Engineering, Technology & Applied Science Research

105-113

Authors: A. Tanovic, I. Androulidakis, F. Orucevic

IPTV service is a new service which is today offered from almost every Telecom operator. One of the advantages of IPTV service stemming from its architecture is certainly the fact that it is very easy to measure what TV channels are the ones mostly watched. This papers desribes this measurement and analysis results in one Telecom operator in Bosnia and Herzegovina. They describe what TV channels are mostly watched in different time periods. We developed a simple weighting algorithm to order the channels by watching rate. Based on it we are providing extensive tables. This paper forms an industrial contribution with results important for marketing but also is scientific contribution because it introduces one new method of scoring TV channels based on previous measurements in their audience. We also developed IPTV Statistics model and described results from this research for a new statistics model. This paper is the continuous of previously published contributions from this area.

121-125

Authors: A. Babaie Lajimi, S. Asghar Gholamian, M. Shahabi

Doubly-fed induction generators (DFIG) are widely used in wind energy generation systems. During a grid voltage drop, performance is degraded with rotor over current deteriorating the fault-ride through (FRT) capability of the DFIG wind-energy generation system. In this paper, a complete mathematical DFIG model is proposed. The rotor is considered fed by a voltage source converter whereas the stator is connected to the grid directly. Output power and electromagnetic torque are controlled using field-oriented control (FOC). Simulation results show the efficiency of the controller in exploiting the maximum power of wind.

76-83

Authors: N. Z. Yahaya, K. M. Begam, M. Awan

Several gate drive control schemes are simulated and the results show that the Fixed Duty ratio (FDR) can help drive synchronous rectifier buck converter (SRBC) correctly with low dead time and hence reduce body diode conduction loss. Even though FDR is prone to cross-conduction effects, the design is simple. Apart from that, Adaptive Gate Delay (AGD) and Predictive Gate Delay (PGD) control schemes have also shown high level of efficiency. However, AGD generates more losses. Even though the total switching loss in PGD has not improved much of only 1 %, more than 82 % efficiency has been achieved in spite of the advantage in FDR and AGD schemes.

90-97

Authors: B. Bhowmik, S. Nag Chowdhury

In this paper we propose an experimental study model S3P2 of a fast fully dynamic programming algorithm design technique in finite directed graphs with few distinct nonnegative real edge weights. The Bellman-Ford’s approach for shortest path problems has come out in various implementations. In this paper the approach once again is re-investigated with adjacency matrix selection in associate least running time. The model tests proposed algorithm against arbitrarily but positive valued weighted digraphs introducing notion of Prograph that speeds up finding the shortest path over previous implementations. Our experiments have established abstract results with the intention that the proposed algorithm can consistently dominate other existing algorithms for Single Source Shortest Path Problems. A comparison study is also shown among Dijkstra’s algorithm, Bellman-Ford algorithm, and our algorithm.

49-53

Authors: D. Azizi, A. Gholami

Electrical insulations are one of the basic parts of electrical machinery in any sizes and characteristics. Focusing on insulating, studies on the operation of industrial-electrical machinery came to the fact that the most important part of a machine is the Stator. This fact reveals the requirement for inspection of the electrical machine insulation along with the electromagnetic tensions. Therefore with respect to insulation system improvement of stator, the HV generator can be optimized. Dielectric parameters such as insulation thickness, spacing, material types, geometry of winding and slot are major design consideration. A very powerful method available to analyze electromagnetic performance is Finite Element Method (FEM) which is used in this paper. The analysis of various stator coil and slot configurations are used to design the better dielectric system to reduce electrical stresses in order to increase the power of generator in the same volume of core. These processes of optimization have been done according the proposed algorithm. In this algorithm the technical constraints have been considered. This paper describes the process used to perform classical design and improvement analysis of stator slot’s insulation with respect to objective function and constraints.

63-69

Authors: D. Pylarinos, K. Siderakis, E. Pyrgioti, E. Thalassinakis, I. Vitellas

Leakage current monitoring is a widely employed technique to monitor the performance of outdoor insulation. The evaluation of leakage current waveforms recorded in the field, offers significant information since insulation’s performance is strongly linked with local conditions, and the waveforms’ shape correlate to different types of surface activity. In this paper, an investigation of leakage current waveforms recorded in a 150 kV coastal Substations suffering which suffers intense marine pollution is presented. Investigation of the recorded waveforms verified the basic waveform shapes described in the literature. Further, several variations of the basic types and complex waveforms, as well as field related waveforms, are presented. The need for added categorization criteria in the case of field measurements is discussed.

23-29

Authors: H. P. Nabi, P. Dadashi, A. Shoulaie

Vector control is one of the most popular multiphase induction machine drive methods due to its dynamic performance. Since all phase currents are needed in vector control drive, by increasing phase numbers, the number of required current sensors increases which is one of the disadvantages of vector control in multiphase machine drives. In this paper vector control of a symmetrical six-phase induction machine with a novel configuration is presented. The aforementioned configuration is designed in a simple way that only three current sensors will be needed. Analytical equations are extracted in this paper to show that some of current components which do not contribute in torque production will be eliminated due to the proposed scheme. Simulation and experimental results are provided to verify the benefits of the proposed configuration.

36-42

Authors: D. Pylarinos

Leakage current (LC) monitoring is a widely employed tool for monitoring the performance of high voltage insulators. LC waveform monitoring is required to acquire a view of the phenomena experienced since the type of LC waveform’s shape is correlated with different types of electrical activity. In case of field monitoring, specially designed measuring systems, capable of operating under field conditions, have to be installed. The Greek Public Power Corporation (PPC) has issued a large project for monitoring the performance of outdoor insulators. A commercially available LC measuring system, was purchased and installed by PPC. The system was able to monitor various outdoor insulators, record several statistical values and intermittently record a LC waveform. The provided software lacked some capabilities that were required for certain research areas and a custom made software had to be developed. In this paper, two stand-alone MATLAB based softwares, “Leakage Current Waveform File Converter” and “Leakage Current Waveform Viewer”, both equipped with a user friendly GUI, are presented. The first software was developed in order to automatically convert multiple files from the CSV format (as extracted from the measuring system) to the MAT format in order to allow data compactness and further processing. The latter software was developed in order to offer a tool for collective viewing, printing and extraction to JPEG format, of LC waveforms in groups of user-defined numbers. The latter function gives the opportunity for easy and fast creation of waveform archives.

1-7

Authors: K. Siderakis, D. Pylarinos, E. Thalassinakis, I. Vitellas, E. Pyrgioti

Pollution of outdoor high voltage insulators is a common problem for utilities, with a considerable impact to power system reliability. In an effort to prevent possible flashovers due to pollution, many methods have been applied, aiming to improve the insulation performance, either by suppressing the formation of surface conductivity or by increasing the possible insulation level. In the case of substations, the selection of the appropriate technique is complex due to certain issues correlated to the nature of the installation. In this paper, several techniques usually implemented by utilities, are investigated based on the experienced gained in the case of Crete, a Greek island in southern Europe, where due to the coastal development of the power system, the majority of high voltage installations are exposed to intense marine pollution. The technique of coating insulators with Room Temperature Vulcanized Silicone Rubber (RTV SIR) has proved rather efficient and therefore is presented extendedly. Correlation of the material behaviour with environmental conditions is discussed and results from long term monitoring, including environmental parameters and leakage current measurements, in a 150 kV Substation are presented. It is shown that RTV SIR coatings have remarkably suppressed surface activity and that porcelain insulators exhibit different activity period when coated.

13-16

Authors: S. Karakalos

The growth mode of MgCl2 on Au foil and Si (111) 7x7 reconstructed surface under UHV conditions, was investigated by X-ray Photoelectron Spectroscopy (XPS). Magnesium chloride grows with the Frank-van der Merve, (FM) growth mode on the Au foil. On Si surface there is evidence for the layer by layer growth of MgCl2 but leaving uncovered silicon areas at the first steps of deposition due to the Si (111)7x7 surface roughness.