Optical Current Transducer Research Articles

Research on optical fiber current transducer using nv center in diamond

Diamond nitrogen-vacancy (NV) center has been widely employed in experimental magnetic field measurement using continuous wave optical detection magnetic resonance (ODMR), which makes it possible for current sensing. An optical fiber current transducer prototype using an NV center is built for electric power application. The DC measurement with an error of less than 4% within 500 A is realized, in which the error of 50 A to 450 A is better than 2%, and the low-frequency AC measurement is preliminarily realized. In this essay, the accuracy of low current measurement is primarily affected by system noise, while the accuracy of heavy current is mainly affected by the width of the ODMR resonance peak. Optimizing the optical path as well as sensing structure meanwhile updating the demodulation algorithm of the measured data is the following work to improve the measurement accuracy.

Lightning Current Measurement Form and Arrangement Scheme of Transmission Line Based on Point-Type Optical Current Transducer.

Lightning strikes are the main cause of transmission line faults, and the accurate lightning current number is an important basis to guide scientific lightning protection. The use of sensors with excellent sensing performance to carry out lightning current monitoring on transmission lines is beneficial to the accumulation of key parameters of original lightning strikes, so it is necessary to study the lightning current measurement structure of transmission lines. In this paper, an optical current-sensing unit is used to monitor the lightning current on transmission lines. A measuring structure that can monitor key parameters of the lightning current under different types of lightning strikes is proposed. First, establish the lightning current return channel model and the equivalent model of the tower, study the influence of the transmission tower on the current in the lightning channel, and analyze the direct measurement position of the lightning current on the tower; establish the multi-wave impedance model of the tower, and build a multi-base tower. The simulation model of the transmission system analyzes the transmission characteristics of the lightning current on the transmission line and the lightning protection line in the case of different types of faults; from the perspective of the measurement of key parameters of the lightning current, the lightning current measurement structure of the transmission system is constructed to analyze different lightning strikes. The measurement effect of each monitoring position in the case of a lightning strike and the waveform characteristics of the fault current in the case of insulator flashover are analyzed.

Anti-crosstalk magnetic field method for straight-light path type optical current transducer based on the background of gas-insulated substation

Anti-crosstalk magnetic field method for straight-light path type optical current transducer based on the background of gas-insulated substation

Random Interference Signal Decomposition and the Normalized Filtering Method of an Optical Fiber Current Transducer

Focusing on the problem of characteristic decomposition and filtering of random interference information measured by an optical fiber current transducer (OFCT), a signal filtering algorithm by combing complete ensemble empirical mode decomposition (CEEMD) with normalized autocorrelation function, is proposed. The CEEMD feature decomposition model of the OFCT signal is established and multiple eigenmode functions of the measured signal are extracted. The normalized autocorrelation function models of different types of intrinsic mode function (IMF) are established. By extracting the characteristics of the autocorrelation function, high-weight IMFs are selected. After the mean filtering process is performed on other IMFs, the signal reconstruction is performed together with the effective modal components. With the premise of signal statistical learning and structural risk minimization principles, a support vector regression model is established to classify the data by linear fitting. The more reliable current information after filtered is obtained. Experiment results demonstrate that the proposed signal filtering algorithm by combining the advantages of CEEMD and normalized autocorrelation function decomposes the signal according to the time-scale characteristics of OFCT data itself, without pre-setting any basis functions. The root mean square error of optimized data is reduced by 39.3%, and the signal quality is greatly improved.

Accurate optical fiber current transducer for high-voltage direct current (HVDC) transmission

Accurate optical fiber current transducer based on the Faraday magneto-optical effect is described for high voltage direct current (HVDC) transmission. The transducer may be used to measure DC and high-order harmonic currents in a ± 800 kV DC transmission field. The performance characteristics of sensitivity, non-linearity, temperature stability, and harmonic accuracy of the prototype were investigated. The results show that the scale factor error in the −40 °C to 70 °C range is below ±0.2%. The presented optical fiber current transducer has potential applications for HVDC detection fields, such as for a polarity bus and a converter valve bridge arm.

Digital Optical CT Application to HVDC Earthing Line Fault Measurements

A digital optical current transducer designed for the measurement of small alternating currents is applied to current measurements for an HVDC earthing line. A novel scanning band pass filter was used to make experimental measurements of small high frequency currents. Currents from 1 kHz to 5 kHz and 0.2 A to 2 A in the presence of 20 A <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> have been experimentally made. With accuracies of less than 0.4% for the 2 A measurement. The optical current transducers can measure currents remotely up to 20 km from the converter station. This new optical current sensor measurement method can allow the location of faults on HVDC earthing lines.

A Linear Optical Current Transducer Implemented With a Strip Aluminum Polarization Grating

There are some significant defects in the existing optical current transducers (OCTs), such as optical power dependence, non-linear demodulation with Malus law, linear birefringence, etc. These defects severely hurt the reliability, stability, and accuracy of OCTs in long-term applications. The main idea to become free of these defects is to have a linear sense of the Faraday rotation angle. To this end, the paper presents a linear OCT based on a strip aluminum polarization grating, which directly converts the Faraday rotation angle into a synchronous line movement of a light spot. It then positions the spot to measure the current. It has no optical power dependence, realizes a linear sense of the Faraday rotation angle, reduces the effect of temperature drift, almost eliminates linear birefringence, improves long-term stability, and achieves a 0.2S class accuracy.

A Grating to Transfer Polarization Rotation to Straight Line Movement - Designs and Applications

This paper presents a grating be used to transfer a polarization rotation to a straight moving facula, so the rotation can be detected by locating the facula displacement with a line array image sensor. It can be used to build a new type of polarimeter with no mechanical rotating device, or an optical current or voltage transducer applied for electrical power systems with no rotary translation converter. The grating is a subwavelength radial polarization one, which is made of aluminum and fabricated by nano-electron beam direct write lithography. It consists of 12,000 units arranged in a line array, and each unit has a $1~\mu \text{m}$ width and a $30^\prime $ angle difference from adjacent ones. Its polarization and temperature characteristics are simulated and experimented. The TM wave transmittance is greater than 78%, and the extinction ratio is better than 27dB.

Measurement of inrush current in transformer based on optical current transducer

The accurate measurement of inrush current is a key problem in transformer protection. Traditional electromagnetic current transformer (CT) has nonlinear characteristics of its core. When the transformer generates inrush current, it will be saturated and lead to current distortion, which will lead to transformer differential protection misoperation. Optical current transducer (OCT) is not affected by saturation and can be used to measure and identify inrush current well. This paper analyses the mechanism of inrush current, the reason of CT saturation and the principle of OCT measurement. The simulation and experimental results show that OCT has better measurement quality than traditional CT and superiority to differential protection.

A Linear Optical Current Transducer Based on Newton’s Ring Sub-Wavelength Grating

This paper presents a novel optical current transducer based on Newton’s ring sub-wavelength grating. It converts the Faraday rotation angle into synchronized rotation of the spot image and locates the spot with a four-quadrant detector to achieve real-time linear measurement of the current. The Newton’s ring grating is used instead of a radial grating as a polarization detection device so the extinction ratio is distributed uniformly in the radial directions and the polarization characteristics have no change with the radial direction, thereby a higher measurement accuracy has been achieved. The angle measurement range can reach ±40 degrees which breaks through the limitations of the intensity demodulation mode. The performance of the transducer has been verified by experiments and a 0.2 S class accuracy achieved with a linear measurement, no interference of optical power fluctuation, and minimized the effect of birefringence.

Identification and Filtering of Random Error in Fiber Optic Current Transducer

With the advantages of excellent insulation performance, wide dynamic measurement range, good frequency response characteristics and high sensitivity, fiber optic current transducer (FOCT) has become the mainstream of current measurement technology. The structure of fiber-optic current transformer is complex, and random error becomes one of the major problems that affect the application of fiber-optic current transformers in power engineering. It is urgent to study the random error characteristics of fiber current transformers and propose effective measures to suppress random errors. The characteristics of random error in FOCT are analyzed, and time series model is established by preprocessing and statistical inspection of FOCT output data. Based on the random error characteristics of the FOCT output signal, it makes prerequisite preparation for the signal filtering optimization modelling and the construction of the state function equation. With the derived random error state function of FOCT, the Wavelet filtering algorithm combining with Kalman filtering algorithm is proposed, then, the time domain and frequency domain local area transforms are used to detect the random error characteristics and identify various types of random error information accurately. Real-time multi-scale decomposition and optimal estimation of random error in FOCT are realized. Experimental results demonstrate that the time series modelling and Wavelet filtering algorithm can accurately identify the random error characteristics of the FOCT and automatically match the parameter filtering to improve current measurement accuracy.

A Linear Optical Current Transducer Based on Crystal Wedge Imaging Detection

This paper proposes a linear optical current transducer based on a crystal wedge imaging detection. It converts the Faraday magneto-optical rotation to the horizontal displacement of the light and dark interference fringes by using the crystal wedge, and then uses a dual-quadrant detector to locate the fringes to achieve a real-time measurement of current. Compared with the usual light intensity detection method it has the outstanding advantages of no optical power dependency, very low temperature drift, and simple algorithm and linear measurement. In addition, a magneto-optical film is employed to replace the magneto-optical crystal to cut down the optical path and the linear birefringence. The dual-quadrant detector is employed to achieve low cost, high resolution, and high precision. The experimental results show that the transducer meets the accuracy class 0.2 S.

Open-Core Optical Current Transducer:Modeling and Experiment

Optical current transducers (OCTs) have clear advantages over conventional current transformers. To better understand the OCT performance, a basic OCT model is developed using finite-element analysis. To model an open-core OCT, the Faraday rotation and detection is implemented in the COMSOL Multiphysics. This paper introduces two experimental setups, which can be used for studying OCT performances under ac and dc excitations. The measured data agree with simulation results and validate the proposed model. The presented model can be developed to study different nonideal effects, in order to identify and mitigate noise sources in OCTs.

Real-time modeling and online filtering of the stochastic error in a fiber optic current transducer

The stochastic error characteristics of a fiber optic current transducer (FOCT) influence the relay protection, electric-energy metering, and other devices in the spacer layer. Real-time modeling and online filtering of the FOCT’s stochastic error tends to be an effective method for improving the measurement accuracy of the FOCT. This paper first pretreats and inspects the FOCT data, statistically. Then, the model order is set by the AIC principle to establish an ARMA (2,1) model and model’s applicability is tested. Finally, a Kalman filter is adopted to reduce the noise in the FOCT data. The results of the experiment and the simulation demonstrate that there is a notable decrease in the stochastic error after time series modeling and Kalman filtering. Besides, the mean-variance is decreased by two orders. All the stochastic error coefficients are decreased by the total variance method; the BI is decreased by 41.4%, the RRW is decreased by 67.5%, and the RR is decreased by 53.4%. Consequently, the method can reduce the stochastic error and improve the measurement accuracy of the FOCT, effectively.

Properties and structure of Faraday rotating glasses for magneto optical current transducer

High heavy metal oxides (60–100mol.%) ternary PbO–Bi2O3–B2O3 (PBB) glasses were fabricated and characterized. Using a homemade single lightway DC magnetic setup, Verdet constants of PBB glasses were measured to be 0.0923–0.1664min/Gcm at 633nm wavelengths. Glasses with substitution of PbO by Bi2O3 were studied in terms of their Faraday effects. PbO–Bi2O3–B2O3=50–40–10mol.% exhibited good thermal stability, high Verdet constant (0.1503min/Gcm) and good figure of merit (0.071). Based on this glass, a magneto optical current sensor prototype was constructed and its sensitivity at different currents was evaluated to be 8.31nW/A.

Statistical modeling of fiber optic current transducer

Abstract Fiber optic current transducer (FOCT) is a new type of current measurement instrument with high accuracy, large dynamic range, wide frequency range and excellent insulating property. Thus, it has been highly concerned for using in high voltage grid. Although these FOCTs have such crucial advantages, the stochastic errors, mainly including random walk, bias instability, quantization noise, may suddenly degrade the system performance in a short period of time. To evaluate the stochastic error characteristics of fiber optic current transducer (FOCT), traditional solution adopts Allan variance method to plot the curve on the log–log scale. Considering the deficiency of severe shock in Allan variance, total variance methodology is proposed to analyze the stochastic error characteristics of FOCT with the aim of overcoming the deficiency. Total variance method transforms time-offset data to frequency-offset data and extends the data to be a virtual sequence nearly as three times long as the initial data by mapping. Additionally, the least square fitting (LSF) is applied to identify and obtain each coefficient of FOCT stochastic error, which helps to evaluate the stochastic error characteristics of FOCT excellently. Simulation results demonstrate that both Allan variance result and total variance result are nearly equivalent, when correlation time is short. However, when correlation time exceeds half total duration of the measurement, Allan variance estimation values tend to shock increasingly severely and total variance curve always extends steadily. Besides, every stochastic error coefficient is decreased effectively by total variance method, comparing with Allan variance method. Total variance methodology overcomes the deficiency of severe shock in Allan variance successfully, and then optimizes evaluation method of FOCT stochastic error characteristics.

Characteristics of rare-earth-doped glass in optical current transducers

By establishing an optical path model of an optical current transducer, the length effects of the rare-earth-doped glass which as the magneto optical sensing material on the measurement output of the optical current transducer were obtained. These effects were presented in terms of linear birefringence and the response sensitivity of rare-earth-doped glass to the magnetic fields. A size factor model of the rare-earth-doped glass was also built to study the length characteristics of rare-earth-doped glass in optical current transducers. An experimental study on the length characteristics of rare-earth-doped glass was then conducted. It can be observed that the glass has a larger response to the current excitation as the length of the rare-earth-doped glass increases.

Effect of temperature on characteristics of rare earth-doped magneto-optical glass in optical current transducer application

First, a theoretical analysis was performed on the effect of temperature and on the performance of the sensing element of rare earth-doped magneto-optical glass material that can be used in an optical current transducer application. The effect comprises two aspects: the linear birefringence and the Verdet constant. On this basis, rare earth-doped glass temperature characteristics were studied, and the experimental results indicated that the linear birefringence of rare earth-doped glass increased with increasing temperature, while its magneto-optical sensitivity decreased. Comparative experiments performed for various concentrations of rare-earth dopant in the glass revealed that changes in the dopant concentration had no significant effect on the performance of magneto-optical glass.

Structural and properties of heavy metal oxide Faraday glass for optical current transducer

The influences of PbO, Bi2O3 and GeO2 contents on mechanical, thermal, magneto-optical and structural properties of PbO–Bi2O3–GeO2–B2O3 glass system were investigated. A magneto-optical current transducer MOCT prototype with sensitivity of 7.56nW/A was constructed based on selected glass with good properties.

Optical Current Transducers and Error Sources in Them: A Review

Optical current transducers are developed vastly in recent decades. For an accurate transducer achievement, different factors should be considered. This paper reviews the most important sources of errors in these devices. First, the main types of transducers are introduced. Afterward, the effects of temperature and vibration on their operational performance are discussed. Then, the birefringence is addressed which is the main error source in the transducers. In each part, the proposed solutions in the papers are reviewed. Finally, the effect of nonideal optical parts on the measurement accuracy is discussed. This paper serves as a brief introduction to common errors in optical current transducers.