Fiber Optic Current Sensor Research Articles

Use of Spun optical fibres in current sensors

The polarisation properties of a Spun optical fibre are studied in connection with their applications in fibreoptic current sensors based on the Faraday effect. A model of this fibre is proposed which represents it as an anisotropic medium with the spiral structure of the fast and slow birefringence axes. A sensor is developed based on an all-fibre low-coherence linear interferometer with a threshold sensitivity of 70 mA Hz-1/2, a maximum measured current of 3000 A, and a scale-factor reproducibility of ±0.6%. It is found that for a given diameter of the fibre contour, the normalised sensitivity is independent of the fibre length. The experimental results confirm the theory.

US Navy places major order for fibre optic current sensors

US Navy places major order for fibre optic current sensors

Optical Fiber Current Sensors for Electric Power Facilities

This paper describes development of optical fiber current sensors along with some of their applications. Optical fiber current sensors based on the Faraday effect have long been expected to replace conventional current transformers as compact and high performance current sensors. Yet because they require complex means for achieving stable characteristics, this type of sensor has never come into widespread practical use. To solve these problems we developed a special sensor fiber made from flint glass and created sensor systems whose sensing method ideally matches the characteristics of the fiber. These sensors we developed are immune to environmental effects such as vibration and temperature changes. They are also compact and flexible, and attach easily around conductors. This paper also introduces some typical applications of these sensors including cable current measurement using a portable type sensor, a fault section locating system for power transmission lines using these sensors, and sensor applications to protective relay systems as verified in field tests.

Sagnac interferometer-type fibre-optic current sensor using single-mode fibre down leads

A Sagnac interferometer-type fibre-optic current sensor using single-mode fibre down leads was proposed. To prevent non-reciprocal phase error, depolarizers are used in the Sagnac coil. This configuration makes the current sensor less costly and more accurate. We fabricated the current sensor for an electric power substation by using the proposed technique and confirmed its characteristics. The dynamic range of 80 dB and ratio error within ±0.5% were satisfied. These results have demonstrated that the Sagnac interferometer-type current sensor using single-mode fibre down leads is suitable as an instrument for electric power plants.

Hybrid Fiber-Optic Current Sensor Using Two Faraday Glass-Slab Magnetic Field Sensors

A novel hybrid fiber-optic current sensor using two Faraday glass slab (FGS) magnetic field sensors is presented. Using the geometry that a current-carrying wire is placed in between two FGS sensors, we are able to construct a very reliable, easy-to-use, remote sensor for measuring the electrical current in the wire. Common mode interferences caused by the other currents are minimized by differentially processing magnetooptic signals.

A simple fiber-optic current sensor using a long-period fiber grating inscribed on a polarization-maintaining fiber as a sensor demodulator

We propose a simple fiber-optic current sensor based on the Faraday rotation effect, which firstly utilizes a fiber-compatible polarization analyzer as a sensor demodulator. The fiber polarization analyzer (demodulator) was fabricated by inscribing a long-period fiber grating on a polarization-maintaining fiber. The manufactured fiber polarization analyzer has the polarization extinction ratio of more than 25 dB at the fixed wavelength of 1522.5 nm. Current sensing up to 600 A rms was demonstrated in a simple and cost-effective way, showing a good linearity.

비틀린 광섬유 센서코일을 이용한 편광분석형 광섬유 전류센서

보호계전 시스템의 전류센서로 사용할 목적으로 편광분석형 광섬유 전류센서를 개발하였다. 광섬유의 선형복굴절에 의한 출력의 왜곡을 최소화하기 위하여 단일모드 광섬유를 미터 당 20회 이상 비틀고 그 끝단에 FRM(Faraday rotator mirror)을 부착하여 센서코일을 제작하였다. 광섬유 센서코일의 비틀림 정도를 달리하며 다양한 환경에서의 전류측정 실험을 행하였다. 실험결과로부터 광섬유 센서코일이 진동 등의 환경적 노이즈를 효율적으로 차단함을 알 수 있었으며 ±3% 이내의 시스템 출력안정도를 얻었다.

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 반사경을 이용한 광섬유형 전류센서의 안정화

편광분석법을 이용한 광섬유형 전류센서를 구성하여 다양한 전류측정 실험을 행하였다. 잔존 선형복굴절의 영향을 최소화하기 위하여 광섬유 센서 코일의 한쪽 끝에 Faraday 미러를 장착하였으며 일반적인 미러를 사용하는 경우와 출력의 안정성을 비교분석 하였다. 센서코일에 변형을 가하는 경우나 장시간에 걸친 안정성 실험에서도 Faraday 미러를 사용하는 경우에 출력의 안정성이 현저하게 증가함을 알 수 있었다.

Faraday plasma current sensor with compensation for reciprocal birefringence induced by mechanical perturbations

A Faraday fiber-optic current sensor was employed to measure the tokamak plasma current. In order to decrease the influence of mechanical perturbations on the sensor sensitivity, a two-pass optical scheme with a variable Faraday mirror at the fiber end is proposed. A decrease, by two orders of magnitude, in the influence of the linear birefringence produced by an external piezoceramic fiber modulator was experimentally observed.

Review of the present status of optical fiber sensors

The current status of optical fiber sensors is reviewed. The optical fiber sensors have certain advantages that include immunity to electromagnetic interference, lightweight, small size, high sensitivity, large bandwidth, and ease in implementing multiplexed or distributed sensors. Strain, temperature and pressure are the most widely studied measurands and the fiber grating sensor represents the most widely studied technology for optical fiber sensors. Fiber-optic gyroscopes and fiber-optic current sensors are good examples of rather mature and commercialized optical fiber sensor technologies. In this paper, among the various fiber-optic sensor technologies, especially, technologies such as fiber grating sensors, fiber-optic gyroscopes, and fiber-optic current sensors are discussed with emphasis on the principles and current status. Today, some success has been found in the commercialization of optical fiber sensors. However, in various fields they still suffer from competition with other mature sensor technologies. However, new ideas are being continuously developed and tested not only for the traditional measurands but also for new applications.

A fiber-optic current sensor with frequency-codified output for high-voltage systems

The authors present a frequency-output fiber-optic current sensor for high-power systems. The sensor exploits the magnetostriction of the ferromagnetic core of a standard current transformer, which is interrogated by a length of single-mode fiber coiled onto it and a Mach-Zehnder interferometer. The deformation of the core due to the magnetic field generated by the current produces a frequency-modulated output signal. The current is obtained from the frequency features of the optical signal, and so the sensor avoids certain shortcomings of other fiber optic current sensors such as light power fluctuations, phase drift, and polarization sensitivity.

Temperature and vibration insensitive fiber-optic current sensor

A robust interferometric fiber-optic current sensor with inherent temperature compensation of the Faraday effect is presented. Sensor configurations based on Sagnac and polarization-rotated reflection interferometers are considered. The sensing fiber is residing and thermally annealed in a coiled capillary of fused silica. The capillary is embedded in silicone within a ring-shaped housing. It is theoretically and experimentally shown that the temperature dependence of the birefringent fiber-optic phase retarders of the interferometers can be employed to balance the temperature dependence of the Faraday effect (0.7/spl times/10/sup -4///spl deg/C). Insensitivity of the sensor to temperature within 0.2% is demonstrated between -35/spl deg/C and 85/spl deg/C. The influence of the phase retarders on the linearity of the sensor is also addressed. Furthermore, the sensitivity to vibration of the two configurations at frequencies up to 500 Hz and accelerations up to 10 g is compared. High immunity of the reflective sensor to mechanical perturbations is verified.

A fiber-optic current sensor based on a differentiating Sagnac interferometer

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.

Magneto-optic properties and sensing performance of garnet YbBi:YIG

A co-doped Bi-substituted rare-earth iron garnet single crystal YbBi:YIG was grown from high temperature solution, and was used first time for magneto-optic optical fiber current sensors. The crystal has the specific Faraday rotation angle −404° cm −1, magneto-optic figure of merit 25.8° dB −1, saturation magnetic field 1400 Oe, and temperature coefficient 4.2×10 −4 K −1 (at room temperature, λ=1.55 μm). It has larger Faraday rotation angle and magneto-optic figure of merit and lower temperature sensibility than pure YIG. A laboratory prototype sensor was established using the YbBi:YIG crystal as Faraday rotator element, and its sensing performance was tested under a 50 Hz factory frequency current. The tested results showed that the sensor system had high accuracy, sensitivity and good linearity.

Vibration insensitive optical fiber current sensor with a modified reciprocal reflection interferometer

A modified reciprocal reflection interferometer (MRRI) is proposed for vibration insensitive optical fiber current sensors (OFCSs). The verifications of experiments are in good agreement with our theoretical analyses. A large vibrational perturbation applied to a segment of lead fiber to simulate the disturbance to the OFCS can be suppressed over 20 dB compared with a conventional reciprocal reflection interferometer (RRI). The noise floor of the OFCS with an MRRI under perturbations is about 1.36 Armsturns/Hz1/2 near the shot noise limit. A good linear demodulation result is obtained and the evaluation of the Verdet constant 1.1?rad/Arms turns approximates the literatural data measured in static environment.

Micromachined optical fiber current sensor

We describe a micromachined optical fiber current sensor. The sensing element consists of a squared silicon membrane (8 mm long and 20 microm thick) that has a cylindrical permanent magnet (NdFeB alloy, 3-mm diameter, 1.5 mm high) fixed on its central region. This structure allows the permanent magnet to vibrate in the presence of the magnetic field gradient generated by an ac. A linear relation between the electrical current and the magnet displacement was measured with white-light interferometry with an optical fiber low-finesse Fabry-Perot microcavity. A measurement range of 0-70 A and a minimum detectable intensity of 20 mA were obtained when distance D between the membrane and the electrical power line was 5 mm. The output signal directly shows a linear response with distance D.

Optical fiber current sensors in high electric field environments

This paper analyzes the response of optical fiber current sensors that are subjected to high electric fields, such as fields encountered in gas-insulated systems. This paper shows that through the electrooptic (EO) Kerr effect, these fields can cause harmonic distortion of the measured ac current waveform. This harmonic distortion was confirmed experimentally. Also, this paper shows that it is possible to simultaneously measure both current and voltage waveforms and the phase between them using this effect. To minimize the electrooptic Kerr effect, optical fiber current sensors must be screened from high-electric fields.

Modified in-line Sagnac interferometer with passive demodulation technique for environmental immunity of a fiber-optic current sensor

A modified in-line Sagnac interferometer (MISI) with passive demodulation Technique (PDT) was proposed to immunize the fiber-optic current sensor (FOCS) from environmental perturbations. A large vibration to simulate the environmental perturbations with acceleration up to 12 g was applied to the lead fiber of the FOCS. The noise floor could be significantly suppressed (20 dB) by the MISI better than by a conventional interferometer. In the same dynamic environments, the PDT could make the FOCS achieve a good linear demodulation with average distortion rates always lower than 0.9%. In addition, all the sensitivities measured in both static and dynamic environments are all approximately 4.5 microrad/(A(rms) turns), which is close to the literatural data measured in static environments. These considerable achievements of high sensitivity, environmental immunity, and free electric shock concerns may lead FOCS's to field-monitoring applications of power delivery lines.

Fiber-Optic Current Sensor Using Passive Demodulation Interferometric Scheme

An interferometer using a Faraday rotator with 22.5 rotation bias is proposed for the use of a fiber-optic current sensor (FOCS) to demodulate phase signals passively. High sensitivities and extra low distortions are obtained by this passive demodulation interferometric scheme (PDIS). The Verdet constant of optical fibers at 1300 nm is evaluated to be 4.5 murad (A rms.turns), which is in good agreement with the literature. With signal distortions always below 0.8 %, the proposed scheme should be significantly effective for the demodulation needs of an FOCS. The PDIS also could enable a FOCS to directly connect with fiber-optic communication networks for the implementation of long-distance remote and multiplexing sensor systems. Moreover, electric shock concerns on current intensity measurements of high-voltage power delivery systems are greatly reduced.