Jovan Radunović

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.

The influence of nonstationary carrier transport on the bandwidth of p-i-n photodiode

The influence of nonstationary carrier transport on the bandwidth and the bandwidth quantum efficiency product of p-i-n photodiodes is analyzed using the complete phenomenological model for two-valley semiconductors. The analysis has been made for various submicron and micron dimensions, for different bias voltages and for several energies of incident pulse excitation, including the variation of the active area of the p-in photodiode. The analysis shows that, as the thickness of the absorption layer varies, the bandwidth could have more than one maximum, especially for smaller bias voltages. The optimal thickness of the absorption layer versus bias voltage and device area is determined, providing maximal bandwidth and maximal bandwidth-quantum efficiency product.

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

Analysis of blocking probability in optical burst switched networks

In this article, we study the blocking probability in a wavelength division multiplexing (WDM) based asynchronous bufferless optical burst switched (OBS) network, equipped with a bank of wavelength converters. Our analysis encloses two wavelength reservation schemes JIT (just-in-time) and JET (just-enough-time), and two-class data rate. The contribution of our work includes: (i) derivation of an accurate model for blocking probability of lower priority bursts in case of a non-preempted model; (ii) provision of the analytical model for blocking probability calculation in the OBS network, which includes these variables: two signaling schemes, partial wavelength conversion, two-class data, traffic intensity, cross-connect speed, number of wavelengths in WDM fiber, number of fibers in the node, number of wavelength converters, and number of nodes in the path; (iii) simulation results, which show that partial wavelength conversion provide quite satisfactory quality of service. We compare performance in a single OBS node, under various sets of parameter values. The OBS network shows great flexibility in terms of used multiclass data, and there is no dependence on the used higher layer protocol.

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.

Nonlinear pulse response of p-i-n photodiode caused by the change of the bias voltage

An analytical expression is derived for nonlinear response of a p-i-n photodiode, commonly used in optical communications. Nonlinearity is caused only by the change of bias voltage, in case of pulse light excitation. The response time increases slowly with increasing the incident pulse power as a result of this nonlinearity. It is assumed in calculations that the optical excitation is not so strong to cause space charge redistribution.

Distributed Dijkstra sparse placement routing algorithm for translucent optical networks

In this paper we study translucent optical networks as an alternative to fully transparent and fully opaque optical networks. In the former networks, a technique called sparse placement is used to overcome the lightpath blocking caused by the signal quality degradation, using much less regenerators, which must strategically be placed, in contrast to a fully opaque network. In this paper we propose a sparse placement algorithm based on two requirements. The first one is signal regeneration necessary to re-amplify, reshape, and retime the optical signals after some predefined transparent distance in order to successfully receive the signals at the destination node. The other is load balance of the traffic in the network aimed at efficient usage of the network capacity resources. We apply a distributed Dijkstra routing algorithm which dynamically changes weights of links during the process of locating regeneration capable nodes. We compare the performance of the proposed algorithm with commonly used sparse placement algorithms through simulation experiments. The benefits are such that load balancing of the network traffic is fully utilized, and with technological development it will be sufficient to equip up to 30% of nodes in the network with electronic regenerations in order to have the same performance as in an opaque network.

Resonant cavity-enhanced Schottky photodiode - modelling and analysis

The theoretical analysis of the linear pulse responses of homostructure GaAs conventional and resonant cavity-enhanced (RCE) Schottky photodiodes is presented in this paper. The results have been obtained by numerical simulation of the complete phenomenological model for a two-valley semiconductor. Besides the drift, as the dominant mechanism of the transport, the model takes into account the diffusion, the influence of the electric field due to the spatial and temporal redistribution of the photogenerated carriers within the absorption layer, the influence of the parasitic time constant and the electron intervalley transfer. The behaviour of the bandwidths and bandwidth-quantum efficiency products when the active area, the width of the absorption layer and the reverse bias voltage change has been investigated. It is shown that conventional and RCE Schottky photodiodes with exactly the same operating parameters have practically identical frequency responses, i.e. bandwidths. For certain thicknesses of the absorption layer the bandwidth-quantum efficiency products have been increased more than fivefold. In comparison with the RCE P-i-N photodetectors having the same operating parameters, the RCE Schottky photodiodes exhibited approximately twofold increased bandwidths.

Optimization of a resonant cavity enhanced MSM photodetector

This paper presents a 2D model and numerical simulation of a submicron resonant cavity enhanced metal-semiconductor-metal photodetector (RCE MSM-PD). Nonstationary effects caused by electron intervalley transfer are taken into account in calculating the RCE MSM-PD response. The analysis of the quantum efficiency and the 3 dB bandwidth shows that there is an optimum channel thickness, for which a maximum bandwidth-quantum efficiency product can be reached.