with simulation of expected performance. It is confirmed that the sensitivity is wavelength dependent and increases from 0.138 nm/A at 540 nm to 0.224 nm/A at 715 nm a minimum current change of 0.2 A and an average dynamic range of 33 dB have been achieved.

A polarimetric fiber optic current sensor based on Bi12SiO20 crystal fluorescence

In this paper, we present a simple fiber optic sensor for magnetic-field/electric current measurement based on broadband fluorescence in a Bi12SiO20 crystal. A simple polarimetric scheme in combination with a standard 105/125 μm multimode fiber, a 405 nm laser diode and a spectrometer to analyze the spectrum is used. The magnetic field induces phase changes measured by the spectral shifts of the wavelength modulated response. The sensitivity is found to be wavelength dependent. It increases from 0.138 nm/A at 540 nm to 0.224 nm/A at 715 nm and is inversely proportional to the Verdet constant. A minimum current of 0.4A can be detected with a dynamic range of up to 32 dB. A detailed polarization analysis is presented.

Optoelectronic system for detecting short-circuits in low voltage networks

The paper presents the concept of using a fiber-optic current sensor with external conversion (OFCS-EC) in a power system. The sensor was developed in the Department of Optoelectronics and was tested in a laboratory. The focus was on the use of OFCS-EC in a real low voltage network. The main purpose of the presented measurement system will be to record network disturbance states with high accuracy. The experiment is to answer the question whether the recorded current waveforms in fault states and the measurement transmission speed will be useful enough to be able to predict, identify and, consequently, prevent losses and damage to devices caused by disturbances in low voltage networks. Full Text: PDF ReferencesS. Ziegler, R.C. Woodward, H.H.C. Iu, L.J. Borle, "Current Sensing Techniques: A Review", IEEE Sens. J. 9, 354 (2009). CrossRef R.M. Silva, H. Martins, I. Nascimento, J.M. Baptista, A.L. Ribeiro, J.L. Santos, P. Jorge, O. Frazão, "Optical Current Sensors for High Power Systems: A Review", Appl. Sci. 2, 602 (2012). CrossRef K. Barczak, K. Mazniewski, "Optical fiber current sensor with external conversion for measurements of low AC electric currents", Proc. SPIE, 10455 (2017). CrossRef K. Barczak, T. Pustelny, D. Dorosz, J. Dorosz, "Polarization maintaining fibers for application in magnetic field measurements", Eur. Phys. J.: Spec Top. 154, 11 (2008). CrossRef K. Barczak, T. Pustelny, D. Dorosz, J. Dorosz, "New Optical Glasses with High Refractive Indices for Applications in Optical Current Sensors", Acta Phys. Pol. A, 116, 247 (2009). CrossRef K. Barczak, "Optical fiber current sensor with external conversion", Proc. SPIE, 10034 (2016). CrossRef K. Barczak, D. Duda, K. Mazniewski, "Optical fiber current sensor with external conversion in high voltage environment", Proc. SPIE, 10830 (2018). CrossRef

Research of Magnetic Shielding on the Closing Gap of Optical Fiber Current Sensor

Reflective optical fiber current sensors have been widely used in electric power and metallurgy. However, the closing gaps between the λ / 4 wave plate and the reflector leads to a strong background current when they are used in strong magnetic fields. In this paper, a mathematical model of the background current was analyzed, and the relationship between the external magnetic field and the background current was identified through experiments. Therefore, a method to reduce the background current by magnetic shielding was proposed. A magnetic ring to shield the magnetic field effectively was designed, and the effects of the structure and relative permeability of the magnetic ring on its shielding rate were established by experiments and numerical simulations. The results showed that the shielding rate exceeded 95% when the length, thickness, and inner diameter of the magnetic ring were 50 mm, 2 mm, and 13 mm, respectively. Overall, this work provided a comprehensive framework that is useful for the analysis and optimization of magnetic shielding and improved the measurement accuracy of optical fiber current sensors in strong magnetic fields.

Optical fiber current sensing based on a macro-bending no-core fiber structure and magnetic fluid

An all fiber current sensor based on magnetic fluid (MF) is proposed. The sensing structure is composed of a piece of no-core fiber (NCF) spliced between two sections of single mode fiber. The MF is used as the cladding of NCF. The sensing principle is based on the cladding mode interference. In order to improve the sensitivity, a bent-melt taper NCF is proposed as the sensing probe for the first time to increase the evanescent field. As a comparison, the sensitivities of optical fiber current sensors with straight NCF, bent NCF, and bent-melt taper NCF are measured in this paper. According to the experimental results, the sensitivities of optical fiber current sensor with bent-melt taper NCF are the highest among the three. The average wavelength sensitivity is 10.48 nm/A with the corresponding measurement range of 0–0.8 A, and the maximum standard deviation is 0.27 nm. The average total relative transmission loss sensitivity is 17.28 dB/A with the corresponding measurement range of 0–0.6 A, and the standard deviation of the maximum loss is 0.31 dB. The proposed sensor has good repeatability, reversibility and high sensitivity.

Experimental Evaluation of the Birefringence Effect on Faraday-Based Fiber-Optic Current Sensors

Experimental Evaluation of the Birefringence Effect on Faraday-Based Fiber-Optic Current Sensors

Excess noise suppression in fiber-optical current sensors with small-radius coiling of the spun fiber

The effect of bending of a high-birefringent spun fiber on excess noise suppression in a Faraday fiber-optic current sensor based on a reflective interferometer is investigated. It is theoretically shown, that spun fiber winding with a small radius results in the emergence of undesired secondary waves in the interferometer. These waves partially fade out in the polarizer of the sensor, which leads to deformation of the optical spectrum and, in turn, to a reduction of excess noise suppression. The form of the interference pattern is refined taking into account the strong bending of the spun fiber. The theoretical model has been experimentally confirmed by acquiring a deformed spectrum for the winding radius of 5 mm and measuring the suppression coefficients for several configurations of fiber winding.

Long-term stability of the toroidal current measurement at JET using fibre optics current sensor

The Fibre Optic Current Sensor (FOCS) is a system that will perform plasma current measurements at ITER during long plasma discharges under intense nuclear radiation. These measurements are important for safe machine operation. The FOCS must perform well in a harsh tokamak environment, which include strong magnetic fields, high temperatures, and also significant levels of neurons and high energy photons. JET is a unique machine where the impact of such conditions on the sensor performance can be investigated experimentally in representative conditions. In this work we analyse stability of the fibre Verdet constant using data obtained with two polarisation detection based FOCS systems installed at JET and operated in various machine scenarios with currents up to 4.2 MA. Analysis of data accumulated during more than four years demonstrates that long-term Verdet constant’s changes are less than 0.5%. However, on a month time scale, windows with deviations up to ±9% from the average value are observed. The reason for these windows is unknown at the moment and will be studied in a future.

Noise suppression for weak current measurement based on neural-network-assisted UHV FOCS

Weak current measurement plays an essential role in the power grid systems, which remains challenging to be achieved with fiber optic current sensor (FOCS) due to ambient and internal noise. In this work, noise suppression method based on back propagation neural network (BPNN) is proposed to calibrate FOCS which is originally applied to ultra-high voltage (UHV) systems so that output accuracy can be improved when it is utilized to detect weak current. The output errors induced by noise, the feature of FOCS output signal and the reason for choosing BPNN are deeply analyzed. Performance of BPNN with different parameters is also investigated and results show that BPNN with 2 hidden layers and 3 neurons meets the requirements of high efficiency and high accuracy in our application. Then, 15750 groups of FOCS output data are collected under different temperature and utilized for network training. With the well-trained BPNN, weak current as low as 0.1 A is successfully detected by UHV FOCS when temperature varies from -30 °C to 70 °C, and ratio error (RE) is limited between -0.2% and 0.2%, showing a better performance on noise elimination than traditional Gaussian filter and Fourier filter.

Distribution Network Communication Base on Reflective Fiber Optic Current Sensor

Fiber optic current sensor has been brought into the practical application. The main research trend is to use special fiber or improve the system structure, so as to deal with the unstable operation of fiber optic current sensor, thereby improving the measurement accuracy of current. The working principle of the reflective fiber optic current sensor is analyzed, and the Jones matrix is applied to characterize the optical components of the system. With the analysis of the error source of the sensor, a mathematical model of optical path error is constructed, including the fabrication error, temperature error, and strain error. Under these error analyses, the design scheme of twisted fiber optic current sensor is further proposed. In view of the structure of the traditional reflective fiber optic current sensor, twisted optical fiber is used for the 1/4 wave plate and sensing fiber part, and the constant-rate twisted optical fiber is used to replace the ordinary sensing fiber. The error caused by the linear birefringence in the optical fiber is reduced, the temperature sensitivity is lowered, the anti-stress effect is improved, and the adverse interference by temperature and strain on the sensing optical fiber is eliminated. The developed fiber optic current sensor is utilized for long-term pilot application in low-frequency distribution network communication. In the simulation test, the reflective fiber optic current sensor designed with a twisted fiber optic structure has a measurement accuracy of 0.5, which meets the system requirements. As error factors is added and corresponding compensation modules are introduced, the measurement accuracy is increased to 0.2. In the pilot applications of distribution network, it can provide comprehensive and real-time information support, thus laying the foundation for the communication management of the distribution network.

Design of a dielectric chiral micro-structured fiber applied in a fiber optic current sensor

During the process of drawing the screwed silicon-based fiber, there will be a uniform rotation rate in it, which results in a decrease of circular polarization degree of the fiber. In order to solve this problem, we presented a kind of dielectric chiral micro-structured fiber owing higher circular polarization degree. Meanwhile, the air holes of fiber will collapse during the progress of fiber drawing, which will change the position of air holes. As a result, the circular polarization degree of the fiber decreases. In order to reduce the change of circular polarization degree caused by the position fluctuation of the air holes, a highly symmetrical micro-structured dielectric chiral fiber was firstly designed in this paper. Then, we established a physical error model considering the fluctuation of the air holes’ position which was the design basis of the air holes’ position, size, and chiral parameters of the specific microstructure fiber. Next, comparing the circular polarization degree S3 of screwed silicon-based fiber and that of the dielectric chiral micro-structured fiber by simulation, it was proved that the dielectric chiral micro-structured fiber we designed has a higher circular polarization degree S3 than that of screwed silicon-based fiber. Finally, we applied the fiber designed in this paper as the fiber sensing coil in a fiber optic current sensor, and compared it with the fiber optic current sensor utilizing the original fiber sensing coil in ratio error. The simulation results proved that compared with the original system, dielectric chiral micro-structured fiber utilized as the fiber sensing coil in a fiber optic current sensor will decrease the ratio error by an order of magnitude in theory.

Short-time and weak signal demodulation for fiber optic current sensors based on backpropagation neural network

It has been challenging to demodulate short-time and weak current signals collected by fiber optic current sensors (FOCSs) under ultra-high voltage, since the background noise can significantly affect the spectra of the current signals. To address this issue, here we propose a novel FOCS demodulation method based on backpropagation neural network, where the impact of the noise on the measurement can be largely reduced. The demodulation method can determine the amplitudes of short time series of weak currents with high resolution and accuracy. To evaluate the performance of the proposed method, the demodulation accuracy and robustness of the method are experimentally investigated and compared with those of the traditional fast Fourier transform (FFT) method. The experimental results show that our method can produce reliable results when demodulating weak current signals over short time windows of less than one period, and achieve a significantly lower standard deviation (6.7 mA) compared with the FFT method (15.6 mA) in the current range 0–0.306 A. The higher robustness against the background noise than the FFT method and the excellent repeatability of our demodulation method are also demonstrated through simulations. These results suggest that the proposed method will provide an effective way to improve the detection performances of FOCSs in fast dynamic measurements.