Slobodan J. Petricevic

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.

Practical application of fiber-optic current sensor in power system harmonic measurement

This paper presents a portable fiber-optic current sensor (FOCS), modified for current harmonic measurement in high-voltage electric power systems. The details of the sensing head redesign are illustrated. Also, both electronic processing block and harmonic analysis algorithm have been illustrated. The practical application of the so-redesigned device has been successfully verified experimentally at a thermal power plant. The measurements have been made for the operation of a 6-kV induction motor with different load conditions and the thyristor excitation of a 15-kV alternating current generator. The experimentally determined current waveforms, the corresponding relative harmonic content computed by discrete Fourier transform, and total harmonic current distortion for various measuring points have been displayed. Important requirements for accurate harmonic measurements have been discussed. The results clearly verified the applicability of the FOCS for monitoring electric power quality as suggested in this paper

Improvements in difference-over-sum normalization method for Faraday effect magnetic field waveforms measurement

This paper presents a detection method for arbitrary magnetic induction and electric current waveform measurement that uses two orthogonally polarized light beams for sensing the Faraday rotation. A procedure is proposed for setting the maximum sensitivity for a sensor with a Faraday crystal that possesses optical activity. Accuracy improvement is achieved by using YVO4 beam displacer instead of polarising prism. The results of the optical magnetic field and corresponding electric current measurements are presented and compared to current measurement by shunt. The Verdet constant of the Faraday crystal is determined and calibration of the sensing system is performed.

A Miniature Pockels Cell with Novel Electrode Geometry

This paper discusses important elements of the Pockels sensing cell design. A novel electrode geometry is analyzed in order to obtain maximum sensitivity response from Pockels crystals (Bi12GeO20). This neither transversal nor truly longitudinal geometry, results in electrical field distribution along the sensing beam path that provides high modulation depth. Demonstrated performance level is in agreement with theoretical studies. Delta-sigma polarization detection method allows high linearity of the detector transfer function and measurement independent on laser intensity variations. Channel gain equalization process necessary for accurate delta-sigma normalization is provided by a walk off prism.

Intensity Fiber-Optic Sensor for Structural Health Monitoring Calibrated by Impact Tester

In this paper, the use of intrinsic intensity fiber-optic sensors for structural health monitoring was investigated. Polyethylene-based composite samples with glass mat reinforcement and embedded telecommunication fibers were subjected to impact using high-speed puncture impact tester as a calibration device. Transfer function of the sensor was generated by linking the light intensity modulation depth with the impact force and the impact point to fiber distance. Conditions for transfer function validity were presented. To detect any possible dangerous impact, a net of crossed fibers was proposed and the net spacing for the given material was calculated. Appropriate non-damaging calibration procedure was proposed, as well as the algorithm for locating the impact point. The method for calculating the impact force, the projectile momentum change, and the place of impact was verified by consecutive strikes on the previously calibrated sample. The sensor can also provide information on the time of the impact and an alarm signal if the force exceeds the damaging threshold force..

Compensation for Temperature-Dependence of the Faraday Effect by Optical Activity Temperature Shift

This paper presents a robust fiber-optic magnetic field, or electric current sensor with temperature compensation. The compensation is based on the optical activity temperature dependence of a Bi12GeO20 crystal. A novel measuring head for this extrinsic fiber-optic sensor is developed. Optical path for temperature measurement passes between optical paths, used to sense the magnetic field, thus ensuring proper temperature sampling. Measurement accuracy is improved from 0.8% to 0.2%.

Performance analysis of the Faraday magnetic field point scanner

Purpose – The purpose of this paper is to discuss results of laboratory tests performed on a point type Faraday magnetic field scanner device designed for monitoring applications.Design/methodology/approach – Automated laboratory setup using a reference magnetic induction source was used to test key parameters such as spatial resolution and signal to noise ratio.Findings – Volume scans of magnitude of the magnetic field induction vector prove applicability of the sensor and demonstrate its advantages.Practical implications – Sensor is applicable for safe and accurate scanning of the magnetic induction spatial distribution.Originality/value – The paper presents a novel test setup.

Wavelet based edge detection algorithm for web surface inspection of coated board web

This paper presents significant improvement of the already installed vision system. System was designed for real time coated board inspection. The improvement is achieved with development of a new algorithm for edge detection. The algorithm is based on the redundant (undecimated) wavelet transform. Compared to the existing algorithm better delineation of edges is achieved. This yields to better defect detection probability and more accurate geometrical classification, which will provide additional reduction of waste. Also, algorithm will provide detailed classification and more reliably tracking of defects. This improvement requires minimal changes in processing hardware, only a replacement of the graphic card would be needed, adding only negligibly to the system cost. Other changes are accomplished entirely in the image processing software.

High performance coated board inspection system based on commercial components

This paper presents a vision system for defect (fault) detection on a coated board developed using three industrial firewire cameras and a PC. Application for image processing and system control was realized with the LabView software package. Software for defect detection is based on a variation of the image segmentation algorithm. Standard steps in image segmentation are modified to match the characteristics of defects. Software optimization was accomplished using SIMD (Single Instruction Multiple Data) technology available in the Intel Pentium 4 processors that provided real time inspection capability. System provides benefits such as: improvement in production process, higher quality of delivered coated board and reduction of waste. This was proven during successful exploitation of the system for more than a year.

Demodulation of quasi-quadrature interferometric signals for use in the totally implantable hearing aids

We propose and experimentally prove an algorithm for demodulation of interferometric signals, modified for use in a totally implantable hearing aid device. A fiber optic configuration, which generates two quasi-quadrature signals by a passive 3x3 coupler, for a non-contact detection of the middle ear ossicle vibration is employed. We simulated the ossicle vibration and large movements and demonstrated the effectiveness of the algorithm to compensate changes of the signal DC values and the phase shift introduced by the coupler. Applying the proposed algorithm we obtained the output signal stability better than 0.5 dB, and the system equivalent input noise of about 31 dB (A) SPL @ 1 kHz.