The 21st century is a century that the information is popularized in full and the Internet resources are abundant, e-learning has gradually become a global phenomenon no only in formal education institutions but also in educational training organizations. Due to the rapid development of broadband Internet, online courses can now offer asynchronous learning activities as well as synchronous learning activities. Some literature have pointed out that online synchronous teaching is the key to engage online learners. How to evaluate the quality of online synchronous teaching becomes an important research topic. However, there is still very little research discussing this issue. Therefore, this study aims to develop a quality scale for evaluating online synchronous teaching from information system perspective. To achieve the research goal, we first identify some general quality indicators from literature survey; we then conduct a focus group interview to select those essential indicators. A questionnaire of the quality scale is then developed based on those essential indicators. A survey with 308 subjects has been conducted and data were collected to analyze the validity of the quality scale. The results showed that the discrimination, reliability and validity are all conformed to the standardization of scale development procedure. The result also showed that the developed quality scale has a good reliability and validity. The developed quality scale would be a good reference for administrators of educational organizations, teachers, and researchers. This quality scale will contribute to the planning and operation of the service of online synchronous teaching for administrators, and for teachers to better instructional designs for their online synchronous teaching. Researchers interested in synchronous teaching and learning can tackle the further research issues.

An average-value model of a rotating rectifier circuit in a brushless excitation system is set forth, where a detailed simulation is required to extract the essential averaged-model parameters using numerical averaging. In the proposed approach, a synchronous machine model with saturation and cross saturation and an arbitrary rotor network representation that uses a voltage-behind-reactance representation for the field winding of the main machine is proposed. This allows the field winding to be represented as branches in a circuit solver, permitting straightforward simulation with connected circuitry. Also a brushless exciter model is introduced to be compatible with the averaged-model, where the exciter armature windings are represented using a voltage-behind-reactance formulation. The resulting average-value model is verified in time domain against detailed simulation, and its validity is demonstrated in all rectifier modes of operation.

Η σύγχρονη γεννήτρια, ή αλλιώς εναλλακτήρας, είναι σύγχρονη μηχανή η οποία μετατρέπει μηχανική ενέργεια σε εναλλασσόμενη ηλεκτρική ενέργεια. Η σύγχρονη μηχανή, χρησιμοποιούμενη ως γεννήτρια, είναι η σπουδαιότερη μηχανή για την παραγωγή ηλεκτρικής ενέργειας και αποτελεί το επίκεντρο κάθε σταθμού παραγωγής ηλεκτρικής ενέργειας. Σκοπός της παρούσας διπλωματικής εργασίας είναι η μελέτη της συμπεριφοράς της σύγχρονης γεννήτριας στη μόνιμη κατάσταση λειτουργίας αναλύοντας τα είδη των σύγχρονων παραμέτρων που προκύπτουν, καθώς επίσης και η μελέτη και ο προσδιορισμός των απωλειών στην ονομαστική κατάσταση λειτουργίας. / The synchronous generator is a type of synchronous machine, which converts mechanical energy into alternating electrical energy. When the synchronous machine is used as a generator, it is the most important machine for the production of electrical energy and it constitutes the epicentre for each station which produces electrical energy. The scope of this present thesis is the study of the behavior of synchronous machine in the steady-state of operation analyzing the types of synchronous parameters and synchronous quantities, as well as the study and determination of losses in the nominal situation of operation. The steady-state tests suggested in this thesis are required for analyzing the performance of a synchronous machine under normal operating conditions.

Thesis (MScEng)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The aim of this study is to critically evaluate the voltage injection position sensorless control technique as applied to the reluctance synchronous machine (RSM) drive and to implement the technique on a 5.5 kW RSM and a 110 kW RSM. The technique is evaluated by using an accurate mathematical model of the RSM in a simulation package, called Simuwin. The negative effects that cross-magnetisation and the slotted air-gap have on the technique are intensively investigated. It was showed that these effects can cause an error in the position estimation of up to 30°. The TMS320F240 DSP was used as the controller for the RSM drives to implement the position sensorless control technique. Measurements on both RSM drives confirm the simulated results. / AFRIKAANSE OPSOMMING: Die doel van hierdie tesis is om die spannings-injeksie posisie sensorlose beheer tegniek soos toegepas op die reluktansie sinchroon masjien (RSM) aandryfstelsel, krities te evalueer en te implementeer op 'n 5.5 kW RSM en op 'n 110 kW RSM. Die tegniek is geevalueer deur 'n akkurate wiskundige model van die RSM saam te stel en die model te gebruik in 'n simulasie pakket, genaamd Simuwin. Daar is veral klem gele op die negatiewe invloed wat kruis-magnetisering en 'n gegleufde lug-spleet op die tegniek het. Dit is bewys dat hierdie eienskappe van die RSM 'n fout in die posisie afskatting van tot 30° kan veroorsaak. Die TMS320F240 DSP is gebruik as beheerder vir die RSM aandryfstelsels om sodoende posisie sensorlose beheer op altwee masjiene toe te pas. Metings op albei stelsels bevestig die simulasies.

The document describe servo drive by B&R and the control algorithms with vector control. There is also mathematic model of synchronous motor, design of control the system of two connected motor and implementation these algorithms in to the PLC and Acopos. The Master’s Thesis contains confrontation of results of real system and ideal model.

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This thesis presents a transient stability method using dynamic phasors. This method can be used to investigate low frequency (<5Hz) and sub-synchronous frequency (5Hz-60Hz) oscillations. It has major advantages as compared to traditional transient stability method and EMT method. It allows modeling of higher-frequency oscillation possible using time domain simulations, which is not achievable with conventional method. It also can be simulated at much larger time step as compared to PSCAD/EMTDC simulation. Comparison of the results with traditional model and detailed EMT model are also present, and they show very accurate results at frequency ranges up to 60Hz.

This report highlights the market for synchronous machines and examines the current situation. Today, the world demands higher volumes of electrical power that is cleaner, more efficient and generated from fossil-free sources. This increases the importance of using efficient and modern that minimise energy losses. A synchronous machine is an electric motor or generator with high efficiency. There is a need for up-to-date knowledge about the current market situation for manufacturers to keep pace with the requirements and regulations, while also satisfying their customer needs. This study investigates the main trends, identifies different manufacturers in different market segments, as well as what type of added value these companies offer to their customers. Data collection combined with a series of interviews have been conducted to understand the current market situation and draw conclusions using models appropriate for the aim of the study. Our findings show that, in many cases, the machines themselves are very similar with only minor variations. The greatest differentiation lies in what additional value manufacturers offer beyond the product itself. This added value is where the markets great opportunities for development lies. This report will thus provide a new and effective way of analysing a market by considering what a company can offer beyond its products, while also incorporating the unique aspects of what their products actually provide. / Denna rapport belyser marknaden för synkronmaskiner och hur den nuvarande situationen ser ut. Idag kräver världen högre volymer av elektrisk kraft, renare kraft och effektivare kraft framställd från fossilfria källor. Detta leder till en ökad vikt av att använda effektiva och moderna motorer som minskar onödiga energiförluster. En synkronmaskin är en elektrisk motor eller generator med hög effektivitet. Det finns ett behov av ny kunskap om den aktuella situationen på marknaden för att tillverkare ska kunna hålla jämna steg med kraven, regleringarna och samtidigt tillfredsställa sina kunders behov. Den här studien undersöker de främsta trenderna, vilka tillverkare som är i vilka typer av marknader, samt vad för värdeerbjudanden företagen erbjuder sina kunder. En datainsamling i kombination med en serie intervjuer har genomförts för att förstå den nuvarande marknadssituationen samt för att dra slutsatser med hjälp av modeller anpassade för denna studie. Våra resultat visar att i många fall är maskinerna mycket lika varandra med endast små variationer. Den största skillnaden ligger i vad mer tillverkare kan erbjuda utöver själva produkten, d.v.s. i deras värdeerbjudanden. Marknadens största utvecklingsmöjligheter ligger inom vilket mervärde ett företag kan erbjuda sina kunder. Denna rapport kommer därmed bidra med ett nytt och effektivt sätt att läsa av en marknad, som både tar hänsyn till vad företaget kan erbjuda utöver sina produkter samt de unika aspekterna gällande vilka mervärden deras produkter faktiskt genererar.

ITC/USA 2006 Conference Proceedings / The Forty-Second Annual International Telemetering Conference and Technical Exhibition / October 23-26, 2006 / Town and Country Resort & Convention Center, San Diego, California / One of the problems for manufacturers and users of flight test data acquisition equipment, is to guarantee synchronization between multiple units acquiring data on the vehicle. Past solutions have involved proprietary interconnects and multiple wire installations increasing weight and complexity and reducing inter-operation of units. This problem has become particularly important given the trend towards commercial busses, especially Ethernet, as a system interconnect. The IEEE1588 standard offers a way to transmitting time accurately over Ethernet. This paper discusses the standard, how it might be implemented, and examines the issues involved in adopting this standard for flight test data acquisition. A particular implementation that results in a synchronized four-wire Ethernet based distributed data acquisition system is discussed in section 3.

International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / To deliver high bandwidth, a ubiquitous inter-/intra-building cable plant consisting of single mode and multimode fiber as well as twisted pair copper is required. The selection of the "glue" to transport and interconnect distributed LANs with central facility resources over a pervasive cable plant is the focus of this paper. A description of the traditional problems that must be overcome to provide very high bandwidth beyond the narrow confines of a computer center is given. The applicability of Asynchronous Transfer Mode (ATM) switching (interconnection) and Synchronous Optical NETwork (SONET) (transport) for high bandwidth delivery is described using the environment and requirements of Sandia National Laboratories. Other methods for distributing high data rates are compared and contrasted. Sandia is implementing a standards based foundation utilizing a pervasive single mode fiber cable plant, SONET transport, and ATM switching to meet the goals of gigabit networking.