A calculated determination and experimental refinement of the optimal value of the single-phase induction motor transformation ratio

Keywords: Induction motor, windings, phase-shifting capacitor, efficiency, positive and reverse sequence currents Induction motors consume almost 70% of the world’s electricity as they are the driving force behind the vast majority of rotary mechanisms [1]. For industrial and domestic purposes alone, about a million new electric motors are commissioned annually. Single-phase induction motors (SPIMs) are superior to all other types of electrical machines that operate on a single-phase AC voltage network because of their simple and robust design and low cost. Therefore, a small improvement in the SPIM energy performance can have a strong impact on energy consumption worldwide and ultimately reduce emissions of harmful substances into environment. This article presents a technique for optimizing SPIM windings in order to maximize efficiency with a given and fixed phase-shifting capacitor. The positive effect of the application of the proposed method is confirmed by the results of SPIM industrial tests with various powers and rotor speeds.

TG pyrolysis of a mixture of dried sludge from urban wastewater and wood pellets and identification of the composition of the resulting gases by infrared spectroscopy

The recent tendency of sewage sludge disposal is targeted towards the gasification for heat generation in small towns far from waste incineration plants. The scope of this article is to present the investigation into the mixture of dried sewage sludge and wood pellets during pyrolysis by thermogravimetry (TG) with evolved gas analysis by TG-coupled Fourier transformation infrared spectroscopy (FTIR) method. The maximum intensity of mass loss of sewage sludge material occurs at 300–310°C temperature and it differs from wood cellulose case of 360°C. The 50:50% mixture of these materials was investigated in more details. Pyrolysis reaction kinetics is described by a variation of three constituent parts from TG data. Prefactor A and activation energy E of the Arrhenius law were found, and reaction order n was determined by the Ozawa method employing Avrami phase change. The maximum of gas evolution is always related to the most intense mass loss, and gas composition correlates with the initial material.

Swirler geometry effects (dh/do ratio) on synthetic gas flames: Part 1: Combustion and emission characteristics

Swirling flows increase combustion performance via favouring flame stability, pollutant emissions, and combustion intensity. The strength of a swirling flow is characterized by a parameter known as swirl number, which is highly related to the dh/do ratio. In this study, effects of the swirler dh/do ratio on combustion and emission characteristics of the synthetic gas flames of premixed 20%CNG/30%H2/30%CO/20%CO2 mixture were experimentally investigated in a laboratory-scale swirl stabilized combustor. For this purpose, twelve different swirl generators were designed and manufactured. dh/do ratios of these swirlers were set as 0.30 and 0.50, and the geometric swirl number was varied between the values of 0.4 and 1.4 (at 0.2 intervals). All experiments were conducted at a fuel-lean equivalence ratio (ϕ = 0.6), room temperature, and local atmospheric conditions of the city of Kayseri, Turkey. A data logger was utilized to plot axial and radial temperatures and NOx, CO, and CO2 profiles, which were exploited to assess combustion and emission performance. Results showed that the dh/do ratio had a non-monotonic effect on the behaviour of combustion and emission of the tested synthetic gas mixture. Depending on the swirl number, increments and decrements were observed in temperature and emission values.

Swirler geometry effects (dh/do ratio) on synthetic gas flames. Part 2: dynamic flame behaviour at external y altered acoustic conditions

In a combustion device, unsteady heat release causes acoustic energy to increase when acoustic damping (energy loss) is not that effective, and, as a result, thermo-acoustic flame instabilities occur. In this study, effects of the swirler dh/do ratio (at different swirl numbers) on dynamic flame behaviour of the premixed 20%CNG/30%H2/30%CO/20%CO2 mixture under externally altered acoustic boundary conditions and stability limits (flashback and blowout equivalence ratios) of such mixture were investigated in a laboratory-scale variable geometric swirl number combustor. Therefore, swirl generators with different dh/do ratios (0.3 and 0.5) and geometric swirl numbers (0.4, 0.6, 0.8, 1.0 1.2 and 1.4) were designed and manufactured. Acoustic boundary conditions in the combustion chamber were altered using loudspeakers, and flame response to these conditions was perceived using photodiodes and pressure sensors. Dynamic flame behaviour of respective mixture was evaluated using luminous intensity and pressure profiles. Results showed that the dh/do ratio has a minor impact on dynamic flame behaviour.

Lietuvos vandens telkinių antropogeninių pokyčių žalos vertinimas

Straipsnyje nagrinėjamos ūkinės veiklos neteisėtų veiksmų sukeltos žalos hidroelektrinių vandens telkiniams, kaip kraštovaizdžio objektams, nustatymo problemos. Siūloma žalą upei, ežerui ar tvenkiniui skaičiuoti priklausomai nuo vandens telkinio vertės, kurią lemia teritorijos gamtosaugos tikslai, vandens telkinio dydis ir būklė bei pažaidos lygis. Paliekant galioti dabartinius žalos kraštovaizdžio kompleksams ir objektams nustatymo pagrindinius principus Lietuvoje, siūlome pasitelkti patikimus hidrografijos šaltinius, objektyvius, nuotoliniu būdu stebimus, hidrologijos rodiklius ir hidroenergetikos duomenis. Svarbiausias upės, ežero ar tvenkinio morfometrinis rodiklis yra vandens paviršiaus plotas, kuris nustatant žalą patikimai ir objektyviai paimamas iš upių, ežerų ir tvenkinių kadastro. Ežero (tvenkinio) vandens lygio ar upės debito pokyčiai dėl neteisėtos ūkinės veiklos stebimi nuotoliniu būdu ir registruojami. Skaičiuojant žalą, vietoje absoliučios vandens lygio pokyčių reikšmės siūlome vertinti pažeidimą santykiniu lygio arba debito pokyčiu, apskaičiuotu kaip neteisėto lygio ar debito pokyčio santykis su maksimaliu ežero (tvenkinio) gyliu arba atitinkamai reglamentuotu upės debitu. Toks santykinio pokyčio vertinimas atspindi esminį vandens telkinio režimo skirtumą tarp didelių bei gilių ir mažų bei seklių telkinių. Straipsnyje pasiūlyta žalos kraštovaizdžiui dėl neteisėtos ūkinės veiklos vandens telkiniuose vertinimo metodika, paremta objektyviais hidrologiniais ir morfometriniais rodikliais bei stebėjimų duomenimis.

Piezoelectric ceramic for energy harvesting from ambient vibration

Direct piezoelectric conversion is very popular in generating power from mechanical stress. There is continuous progress in power harvesting from mechanical vibration. In this article, experimental tests on a piezoelectric circular plate, to evaluate the electric power produced by the piezoelectric conversion at low acceleration over a wide range of ambient vibration frequency, are presented. The experimental analysis is presented and discussed. The results demonstrate the potentiality of using low-cost piezoelectric diaphragms to harvest energy from ambient vibration. Under low acceleration (5.36 m/s2), the vibration frequency was varied in the range of 10– 200 Hz and the generated power was measured. Under a very small dynamic force (less than 0.06 N), the output power of 1.5 mW was obtained with an 8.5 mm drum harvester across a load resistance of 17.8 kΩ at a frequency of 173 Hz.

Vertės įveiklinimas įtraukiant vartotojus į energetikos sektoriuje vykstančius procesus

Energetikos sektorius yra itin reikšmingas valstybių, organizacijų raidai, svarbų vaidmenį atlieka ir žmogaus gyvenime. Tiek siekis artėti prie klimatui neutralios visuomenės, tiek žiedinės ekonomikos principų diegimas yra priklausomi nuo šių raidos krypčių priimtinumo ir plataus jų pritaikymo. Viena vertus, didelė visuomenės dalis yra linkusi pritarti šioms raidos kryptims, kita vertus, taip pat ženkli visuomenės dalis nėra linkusi aktyviai įsitraukti į energetikos sektoriuje vykstančius procesus ir savo veikla prisidėti prie greitesnio visuotinai priimtų tikslų pasiekimo. Visuomenėje vyrauja nuomonė, kad dėl susiklosčiusios situacijos visų pirma yra atsakingos valstybinės institucijos ir įmonės, bet ne jų pačių vartojimo ir apskritai elgsenos įpročiai. Vartotojų įsitraukimo prielaidos pirmiausia glūdi jų patirtinoje naudoje, kuri neapsiriboja ekonomine ar funkcine vertės dimensijomis, bet apima ir emocinę bei socialinę vertes. Taip pat išryškėja būtinybė tinkamai pranešti ir edukuoti apie patirtiną naudą. Todėl šiame straipsnyje pristatomo tyrimo tikslas yra nustatyti, kas svarbu vertės įveiklinimui įtraukiant vartotojus į energetikos sektoriuje vykstančius procesus. Vertės koncepcijos, vertės įveiklinimo nulemti įsitraukimo tyrimai energetikos sektoriuje prasidėjo visai neseniai ir nepasižymi gausa. Todėl tikslui pasiekti pasirinkta žvalgomojo tyrimo strategija, kuri taikoma tyrinėjant neapibrėžtus ryšius tarp kintamųjų, identifikuojant galimas tolesnių tyrimų kryptis ir formuojant pirmines įžvalgas. Tyrime derinti keli metodai: kokybinis – problemos analizei ekspertiniu požiūriu taikytas interviu metodas; kiekybinis – vartotojų preferencijoms nustatyti taikyta anketinė apklausa. Tyrimo rezultatų analizė parodė, kad svarbiausias veiksnys, lemiantis elektros tiekėjo pasirinkimą, yra siūloma kilovatvalandės kaina. Neatidėliotinas tiekėjo reagavimas į iškilusias problemas, konsultavimas yra antras pagal svarbą veiksnys, o elektros energijos tiekėjo reputacija – trečias pagal svarbą. Rezultatai leidžia teigti, kad svarbiausias veiksnys renkantis elektros tiekėją yra susijęs su ekonomine vertės dimensija, toliau pagal svarbą – funkcinė ir galiausiai emocinė vertės dimensijos. Vertinant apsisprendimą rūšiuoti atliekas, svarbiausias veiksnys yra nemokamas surinkimas iš gyvenamosios vietos ar arti jai esančios, o antras pagal svarbą – supratimas, kad rūšiuojant atliekas prisidedama prie klimatui neigiamų padarinių švelninimo. Trečias pagal svarbą veiksnys yra galimybė naudotis panašia į depozitinės taros surinkimo sistema. Galima teigti, kad svarbiausias veiksnys apsisprendimui rūšiuoti atliekas yra susijęs su ekonomine vertės dimensija, toliau svarbios emocinė ir galiausiai funkcinė vertės dimensijos. Be to, veiksnių svarba priklauso ir nuo amžiaus kategorijos: 18–29 m. amžiaus kategorijoje svarbesnę vietą užima emocinė vertė, o 30–39 ir 40–49 m. amžiaus kategorijose – ekonominė vertės dimensija. Tyrimo rezultatų analizė atskleidė, kad informacija apie elektros tiekėją ir atliekų rūšiavimą, vartotojų požiūriu, turėtų būti intensyviau ir aiškiau komunikuojama, ypač oficialių institucijų internetiniuose puslapiuose ar institucijų socia­linių tinklų paskyrose, taip pat internetinėje žiniasklaidoje.

Identification of a mathematical model for a single-shaft power-generating GTE

The design and development processes of gas turbine engines rely on the usage of mathematical models representing the physics of engine functioning processes. One way of increasing the validity of a mathematical model is its identification based on engine test results. The identification of mathematical models of modern power-generating gas turbine engines (GTEs) presents a demanding and time-consuming task due to the necessity to identify the main controlled engine parameters determined in the course of experimental studies depending on a large number of the parameters that are not controlled during the experiment. In this regard the actual direction of reducing the labour intensity of the process of mathematical model identification is using identification program complexes. The object of the study was to solve the problem of structural-parametrical identification of the power-generating GTE functioning model detailing the turbine flow path calculations to the level of blade rows in order to obtain the GTE mathematical model that describes the characteristics of a real engine with given accuracy. To achieve the objective, the following problems were solved: variable parameters, controlled parameters and characteristics, ranges of their variations were selected from the total number of the mathematical model input data, the objective functions were defined; the task of the parametric identification according to the results of bench tests through GTE operating modes was performed; analytical approximating dependences for correcting coefficients (variable parameters) were obtained; structural-parametric identification of the mathematical model was performed. The novelty of the obtained results is the identification of the mathematical model of the nonlinear component GTE of the second level performed without model linearization (without its level lowering) by using the Optimum software packages. The methodological approach for the parametric identification of the mathematical model is proposed. This approach allows reducing the number of variable parameters under the modes lower that the maximum. It shows that the identified model allows obtaining the prediction results of the GTE parameters and characteristics through operating modes with a deviation of no more than 1.4% from the experimental data and, therefore, it will allow reduction of terms and an increase in the quality of power unit development.

The operation of the last stage of steam turbine at low-flow rate modes

At the present time, thermal power plants and combined heat and power plants operate in highly manoeuvrable modes with almost daily deep unloading, shutdowns on weekends and holidays followed by launches from various thermal conditions. During start-ups, the operation at partial modes and shutdowns, the turbine flow path operates at low-flow rate modes and, as a result, varying tear-off phenomena appear — depending on a relative volumetric flow rate of steam Gv2 in the low-pressure cylinder starting from the last stage. This is especially true for the operation of the low-pressure path for cogeneration turbines. Under low-flow rate modes a change in the flow structure occurs accompanied by the appearance of the bushing tear-off, the rotating vortex in the gap between stator blades and rotor blades, and an increase in pressure in the main flow when switching to the operation at the compressor mode. The formation of the tear-off area is accompanied by a significant increase in the temperature of steam during its overheating due to ventilation losses created by vortex structures in the areas of tear-off. The temperature change along the working blade length is considered, the characteristic points of this change depending on the relative volumetric flow rate of steam are highlighted. The boundaries of transition from the wet steam to the su— perheated steam with decreasing Gv2 are determined. The power consumption for the operation of the stage with a decrease in the flow rate of steam and a change in the flow structure is considered.

A comparative study between PI and cascaded sliding regulator based on rotor flux oriented control for photovoltaic pumping system and fuzzy MPPT optimization

In this paper, a comparative study between the PI and the cascaded sliding regulator is made, based on rotor flux oriented control for the photovoltaic pumping system. In order for the motor-pump to be always optimized and operate at the maximum power for each change of illumination or temperature, it is necessary to integrate the MPPT tracking system, we used the fuzzy MPPT technique. The three-phase converter is controlled by the technique of vector width modulation (SVPWM), characterized by low response time and oscillation. Simulations of the proposed structures are validated under Matlab/Simulink. The obtained results show the superiority of cascaded sliding mode control combined with fuzzy MPPT technique, they confirm the effectiveness of this control structure in terms of parametric robustness and ensure proper operation over the entire speed range.