Optical Current Sensor Research Articles

Plasma current measurement at JET using polarimetry-based fibre optic current sensor

The ITER Fibre Optic Current Sensor (FOCS) is a dc coupled current measurement system that will provide back-up ITER plasma current measurements using a sensing fibre located on the outer surface of the vacuum vessel. To address the impact of a harsh tokamak environment on the sensor performance we installed a FOCS system on JET and performed current measurements in various machine operating scenarios for currents up to 3 MA. Me have observed a good agreement between the FOCS and the reference Continuous External Rogowski (CER) coils data. The linearity of the FOCS response was demonstrated. The FOCS has performance characteristics compatible with the ITER requirements and in contrast to the CER is non-sensitive to magnetic crosstalk effects.

Polarization Error Analysis of an All-Optical Fibre Small Current Sensor for Partial Discharge

In view of the characteristics of the small amplitude of a current signal, an all-optical fibre small-current sensor for partial discharge is devised. A novel type of sensor head with electric winding light is proposed. A complete optical model of the optical fibre current sensor is developed under the effect of polarization error factors. In addition, the effect of polarization error factors on the optical fibre sensing system is simulated. The simulation results show that as the extinction ratio increases, the output relative error of the optical fibre small-current sensor decreases. The effect of the fast and slow axis misalignment errors of a polarizing beam splitter is similar to the effect of the alignment angle error of an optical fibre polarizer. It is observed that the relative error curve follows a sine function. Meanwhile, the output relative error increases first and then oscillates with an increase in the linear birefringence. We conclude that the linear birefringence of the sensing optical fibre is the main error source for the measurement accuracy of the sensing system. Finally, an experimental system for the optical fibre small-current sensor is implemented. The experimental results show that the effect of linear birefringence on the fibre current sensing system can be suppressed by introducing a large amount of circular birefringence into the sensing optical fibre. The theoretical mechanism of these errors is analysed, which can be applied to implement corresponding measures to reduce the effect of error factors on the sensing system and further improve the measurement accuracy of the optical fibre small-current sensor.

Influence of Polarization Crosstalk of Y Branch Loop on Scale Factor in Fiber Optic Current Sensor

The influence of polarization crosstalk of Y branch loop on scale factor is analyzed in detail. In the Y branch loop, the scale factor is affected by only the output alignment angle of the PBS. The experiment result shows the range of output alignment angle of the PBS should not exceed from 0.2 to 2.5 over a range from - 40°C to 70°C which corresponds to angle 1.8 at room temperature to make sure the measurement accuracy within ±0.2% from 0 to 100kA.

Analysis of interelectrode short-circuit current in industrial copper electrorefining cells

Abstract In the process of copper electrorefining, detecting and treating the interelectrode short-circuit faults is one of the main tasks in the workshop. In this paper, the cathode current in industrial copper electrorefining cells was measured by an optical fiber current sensor, and the current curves caused by interelectrode short-circuit have been obtained. The relationship between the characteristics of cathode current and the mechanism of interelectrode short-circuit is discussed. A rapid diagnostic method of short-circuit faults by monitoring the change of cathode current slope and standard deviation is proposed. The applicable scope of the method is also given.

Reflective Detection Method of Partial Discharge Using Optical Fiber Sensor

AbstractAiming at the characteristic of small amplitude of partial discharge current signal, all-optical fiber current sensing system is designed. Two kinds of optical fiber current sensor structures are proposed, which are linear and reflective. The optical path systems of two kinds of fiber optical current sensor are modeled based on Jones matrix. In addition, the output sensitivities of two structures are compared. The results indicate that the sensitivity of the two current sensor structures can be improved, and the output sensitivity of the reflective fiber optical current sensor is twice as high as that of the linear sensor. At the same time, the complete optical path model of optical fiber sensing system is established under the influence of fiber birefringence errors. Finally, the birefringence errors of sensing fiber are simulated. It is concluded that the reflective fiber optical current sensor can suppress the influence of linear birefringence on the accuracy of the sensing system by introducing a large amount of circular birefringence in the sensing fiber.

A chiral photonic crystal fiber sensing coil for decreasing the polarization error in a fiber optic current sensor

The residual linear birefringence inside the sensing coil is one of the main factors causing polarization error and accuracy decline of a fiber optic current sensor. To relieve the residual linear birefringence in fiber optic current sensors, a chiral photonic crystal fiber was utilized as the sensing coil, whose air filling ratio, lattice constant and chiral parameter were designed according to the analysis of the circular polarization degree affected by the diameter variation of the innermost air holes. The simulations demonstrated that there is a better circular-polarization-maintaining performance for the chiral photonic crystal fiber than that for the screwed silicon-based fiber. As the sensing coils, it is by an order of magnitude that the accuracy of current measurement is improved in the fiber optic current sensor.

Concept of control and data acquisition system for modern digital power substation

The article deals with the issue of standardization of approach to definition of modern digital substation is considered. The approaches proposed and partially implemented by equipment manufacturers are described, such as data collection and processing by means of relay protection and automation with the use of proprietary algorithms, wireless and optical current and voltage sensors, etc. The authors propose the use of a unified system for collecting and processing data generated and used in the operation of an electric substation. The structure of the signal transmission system for the main groups of electrical power equipment is described, the requirements for the predictive diagnostics system that allows maintaining the equipment based on its technical condition are described.

Study on the Application of Optical Current Sensor for Lightning Current Measurement of Transmission Line.

Accurate and reliable lightning current data are the basis of lightning protection design. To measure lightning current data at different measurement locations in a transmission system, the limitations of traditional lightning current sensors are analyzed, and optical current sensing technology is adopted, which has the advantages of no magnetic saturation and no bandwidth limitation. Compared with traditional application environments, the sensing technology is used in special environments in transmission systems. This paper analyzes the influence of environmental factors on sensors, and combines the extreme environmental requirements, such as temperature and insulation requirements, to study the sensor. Starting from the sensitivity, the sensing characteristics of the sensor are analyzed. The sensor is designed according to three aspects: sensing material selection, spatial measuring position, and sensing material size optimization, such that it can satisfy the different measurement requirements of towers, overhead ground wires, and transmission lines, respectively. The experiments indicate that the developed sensors can meet the measurement sensitivity requirements of different types of lightning strikes. The experimental results of sensors exhibit a reasonable amplitude measurement accuracy, linearity, and waveform measurement capability. These results provide important theoretical and experimental bases for the application of optical current sensing technology to the measurement of the lightning current of transmission systems.

Features of the characteristics of fiber optic current and voltage sensors

Features of the characteristics of fiber optic current and voltage sensors

A Compact FBG-Based Magnetostrictive Optical Current Sensor With Reduced Mass of Terfenol-D

In this letter, we performed finite element method (FEM) simulations, fabrication, and experimental characterization of two prototypes of fiber-optic current sensors (FOCS) based on fiber Bragg grating (FBG) and Terfenol-D for monitoring current in high-voltage transmission lines. The proposed prototypes were designed in geometrical configurations that allowed a massive reduction of more than 98% in the amount of Terfenol-D employed compared to FBG-based FOCS proposed previously. Using only 5.6 and 2.0 g of Terfenol-D in each prototype, we show that not only the cost of the sensor can be reduced but also greater sensitivity, linearity, and fast response-time to transient events were achieved.

Upgrade of poloidal field coils current measurement system on Experimental Advanced Superconducting Tokamak

Measuring poloidal field (PF) current with a high accuracy is a basic requirement for the operation of a tokamak. A fiber optic current measurement system consisting of 12 fiber optic current sensor (FOCS) was installed on the Experimental Advanced Superconducting Tokamak (EAST) PF busbars in 2018. Before installation, the FOCS sensor heads were calibrated for a temperature range between -5 °C and 55 °C to meet the PF busbars current measurement accuracy requirement (0.4%). To reduce the sensor head magnetic crosstalk, a model has been developed and validated for FOCS sensor heads. When used to sense EAST PF busbar currents during experiments, the FOCS showed excellent performance. Compared with the Rogowski coil, there was no time-dependent drift or magnetic crosstalk in the FOCS output, and the noise of the FOCS was smaller than the Rogowski coil.

A fiber optic current sensor on tunnel boring machine for current measurement application in tunnel geological prediction

A fiber optic current sensor (FOCS) used for current measurement application on tunnel boring machine (TBM) in tunnel geological prediction is proposed in this paper. Compared with the FOCS designed for power gird, the sensor developed in this paper is especially suitable for measuring the current which flows in a large diameter conductor, such as TBM. Aiming at solving the signal fading problem and sensitivity drift induced by the harsh working environment, the proposed FOCS utilizes a technique which is based on rotatable half-wave retarder and alternated current measurement. Verified by mathematical analysis and laboratory test, the rotatable half-wave retarder technique has been proved to be effective in solving the signal fading. The alternated current measurement method has been employed by a TBM which works for a water-diversion tunnel project, and the measurement record of field test suggests that the method reduces the sensitivity drift in long time measurement. Comparing with direct measurement, the coefficient of variance of the measuring result has been reduced significantly.

Optical current sensing mechanism under a non-uniform magnetic field.

The effect of the inhomogeneous magnetic field on the Faraday rotation angle and output light intensity was analyzed using finite element simulation, at different distances between the conductor and the magneto-optical glass. The results show that under an inhomogeneous magnetic field, the magnetic birefringence effect due to the Cotton-Mouton effect decreases the output light intensity of the straight-through optical path. The Faraday rotation angle is non-linearly inversely proportional to the distance. Based on these results, which were verified by the theoretical model, a reasonable geometric arrangement of the sensing component of a straight-through optical current sensor is proposed.

Thermally induced error analysis and suppression of optic fiber delay loop in the different variable rate of temperature

Fiber delay loop is a vital part of some kinds of optical fiber sensing systems such as optical fiber current sensors, optical fiber voltage sensors, and optical fiber gyroscopes. Its environmental temperature adaptability has always been one of the main problems that constrain system performance. The paper took Sagnac fiber current transformer as the research object, then the theoretical model of the relationship between the thermally induced error of the fiber optic current transformer and the temperature variation rate of the fiber delay loop was established. The transient heat transfer performances of optical fiber delay loop were analyzed by using the finite element method. The analysis results show that the thermal error depends on the temperature variation rate, and the influence of the temperature variation rate can be reduced effectively by adopting a heating insulation cavity. The results also show that the ability of temperature inhibition can be controlled flexibly by adjusting the design parameters of the insulation cavity. It has potential application value in some optic fiber sensing systems that need high precision and high working stability under the turbulence of temperatures.

Reliability assessment of an optical current sensor based on accelerated aging tests

The operational reliability directly affects the practical application of optical current transformers (OCTs) in smart substations. As the key component of the OCT, the reliability of the optical current sensor (OCS) largely determines the reliability level of the OCT. This paper proposes a reliability assessment method of the OCS based on accelerated aging tests. The failure modes and failure mechanisms of the OCS are analyzed, and the concept of OCS insertion loss variation is proposed. An allowable range of insertion loss variation is selected as the failure criterion of the OCS. From the viewpoint of the OCS measurement error generated by the quantization error of the analog-to-digital converter, the allowable range of insertion loss variation is obtained. By selecting a high temperature as the accelerated thermal stress, we design the accelerated aging test scheme of the OCS and analyze the sample test data to obtain the activation energy of the OCS insertion loss failure. Based on this activation energy, the median time to failure and instantaneous failure rate curve of the OCS at normal temperature are obtained. The results indicate that the designed OCS has an expected service life of 50 years and a low instantaneous failure rate at normal temperature. This paper provides basic critical reliability analysis data for the system reliability assessment of OCTs.

Low-temperature phyto-synthesis of copper oxide nanosheets: Its catalytic effect and application for colorimetric sensing

The last decade has seen a remarkable detonation in modifying chemical processes for nanomaterial synthesis to make them ‘green’. Owing to the unique properties of nanomaterial and with regard to environmental issues, in this study, a new alternative and fast eco-friendly approach for the synthesis of copper oxide nanosheets (CuO-NSs) using Terminalia catappa (Indian almond) leaf extract as a renewable and non-toxic reducing agent and efficient stabilizer was reported. It is noteworthy to mention that the present fabrication process can open up the possibility of fast, low cost and high efficiency synthesis of CuO nanostructures with an interesting morphology of nanosheets at ambient temperature and pressure. Optimization of important factors such as pH, the quantity of leaf extract, copper precursor concentration, incubation time and temperature on the formation of CuO-NSs were investigated. The formation of bioreduced CuO-NSs was certified by UV–Vis spectroscopy, XRD, TEM analysis and FT-IR spectroscopy. Due to good stability, and excellent catalytic activity of the synthesized CuO-NSs, they are exerted to degrade of MB dye in water as a model color pollutant in the presence of NaBH4 at room temperature. Furthermore, color properties of CuO nanostructures aid us to apply these biosynthesized nanomaterials in the design of optical sensors for detection of Fe2+ and Fe3+ ions. In view of many advantages of the current optical sensors based on CuO-NSs, such as eco-friendly, cost-effective, and straightforward design, the sensing system presents a potential application in environmental science.

Temperature independent polarization-maintaining photonic crystal fiber with regular pentagon air hole distribution

The research of polarization-maintaining photonic crystal fiber with temperature insensitive characteristic is one of the important methods to solve the temperature dependence problem in the engineering application of an optical sensing system. This paper presents a new kind pentagonal polarization-maintaining photonic crystal fiber, and its polarization characteristic under the influence of temperature was analyzed based on the theory of the thermal expansion effect and thermal optic effect. The results show that the temperature dependence of the proposed fiber is significantly lower than that of the hexagonal photonic crystal fiber with the same design parameters at -50℃˜80℃. It has potential application value in some optic fiber sensing systems that need high precision and working stability under the turbulence of temperatures, such as fiber optical voltage sensor, fiber optical current sensor and fiber optic gyroscope.

Fiber-optic current sensor for plasma current on experimental advanced superconducting tokamak

The plasma current is an essential parameter for tokamak operation. Fiber optic current sensors, based on the Faraday Effect, are one of the best choices to measure the plasma current in a steady-state discharge. Such an fiber-optic current sensor (FOCS) was successfully installed on the Experimental Advanced Superconducting Tokamak (EAST). The FOCS is a closed-loop FOCS, based on a polarization-rotated reflection interferometer. The sensing optical fiber is installed inside the EAST vacuum vessel while the signal processing system is kept outside the vacuum vessel. In order to guide the optical fiber out of EAST vacuum vessel, we have developed and assembled a polarization maintaining optical fiber bulkhead connector. When the tokamak device is operating, the variations in the magnetic field will give rise to vibrations and even shocks. We have tested the influence of vibrations and shocks on fiber-optic current sensor. In EAST experiment, the FOCS has achieved the plasma current measurement up to 800 kA. Furthermore, the FOCS has responds to the rapid change in current during the plasma disruption. From the results from a different range of plasma current shots, the fiber-optic current sensor performed very well to sense the plasma current of the EAST.

Assessment of the environmental effects on the ITER FOCS operating in reflective scheme with Faraday mirror

Plasma current measurements will play an important role in ITER to provide real-time plasma control and machine protection. Performance of standard electromagnetic sensors may be not sufficient to fulfill this task due to a combined effect of steady-state operation and the presence of strong nuclear radiation. The Fiber Optics Current Sensor (FOCS) is a back-up system included in the ITER design. Faraday mirror (FM) can be a part of the FOCS, which allows to improve the system performance. It is required that the polarization rotation angle is equal to 90° with acceptable deviations below 0.3°. We have experimentally investigated the effect of thermal perturbations and gamma-radiation on the rotation angle of commercial FMs. The FM rotation thermal sensitivity was found to be in a range 0.105 – 0.124°/°C. Gamma-irradiation resulted in a 1.2° change, saturated after a 12.5 kGy dose. Based on these results we conclude that the cubical area is the preferable location for the FM despite that implies placing additional link fibers to reach the ITER vacuum vessel.

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.