Study on thermal model for calculating transformer hot Spot temperature

A power transformer is a static piece of apparatus with two or more windings which, by electromagnetic induction, transforms a system of alternating voltage and current into another system of voltage and current usually of different values and at same frequency for the purpose of transmitting electrical power. The hot spot temperature depends on instantaneous load and ambient temperature, winding design and also cooling model. There are two possible methods for hotspot temperature determination. The first method is to measure the hot spot temperature using a fiber optic, and other is to calculation the hotspot temperature using transformer thermal models. It was noticed that the hot spot temperature rise over top oil temperature due to load changes is a function depending on time as well as the transformer loading (overshoot time dependent function). It has also been noticed that the top oil temperature time constant is shorter than the time constant suggested by the present IEC loading guide, especially in cases where the oil is guided through the windings in a zigzag pattern for the ONAN and ONAF cooling modes. This results in winding hottest spot temperatures higher than those predicted by the loading guides during transient states after the load current increases, before the corresponding steady states have been reached. This thesis presents more accurate temperature calculation methods taking into account the findings mentioned above. The models are based on heat transfer theory, application of the lumped capacitance method, the thermal-electrical analogy and definition of nonlinear thermal resistances at different locations within a power transformer. The methods presented in this thesis take into account all oil physical parameters change and loss variation with temperature. In addition, the proposed equations are used to estimate the equivalent thermal capacitances of the transformer oil for different transformer designs and winding-oil circulations. The models are validated using experimental results, which have been obtained from the normal heat run test performed by the transformer manufacturer at varying load current on a 250-MVA-ONAFcooled unit, a 400-MVA-ONAF-cooled unit and a 2500-KVA-ONAN-cooled unit. The results are also compared with the IEC 60076-7:2005 loading guide method. Keywords: power transformers, hot spot temperature, top oil temperature, non-linear therma

Response of the Medial Octavolateral Nucleus (MON) in the Goldfish, <i>Carassius auratus</i>, to constant-amplitude and amplitude-modulated water wave stimuli

Lateral line units in the MON of goldfish exhibited phasic or tonic responses to constant-amplitude stimuli. When stimulated with amplitude-modulated stimuli, most MON units exhibited phasic-tonic or tonic responses that were phase-locked to the modulation frequency. On average, phase-locking to the modulation frequency was greater than phase-locking to the carrier frequency. Thus, MON responses to amplitude-modulated sine wave stimuli differed from those of afferent fibres in the posterior lateral line nerve (strong phase-coupling to both carrier and modulation frequency) and were similar to those of midbrain lateral line units (strong phase-coupling only to the modulation frequency). When modulation depth was maximal (96%), units responded to each modulation cycle with about the same number of spikes. When modulation depth was less than maximal, units tended to discharge with a decreasing number of spikes to increasing numbers of AM cycles. When modulation depth was 24% or smaller, discharge patterns resembled the responses to unmodulated CFs, i.e. units responded with an on-response to the first AM cycle but responded only weakly to successive AM cycles. Lateral line units in the MON of goldfish increased their discharge rates and the degree of phase-locking with increasing displacement amplitudes of the vibrating sphere. Most level response functions were steep, i.e., discharge rates increased over a narrow range of displacements (50 μm to 175 μm). Goldfish medullary lateral line units encode a wide range of stimulus displacements. </p

Corporate Future Foresight in Government: A necessity or a luxury?

In the era of continuous change, governments increasingly find themselves in the face of growing uncertainty and increasing need for future foresight. This research aims to test the relationships between the corporate future foresight maturity level, environmental hostility level and the value contribution of foresight activities in government entities in Dubai. Adopting a quantitative approach, 39 government entities participated in the cross-sectional survey used in this research. The results show that there is a significant positive relationship between the future foresight maturity level among government entities and the value contribution of foresight activities. Also, the results revealed no significant relationship between environmental hostility level and the value contribution of foresight activities. Additional findings revealed a high need for integrating future foresight activities with low competition intensity, high technological and market turbulence in government’s contextual environment. Also, they revealed a better practice level in future foresight practices among government entities. This research is concluded by discussing the results, highlighting their academic and practical contributions, understanding the study’s limitations and recommending areas for further research

Dry reforming of associated natural gas using catalytic membrane reactors.

The mitigation and utilization of greenhouse gases, such as carbon dioxide (CO2), are among the most important challenges in the area of energy research. Dry reforming of propane (C3H8) (DRP), which uses both CO2 and C3H8 as reactants, is a potential method to utilize the previously-mentioned gases in the atmosphere. Associated natural gas containing high concentrations of CO2 and C3H8 could therefore be utilized for hydrogen and synthesis gas (syngas) production in the near future, without need for the removal of CO2 from the source gas. Thus, the DRP reaction is a suitable process to convert C3H8 and CO2 to more useful raw materials. The reforming of (CO2) with associated natural gas can be adapted to generate a synthetic gas having 1:1 hydrogen to carbon monoxide (CO) ratio. This type of gas synthesis may be used during the production of a large number of industrially-important chemicals. From an environmental point of view, this reaction can also be used to mitigate the so-called "greenhouse effect", since the conversion of these gases into valuable chemical(s) and feed stocks could alleviate and significantly reduce the emissions of CO2 and associated natural gas into the atmosphere. In this thesis, a catalytic membrane reactor has been used to carry out experiments on the conversion of reactants, product selectivity and distribution, catalyst selection and activity. Interpretation of the reaction mechanism and kinetics of this important reaction are also presented. Previous experimental research has been centered on the reactor development, catalyst impregnation and the feasible applications in industry. The Group VIII metals of the periodic table of elements, supported on oxides, have been found to be effective for this reaction. Carbon deposition causing catalyst deactivation was found to be one of the major challenges inhibiting the large-scale application of the reaction. Nickel (Ni)-based catalysts impregnated on an alumina wash-coated tubular membrane support showed carbon-free operation and was thus used to generate important data regarding the performance of membrane reactors for this reaction. In this work, the membrane reactor investigated for CO2 reforming with associated natural gas operated in pore-flow through mode, using a catalyst-impregnated porous membrane that had no separating functions, but which acted as a support for the catalyst. The catalyst was therefore immobilized as highly-dispersed nanoparticles in the pore of the membrane structure. CO2 and associated natural gas were forced through the pores of the membrane where the catalytic reaction took place. The membrane, in effect, worked as a contact zone for the reactants and the catalyst. Because of fast convective flow, internal diffusion limitations were reduced as the products were immediately removed from the membrane pore, avoiding product accumulation within the membrane and therefore eliminating consecutive reactions. As a consequence, the effective product yield was not influenced by mass transfer limitations and selectivity for the desired product could be increased. The reverse water-gas-shift reaction was a possible cause for the reduced yield of hydrogen. The reduction or elimination of the mass transfer limitation is particulary important for CO2 reforming with associated natural gas, where there is a high propensity for consecutive reactions. This research investigated the catalytic dry reforming of propane over Zr/Ni/Pd/Cu/-Al2O3 catalysts under the temperature range 600ºC/873.15ºK to 700ºC/973.15 ºK. These catalysts (supported on alpha-Al2O3) were chosen for this study because primary studies showed better selectivity and activity, and smaller deactivation resistance than for other catalysts. The thermal structure, pore size distribution, gas permeability and chemical structure of such Hybrid Ceramic Membranes (HCMs) were characterised using various methods, including gas permeability measurement, Scanning Electronic Microscopy (SEM), Accelerated Surface Area and Porosimetry analysis (ASAP), nitrogen Adsorption, Energy Dispersive X-ray Analysis (EDXA) and gas permeation mechanisms through the catalytic porous membrane. The initial experimental results from the HCMs exhibited good thermal stability, gas permeability and hydrophilic properties, as the accompanied water vapour that was formed could permeate through membranes better than the gases that resulted from the dry reforming of propane with CO2 (C3H6, C2H6, C2H4, CH4 and CO). Preliminary experiments were conducted to check the working condition of the catalyst testing unit. The results were quantitatively analysed and a typical productive reactive run was selected as a representative sample. The experimental reactive runs were conducted using three different sets of ceramic membrane supports under various operating conditions, including pressure at 1.0, 2.0 and 3.0 bars, temperature at 600ºC/873.15ºK, 650ºC/923.15ºK and 700ºC/973.15ºK, and overall inlet premixed reactant fed gas flow rates of 100ml/min, 200ml/min and 300ml/min, fed at a flow ratio of 1:1, 1:2 and 2:1. The best experimental reactant fed gas conversion results of 34%, and 58% of CO2 and C3H8 respectively were obtained at a pressure of 2 bar, a temperature of 650ºC/923.15ºK and a flow rate of 200ml/min that was fed at ratio of 2:1. The production gas selectivities were of 68%, 25%, 28%, 26%, and 55% for C3H6, C2H6, C2H4, CH4, and CO respectively and liquid yield namely water. Thus a catalytic membrane reactor (CMR) for the dry reforming of CO2 and propane was presented along with its typical performance characteristics. This reactor structure was implemented here to achieve an efficient integration not only on the reactor section but also in the process scale as recommended in this study

INTERNALISASI PLURALISME AGAMA DALAM PEMBELAJARAN SOSIAL DAN EMOSIONAL

Based on the results of the thinking of researchers who consider the importance of social and emotional knowledge framed with pluralism to develop the competence of students as social beings in schools. This research provides a conduction to the internalization of pluralism through culture that can be a source of positive support for individuals. This is especially true for minority and immigrant groups in pluralist societies where houses of worship can be homes of community and identity, especially when the dominant group suppresses public expression and acceptance of group norms and values.Berdasarkan hasil pemikiran peneliti yang menganggap pentingnya pengetahuan sosial dan emosional dibingkai dengan pluralisme untuk mengembangkan kompetensi siswa sebagai makhluk sosial di sekolah. Penelitian ini memberikan konduksi terhadap internalisasi pluralisme melalui budaya yang dapat menjadi sumber dukungan positif bagi individu. Hal ini terutama berlaku untuk kelompok minoritas dan imigran dalam masyarakat pluralis di mana rumah ibadah dapat menjadi rumah komunitas dan identitas, terutama ketika kelompok yang dominan menekan ekspresi publik dan penerimaan norma dan nilai-nilai kelompok

Synthesis, Characterization and Flocculation Properties of Acacia tortilis Grafted with Styrene

هدفت هذه الدراسة لتحضير وتشخيص صمغ الأكاسيا المدمج ودراسة تطبيقاتها كمواد ذات خصائص تجميعية. حُضرت العينات المدمجة باستخدام تراكيز متباينة من المونومر وكذلك من جرعات أشعة جاما‘ شُخصت العينات باستخدام مطيافية الأشعة تحت الحمراء‘ والتحليل الحراري الوزني‘ واللزوجة‘ وقياس الأس الهيدروجيني‘ وكذلك كفاءة الدمج. بينت النتائج أن كفاءة الدمج تعتمد بصورة أساسية على تركيز المونومر. بالإضافة الى ذلك فقد وُجد أن كل من جرعة الأشعة وتركيز المونومر لها آثار كبيرة على لزوجة المحاليل المائية للعينات المدمجة. أظهرت العينتان 3c و 1b أعلى قيم للزوجة وهى 49 cp و 44 cp مقارنة بالعينة الخام والتى لها لزوجة تبلغ 10 cp . بينت نتائج التحليل الحراري أن العينة الخام تتفكك فى ثلاث مراحل عند درجة حرارة 199.3 و 284.0 و 439.0 درجة مئوية. وقد وجد أن العينات المدمجة أكثر إستقراراً حراريا من الصمغ الخام. أخيراً فقد وُجد أن للعينات المدمجة خصائص تجميعية أفضل من الصمغ الخام

The Relationship between Strategic Management and Organizational Effectiveness of Soft Drinks Manufacturers in Libya

The strategic management process (SMP) is key part of the business success and organizational effectiveness. The SMP is comprised environmental analysis, strategy formulation, strategy implementation, and strategic control. This study investigates the relationship between strategic management process and organizational effectiveness of soft drinks manufacturer in Libya. Data were collected from executive in soft drinks manufacturer. Descriptive statistics were calculated and correlation analysis and regression analysis was used to test the hypothesized relationships. It was found that strategic management process has great impact and related to the organizational effectiveness

Study of the Azo Hydrazone Tautomerism in the 4-(9-Anthrylazo) Phenol

The spectroscopic study on 4-(9-anthrylazo) phenol has revealed that the azo dye under study exists in two tautomeric forms which are azo phenol and hydrazo keto forms in ratio of almost (1:1). The azo hydrazone tautomerism was confirmed by the use of IR spectroscopy and HNMR in which the characteristic absorption bands and chemical shifts for both tautomers were assigned