Volume 69 (2018): Edizione 3 (June 2018)

A significant part of severe accidents (blackouts) in electric power systems (EPS) is associated with incorrect operation of relay protection and automation (RPA). One of the main reasons for the incorrect actions of the RPA devices is its rough settings, which often does not correspond to the real operating conditions for specific device. An analysis of currently used methods and tools for RPA setting up, shown that they are largely relied on the guidelines of previous decennaries. Respectively modern techniques have the same drawbacks associated with accounting the processes in specific RPA and primary transducers and its errors by approximate coefficients. It is possible to solve the indicated problem with a highly detailed analysis of the operation of key elements of RPA schemes in the specific operating conditions. The obtained results allow to estimate the processes in protected objects, processing errors in instrumental current (ICT) and voltage (IVT) transformers, as well as in RPA itself. Such possibility could be achieved by the detailed RPA mathematical modeling. The combination of an adequate EPS simulator and RPA models allows configuring parameters of the RPA settings ensuring its correct operation in real EPS. The article presents result of this research for distance protection

Security in mobile ad hoc networks (MANETs) has been an actively researched topic for the several years. As opposed to wired networks, MANETs have dynamic topology, limited resources, limited bandwidth and are usually deployed in emergency scenarios outside, where landscape plays important role. MANETs are susceptible to insider and outsider attacks and bring new security challenges which were not present in the wired networks. The most important difference is that every node in MANET acts as a router and routes traffic throughout the network. Compromising one node can hugely affect network performance. In this paper, we present our security architecture for MANETs which secures important aspects of the network. We bring trust model into the network and nodes are secured by different mechanisms tailored specifically for the use in distributed environment. We use Omnet++for network simulations. Simulations use delays measured on the real hardware and we analyze performance of the network during different data plane and control plane loads

This paper considers two methods for voice channel seizure in one GSM cell, which uses VAMOS technics for traffic efficiency improvement. An important characteristic for models comparison is call loss caused by unsuccessful connection pairing in one timeslot. The first method gives priority to voice connection quality, and the other one to traffic efficiency. The methods are estimated by the simulation, which is first tested by comparing its results to the calculation results for a very small system. The influences of traffic intensity, allowed power difference of two paired connections and attenuation coefficient on the loss caused by unsuccessful pairing are assessed.

The paper deals with the design of an analog circuit to substitute the role of a real intensity Mach-Zehnder modulator for the preliminary tuning of bias controllers. The proposed circuit has similar harmonic distortion as an electro-optic modulator biased around the quadrature operating point. The designed device utilizes a shaping circuit based on a differential pair of bipolar junction transistors. The harmonic distortion of both the Mach-Zehnder intensity modulator and the differential amplifier are analysed. A method to design the emulating circuit of desired features is described and explained and a the comparison of the measured results to the theory is presented.

Besides their magnetic properties, Mn-Zn ferrites are also characterized by appreciable electrical properties. This electro- magnetic nature of Mn-Zn ferrites material properties causes a dimensional resonance to occur in samples. The latter hinders measurements of the frequency dependences of intrinsic permittivity and electrical conductivity. In the paper, we present a sign in measurement results that shows the frequency range in which dimensional resonance has already occurred. Above this range, properties extracted from measurements are not intrinsic any longer. We refer to the sign to determine the last point of the measurement data set that is used as an input for an equivalent circuit modelling of the electrical properties. This “last point” criterion helps to exclude the possibility of modelling apparent properties instead of intrinsic ones. The results obtained show that the frequency dependent electrical properties may be well modeled even if the upper limit of the input frequency range to the curve fitting is below the frequency range in which the dimensional resonance occurs.

The next generation of chip multi-processors point to the integration of thousands of processing cores, demanding high- performance interconnects, and growing the interest in optically interconnected networks. In this article we report on an interlayer silicon-based switch design that switches two channels simultaneously from an input waveguide into one of the two output ports. The introduced interlayer switch allows to design interconnects with previously unattainable functionality, higher performance and robustness, and smaller footprints with low insertion loss (< 1 dB), and high extinction ratio (> 18 dB). Interlayer switching combined with wavelength-routed and circuit-switched networks yield a low latency and low- loss interconnect architecture. Quantitative comparison between the proposed interconnect architecture and other reported structures in terms of loss, number of wavelengths and microring resonators reveals the proficiency of our design. For a 64-core interconnect implemented in 4 layers, the proposed architecture indicates an average loss reduction up to 42% and 43% with respect to single-layer lambda-router and GWOR.

An analysis, design and simulation of digital controlled symmetrical seven levels inverter is presented in this paper. Against the contemporary use of two asymmetrical DC sources with two H-bridge cells to generate seven levels inverter two DC sources of equal voltage ratings are used through digital control strategy to realize seven levels output voltage. By utilizing limited number of active switching components and avoiding the usual complex PWM control techniques for multilevel inverters by way of digital control strategy, high efficiency multilevel inverter systems due to reduction in total harmonic distortion and switching losses is guaranteed. Owing to symmetry of the H-bridge cells, a simple and single programmed counter built around J-K flip is required irrespective of number of cascades. The analyzed and designed system has been simulated in MATLAB/SIMULINK environment. With an R-L load of 200 Ω and 200 mH, improved total harmonic distortions (THDs) for the inverter current and voltage are 7.59% and 16.89% respectively. The obtained results show that the control-circuit-based multilevel inverter topology is most suited for applications in solar powered inverter systems.

The paper presents results related to graphene growth by the method of precipitation on the boundary between a transition metal (nickel or cobalt) and a dielectric (SiO₂ ). The source of graphene is a thin evaporated carbon layer. Carbon in the annealing process diffunds through the transition metal and precipitates on the surface of the dielectric substrate as the structure cools down. Relatively thick layer of copper, which is evaporated over carbon as a cover, prevents carbon to diffund to the surface of the metallization. The structure of the metallization for graphene forming is then Cu/C/(transition metal)/SiO₂ /Si. We consider the utilization of the diffusion barrier to be the contribution of our work to graphene formation using this method. Even though both transition metals are of similar features, the necessary conditions for growth of high- quality graphene are different. In case of nickel, long annealing times within the whole range of annealing temperatures are necessary, while in case of structures with cobalt annealing time of 20 minutes at 900°C is enough for graphene growth. By annealing the Cu(300 nm)/C(20 nm)/Ni(50 nm)/SiO₂ structure at the temperature of 800 °C for 60 minutes we obtained single-layer graphene (SLG).

In this paper it is presented that run-length limited error control codes could be constructed from any two or more- dimensional binary product codes as long as at least one of the one-dimensional binary component codes is or can be converted to a run-length limited error control code. The advantages of this construction are as follows: It does not require any additional redundancy except that which is already contained in the original error control code and that the encoding and decoding procedure used for the underlying error control code do not to be changed

This paper presents a systematic optimization methodology to achieve an accurate estimation of series inductance of inductors implemented in standard CMOS technologies. Proposed method is based on an optimization procedure which aims to obtain adjustment factors associated to main physical inductor characteristics, allowing to estimate more accurate series inductance values that can be used in design stage. Experimental measurements of diverse square inductor geometries are shown and compared with previous approaches in order to demonstrate and validate presented approach

In this paper, combination of the cross-Wigner distribution (XWD) and the Viterbi algorithm (VA) for the instantaneous frequency (IF) estimation of frequency modulated (FM) signals in high noise environments is proposed. The favourable properties of the VA, the IF reconstruction based on minimization of the path penalty functions, and the XWD, iterative accuracy improvement of the IF estimation, give hybrid IF estimator with improved accuracy for high noise environments

In the recently published short paper author deals with the derivation of the scalar potential pertaining to the point charge as well as of the vector potential pertaining to the point current. He shows his alternative approach and compares it to the ”traditional” methods commonly used in textbooks. Here we want to show that use of the generalised functions (symbolic functions, distributions) in the domain of electromagnetic field theory provides more straightforward and more rigorous approach to the problem.