脉冲大电流校准及溯源技术研究

为解决1~100kA的脉冲大电流校准问题,建立了脉冲大电流校准系统,开展了脉冲大电流校准及溯源技术研究。校准系统由脉冲大电流发生装置、脉冲分流器组、光纤电流传感器、罗氏线圈电流传感器、宽带数据采集系统及测量软件组成;通过该校准系统,可开展脉冲幅度为1~100kA,持续时间为20μs~100ms的脉冲大电流发生/测量系统的校准,开展罗氏线圈传感器、光纤电流传感器等测量器具的校准,校准不确定度优于1%。     

变压器工频短路电流测量技术研究

针对变压器工频短路电流测量需求,研究了外积分式罗氏线圈技术和光纤电流传感技术。建立了2种传感器的低频数学模型,基于MATLAB/Simulink仿真计算传感器对工频短路电流的响应特性,结果表明:罗氏线圈对工频短路电流的测量精度受其下截止频率影响,下截止频率越低,测量精度越高;光纤电流传感器理论上可以精确复现工频短路电流。采用多种电流传感器进行变压器工频短路电流现场对比测试,结果表明:电流比较仪、光纤电流传感器及下截止频率为0.02Hz的罗氏线圈测得的电流波形吻合较好,而下截止频率为0.2Hz的罗氏线圈测量结果出现了明显的偏移,且无法归零,与仿真分析结论基本一致。对于外积分式罗氏线圈,为保证高精度测量,建议下截止频率应低于0.1Hz;光纤电流传感器具有极好的直流及低频响应特性,是工频短路电流高精度测量的理想方案。     

High sensitivity optical fiber current sensor based on polarization diversity and a Faraday rotation mirror cavity

A novel high sensitivity optical fiber current sensor (OFCS) based on polarization diversity and a Faraday rotation mirror cavity is proposed and demonstrated. Comparing with single-channel detection in a conventional OFCS, a signal power gain of 6?dB and a signal-to-noise ratio improvement of over 30?dB have been achieved in the new scheme. The cavity amplifies magnetic field-induced nonreciprocal phase modulation, while the Faraday rotation mirrors suppress the reciprocal birefringence. A linear response is obtained for current amplitude as low as several mA at an AC frequency of 1?kHz.     

Rogowski Sensor for Plasma Current Measurement in J-TEXT

Rogowski coil is very useful in transient current measurement. Rogowski sensor consisting of Rogowski coil and integrator is one of the most important diagnostic instrumentations in Tokamak. In recent years, new structures of Rogowski coil based on printed circuit board (PCB) are developed to replace traditional handmade Rogowski coil for more excellent accuracy, better temperature stability, more accordant mutual-inductance, more symmetrical windings, and other advantages. However, the existing structures of Rogowski coil based on PCB are useless in Tokamak because the required Rogowski coil installed on the vacuum vessel should have long diameter and little space. This presentation provides a new twin-loops Rogowski coil (TRC) consisting of several PCB strips. TRC has all the advantages of existing PCB Rogowski coils and can meet the limited space requirement in Tokamak at the same time. A special experiment is carried out to prove that the mutual-inductance of TRC is immune to the variation of center position of plasma current. Moreover, a differential long-term integrator is designed to cooperate with the TRC. Two switches are used in the integrator to release the remaining electric charges on integrating capacitors once the measurement is over. Then, the error accumulation of integrator is canceled in repetitious measurements. The designed new Rogowski sensor can be used to measure long pulse current below 1 s.      

宽带脉冲大电流测量及大数据分析技术

多磁路调压变压器的脉冲电流具有频带宽、幅度大的特点,其测量与大数据分析易受到噪声等影响。本文研究了多磁路调压变压器宽带脉冲大电流测量与大数据分析技术,设计了基于法拉第磁光效应和光纤电流传感器的宽带脉冲大电流测量系统方案,采用卷积神经网络对测量得到的海量数据进行处理,消除测量过程中干扰对测量结果的影响。通过与罗氏线圈的测量结果比对,本文研究的方法测量结果的脉冲波形一致性好、脉冲峰值检测准确度较高,脉冲幅值误差符合测试要求。     

Call for Papers

Abstract

A high-bandwidth optical fibre current sensor has been developed at Salford to monitor the waveform of the driving current pulse feeding into a discharge-pumped excimer laser. The sensor is a conventional intrinsic Faraday effect device but overcomes the normal bandwidth-sensitivity limits because the very large electrical current pulse used to drive the excimer laser allows detectable polarization rotation over a 60 cm length of fibre. The performance of the intrinsic sensor is compared with that of a current-viewing resistor, and of a Be₁₂GeO₂₀ crystal sensor.     

Development of a portable fiber-optic current sensor for power systems monitoring

The paper presents a portable fiber-optic current sensor (FOCS), based on the Faraday effect, with a magnetic concentrator. Both the optical sensing head and electronic processing block are illustrated. A detailed experimental study to confirm the performance of the device is also reported. According to the measured values of ac rms current up to 1 kA, a calibration procedure was performed. The paper provides an analysis of the results obtained for various conductor displacements within the concentrator. The well-known temperature dependence of the Faraday current sensor and its influence on the measurement accuracy are tested by means of a special double-layer thermal insulated chamber. The calibrated and characterized FOCS is applied for harmonic analysis of the current. The results clearly illustrate the nature of the sensing process and demonstrate odd-order harmonics presence, as predicted by the mathematical model. The paper indicates that the developed device is suitable for the power systems monitoring.     

Faraday compensator of reciprocal optical anisotropy utilizing a polarization ring interferometer

It is shown that a polarization ring interferometer containing a Faraday cell can be used to compensate the reciprocal anisotropy in round-trip optical circuits. It is established theoretically and experimentally that, unlike the case of conventional Faraday mirrors, the quality of the restoration of the polarization in a compensator based on a polarization ring interferometer is practically independent of the Faraday rotation angle. A deviation of the Faraday rotation angle from 45° leads only to an additional power loss. The novel compensators can be used in fiber-optic circuits with a wideband light source or with several sources having different wavelengths. Pis’ma Zh. Tekh. Fiz. 25, 57–63 (May 26, 1999)     

Self-Integrating Rogowski Coil for High-Impulse Current Measurement

This paper presents the operating principle, the performance under impulse condition, and the design of a self-integrating Rogowski coil for measuring high-impulse currents. Oscillatory and overdamped unidirectional impulse currents are generated up to 10 kA and measured by different methods, namely, two commercial impulse current transformers, a resistive shunt, and the newly designed self-integrating Rogowski coil. For the resistive method, the voltage drop across the shunt affects the total voltage measured across the test object and causes distortion in the case of simultaneous measurement by an impulse current transformer having a small aperture. The Rogowski coil theory under impulse current conditions is presented. The concept of transmission lines is used, and the line parameters are optimized to achieve a self-integrating mode and avoid spurious effects of reflections and stray capacitances. The output voltage linearity of the designed self-integrating Rogowski coil is checked using different linear and nonlinear loads and coil termination resistances. It is found that at a termination resistance of 1 $Omega$, satisfactory impulse current waveforms are measured by taking the commercial impulse current transformer as a reference signal. Results reveal that the measurement errors for the current peak and front and tail times are $pm$2%, $leq$6%, and $leq$ 12%, respectively. Overdamped impulse currents are generated by different generator capacitances, where comparisons between the measured and calculated current waveform parameters have shown good agreement.      

Permanent magnets for Faraday rotators inspired by the design of the magic sphere

Faraday polarization rotators are commonly used in laser experiments. Most Faraday materials have a nonnegligible absorption, which is a limiting factor for high power laser optical isolators or for intracavity optical diodes. By using a stronger magnetic field and a shorter length of Faraday material, one can obtain the same polarization rotation and a reduced absorption. In this paper, we describe two permanent magnet arrangements that are easy to build and produce magnetic fields up to 1.7 T, substantially more than commonly used. The field homogeneity is largely sufficient for a 30 dB isolation ratio. We finally discuss the prospects for producing even larger fields with permanent magnets.     

Magneto-optic microscope for visually detecting subsurface defects

A visual test method for detecting microdefects under fine surfaces is described. A new MO microscope that has a laser source, a CCD camera, and an exciting coil is developed for this work. A pulse generator supplies an intermittent square pulse to the exciting coil, which can intensify eddy currents yet reduce the working temperature of the exciting coil and sample. The magnetic field variation produced by the imbedded defect causes a rotation of the polarization plane of the reflected beam. Therefore the reflected beam carries an image of the defect, which is received by a CCD camera. The optical arrangement guarantees that no light is reflected back to the laser. The system was tested with a calibrator, which has an artificial subsurface defect; such a test attains a visual detected image. To our knowledge this is the first time an image of a subsurface defect has been distinctly detected with a MO sensor system.     

Mutual Inductance of a Precise Rogowski Coil in Dependence of the Position of Primary Conductor

The Rogowski coil is a well-known current-to-voltage transducer. To use it for the high-accuracy measurement of ac current (at power supply frequency), all influencing quantities and their contribution should be recognized and analyzed. Thus, the partial influence due to the deviation from the central position of the primary conductor for a real sensor, with the nonhomogeneous density of secondary turns, is given in this paper. The measured deviation of mutual inductance in this case showed very good agreement with the theoretical prediction, which is promising for the expected application of such a sensor.      

Stray magnetic-field response of linear birefringent optical current sensors

It is well known that the line integral, describing Faraday rotation in an optical medium, reduces to zero at low frequencies for a closed path that does not encircle a current source. If the closed optical path possesses linear birefringence in addition to Faraday rotation, the cumulative effects on the state of polarization result in a response to externally located current-carrying conductors. This effect can induce a measurable error of the order of 0.3% during certain steady-state operating conditions.     

A novel electro-optic hybrid current measurement instrument forhigh-voltage power lines

Details of an electro-optic, hybrid current-sensing instrument, and its application to high-voltage power line current measurement, are presented. The current is first detected via a Rogowski coil, followed by conversion of the detected current into a frequency-modulated optical pulse signal in the high-voltage area. Subsequently, the optical pulse signal is transmitted to the ground through an optical fiber cable. Finally, the measured current is recovered from the optical pulse signal by a ground-located signal-processing module. Compared with conventional current transformers, widely used for high-voltage line current measurement, this instrument provides a significant reduction in size, weight, and cost, together with features of convenient installation, secure operation, and high accuracy. Furthermore, it can be configured to be compatible with conventional secondary meters widely used in today's power plants and substations. In 1996, a prototype of this instrument was demonstrated online at a power substation and has shown good accuracy, stability, and safety for more than two years     

Magnetooptic spectroscopy of EuS, EuSe, and EuTe

The absorption Coefficient and the interband Faraday rotation of EuS, EuSe, and EuTe thin films have been measured as a function of the photon energy (1-6 eV), the temperature (2.7-300 K), and the applied magnetic field (0.1-11.5 kOe). From the Faraday rotation (FR) we compute the circular magnetic dichroism and from both and the optical constantsnandkwe derive the imaginary part of the off-diagonal elements of the complex conductivity tensor Im σxy. Integral values of the latter depend on the spin polarization of electronic states and permit a distinction between pd and fd transitions.     

Magneto-optical current sensor by domain wall motion inorthoferrites

A brief review of the latest developments on optical current measurements based on the Faraday effect is presented. In all existing magneto-optical current transformers, the main measured parameter is the polarization state of the light transmitted by a sensor element. A new transformer is described by means of new results concerning the domain wall excitation. The measured parameter is the geometrical position of the boundary between domains with opposite magnetizations. In a wide frequency band, including DC currents, the measurement results are a linear function of the measured current. They are not affected by temperature changes and mechanical factors     

A fiber-optic current sensor based on a differentiating Sagnacinterferometer

A fiber-optic current sensor (FOGS) based on a differentiating Sagnac interferometer (DSI) is demonstrated to measure high-voltage ac current in electric power systems from 5 A to 3200 A. A transducer consisting of Rogowski coil and piezoelectric cylinder (PZT) is used as the phase modulator, which is placed in the high-voltage side. The DSI is placed in the ground side. A simple analytical expression for the sensor has been derived, and the input-output performance and the temperature dependence of FOGS have been experimentally investigated. The simple sensor geometry gives high accuracy and sensitivity, wide dynamic range, and immunity from slow-variance temperature and other environmental fluctuations     

Simultaneous measurement of current and voltage by use of one bismuth germanate crystal

An optical fiber sensor is presented that allows current and voltage to be measured simultaneously by use of only one block of bismuth germanate crystal. The polarized light from the sensing crystal is split into two light beams: One beam is utilized for current measurement based on the Faraday effect, and the other one is utilized for voltage measurement based on the Pockels effect. Compared with the existing optical sensors that can measure current and voltage simultaneously, this sensor is simple and inexpensive and allows measurement of electric power. The simultaneous measurements of ac electric current from 0.05 to 10 A, voltage from 1 to 235 V, and power from 2 to 1000 W have been achieved with good linear-response characteristics. The input characteristics and measurement uncertainties that are due to the nonlinear error of the sensing system are also discussed.     

Demonstration of a folded Sagnac sensor array immune to polarization-induced signal fading

We demonstrate a new folded Sagnac sensor array design that combines a Faraday rotator mirror and a polarization beam splitter to eliminate the optical noise pulses otherwise generated in a folded Sagnac sensor array. A depolarization scheme compatible with this configuration is also proposed and demonstrated experimentally. It is shown that this new configuration passively eliminates polarization-induced signal fading on every sensor in the array. The minimum detectable phase was measured to be approximately 1.1 microrad/square root of Hz, in agreement with theory.     

Off-diagonal impedance in amorphous wires and its application to linear magnetic sensors

We investigated the magnetic-field behavior of the off-diagonal impedance in Co-based amorphous wires under sinusoidal (50 MHz) and pulsed (5 ns rise time) current excitations. For comparison, we measured the field characteristics of the diagonal impedance as well. In general, when an alternating current is applied to a magnetic wire, the voltage signal is generated not only across the wire but also in a pickup coil wound on it. These voltages are related to the diagonal and off-diagonal impedances, respectively. We demonstrate that these impedances have a different behavior as functions of axial magnetic field: the diagonal impedance is symmetrical, whereas the off-diagonal one is antisymmetrical with a near-linear portion within a certain field interval. For the off-diagonal response, the dc bias current is necessary to eliminate circular domains. In the case of the sinusoidal excitation without a dc bias current, the off-diagonal response is very small and irregular. In contrast, the pulsed excitation, combining both high- and low-frequency harmonics, produces the off-diagonal voltage response without additional biasing. This behavior is ideal for a practical sensor circuit design. We discuss the principles of operation of a linear magnetic sensor based on a complementary metal-oxide-semiconductor transistor circuit.