Statistical analysis of frequency and duration of forced outages for subtransmission transformers
- Authors: Mendu, Bongumsa Welcome
- Date: 2019
- Subjects: Electric transformers , Electric power failures
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/393839 , uj:32601
- Description: Abstract : In a power system, the function of a power transformer is to adjust the voltage to an appropriate value in different parts of the power grid by stepping it up or down. However, power transformer outages are a major source of unreliability of power supply and their outage directly affects the system. Transformer outages contribute significantly to financial loss due to power outages and the high cost of repair or replacement. Hence, power transformer outages constitute an important subject that needs to be investigated. A literature review on analysis of outages for power transformer population was done. Factors such as voltage levels, age and transformer ranges were considered in various studies. Several studies analysed different data lengths of transformers outages. Previous studies also addressed number of failures. Statistical methods and models such as Weibull distribution, regression model, Cox’s regression model, probability density function, were utilised in the analyses. However, no previous studies considered subtransmission transformer outages for primary voltages ranging between 44 – 132 kV. It was observed that the frequency of subtransmission transformer outages, in terms of various variables of events, had not been analysed previously. No studies had investigated the dependence of variables and the significance of that dependence between variables before. The duration of outages for distribution network components had been studied, but no studies particular to subtransmission transformer outages had been done. The aim of this study was to analyse the historical subtransmission transformer forced outage data for transformers with primary voltage of 44 kV, 66 kV, 88 kV and 132 kV based on 10-year data. The focus of the study was to analyse subtransmission transformer forced outages with respect to frequency and duration, utilising statistical techniques. Under the frequency of forced outages, the combination of actual number of outages and failure rates allowed the identification of critical levels of variables that needed prioritisation in order to improve frequency of forced outages. The bivariate bar graphs, combined with chi-squared test,... , M.Phil. (Electrical Engineering)
- Full Text:
- Authors: Mendu, Bongumsa Welcome
- Date: 2019
- Subjects: Electric transformers , Electric power failures
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/393839 , uj:32601
- Description: Abstract : In a power system, the function of a power transformer is to adjust the voltage to an appropriate value in different parts of the power grid by stepping it up or down. However, power transformer outages are a major source of unreliability of power supply and their outage directly affects the system. Transformer outages contribute significantly to financial loss due to power outages and the high cost of repair or replacement. Hence, power transformer outages constitute an important subject that needs to be investigated. A literature review on analysis of outages for power transformer population was done. Factors such as voltage levels, age and transformer ranges were considered in various studies. Several studies analysed different data lengths of transformers outages. Previous studies also addressed number of failures. Statistical methods and models such as Weibull distribution, regression model, Cox’s regression model, probability density function, were utilised in the analyses. However, no previous studies considered subtransmission transformer outages for primary voltages ranging between 44 – 132 kV. It was observed that the frequency of subtransmission transformer outages, in terms of various variables of events, had not been analysed previously. No studies had investigated the dependence of variables and the significance of that dependence between variables before. The duration of outages for distribution network components had been studied, but no studies particular to subtransmission transformer outages had been done. The aim of this study was to analyse the historical subtransmission transformer forced outage data for transformers with primary voltage of 44 kV, 66 kV, 88 kV and 132 kV based on 10-year data. The focus of the study was to analyse subtransmission transformer forced outages with respect to frequency and duration, utilising statistical techniques. Under the frequency of forced outages, the combination of actual number of outages and failure rates allowed the identification of critical levels of variables that needed prioritisation in order to improve frequency of forced outages. The bivariate bar graphs, combined with chi-squared test,... , M.Phil. (Electrical Engineering)
- Full Text:
The impact of harmonic distortion on power transformers operating near the thermal limit
- Authors: Geduldt, Owen Christopher
- Date: 2009-02-26T12:19:56Z
- Subjects: Electric distortion , Harmonics (Electric waves) , Eddy currents (Electric) , Electric transformers
- Type: Thesis
- Identifier: uj:8160 , http://hdl.handle.net/10210/2166
- Description: M.Ing. , The study looks into the impact of harmonic distortion on power-plant equipment in general, and then focuses on the impact it has on power transformers operating near the thermal limit. The feasibility of the study is firstly evaluated and then the theory on harmonics and transformer losses is analysed. The study had been narrowed down to power transformers due to the high numbers of failures nationally and internationally attributed to unknown causes. A transformer model is then developed through theoretical considerations. Finally, a case study is done on the capability of a fully loaded transformer under harmonics conditions evaluated through transformer capability calculations and the proposed transformer model. Thereafter the transformer model developed is verified with measured results. The main impact of harmonic current distortion on power transformers is an increase in the rated power losses that results in a temperature rise inside the power transformer. The heat build-up can lead to degradation of insulation, which can shorten the transformer’s life and lead to eventual breakdown. The harmonic current distortion impacts transformer losses – namely, ohmic losses, the winding eddy current losses and other stray losses. All of these harmonic effects on transformer losses are verified theoretically, mathematically and practically. The harmonic impact on the transformer capability is then evaluated through a numerical example of a transformer feeding a harmonic load. The transformer capability is determined via two methods – namely, harmonic capability calculations in the standard “IEEE Recommended Practice for Establishing Transformer Capability when Supplying Nonsinusoidal Load Currents”, [11] and a proposed transformer model derived from theoretical and mathematical analysis. The results show that an increase in the winding eddy current losses can decrease the maximum permissible nonsinusoidal load current substantially. If the load current of the transformer is derated accordingly it translates into a loss of the output power capacity of the power transformer. The standard recommended capability calculations for winding eddy current losses are conservative and not satisfactorily accurate. This results in a large loss of power capacity. The proposed transformer model includes a parameter that estimates the winding eddy current loss in the transformer that results in a smaller loss in power capacity. Furthermore, it was shown that the harmonic current distortion levels could exceed the permissible levels although the harmonic voltage distortion levels are within acceptable levels. The proposed transformer equivalent model is thereafter practically verified with experimental results of papers published by M.A.S. Masoum, E.F. Fuchs and D.J. Roesler, [19], [20] and [29].
- Full Text:
- Authors: Geduldt, Owen Christopher
- Date: 2009-02-26T12:19:56Z
- Subjects: Electric distortion , Harmonics (Electric waves) , Eddy currents (Electric) , Electric transformers
- Type: Thesis
- Identifier: uj:8160 , http://hdl.handle.net/10210/2166
- Description: M.Ing. , The study looks into the impact of harmonic distortion on power-plant equipment in general, and then focuses on the impact it has on power transformers operating near the thermal limit. The feasibility of the study is firstly evaluated and then the theory on harmonics and transformer losses is analysed. The study had been narrowed down to power transformers due to the high numbers of failures nationally and internationally attributed to unknown causes. A transformer model is then developed through theoretical considerations. Finally, a case study is done on the capability of a fully loaded transformer under harmonics conditions evaluated through transformer capability calculations and the proposed transformer model. Thereafter the transformer model developed is verified with measured results. The main impact of harmonic current distortion on power transformers is an increase in the rated power losses that results in a temperature rise inside the power transformer. The heat build-up can lead to degradation of insulation, which can shorten the transformer’s life and lead to eventual breakdown. The harmonic current distortion impacts transformer losses – namely, ohmic losses, the winding eddy current losses and other stray losses. All of these harmonic effects on transformer losses are verified theoretically, mathematically and practically. The harmonic impact on the transformer capability is then evaluated through a numerical example of a transformer feeding a harmonic load. The transformer capability is determined via two methods – namely, harmonic capability calculations in the standard “IEEE Recommended Practice for Establishing Transformer Capability when Supplying Nonsinusoidal Load Currents”, [11] and a proposed transformer model derived from theoretical and mathematical analysis. The results show that an increase in the winding eddy current losses can decrease the maximum permissible nonsinusoidal load current substantially. If the load current of the transformer is derated accordingly it translates into a loss of the output power capacity of the power transformer. The standard recommended capability calculations for winding eddy current losses are conservative and not satisfactorily accurate. This results in a large loss of power capacity. The proposed transformer model includes a parameter that estimates the winding eddy current loss in the transformer that results in a smaller loss in power capacity. Furthermore, it was shown that the harmonic current distortion levels could exceed the permissible levels although the harmonic voltage distortion levels are within acceptable levels. The proposed transformer equivalent model is thereafter practically verified with experimental results of papers published by M.A.S. Masoum, E.F. Fuchs and D.J. Roesler, [19], [20] and [29].
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Integreerbare stuurtegnologie vir bipolere drywingselektroniese skakelaars tot 2000 A
- Van der Merwe, Gabriel Jacobus
- Authors: Van der Merwe, Gabriel Jacobus
- Date: 2014-02-12
- Subjects: Electric transformers
- Type: Thesis
- Identifier: uj:3933 , http://hdl.handle.net/10210/9295
- Description: M.Ing. (Electrical and Electronic Engineering) , In an attempt to build a 2000A transistor switch. with the possibility of integrating the electromagnetic components, different transistor switch and transformer configurations were investigated and compared. A standard high frequency monolithic transformer was investigated for the integration with the rest of the circuit. Different problems were found as will be discussed. A saturation of the transformer to one side occurred, and a control circuit for this was developed and is discussed. A different approach to transformers, matrix transformers, was investigated for the application in high current, low voltage supplies, such as a compensating supply for a compensated Darlington transistor. From the matrix transformers a new kind of transformer connection style, namely a symmetric transformer, followed. The symmetrical transformer was investigated for the possible use in monolitic transformers, and compared with halfbridge, fullbridge and push-pull transformer configurations. It was decided to proceed further with matrix transformers. A design of a 400A 1.5Vsupply, was done to serve as a compensating supply in a 2000A compensated Darlington transistor switch. The supply was built up and analysed. Different switch configurations were investigated for use as possible transistor switches. The compensated Darlington was considered to be the best. Unexpected switch off problems occurred. These are discussed and an optimum switch off topology is suggested. A 2000A transistor switch was designed and built. Full current could not be reached and results are presented up to 650A.
- Full Text:
- Authors: Van der Merwe, Gabriel Jacobus
- Date: 2014-02-12
- Subjects: Electric transformers
- Type: Thesis
- Identifier: uj:3933 , http://hdl.handle.net/10210/9295
- Description: M.Ing. (Electrical and Electronic Engineering) , In an attempt to build a 2000A transistor switch. with the possibility of integrating the electromagnetic components, different transistor switch and transformer configurations were investigated and compared. A standard high frequency monolithic transformer was investigated for the integration with the rest of the circuit. Different problems were found as will be discussed. A saturation of the transformer to one side occurred, and a control circuit for this was developed and is discussed. A different approach to transformers, matrix transformers, was investigated for the application in high current, low voltage supplies, such as a compensating supply for a compensated Darlington transistor. From the matrix transformers a new kind of transformer connection style, namely a symmetric transformer, followed. The symmetrical transformer was investigated for the possible use in monolitic transformers, and compared with halfbridge, fullbridge and push-pull transformer configurations. It was decided to proceed further with matrix transformers. A design of a 400A 1.5Vsupply, was done to serve as a compensating supply in a 2000A compensated Darlington transistor switch. The supply was built up and analysed. Different switch configurations were investigated for use as possible transistor switches. The compensated Darlington was considered to be the best. Unexpected switch off problems occurred. These are discussed and an optimum switch off topology is suggested. A 2000A transistor switch was designed and built. Full current could not be reached and results are presented up to 650A.
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Tabu search-based optimal choice of lines for voltage derating in lightly loaded, high voltage constrained networks
- Authors: Melato, Popi Elizabeth
- Date: 2016
- Subjects: Electric power systems , Electric power systems - Control , Electric power system stability , Electric transformers
- Language: English
- Type: Masters (Thesis)
- Identifier: http://ujcontent.uj.ac.za8080/10210/388755 , http://hdl.handle.net/10210/213418 , uj:21150
- Description: Abstract: In power system planning, the general concern is the ability of a power system to supply increasing loads without undervoltages. Nonetheless, decrease in loads can also occur in power systems, e.g., when mines are decommissioned leading to shrinkage in load. Depending on the scale of the load reduction, problem of steady overvoltages can arise. This study proposes an investigation of using of step-down transformers to reduce steady state overvoltages in a lightly loaded network comprising of long corridors. The investigation evaluates the proposal of installing transformers at both ends of the length network, forming a ring of transformers to derate the operating voltage of the derated network. The load flow simulation studies are initially carried out manually by scaling the load down using the Power System Software for Engineers (PSS/E). The load flow studies for the lowest load served without violations are carried out for the case without transformers and the derated case with transformers. The study further proposed the use of Python program to automate the studies through scaling the load down until the voltage limits are reached by sending commands to PSS/E using Python syntax. In addition to this, the use of Tabu Search (TS) algorithm is proposed for optimally selecting a combination of lines to accommodate the least load within the voltage limits. The load is scaled down automatically in PSS/E using Python program with the least load served as an objective function and the constraints being the voltage limits. The study found that the use of step-down transformers can successfully reduce the steady state overvoltages in a lightly loaded network. The introduction of Python program to automate the studies was successful. Lastly, intelligence of Tabu Search algorithm can successfully select the optimal combination of lines to serve the least load without voltage violations. , M.Phil. (Electrical and Electronic Engineering)
- Full Text:
- Authors: Melato, Popi Elizabeth
- Date: 2016
- Subjects: Electric power systems , Electric power systems - Control , Electric power system stability , Electric transformers
- Language: English
- Type: Masters (Thesis)
- Identifier: http://ujcontent.uj.ac.za8080/10210/388755 , http://hdl.handle.net/10210/213418 , uj:21150
- Description: Abstract: In power system planning, the general concern is the ability of a power system to supply increasing loads without undervoltages. Nonetheless, decrease in loads can also occur in power systems, e.g., when mines are decommissioned leading to shrinkage in load. Depending on the scale of the load reduction, problem of steady overvoltages can arise. This study proposes an investigation of using of step-down transformers to reduce steady state overvoltages in a lightly loaded network comprising of long corridors. The investigation evaluates the proposal of installing transformers at both ends of the length network, forming a ring of transformers to derate the operating voltage of the derated network. The load flow simulation studies are initially carried out manually by scaling the load down using the Power System Software for Engineers (PSS/E). The load flow studies for the lowest load served without violations are carried out for the case without transformers and the derated case with transformers. The study further proposed the use of Python program to automate the studies through scaling the load down until the voltage limits are reached by sending commands to PSS/E using Python syntax. In addition to this, the use of Tabu Search (TS) algorithm is proposed for optimally selecting a combination of lines to accommodate the least load within the voltage limits. The load is scaled down automatically in PSS/E using Python program with the least load served as an objective function and the constraints being the voltage limits. The study found that the use of step-down transformers can successfully reduce the steady state overvoltages in a lightly loaded network. The introduction of Python program to automate the studies was successful. Lastly, intelligence of Tabu Search algorithm can successfully select the optimal combination of lines to serve the least load without voltage violations. , M.Phil. (Electrical and Electronic Engineering)
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Enhanced voltage regulation in lightly-loaded, meshed distribution networks using a phase shifting transformer
- Authors: Sithole, Frederick Silence
- Date: 2013-06-03
- Subjects: Electric transformers , Electric power systems - Load dispatching , Electric power plants - Load , Voltage regulators
- Type: Thesis
- Identifier: uj:7576 , http://hdl.handle.net/10210/8439
- Description: M.Ing. (Electrical and Electronic Engineering) , Long transmission lines in power system require high line loading in order to lower voltage limits due to line losses. For relatively long lines, line charging is high and thus higher voltage limits reached at low loading. It follows then that it is a challenge to maintaining the voltages between the acceptable limits for relatively long lines. This dissertation highlights the problems experienced when load varying from very low to very high is supplied by very long parallel lines of different impedance characteristic. When the load is extremely high, there are low voltages experienced which are solved by use of shunt capacitors and/or adding more lines. When the load is extremely low, there are high voltages experienced which are solved by use of shunt reactors and/or switching some of the lines off. The type of solutions to this two loading extremes as indicated above, can be problematic, in that; new lines requires servitudes which can take too long, shunt capacitors and reactors in this type of the network is not desirable since the introduction of too many of these devices have maintenance implications and they would require continuous switching to maintain acceptable voltages, resulting in complicated operation of the network. This research proposes the use of a phase shifting transformer located on one of two parallel corridors supplying power to a load located remotely from the rest of the system. The transformer is able to rearrange the active power flows to vary loadings of the corridors and the improvements in voltage regulation can be realised during both low and high load conditions.
- Full Text:
- Authors: Sithole, Frederick Silence
- Date: 2013-06-03
- Subjects: Electric transformers , Electric power systems - Load dispatching , Electric power plants - Load , Voltage regulators
- Type: Thesis
- Identifier: uj:7576 , http://hdl.handle.net/10210/8439
- Description: M.Ing. (Electrical and Electronic Engineering) , Long transmission lines in power system require high line loading in order to lower voltage limits due to line losses. For relatively long lines, line charging is high and thus higher voltage limits reached at low loading. It follows then that it is a challenge to maintaining the voltages between the acceptable limits for relatively long lines. This dissertation highlights the problems experienced when load varying from very low to very high is supplied by very long parallel lines of different impedance characteristic. When the load is extremely high, there are low voltages experienced which are solved by use of shunt capacitors and/or adding more lines. When the load is extremely low, there are high voltages experienced which are solved by use of shunt reactors and/or switching some of the lines off. The type of solutions to this two loading extremes as indicated above, can be problematic, in that; new lines requires servitudes which can take too long, shunt capacitors and reactors in this type of the network is not desirable since the introduction of too many of these devices have maintenance implications and they would require continuous switching to maintain acceptable voltages, resulting in complicated operation of the network. This research proposes the use of a phase shifting transformer located on one of two parallel corridors supplying power to a load located remotely from the rest of the system. The transformer is able to rearrange the active power flows to vary loadings of the corridors and the improvements in voltage regulation can be realised during both low and high load conditions.
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Toepassing van hoë frekwensie mutators in sweismasjiene
- Authors: Van Rhyn, Pierre
- Date: 2014-02-13
- Subjects: Welding - Equipment and supplies , Electric transformers
- Type: Thesis
- Identifier: uj:3939 , http://hdl.handle.net/10210/9300
- Description: M.Ing. (Electrical & Electronic Engineering) , Please refer to full text to view abstract
- Full Text:
- Authors: Van Rhyn, Pierre
- Date: 2014-02-13
- Subjects: Welding - Equipment and supplies , Electric transformers
- Type: Thesis
- Identifier: uj:3939 , http://hdl.handle.net/10210/9300
- Description: M.Ing. (Electrical & Electronic Engineering) , Please refer to full text to view abstract
- Full Text:
Dynamic and steady state behaviour of a synchronous reluctance machine with leading reactive power through an auxiliary winding
- Ogunjuyigbe, Ayodeji Samson, Jimoh, Adisa A., Nicolae, Dan-Valentin
- Authors: Ogunjuyigbe, Ayodeji Samson , Jimoh, Adisa A. , Nicolae, Dan-Valentin
- Date: 2007
- Subjects: Electric machinery , Electric transformers
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/15599 , uj:15680 , Citation: Ogunjuyigbe, A.S., Jimoh, A.A. & Nicolae, D.V. 2007.Improving synchronous reluctance machine performance by direct capacitance injection through an auxiliary winding. Proceedings of the International Conference on Electrical Machines and Systems ICEMS 2007, paper IMP-05:1055-1060.
- Description: In attempt to improve the performance of synchronous reluctance machine the structure of the machine is modified to include an additional winding on the stator and injection of capacitance. This paper examines the dynamic and steady state behaviour of the modified machine based on its mathematical model and experiments performed on a practical prototype. The experimental results corroborate the solutions of the mathematical model as obtained through simulation. The modified machine shows significant improvement in performance over the conventional one.
- Full Text:
- Authors: Ogunjuyigbe, Ayodeji Samson , Jimoh, Adisa A. , Nicolae, Dan-Valentin
- Date: 2007
- Subjects: Electric machinery , Electric transformers
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/15599 , uj:15680 , Citation: Ogunjuyigbe, A.S., Jimoh, A.A. & Nicolae, D.V. 2007.Improving synchronous reluctance machine performance by direct capacitance injection through an auxiliary winding. Proceedings of the International Conference on Electrical Machines and Systems ICEMS 2007, paper IMP-05:1055-1060.
- Description: In attempt to improve the performance of synchronous reluctance machine the structure of the machine is modified to include an additional winding on the stator and injection of capacitance. This paper examines the dynamic and steady state behaviour of the modified machine based on its mathematical model and experiments performed on a practical prototype. The experimental results corroborate the solutions of the mathematical model as obtained through simulation. The modified machine shows significant improvement in performance over the conventional one.
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Accurate modelling and experimental measurement of losses in planar inductors
- Authors: Imre, Tarik Gurhan
- Date: 2012-01-24
- Subjects: Electric inductors , Electric transformers , Electric circuits , Power electronics
- Type: Thesis
- Identifier: uj:1928 , http://hdl.handle.net/10210/4289
- Description: M.Ing. , Low profile power electronics components are currently in great demand. The rapid advances in semiconductor and micro-electronics technology during the last ten years have played a major role in the creation of this demand. These advances are in turn driven by the need for compact design in computing, communication, consumer electronic goods and control systems with direct consequences in power supply design and manufacture. The study covered by this thesis involves the design, manufacture and thermal analysis of a planar inductor, which is a typical planar power electronics component. First, a throughout literature survey of planar magnetics revealed that satisfactory experimental procedures for the thermal analysis of passive power electronic components under operating conditions representative of modern applications are seldomly applied. Secondly, a computer based field-solver program and analytical methods are used to design and analyse a planar inductor. The applicability of different methods for determination of low power loss in passive components is discussed next. Finally, an experimental method suitable for low power loss determination is proposed and investigated. This method can be used in the analysis of inductors or capacitors of different sizes. It has a wide spectrum of application due to the advantages of frequency independence and different possible power levels.
- Full Text:
- Authors: Imre, Tarik Gurhan
- Date: 2012-01-24
- Subjects: Electric inductors , Electric transformers , Electric circuits , Power electronics
- Type: Thesis
- Identifier: uj:1928 , http://hdl.handle.net/10210/4289
- Description: M.Ing. , Low profile power electronics components are currently in great demand. The rapid advances in semiconductor and micro-electronics technology during the last ten years have played a major role in the creation of this demand. These advances are in turn driven by the need for compact design in computing, communication, consumer electronic goods and control systems with direct consequences in power supply design and manufacture. The study covered by this thesis involves the design, manufacture and thermal analysis of a planar inductor, which is a typical planar power electronics component. First, a throughout literature survey of planar magnetics revealed that satisfactory experimental procedures for the thermal analysis of passive power electronic components under operating conditions representative of modern applications are seldomly applied. Secondly, a computer based field-solver program and analytical methods are used to design and analyse a planar inductor. The applicability of different methods for determination of low power loss in passive components is discussed next. Finally, an experimental method suitable for low power loss determination is proposed and investigated. This method can be used in the analysis of inductors or capacitors of different sizes. It has a wide spectrum of application due to the advantages of frequency independence and different possible power levels.
- Full Text:
Translational contactless power supply systems with ultrasonic frequencies
- Authors: Barnard, Jacobus Marthinus
- Date: 2012-11-27
- Subjects: Power resources , Electric current converters , Electric transformers
- Type: Thesis
- Identifier: uj:7412 , http://hdl.handle.net/10210/8242
- Description: D.Ing. , In this thesis, contactless power transmission with sliding transformers to mobile loads is investigated. The sliding transformer comprises an extended primary winding - placed along the path of travel - which is fed through a core containing a secondary winding and which is attached to a mobile load. In the first chapter problems with existing power supply systems are discussed whereafter several possible applications of such a system are identified. In this chapter different methods of obtaining contactless power transmission are also discussed and a brief discussion of a practical, cost effective system is given. In chapter two the application of different resonant topologies to compensate the large structural inductance of the sliding transformer is investigated. A Series Resonant, Series Loaded topology is identified as the most practical and efficient topology for this application and a more detailed analysis of this topology - as applied to this case - is given. Formulas to calculate the sliding transformer parameters are given in the third chapter and two quantities relating the optimization of sliding transformers to the parameters thereof, are defined. Methods to optimize sliding transformers in terms of these two quantities, and also with respect to EMI, are also discussed in this chapter. The design of a five meter long experimental system which delivers 15 kVA to a mobile load is given in chapter four and experimental results of this system are presented. In chapter five a detailed investigation into different output power control methods is conducted. The effect of these control methods on EMI is investigated by means of numerical simulation of a Series Resonant, Series Loaded system under these different control methods. The most complex control method which generates the most EMI, namely frequency and pulse burst control, is implemented into the experimental system to investigate the limitations thereof. Experimental results of this controlled system are presented. It is found that this control method increases the control range obtainable with classical frequency control but introduces many limitations due to discontinuous primary current. It is concluded in the last chapter that it is possible to optimize sliding transformers within achievable cost constraints to such an extent that such systems have acceptable efficiencies and that reasonable system lengths are obtainable.
- Full Text:
- Authors: Barnard, Jacobus Marthinus
- Date: 2012-11-27
- Subjects: Power resources , Electric current converters , Electric transformers
- Type: Thesis
- Identifier: uj:7412 , http://hdl.handle.net/10210/8242
- Description: D.Ing. , In this thesis, contactless power transmission with sliding transformers to mobile loads is investigated. The sliding transformer comprises an extended primary winding - placed along the path of travel - which is fed through a core containing a secondary winding and which is attached to a mobile load. In the first chapter problems with existing power supply systems are discussed whereafter several possible applications of such a system are identified. In this chapter different methods of obtaining contactless power transmission are also discussed and a brief discussion of a practical, cost effective system is given. In chapter two the application of different resonant topologies to compensate the large structural inductance of the sliding transformer is investigated. A Series Resonant, Series Loaded topology is identified as the most practical and efficient topology for this application and a more detailed analysis of this topology - as applied to this case - is given. Formulas to calculate the sliding transformer parameters are given in the third chapter and two quantities relating the optimization of sliding transformers to the parameters thereof, are defined. Methods to optimize sliding transformers in terms of these two quantities, and also with respect to EMI, are also discussed in this chapter. The design of a five meter long experimental system which delivers 15 kVA to a mobile load is given in chapter four and experimental results of this system are presented. In chapter five a detailed investigation into different output power control methods is conducted. The effect of these control methods on EMI is investigated by means of numerical simulation of a Series Resonant, Series Loaded system under these different control methods. The most complex control method which generates the most EMI, namely frequency and pulse burst control, is implemented into the experimental system to investigate the limitations thereof. Experimental results of this controlled system are presented. It is found that this control method increases the control range obtainable with classical frequency control but introduces many limitations due to discontinuous primary current. It is concluded in the last chapter that it is possible to optimize sliding transformers within achievable cost constraints to such an extent that such systems have acceptable efficiencies and that reasonable system lengths are obtainable.
- Full Text:
Dynamic and steady state behavior of a synchronous reluctance machine with leading reactive power through an auxiliary winding
- Ogunjuyigbe, Ayodeji Samson, Jimoh, Adisa A., Nicolae, Dan-Valentin
- Authors: Ogunjuyigbe, Ayodeji Samson , Jimoh, Adisa A. , Nicolae, Dan-Valentin
- Date: 2008
- Subjects: Electric machinery , Electric transformers
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/18445 , uj:16000 , Citation: Ongunjuyigbe, A.S.O, Jimoh, A.A. & Nicolae, D.A. 2008. Dynamic and steady state behavior of a synchronous reluctance machine with leading reactive power through an auxiliary winding. Proceedings of the 9th International Conference on Modeling and Simulation of Electric Machines, Converters and Systems ELECTRIMACS, June 2008.
- Description: Abstract In attempt to improve the performance of synchronous reluctance machine the structure of the machine is modified to include an additional winding on the stator and injection of capacitance. This paper examines the dynamic and steady state behaviour of the modified machine based on its mathematical model and experiments performed on a practical prototype. The experimental results corroborate the solutions of the mathematical model as obtained through simulation. The modified machine shows significant improvement in performance over the conventional one.
- Full Text:
- Authors: Ogunjuyigbe, Ayodeji Samson , Jimoh, Adisa A. , Nicolae, Dan-Valentin
- Date: 2008
- Subjects: Electric machinery , Electric transformers
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/18445 , uj:16000 , Citation: Ongunjuyigbe, A.S.O, Jimoh, A.A. & Nicolae, D.A. 2008. Dynamic and steady state behavior of a synchronous reluctance machine with leading reactive power through an auxiliary winding. Proceedings of the 9th International Conference on Modeling and Simulation of Electric Machines, Converters and Systems ELECTRIMACS, June 2008.
- Description: Abstract In attempt to improve the performance of synchronous reluctance machine the structure of the machine is modified to include an additional winding on the stator and injection of capacitance. This paper examines the dynamic and steady state behaviour of the modified machine based on its mathematical model and experiments performed on a practical prototype. The experimental results corroborate the solutions of the mathematical model as obtained through simulation. The modified machine shows significant improvement in performance over the conventional one.
- Full Text:
Synchronous reluctance machine with magnetically-coupled, double three-phase windings
- Ogunjuyigbe, A. S. O., Obe, E. S., Nicolae, Dan-Valentin, Jimoh, A. A.
- Authors: Ogunjuyigbe, A. S. O. , Obe, E. S. , Nicolae, Dan-Valentin , Jimoh, A. A.
- Date: 2009
- Subjects: Electromagnetism , Electric transformers
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22421 , uj:16198 , Citation: Ogunjuyigbe, A.S.O, et al. 2009. Synchronous reluctance machine with magnetically-coupled, double three-phase windings. Proceedings of the Electromotion Joint Symposium, 1-3 September 2009, Lille, France.
- Description: Abstract: Please refer to full text to view abstract Please refer to full text to view abstract
- Full Text:
- Authors: Ogunjuyigbe, A. S. O. , Obe, E. S. , Nicolae, Dan-Valentin , Jimoh, A. A.
- Date: 2009
- Subjects: Electromagnetism , Electric transformers
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/22421 , uj:16198 , Citation: Ogunjuyigbe, A.S.O, et al. 2009. Synchronous reluctance machine with magnetically-coupled, double three-phase windings. Proceedings of the Electromotion Joint Symposium, 1-3 September 2009, Lille, France.
- Description: Abstract: Please refer to full text to view abstract Please refer to full text to view abstract
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Serie injeksie as alternatief tot tapverstelbare transformators in EGAT kragverspreidingsnetwerke
- Van Niekerk, Hendrik Christoffel
- Authors: Van Niekerk, Hendrik Christoffel
- Date: 2015-10-14
- Subjects: Electric power distribution - South Africa , Electric transformers
- Type: Thesis
- Identifier: uj:14348 , http://hdl.handle.net/10210/14806
- Description: M.Ing. (Electrical and Electronic Engineering) , Please refer to full text to view abstract
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- Authors: Van Niekerk, Hendrik Christoffel
- Date: 2015-10-14
- Subjects: Electric power distribution - South Africa , Electric transformers
- Type: Thesis
- Identifier: uj:14348 , http://hdl.handle.net/10210/14806
- Description: M.Ing. (Electrical and Electronic Engineering) , Please refer to full text to view abstract
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Optimalisasie van stelsels met wisselspanningstussenkringmutators as elektroniese koppelstelsels tussen wisselspanningsnette en gelykspanningsnette
- Authors: Ferreira, Jan Abraham
- Date: 2014-04-03
- Subjects: Electric transformers , Electric current converters , Electric currents, Alternating , Bipolar transistors , Field-effect transistors
- Type: Thesis
- Identifier: uj:4642 , http://hdl.handle.net/10210/9983
- Description: M.Ing. (Electrical and Electronic Engineering) , The possibilities and technology of converters with an alternating voltage link are investigated for high specific power conversion at high frequencies. With a view to the functional description of these power converters, s i muLat i on techniques are considered for both system and circuit analysis. A thorough investigation is made into the design of high frequency power transformers, which play an important role in this class of power circuits. This includes a theoretical analysis in conjunction with the 'practical implementation of a design procedure for minimal eddy current losses in the windings as well as experimental work on losses in ferrite cores. For the remainder of the study, attention is focussed on the two pulse inverter which is responsible for the generation of the alternating voltage in the high frequency link. The suitability of bipolar and field effect transistors for power switching, is critically examined and a voltage compensation on the bipolar Darlington, which reduces on-state losses, yielded good results upon application. A study on the feasibility of non-dissipative snubber techniques on the centre tapped inverter is presented, thus supplying a practical way of reducing switching losses without affecting the efficiency of the system. An additional, yet simple, network is added to the snubber circuits of the two pulse inverter which is operational during low load conditions.' in order also to have low switching losses under these circumstances. Finally a 50 k~v, 10 kHz centre tapped inverter was developed and built.
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- Authors: Ferreira, Jan Abraham
- Date: 2014-04-03
- Subjects: Electric transformers , Electric current converters , Electric currents, Alternating , Bipolar transistors , Field-effect transistors
- Type: Thesis
- Identifier: uj:4642 , http://hdl.handle.net/10210/9983
- Description: M.Ing. (Electrical and Electronic Engineering) , The possibilities and technology of converters with an alternating voltage link are investigated for high specific power conversion at high frequencies. With a view to the functional description of these power converters, s i muLat i on techniques are considered for both system and circuit analysis. A thorough investigation is made into the design of high frequency power transformers, which play an important role in this class of power circuits. This includes a theoretical analysis in conjunction with the 'practical implementation of a design procedure for minimal eddy current losses in the windings as well as experimental work on losses in ferrite cores. For the remainder of the study, attention is focussed on the two pulse inverter which is responsible for the generation of the alternating voltage in the high frequency link. The suitability of bipolar and field effect transistors for power switching, is critically examined and a voltage compensation on the bipolar Darlington, which reduces on-state losses, yielded good results upon application. A study on the feasibility of non-dissipative snubber techniques on the centre tapped inverter is presented, thus supplying a practical way of reducing switching losses without affecting the efficiency of the system. An additional, yet simple, network is added to the snubber circuits of the two pulse inverter which is operational during low load conditions.' in order also to have low switching losses under these circumstances. Finally a 50 k~v, 10 kHz centre tapped inverter was developed and built.
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Statistical analysis of frequency and duration of forced outages for subtransmission circuit breakers
- Sikhakhane, Siyabonga Thulasizwe
- Authors: Sikhakhane, Siyabonga Thulasizwe
- Date: 2019
- Subjects: Electric transformers , Electric power failures , Electric circuit-breakers
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/393847 , uj:32602
- Description: Abstract : Outages on the power system may affect the economy and jeopardise critical services such as transport, communication, emergency, and security services. Breaker failures, in particular, tend to result in serious injuries, death, affected customers, poor network performance statistics, negative regulatory perceptions, loss of revenue, and equipment replacement costs. The most relevant work published in the current literature on analysis of populations of breaker statistical analysis is limited to air blast breakers operating at 115kV, 230kV, and 500kV. The most relevant knowledge on the statistical analysis of unplanned sub transmission outages is restricted to only transformer outages. The analysis of outage datarestoration time focuses on all the events on the broad distribution system. Based on the literature review conducted, the statistical analysis of data for populations of substation equipment remains an under-studied area of research. More specifically, none of the current literature focuses on sub-transmission breaker outage frequency and outage restoration time. This study focused on the statistical analysis of sub-transmission breaker forced outage frequency and forced outage restoration times. In the case of circuit breaker outage frequencies, the following was done: • The various variables of breaker unplanned outage frequencies were analysed by using breaker unplanned actual number of outages and outage rates. • The dependence between variables was explored by using two-dimensional charts. • The significance of the observed dependence between variables was then quantified using a chi-squared test. In the case of outage restoration times, the following was done:.. , M.Phil. (Electrical and Electronic Engineering)
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- Authors: Sikhakhane, Siyabonga Thulasizwe
- Date: 2019
- Subjects: Electric transformers , Electric power failures , Electric circuit-breakers
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/393847 , uj:32602
- Description: Abstract : Outages on the power system may affect the economy and jeopardise critical services such as transport, communication, emergency, and security services. Breaker failures, in particular, tend to result in serious injuries, death, affected customers, poor network performance statistics, negative regulatory perceptions, loss of revenue, and equipment replacement costs. The most relevant work published in the current literature on analysis of populations of breaker statistical analysis is limited to air blast breakers operating at 115kV, 230kV, and 500kV. The most relevant knowledge on the statistical analysis of unplanned sub transmission outages is restricted to only transformer outages. The analysis of outage datarestoration time focuses on all the events on the broad distribution system. Based on the literature review conducted, the statistical analysis of data for populations of substation equipment remains an under-studied area of research. More specifically, none of the current literature focuses on sub-transmission breaker outage frequency and outage restoration time. This study focused on the statistical analysis of sub-transmission breaker forced outage frequency and forced outage restoration times. In the case of circuit breaker outage frequencies, the following was done: • The various variables of breaker unplanned outage frequencies were analysed by using breaker unplanned actual number of outages and outage rates. • The dependence between variables was explored by using two-dimensional charts. • The significance of the observed dependence between variables was then quantified using a chi-squared test. In the case of outage restoration times, the following was done:.. , M.Phil. (Electrical and Electronic Engineering)
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Impact of parameters of transmission line interconnecting transformers on power system performance
- Authors: Dyantyi, Ayanda Theophilus
- Date: 2016
- Subjects: Electric transformers , Electric power systems , Electric power transmission , Data transmission systems
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/57230 , uj:16371
- Description: Abstract: Power transformers are used to form a connection between distribution, sub-transmission and transmission power lines in order to allow electric power to flow between networks of different voltages. Thus, the desired value of transformer reactance value is determined at the design stage. In most cases, once a transformer is commissioned, its tap changer setting is fixed at a particular position, and the position is likely to be changed only during maintenance. In this dissertation, an investigation into the impact of parameters of high voltage transmission line interconnecting transformers on power system on the performance of the power system is being done. The specific transformer parameters that are considered are reactance and tap changer settings. The performance aspects that are investigated are active power flow, system losses, and voltage stability. From the findings of the investigation, it is observed that the reactance value of a transformer has an influence on power flow, system losses, and voltage stability. Therefore, in networks where the likelihood of fault current occurrence is low, the reactance of the transformer can be varied in order to improve the performance of the power system. Moreover, transformer tap changer positions have a higher influence on power flow, system losses, and voltage stability. It is concluded that at the design stage, transformer reactance values need to be carefully selected for the improvement of power system performance. During the commissioning and maintenance of transformer units, there is a need for power system planners and operators to carefully select the tap changer position and fix it in a position that yields better results with regard to power flow, system losses, and voltage stability of the power system. , M.Ing. (Electrical and Electronic Engineering)
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- Authors: Dyantyi, Ayanda Theophilus
- Date: 2016
- Subjects: Electric transformers , Electric power systems , Electric power transmission , Data transmission systems
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/57230 , uj:16371
- Description: Abstract: Power transformers are used to form a connection between distribution, sub-transmission and transmission power lines in order to allow electric power to flow between networks of different voltages. Thus, the desired value of transformer reactance value is determined at the design stage. In most cases, once a transformer is commissioned, its tap changer setting is fixed at a particular position, and the position is likely to be changed only during maintenance. In this dissertation, an investigation into the impact of parameters of high voltage transmission line interconnecting transformers on power system on the performance of the power system is being done. The specific transformer parameters that are considered are reactance and tap changer settings. The performance aspects that are investigated are active power flow, system losses, and voltage stability. From the findings of the investigation, it is observed that the reactance value of a transformer has an influence on power flow, system losses, and voltage stability. Therefore, in networks where the likelihood of fault current occurrence is low, the reactance of the transformer can be varied in order to improve the performance of the power system. Moreover, transformer tap changer positions have a higher influence on power flow, system losses, and voltage stability. It is concluded that at the design stage, transformer reactance values need to be carefully selected for the improvement of power system performance. During the commissioning and maintenance of transformer units, there is a need for power system planners and operators to carefully select the tap changer position and fix it in a position that yields better results with regard to power flow, system losses, and voltage stability of the power system. , M.Ing. (Electrical and Electronic Engineering)
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Electromagnetic design of integrated resonator-transformers
- Authors: Strydom, Johan Tjeerd
- Date: 2009-02-26T12:22:31Z
- Subjects: Electric transformers , Electric resonators , Electromagnetic devices
- Type: Thesis
- Identifier: uj:8178 , http://hdl.handle.net/10210/2182
- Description: D.Ing. , In the field of power electronics, the relentless demand for higher efficiencies, lower costs and ever-decreasing volume and profile have driven the development of many innovative technologies. Planarization and hybridization have become a substantial part of present system integration methodology. With the subsequent size reduction, the effects of layout and component parasitics are becoming vital issues in the development of innovative structures. The component ‘parasitics’ can be considered dimensional effects of the component structure that are not considered during the design process. The concept of electromagnetic integration is aimed at the utilization and modification of these dimensional effects. This leads to an integrated structure that fulfills multiple electromagnetic functions with the potential for improved power density, efficiency and reliability. In this dissertation, a family of electromagnetically integrated passives is presented. The related electromagnetic modeling and design approach of these complex electromagnetic structures is presented through a case study of L-L-C-T structures. The development of a sufficiently accurate, yet simplified electromagnetic model for design purposes is presented for the case study. With the electromagnetic model as basis, a comprehensive electromagnetic loss model is created. The electromagnetic design and loss models are combined into a design evaluation program. The graphical output of this design evaluation program allows for rapid selection of improved designs based on external cost criteria. This led to numerous insights into the relationships between the design variables. Through modification of the program, some fundamental limits of the integration approach are addressed. A case study design for a 1MHz, 500W dc-dc converter was considered to evaluate the design program. To assess the accuracy of the electromagnetic modeling, three L-L-C-T prototypes are constructed and experimentally tested. The construction process presented improved power density by 80% over previous processes. The electromagnetic component parameters for three prototypes were within 10% of the required design values, while the electromagnetic loss model estimations were within measurement error. The design evaluation program was enlisted in the design of two of these prototypes. This resulted in a 100% further improvement in power density (480W/in3 or 29.3W/cm3) compared to the original prototype without a loss in efficiency.
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- Authors: Strydom, Johan Tjeerd
- Date: 2009-02-26T12:22:31Z
- Subjects: Electric transformers , Electric resonators , Electromagnetic devices
- Type: Thesis
- Identifier: uj:8178 , http://hdl.handle.net/10210/2182
- Description: D.Ing. , In the field of power electronics, the relentless demand for higher efficiencies, lower costs and ever-decreasing volume and profile have driven the development of many innovative technologies. Planarization and hybridization have become a substantial part of present system integration methodology. With the subsequent size reduction, the effects of layout and component parasitics are becoming vital issues in the development of innovative structures. The component ‘parasitics’ can be considered dimensional effects of the component structure that are not considered during the design process. The concept of electromagnetic integration is aimed at the utilization and modification of these dimensional effects. This leads to an integrated structure that fulfills multiple electromagnetic functions with the potential for improved power density, efficiency and reliability. In this dissertation, a family of electromagnetically integrated passives is presented. The related electromagnetic modeling and design approach of these complex electromagnetic structures is presented through a case study of L-L-C-T structures. The development of a sufficiently accurate, yet simplified electromagnetic model for design purposes is presented for the case study. With the electromagnetic model as basis, a comprehensive electromagnetic loss model is created. The electromagnetic design and loss models are combined into a design evaluation program. The graphical output of this design evaluation program allows for rapid selection of improved designs based on external cost criteria. This led to numerous insights into the relationships between the design variables. Through modification of the program, some fundamental limits of the integration approach are addressed. A case study design for a 1MHz, 500W dc-dc converter was considered to evaluate the design program. To assess the accuracy of the electromagnetic modeling, three L-L-C-T prototypes are constructed and experimentally tested. The construction process presented improved power density by 80% over previous processes. The electromagnetic component parameters for three prototypes were within 10% of the required design values, while the electromagnetic loss model estimations were within measurement error. The design evaluation program was enlisted in the design of two of these prototypes. This resulted in a 100% further improvement in power density (480W/in3 or 29.3W/cm3) compared to the original prototype without a loss in efficiency.
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