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Static two-dimensional calculation of the capacitance and impedance of open microstrip-like structures using variational methodsPapageorgiou, Vassilios A. 18 August 2009 (has links)
This work examines and implements two different techniques for the estimation of the capacitance and impedance of microstrip-like open structures. Both theories, one developed by Yamashita and Mittra and the other by Itoh and Hebert are based on variational methods. The results for the capacitance and impedance of a microstrip-like structure are calculated numerically and compared with measurements taken using a sample. The results presented in this thesis indicate that the first method produces results with large error and it can be used for microstrip structures with only one strip. The second method produces very accurate results for the microstrip structure under consideration and is the one recommended. / Master of Science
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An automatic test generation method for chip-level circuit descriptionsBarclay, Daniel Scott January 1987 (has links)
An automatic method generates tests for circuits described in a hardware description language (HDL). The input description is in a non-procedural subset of VHDL, with a simplified period-oriented timing model. The fault model, based on previous research, includes micro-operation and control statement faults. The test method uses path-tracing, working directly from the circuit description, not a derived graph or table. Artificial intelligence problem-solving techniques of goals and goal solving are used to represent and manipulate sensitization, justification, and propagation requirements. Backtracking is used to recover from incorrect choices. The method is implemented in ProLog, an artificial intelligence language. Results of this experimental ProLog implementation are summarized and analyzed for strengths and weaknesses of the test method. Suggestions are included to counter the weaknesses. A user's manual is included for the experimental implementation. / M.S.
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On-line pspice based simulation of DC electrical engineering circuitsReddy, Smitha 01 April 2001 (has links)
No description available.
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The dynamic behaviour of distance protection relays on series compensated lines under fault conditions.Magagula, Xolani. January 2014 (has links)
M. Tech. Electrical Engineering / Investigates the reasons behind the poor performance of distance relays on series compensated lines. In order to achieve this objective, a case study will be established in a power system software (DigSilent Power Factory). Furthermore, a practical incident that occurred on Eskom's compensated network will be examined. However, prior to investigating the performance of the distance relay on transmission lines, there are some other critical aspects that have to be thoroughly understood. These aspects include amongst others: transmission line modelling ; numeric relay algorithms ; distance protection philosophies ; series compensation phenomena ; analysis of distance relays performance on both compensated and uncompensated lines and the action and influence of the MOV. The study will provide a better understanding regarding the dynamic behaviour of the impedance protection relay under fault conditions on series compensated lines and the behaviour of the MOV during a fault.
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Life assessment and life extension of high voltage equipment in transmission substations.Singh, Omchand. January 2004 (has links)
In order to sustain transmission grid availability and reliability it is imperative that the
condition of vital and costly high voltage equipment is ascertained on a continuous or
regular basis. It is necessary to establish the effective diagnostic tools or surveillance
devices that can be used to assess equipment condition.
Emphasis has been placed on refining well-established and more novel but
developing condition assessment techniques. It is important to note that condition
assessment of equipment also allows the opportunity to predict failure. Based on a
complete and systematic assessment, the failure of defective equipment may be
evident or predicted in time, thus preventing a forced outage and loss of valuable
'system minutes'. It has also become necessary to extend the life of existing
equipment since most of them are reaching the end of their useful life. Replacement
strategies have proven to be ineffective due to financial and resource constraints
experienced by utilities.
Life extension is the work required to keep equipment operating economically beyond
its anticipated life, with optimum availability, efficiency and safety. One of its principal
components is condition assessment, with the possibility of predicting remnant life.
As a result, refurbishment projects are then raised. Refurbishment by replacement,
uprating, modifications or change of design of certain key components to extend the
life usually requires a substantial amount of capital to be invested. These projects
must be economically justified.
This thesis focuses on establishing condition assessment techniques for major power
equipment such as power transformers. Assessment techniques for instrument
transformers and circuit breakers are included, since these are commonly replaced
or modified under refurbishment projects.
An experimental investigation was carried out to determine the effectiveness of
integrating data of two diagnostic techniques i.e. dissolved gas analysis (on-line) and
acoustic detection of partial discharges. It was found that there is a correlation
between data obtained from an acoustic detection system and an on-line single gas
(Hydrogen) analyser. By integrating the data of both on-line monitoring systems, the
diagnostic process is further enhanced. In addition, the location of a fixed discharge
source was verified by using an acoustic detection system. Further, the sensitivity of
the acoustic technique to partial discharge inception voltage, relative to the
established electrical detection technique was determined for the experimental
arrangement used. The results obtained indicated that this is an effective technique
for the evaluation of activity within a transformer structure. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2004.
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Operating strategies to preserve the adequacy of power systems circuit breakersDam, Quang Binh 24 March 2009 (has links)
The objective of the proposed research is to quantify the limits of overstressed and aging circuit breakers in terms of probability of failure and to provide guidelines to determine network reconfigurations, generator commitment, and economic dispatch strategies that account for these limits. The proposed temporary power system operating strategies address circuit breaker adequacy issues and allow overstressed breakers to be operated longer and more reliably until they are replaced with adequate equipment.
The expansion of electric networks with new power sources (nuclear plants, distributed generation) results in increased short-circuit or fault currents levels. As fault currents increase, they will eventually exceed circuit breaker ratings. Circuit breakers exposed to fault currents in excess of their ratings are said to be overstressed, underrated, or inadequate. Insufficient ratings expose overstressed breakers to increased failure probabilities. Extensive common-mode outages caused by circuit breaker failures reduce the reliability of power systems. To durably avoid outages and system unreliability, overstressed breakers must eventually be replaced.
Large-scale replacements of overstressed breakers cannot be completed in a short time because of budgetary limits, capital improvement schedules, and manufacturer-imposed constraints. Meanwhile, to preserve the ability of old and overstressed breakers to safely interrupt faults, short-circuit currents must be kept within the limits imposed by the ratings and the age of these breakers by using the substation reconfiguration and generator commitment strategies described in this study.
The immediate benefit of the above-mentioned operating strategies is a reduction of the failure probability of overstressed breakers obtained by avoiding the interruption of currents in excess of breaker ratings. Other benefits include (i) increased network reliability, (ii) restored operating margins with respect to existing equipment, and (iii) prioritized equipment upgrades that enhance the long-term planning of power systems.
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Analysis of power ground planesTrinkle, Joachim January 2006 (has links)
[Truncated introduction] A major contribution of this thesis is the observation that the N port impedance parameters for the distribution planes can be modelled as simple LC series elements in the frequency range over which the interesting interactions between the loading elements and the planes occur. Loosely speaking, the C represents the inter-plane capacitance and the L is associated with a first order frequency trend of the transfer and input impedances associated with the planes. In the literature, values for L have been obtained for power ground plane structures using curve fitting techniques [38]. In this thesis, formulae are developed for L based on the modal summation expression. As for the impedance case, the approach developed in the thesis that removes the singular behaviour, results in computational efficient expressions. Preliminary results on the simple LC model were presented by the author in [42, 43] The results reported in the thesis extend this work in the light of the new impedance model proposed. The simple LC characterisation enables the development of new low frequency expression for the input and transfer impedance for ports on planes loaded with many decoupling capacitors. The expressions are based on a one off frequency independent decomposition of the inductance matrix associated with the placement of the capacitors. The eigen-mode decomposition eliminates the need for matrix inversion at each frequency point and leads to an efficient computational procedure for calculating the impedance of loaded planes. Furthermore, the interaction between the capacitors and planes is clearly seen in the analytical expressions. This has led to new insights regarding the interaction of multiple capacitors with supply planes in terms of location, resonance mechanisms, pole locations and damping. These insights are beneficial to the understanding and optimisation of printed circuit board power distribution systems.
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Modelling Wave Power by Equivalent Circuit TheoryHai, Ling January 2015 (has links)
The motion of ocean waves can be captured and converted into usable electricity. This indicates that wave power has the potential to supply electricity to grids like wind or solar power. A point absorbing wave energy converter (WEC) system has been developed for power production at Uppsala University. This system contains a semi-submerged buoy on the water surface driving a linear synchronous generator placed on the seabed. The concept is to connect many small units together, to form a wave farm for large-scale electricity generation. A lot of effort has gone into researching how to enhance the power absorption from each WEC unit. These improvements are normally done separately for the buoy, the generator or the electrical system, due to the fact that modelling the dynamic behavior of the entire WEC system is complicated and time consuming. Therefore, a quick, yet simple, assessment tool is needed. This thesis focuses on studying the use of the equivalent circuit as a WEC system modelling tool. Based on the force analysis, the physical elements in an actual WEC system can be converted into electrical components. The interactions between the regular waves, the buoy, and the Power Take-off mechanism can be simulated together in one circuit network. WEC performance indicators like the velocity, the force, and the power can be simulated directly from the circuit model. Furthermore, the annual absorbed electric energy can be estimated if the wave data statistics are known. The linear and non-linear equivalent circuit models developed in this thesis have been validated with full scale offshore experimental results. Comparisons indicate that the simplest linear circuit can predict the absorbed power reasonably well, while it is not so accurate in estimating the peak force in the connection line. The non-linear circuit model generates better estimations in both cases. To encourage researchers from different backgrounds to adapt and apply the circuit model, an instruction on how to establish a non-linear equivalent circuit model is supplied, as well as on how to apply the model to accelerate the decision making process when planning a WEC system.
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Characterisation of a PEM electrolyser using the current interrupt method / Christiaan Adolph MartinsonMartinson, Christiaan Adolph January 2012 (has links)
The need to characterise a PEM electrolyser is motivated by a South African hydrogen
company. One of two electrochemical characterisation methods, namely the current
interrupt method or electrochemical impedance spectroscopy, is investigated to
characterise the PEM electrolyser. Various literature sources can be found on the
electrochemical characterisation methods.
In this study the current interrupt method is used for the electrochemical characterisation
of a PEM electrolyser. The current interrupt method is an electrical test method
that will be used to obtain an equivalent electric circuit model of the PEM electrolyser.
The equivalent electric circuit model relates to various electrochemical characteristics
such as the activation losses, the ohmic losses and the concentration losses.
Two variants of the current interrupt method, namely the natural voltage response
method and the current switching method, are presented. These methods are used to
obtain two different equivalent electric circuit models of the PEM electrolyser. The
parameters of the first equivalent electric circuit, namely the Randles cell, will be
estimated with the natural voltage response method. The parameters of the second
equivalent electric circuit, namely the Randles-Warburg cell, will be estimated with
the current switching method.
Simulation models of the equivalent electric circuits are developed and tested. The
simulation models are used to verify and validate the natural voltage response method
and the current switching method. The parameters of the Randles cell simulation
model is accurately calculated with the natural voltage response method. The
parameters of the Randles-Warburg cell simulation model is accurately calculated with
the current switching method.
The natural voltage response method and the current switching method are also
practically implemented. The results is used to indicate the various electrochemical
characteristics of the PEM electrolyser. A Nafion 117 type membrane was tested with the current interrupt method. The membrane resistance parameters of Randles cell
were estimated with the natural voltage response method. These values are validated
with conductivity measurements found in literature. The results of the Randles-
Warburg cell is validated with a system identification validation model. / Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013
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Characterisation of a PEM electrolyser using the current interrupt method / Christiaan Adolph MartinsonMartinson, Christiaan Adolph January 2012 (has links)
The need to characterise a PEM electrolyser is motivated by a South African hydrogen
company. One of two electrochemical characterisation methods, namely the current
interrupt method or electrochemical impedance spectroscopy, is investigated to
characterise the PEM electrolyser. Various literature sources can be found on the
electrochemical characterisation methods.
In this study the current interrupt method is used for the electrochemical characterisation
of a PEM electrolyser. The current interrupt method is an electrical test method
that will be used to obtain an equivalent electric circuit model of the PEM electrolyser.
The equivalent electric circuit model relates to various electrochemical characteristics
such as the activation losses, the ohmic losses and the concentration losses.
Two variants of the current interrupt method, namely the natural voltage response
method and the current switching method, are presented. These methods are used to
obtain two different equivalent electric circuit models of the PEM electrolyser. The
parameters of the first equivalent electric circuit, namely the Randles cell, will be
estimated with the natural voltage response method. The parameters of the second
equivalent electric circuit, namely the Randles-Warburg cell, will be estimated with
the current switching method.
Simulation models of the equivalent electric circuits are developed and tested. The
simulation models are used to verify and validate the natural voltage response method
and the current switching method. The parameters of the Randles cell simulation
model is accurately calculated with the natural voltage response method. The
parameters of the Randles-Warburg cell simulation model is accurately calculated with
the current switching method.
The natural voltage response method and the current switching method are also
practically implemented. The results is used to indicate the various electrochemical
characteristics of the PEM electrolyser. A Nafion 117 type membrane was tested with the current interrupt method. The membrane resistance parameters of Randles cell
were estimated with the natural voltage response method. These values are validated
with conductivity measurements found in literature. The results of the Randles-
Warburg cell is validated with a system identification validation model. / Thesis (MIng (Computer and Electronic Engineering))--North-West University, Potchefstroom Campus, 2013
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