Zois I.P.,Public Power Corporation of Greece
Journal of Physics: Conference Series | Year: 2016
The motivation for this work came from an attempt to give an alternative definition for the meter, the SI unit for measuring length. As a starting point towards this goal we present the underlying theory behind our approach which uses ideas from quantum field theory and non-commutative geometry, in particular the notion of an odd K-cycle which is based on the Dirac operator (and its inverse, the Dirac propagator). Using physics terminology, the key point in our strategy is this: instead of measuring ordinary length in space-time we measure the "algebraic (or spectral) length" in the space of quantum states of some fermion acted upon by the Dirac propagator. © Published under licence by IOP Publishing Ltd.
Vasile-Pafili S.M.V.,Public Power Corporation of Greece |
Bartzis J.G.,University of Western Macedonia
Applied Thermal Engineering | Year: 2010
This paper presents an experimental investigation of a carbohydrazide application on three Units with mixed metallurgy boilers water-steam cycles in the Power Plant of Ptolemais (Greece). The tests were performed using carbohydrazide as an oxygen scavenger and metal passivation agent, with the parallel application of different alkalization agents on All-Volatile regime, in order to find the most appropriate. The optimization of this carbohydrazide application concerns the adaptation of the final products dosage for the Units needs. The tests that were performed, the measurements, the analyses and other relevant data, the results evaluation and the conclusions, are presented. The results were obtained under real industrial conditions and may provide a general tool for developing the know-how of this kind of treatment. © 2010 Elsevier Ltd. All rights reserved.
Argyropoulos G.,Aristotle University of Thessaloniki |
Grigoratos T.,Aristotle University of Thessaloniki |
Voutsinas M.,Public Power Corporation of Greece |
Samara C.,Aristotle University of Thessaloniki
Environmental Science and Pollution Research | Year: 2013
Ambient concentrations of PM10 and associated elemental and ionic species were measured over the cold and the warm months of 2010 at an urban and two rural sites located in the lignite-fired power generation area of Megalopolis in Peloponnese, southern Greece. The PM10 concentrations at the urban site (44.2 ± 33.6 μg m-3) were significantly higher than those at the rural sites (23.7 ± 20.4 and 22.7 ± 26.9 μg m-3). Source apportionment of PM10 and associated components was accomplished by an advanced computational procedure, the robotic chemical mass balance model (RCMB), using chemical profiles for a variety of local fugitive dust sources (power plant fly ash, flue gas desulfurization wet ash, feeding lignite, infertile material from the opencast mines, paved and unpaved road dusts, soil), which were resuspended and sampled through a PM10 inlet onto filters and then chemically analyzed, as well as of other common sources such as vehicular traffic, residential oil combustion, biomass burning, uncontrolled waste burning, marine aerosol, and secondary aerosol formation. Geological dusts (road/soil dust) were found to be major PM10 contributors in both the cold and warm periods of the year, with average annual contribution of 32.6 % at the urban site vs. 22.0 and 29.0 % at the rural sites. Secondary aerosol also appeared to be a significant source, contributing 22.1 % at the urban site in comparison to 30.6 and 28.7 % at the rural sites. At all sites, the contribution of biomass burning was most significant in winter (28.2 % at the urban site vs. 14.6 and 24.6 % at the rural sites), whereas vehicular exhaust contribution appeared to be important mostly in the summer (21.9 % at the urban site vs. 11.5 and 10.5 % at the rural sites). The highest contribution of fly ash (33.2 %) was found at the rural site located to the north of the power plants during wintertime, when winds are favorable. In the warm period, the highest contribution of fly ash was found at the rural site located to the south of the power plants, although it was less important (7.2 %). Moderate contributions of fly ash were found at the urban site (5.4 and 2.7 % in the cold and the warm period, respectively). Finally, the mine field was identified as a minor PM10 source, occasionally contributing with lignite dust and/or deposited wet ash dust under dry summer conditions, with the summertime contributions ranging between 3.1 and 11.0 % among the three sites. The non-parametric bootstrapped potential source contribution function analysis was further applied to localize the regions of sources apportioned by the RCMB. For the majority of sources, source regions appeared as being located within short distances from the sampling sites (within the Peloponnesse Peninsula). More distant Greek areas of the NNE sector also appeared to be source regions for traffic emissions and secondary calcium sulfate dust. © 2013 Springer-Verlag Berlin Heidelberg.
Itskos G.,Center for Research and Technology Hellas |
Itskos S.,Public Power Corporation of Greece |
Koukouzas N.,Center for Research and Technology Hellas
Fuel Processing Technology | Year: 2010
The chemical and mineralogical composition of lignite fly ash (FA) varies as a function of the prevalent conditions in both the processes of power production and lignite mining. The differentiation of the qualitative and quantitative composition of the highly-calcareous lignite fly ash, as a function of its particle size distribution, is verified in this paper. According to the results of the conducted research, a fine-grained fraction of considerable amount presents properties that obstruct the sustainable exploitation of calcareous lignite fly ash in cement industry applications. On the other hand, the same grain fraction (because of its hydraulic properties) can be utilized in other sort of applications, based on different criteria, i.e. in road constructions. The coarse-grained fraction (which reflects a low proportion to the total fly ash output) presents the same undesired characteristics as well. Rather, the intermediate grain fraction (75-150 μm) presents the highly desirable properties when fly ash is utilized as a pozzolanic additive. In addition, the mechanism of the formation of the intermediate grain fraction strongly prevents the factors that cause the variation of fly ash-quality. It is therefore the optimum part of the whole amount of lignite FA, to be utilized as additive in cement manufacturing. The outcomes of this paper will hopefully contribute towards the crucial goal of the expansion of the utilization of calcareous lignite fly ash by proposing a more effective way of using this material, basically by taking advantage of its fundamental chemical and mineralogical properties. © 2010 Elsevier B.V. All rights reserved.
Adamakos A.N.,Public Power Corporation of Greece |
Titsias M.K.,Athens University of Economics and Business
ACM International Conference Proceeding Series | Year: 2016
In the context of the liberalization of the Greek Energy Market, load forecasting is essential in various system programming procedures. Short-term load forecasting extends from one to seven days, although in this paper a model is proposed for the next calendar day in step of sixty minutes. The objective is to design and implement a software-based short-term load forecasting model for the Greek interconnected transmission system that will show improved performance compared to previous methods. The proposed model introduces a categorization of the forecasted days along with a dedicated artificial neural network for each category. Appropriate input vectors are selected at the training process for each custom-built network. © 2016 ACM.
Margaris I.D.,National Technical University of Athens |
Papathanassiou S.A.,National Laboratory for Sustainable Energy |
Hatziargyriou N.D.,National Technical University of Athens |
Hansen A.D.,National Technical University of Athens |
And 3 more authors.
IEEE Transactions on Sustainable Energy | Year: 2012
This paper presents an investigation on wind turbine (WT) contribution to the frequency control of noninterconnected island systems. The capability of WTs to participate in the primary frequency control and offer primary reserve is discussed. The investigation includes both transient frequency support (inertial response) and permanent frequency response (droop characteristic), as well as the combined application of these concepts. A quantitative analysis is presented for the expected benefits and drawbacks of each method, including the appropriate selection of their parameters. The power system of Rhodes Island has been selected as a study case, which includes different types of conventional generation and the three basic WT types, based on Active-Stall Induction Generator (ASIG), Doubly Fed Induction Generator (DFIG), and Permanent Magnet Synchronous Generator (PMSG). © 2012 IEEE.
Halevidis C.D.,National Technical University of Athens |
Koufakis E.I.,Public Power Corporation of Greece
IEEE Transactions on Power Systems | Year: 2013
The open neutral condition, in distribution networks, can cause significant damage to customer installations. Due to this, the continuity of the neutral conductor is important to the power utilities. In this paper, a power flow algorithm for three-phase four-wire distribution networks with protective multiple earthing (PME), during an open neutral condition, is presented. This algorithm is based on a modified backwards-forwards technique. Additionally, the return current flow is explicitly modeled. Results from three different distribution feeders with different load unbalance and topology are presented and discussed. Furthermore, the effects of the grounding resistances, the load model (constant admittance or constant power), and the neutral breakage point (abruption point) on the voltage levels, are investigated. © 2012 IEEE.
Konidaris D.N.,Public Power Corporation of Greece
Journal of the Air and Waste Management Association | Year: 2010
This paper analyzes the natural desulfurization process taking place in coal-fired units using Greek lignite. The dry scrubbing capability of Greek lignite appears to be extremely high under special conditions, which can make it possible for the units to operate within the legislative limits of sulfur dioxide (SO2) emissions. According to this study on several lignite-fired power stations in northern Greece, it was found that sulfur oxide emissions depend on coal rank, sulfur content, and calorific value. On the other hand, SO2 emission is inversely proportional to the parameter γCO2max, which is equal to the maximum carbon dioxide (CO 2) content by volume of dry flue gas under stoichiometric combustion. The desulfurization efficiency is positively correlated to the molar ratio of decomposed calcium carbonate to sulfur and negatively correlated to the free calcium oxide content of fly ash. Copyright 2010 Air & Waste Management Association.
Zois I.P.,Public Power Corporation of Greece
Journal of Space Weather and Space Climate | Year: 2013
Aims: We study both the short term and long term effects of solar activity on the large transformers (150 kV and 400 kV) of the Greek national electric grid. Methods: We use data analysis and various statistical methods and models. Results: Contrary to common belief in PPC Greece, we see that there are considerable both short term (immediate) and long term effects of solar activity onto large transformers in a mid-latitude country like Greece. Our results can be summarised as follows: 1. For the short term effects: During 1989-2010 there were 43 ''stormy days'' (namely days with for example Ap ≥ 100) and we had 19 failures occurring during a stormy day plus or minus 3 days and 51 failures occurring during a stormy day plus or minus 7 days. All these failures can be directly related to Geomagnetically Induced Currents (GICs). Explicit cases are briefly presented. 2. For the long term effects, again for the same period 1989-2010, we have two main results: (i) The annual number of transformer failures seems to follow the solar activity pattern. Yet the maximum number of transformer failures occurs about half a solar cycle after the maximum of solar activity. (ii) There is statistical correlation between solar activity expressed using various newly defined long term solar activity indices and the annual number of transformer failures. These new long term solar activity indices were defined using both local (from the geomagnetic station in Greece) and global (planetary averages) geomagnetic data. Applying both linear and non-linear statistical regression we compute the regression equations and the corresponding coefficients of determination.© I.P. Zois, Published by EDP Sciences 2013.
Georgiou G.,Public Power Corporation of Greece
Journal of Computer Systems, Networks, and Communications | Year: 2010
Wireless Broadband offers incredibly fast, "always on" Internet similar to ADSL and sets the user free from the fixed access areas. In order to achieve these features standardisation was achieved for Wireless LAN (WLANs) and Wireless Metropolitan Area Networks (WMANs) with the advent of IEEE802.11 and IEEE802.16 family of standards, respectively. One serious concern in the rapidly developing wireless networking market has been the security of the deployments since the information is delivered freely in the air and therefore privacy and integrity of the transmitted information, along with the user-authentication procedures, become a very important issue. In this article, we present the security characteristics for the WiFi and the WiMAX networks. We thoroughly present the security mechanisms along with a threat analysis for both IEEE 802.11 and the 802.16 as well as their amendments. We summarise in a comparative manner the security characteristics and the possible residual threats for both standards. Finally focus on the necessary actions and configurations that are needed in order to deploy WiFi and WiMAX with increased levels of security and privacy. Copyright © 2010 P. Trimintzios and G. Georgiou.