Pedja Mihailovic

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.

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.

Development of a Fibre Optic Impulse Current Sensor for High Voltage Equipment Tests

This paper presents the procedure for design and testing of the Fibre Optic Impulse Current Sensor (FOICS) based on the Faraday effect. A laboratory prototype based on the Bi12GeO20 Faraday crystal is realised. Experimentally determined 8/20 μs standard impulse current waveforms for different magnitudes obtained by applying FOICS and a conventional shunt sensing system are discussed. The results indicate that FOICS is suitable for the accurate and safe masurement of impulse current. This paper can aid engineers and PhD students in learning the comprehensive application of an attractive fibre optic technique for measurements in high voltage power systems. During the past three academic years, the FOICS development project has received favourable comments from students.

Compensation of Verdet Constant Temperature Dependence by Crystal Core Temperature Measurement

Compensation of the temperature dependence of the Verdet constant in a polarimetric extrinsic Faraday sensor is of major importance for applying the magneto-optical effect to AC current measurements and magnetic field sensing. This paper presents a method for compensating the temperature effect on the Faraday rotation in a Bi12GeO20 crystal by sensing its optical activity effect on the polarization of a light beam. The method measures the temperature of the same volume of crystal that effects the beam polarization in a magnetic field or current sensing process. This eliminates the effect of temperature difference found in other indirect temperature compensation methods, thus allowing more accurate temperature compensation for the temperature dependence of the Verdet constant. The method does not require additional changes to an existing Δ/Σ configuration and is thus applicable for improving the performance of existing sensing devices.

Analog front end stage of a fiber optic magnetic field point scanner

Fiber optic Faraday magnetic field scanners are sophisticated sensing devices whose important part is electronic signal processing block. This paper presents some aspects of a design of an AFE (Fig. 2) for FOFMS that meets these requirements. Electronic section containing the AFE has been constructed and implemented into electronic processing section containing analog to digital conversion (ADC). This unit has been integrated into a sensor and used to collect and process data in order to asses the sensor performance figures.

High input impedance ADC driver with error compensation

A novel high impedance JFET high voltage follower combined with ADC driver and a dedicated error compensation feedback is discussed in this paper. Proposed circuit builds around required ADC driver and its transfer curve by adding few low cost components to turn it into a high impedance input ADC driver with high voltage capability and error compensation ability. Such a circuit is applicable in instrumentation dedicated to voltage measurement.