No description available.

No description available.

To measure losses in a transformer with today’s methods is either slow or insecure. There s a new method developed by Alstom that hasn't been actualize in to a test-system and that has been the assignment in this project. The idea is built on a switched system and a CLR- circuit in the resonant frequency. The test-system has a calculated power-loss that make the efficiency to be as high as 99,8% and in reality over 95%. But in the end it was discovered that the circuit was only able to deliver 70A when the thought was 200 A. More over was with the frequency of 200 kHz the signal was so distorted that all results over 100 kHz should be questioned. The goal was a efficiency of 99%. That was one of the basis in our calculation and dimensioning. When we order the components we foundbetter than we needed och the efficiency was improved. In the reality the efficiency is 95% and we think it's because the measurements-instruments accuracy and the distortion. In some measurements the efficiency went over 100% and that greatly improve that idea. Every part of the circuit was simulated piece bye piece and then together. That to increase the understanding of the system and to see that themodel works. The simulated efficiency was very low compared to calculated and in reality. The fact was gathered from literature, technical reports from Alstom and meetings with Per Ranstad et. al. / Om man vill mäta förluster på en transformator skerdetta antingen väldigt osäkert eller väldigt långsamt. Det finns en ny metod som Alstomtagit fram, som inte realiserats i ett bestående testsystem förrän nu, vilket har varit detta projekt. Det hela bygger på ett switchat system och en CLR krets i resonansfrekvens. Det resulterade testsystemet hade en beräknad verkningsgrad på 99,8 % och i verkligheten över 95%. Dock i slutskedet upptäcktes att kretsen endast orkade mata ut 70 A jämfört med det tänkta 200 A. Dessutom vid frekvensen 200 kHz blev signalen väldigt förvrängd av störningar och de resultat för frekvenser från 100 kHz och uppåt kan därför ifrågasättas. Vi satte ett mål på en verkningsgrad på 99% som vi grundade våra räkningar och dimensioneringar på. När materialet skulle beställas hittades bättre komponenter än vad vi satt upp och verkningsgraden förbättrades. Varför verklighetens verkningsgrad hamnar på 95% tror vi har med noggrannheten på mätinstrumenten att göra och störningssignalen. Vissa mätningar uppgick till över 100% verkningsgrad som gör att misstankarna för mätinstrumenten stiger. Alla kretsdelar simulerades bit för bit och ihop för att öka förståelsen för systemet samt se att lösningen funkar. Den simulerade verkningsgraden blev väldigt lågt jämfört med beräknat och verkligheten. Fakta vi använt kommer från flera litteraturer, tekniska rapporter från Alstom och möten med Per Ranstad m.fl.

Abstract: This report covers primarily the work of documenting electromagnetic fields generated by one of the later parts in the electrical power distribution chain: The electrical substation, wherein 10 kV is transformed to 400 V for use by private consumers. Thus it is one of the most widespread and frequently occurring parts in the Swedish power grid and of particular interest, as electrical substations are found everywhere in populated areas, often in close vicinity to people and animals. The report deals with a number of formulated questions and/or hypothesis’ stated at the onset of the work undertaken, theory that is relevant for the topics the report covers, the details of the field work undertaken and the following analysis of the readings, which in term provide answers for the questions stated in the beginning. It also covers what is the currently known short term and long term risks associated with electromagnetic fields in the power frequent spectrum and of varying intensity in the vicinity of humans. The analysis also provides recommendations and identifies several points to carefully consider when planning for new installations or replacements of some parts of existing installations. For enhanced reading comprehension there is, aside from sections with pictures and attached explanatory texts and templates, several graphs, one-line diagram and maps of the power grid among the appendixes to the rapport.

Electrical power systems play a key role in production and services in both the industrial and commercial sectors and significantly affect the private lives of citizens. A major asset of any power delivery system is the transformer. Transformers represent extensive investment in any power delivery system, and because of the notable effect of a transformer outage on system reliability, careful management of this type of asset is critical. In North America, a large proportion of transformers is approaching the end of their life and should be replaced. In many cases, unexpected transformer outages can be catastrophic and cause both direct and indirect costs to be incurred by industrial, commercial, and residential sectors. Direct costs include but are not limited to loss of production, idle facilities and labour, damaged or spoiled product, and damage to equipment. For commercial customers, the effects may include damage to electrical and electronic equipment, and in some cases damage to goods. For residential customers, outages may cause food spoilage or damage to electrical equipment. In addition to direct costs, there are several types of indirect costs may also result, such as accidental injuries, looting, vandalism, legal costs, and increases in insurance rates. The main goal of this research was to assess the health and remaining lifetime of a working transformer. This information plays a very important role in the planning strategies of power delivery systems and in the avoidance of the potentially appalling effects of unexpected transformer outages. This thesis presents two different methods of assessing transformer end of life and three distinct methods of determining the health index and health condition of any working transformer. The first method of assessing transformer end of life is based on the use of Monte Carlo technique to simulate the thermal life of the solid insulation in a transformer, the failure of which is the main reason for transformer breakdown. The method developed uses the monthly average ambient temperature and the monthly solar clearness index along with their associated uncertainties in order to estimate the hourly ambient temperature. The average daily load curve and the associated uncertainties in each hourly load are then used to model the transformer load. The inherent uncertainties in the transformer loading and the ambient temperature are used to generate an artificial history of the life of the transformer, which becomes the basis for appraising its remaining lifetime. The second method of assessing transformer end of life is essentially an economic evaluation of the remaining time to the replacement of the transformer, taking into consideration its technical aspects. This method relies on the fact that a transformer fails more frequently during the wear-out period, thus incurring additional maintenance and repair costs. As well, frequent failures increase during this period also costs related to transformer interruptions. Replacing a transformer before it is physically damaged is therefore a wise decision. The bathtub failure model is used to represent the technical aspects of the transformer for the purposes of making the replacement decision. The uncertainties related to the time-to-failure, time-to-repair, time-to-switch, and scheduled maintenance time are modeled using a Monte Carlo simulation technique, which enables the calculation of the repair costs and the cost of interruptions. The repair, operation, and interruption costs are then used to generate equivalent uniform annual costs (EUACs) for the existing transformer and for a new transformer, a comparison of which enables the determination of the most economical replacement year. The case studies conducted using both methods demonstrate their reliability for determining transformer end of life for assessing the appropriate time for replacement. Diagnostic test data for 90 working transformers were used to develop three methods of estimating the health condition of a transformer, which utilities and industries can use in order to assess the health of their transformer fleet. The first method is based on building a linear relation between all parameters of diagnostic data in order to determine a transformer health index, from which the health condition of the transformer can be evaluated. The second method depends on the use of artificial neural networks (ANN) in order to find the health condition of any individual transformer. The diagnostic data for the 90 working transformers together with the health indices calculated for them by means of a specialized transformer asset management and health assessment lab, were used to train an ANN. After the training, the ANN can estimate a health index for any transformer, which can be used in order to determine the health condition of the transformer. The third method is based on finding a relation between the input data and the given health indices (calculated by the specialized transformer asset management and health assessment lab) using the least squares method. This relation then can be used to find the health index and health condition of any working transformer. The health condition determined based on these methods shows excellent correlation with the given health condition calculated by the specialized transformer asset management and health assessment lab.

The partial discharges (PD) measurement approach in power equipments is a very important inspection technique for insulation deterioration assessment. The PD based approach possesses the greatest potential for further development. This study proposes a noncontact type acoustic measurement system. We first investigate an acoustic measurement method in the laboratory. To prove the accuracy of the acoustic measurements, we proceed with, in the laboratory, signal-pattern comparison between the acoustic measurement method and the pulse current method. This study creates polar-coordinate and discharge type identification patterns. We propose the use of the q-£p-t patterns, the polar-coordinate patterns and discharge type identification patterns, with mutual cross-reference, to identify the discharge type. Then this study applies the wavelet transform to suppress noises; a wavelet mother function most similar to the acoustic PD signals is chosen and then set the filtering threshold value for the wavelet transform. The signals' features will be extracted after the noises are eliminated. The experimental results indicate that the application of wavelet transform can effectively eliminate the field noises. Next, the features will be used to build the training database for the back-propagation neural network (BNN) to construct the discharge patterns' recognition and identification system. Finally, we apply the finished neural networks to field signal-pattern identification. The proposed acoustic measurement system is applied on line to epoxy-resin transformers, power distributors, and the like. The superior measurement results we obtained shall be able to correctly identify power equipment's PD fault types.

No description available.

The design, simulation, and measurement of two bulk-driven down-conversion mixers with on-chip transformer baluns in 0.18 μm CMOS is presented. Applying either the RF signal or the local oscillator (LO) signal to the bulk connection of the transistors allows the amplification and switching stages of a conventional mixer to be combined into a single stage, thus improving the voltage headroom of the mixer. The addition of a transformer balun to the mixers improves the input impedance match, provides passive voltage gain, and performs single-ended to balanced conversion. A semi-analytical power-series analysis of the mixers is also presented. The mixer in which the RF signal is applied to the gates of the mixing transistors achieves a measured input-referred 1-dB compression point (P1dB) of −14 dBm, an input-referred third-order intercept point (IIP3) of −5.2 dBm, a gain of 13.6 dB, a noise figure (NF) of 26 dB, and an LO-to-RF isolation of 50 dB. The overall performance of both mixers is found to be comparable with other CMOS mixers, but with a higher noise figure (which can be mitigated with a high gain low-noise amplifier (LNA)).

就全世界來看，大型電力變壓器仍是個高度成長的產業，由於其資金以及技術門檻均高，台灣有能力製造大型變壓器的廠商僅4家，但是又因台灣市場規模過小，無法支撐該產業的成長，故廠商紛紛有了必須至海外開拓市場的壓力。而由於大型電力變壓器的特殊性，相關研究較少，故本研究主要針對那些因素影響大型電力變壓器廠商在地主國經營進行研究，同時希望提供給業者相關建議。在研究中，主要針對內、外部的影響因素來進行個案的探討。內部方面，透過文獻探討，本研究選擇了母公司策略、母公司資源，以及母公司管控三個要素來觀察；外部方面則是針對地主國市場特性的研究。觀察個案公司在內、外部的眾多因素影響之下，其子公司的策略構想、組織架構與運作流程，以及行銷組合上有何異同，並進一步觀察並比較其績效的良窳。 研究發現，母公司的策略是向海外發展子公司的主要因素，而子公司的策略構想則會受到當地市場機會的影響；在子公司的管控方面，為了便於整合與管控，子公司主要的組織設計以及流程會依循母公司的管理架構，但是又由於市場特殊性的不同，當有需要不同的在地人才或是其他資源時，則會進行微調，而此時母公司也會依照子公司的需求以及自身的資源狀況提供所需的資源；而在子公司的行銷組合方面，則是主要受到當地市場特性所影響。

This thesis first describes the reverse method of transformer design. An existing magnetic model for full-core shell-type transformers, based on circuit theory, is summarised. A magneto-static finite element model is introduced and two sample transformers are analysed. The magnetic model based on finite element analysis is shown to be more accurate than the model based on circuit theory. Partial-core resonant transformers are then introduced and their characteristics are explained using an equivalent circuit model. A method of measuring the winding inductances under resonant operation is developed and used to investigate the characteristics of two different tuning methods. A finite element model of the partial-core resonant transformer is developed by adopting the model for full-core shell-type transformers. The model results accurately match the measured inductance variation characteristics of three sample transformers and predict the onset of core saturation in both axial-offset and centre-gap arrangements. A new design of partial-core resonant transformer is arrived at, having an alternative core and winding layout, as well as multiple winding taps. The finite element model is extended to accommodate the new design and a framework of analysis tools is developed. A general design methodology for partial-core resonant transformers with fixed inductance is developed. A multiple design method is applied to obtain an optimal design for a given set of specifications and restrictions. The design methodology is then extended to devices with variable inductance. Three design examples of partial-core resonant transformers with variable inductance are presented. In the first two design examples, existing devices are replaced. The new transformer designs are significantly lighter and the saturation effects are removed. The third design example is a kitset for high-voltage testing, with the capability to test any hydro-generator stator in New Zealand. The kitset is built and tested in the laboratory, demonstrating design capability. Other significant test results, for which no models have yet been developed, are also presented. Heating effects in the core are reduced by adopting an alternative core construction method, where the laminations are stacked radially, rather than in the usual parallel direction. The new kitset is yet to be used in the field.