Reliability evaluation of an electric power distribution system : a case study in Gauteng Metropolitan Municipality
- Authors: Choma, August M.
- Date: 2018
- Subjects: Engineering - Management , Electric power distribution , Electric power systems
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/293822 , uj:31957
- Description: M.Ing. (Engineering Management) , Abstract: The electrical power is a basic public service. The electrical power reliability is very essential since most of the infrastructures are dependent on it. Unplanned power outages may compromise the services such as transport, communications systems and emergency and the security services. Unplanned power outages are also inconvenient and very costly to both commercial and residential customers. As a result, the research study identify the factors that contribute to poor reliability of distribution networks and from the findings the alternative strategies are proposed and discussed. The study is intended to help electrical utilities such as municipalities to efficiently investigate the distribution network that is affected and apply the scheduled reliability development tactics to achieve the best performance. The literature review was carry out to review the existing body of the knowledge in relation to the root causes of unplanned power outages, overview of distribution reliability performance indices and the solutions that can be used to improve the performance of distribution system. A case study strategy was presented within one of the Gauteng Metropolitan Municipality with three year (2015-2017) historical power outage data of medium voltage feeders. It was found that most of these failures of medium voltage feeders under the case study take place due to equipment failures contributing high (total of 37 fault incidents in three years). Equipment failures presented a high risk, in particular the LV (Low voltage) transformer fault. Overhead line faults contributed to total of 29 fault incidents, 25 faults incidents for underground cable faults, 14 fault incidents for copper/cable theft, 12 fault incidents for electricity theft, 9 fault incidents for vandalism and 7 faults incident for extreme weather events. New factors such as motor vehicle accident, Feld fire and found no fault (unknowns) were discovered from the case study and not covered from the literature review. Metropolitan Municipality currently uses only expected reliability indices of each year to assess the distribution network performance. The research study presented the predictive reliability assessment strategy that can be used by managers and engineers of the municipality for predicting the distribution network problems of medium voltage feeders, which is by using the probability distribution of both SAIFI and SAIDI of each year.
- Full Text:
- Authors: Choma, August M.
- Date: 2018
- Subjects: Engineering - Management , Electric power distribution , Electric power systems
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/293822 , uj:31957
- Description: M.Ing. (Engineering Management) , Abstract: The electrical power is a basic public service. The electrical power reliability is very essential since most of the infrastructures are dependent on it. Unplanned power outages may compromise the services such as transport, communications systems and emergency and the security services. Unplanned power outages are also inconvenient and very costly to both commercial and residential customers. As a result, the research study identify the factors that contribute to poor reliability of distribution networks and from the findings the alternative strategies are proposed and discussed. The study is intended to help electrical utilities such as municipalities to efficiently investigate the distribution network that is affected and apply the scheduled reliability development tactics to achieve the best performance. The literature review was carry out to review the existing body of the knowledge in relation to the root causes of unplanned power outages, overview of distribution reliability performance indices and the solutions that can be used to improve the performance of distribution system. A case study strategy was presented within one of the Gauteng Metropolitan Municipality with three year (2015-2017) historical power outage data of medium voltage feeders. It was found that most of these failures of medium voltage feeders under the case study take place due to equipment failures contributing high (total of 37 fault incidents in three years). Equipment failures presented a high risk, in particular the LV (Low voltage) transformer fault. Overhead line faults contributed to total of 29 fault incidents, 25 faults incidents for underground cable faults, 14 fault incidents for copper/cable theft, 12 fault incidents for electricity theft, 9 fault incidents for vandalism and 7 faults incident for extreme weather events. New factors such as motor vehicle accident, Feld fire and found no fault (unknowns) were discovered from the case study and not covered from the literature review. Metropolitan Municipality currently uses only expected reliability indices of each year to assess the distribution network performance. The research study presented the predictive reliability assessment strategy that can be used by managers and engineers of the municipality for predicting the distribution network problems of medium voltage feeders, which is by using the probability distribution of both SAIFI and SAIDI of each year.
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Modelling of different long-term electrical forecasts and its practical applications for transmission network flow studies
- Authors: Payne, Daniel Frederik
- Date: 2009-02-26T12:22:02Z
- Subjects: Electric power-plants , Load forecasting , Electric power systems , Electric power distribution , Load dispatching
- Type: Thesis
- Identifier: uj:8174 , http://hdl.handle.net/10210/2179
- Description: D.Phil , The prediction of the expected transmission network loads as required for transmission network power flow studies, has become very important and much more complex than ten to twenty years ago. Therefore a single forecast is no longer the answer to the problem. The modelling of different long-term electrical forecasts makes it possible to compare a number of different forecasts. The modelling provides the further option that each expected load can be entered as a range and then the developed balancing algorithm checks for consensus (feasibility). If feasibility exists, then the different forecasts are reconciled (a feasible solution is determined). Factors such as international and national market trends, economical cycles, different weather patterns, climate cycles and demographic changes are studied. The factors that have significant impact on the transmission electrical loads are integrated in ten different forecasts. It thus gives more insight into the electrical industry and makes the forecast results more informative and therefore reduces the uncertainty in the future expected loads.
- Full Text:
- Authors: Payne, Daniel Frederik
- Date: 2009-02-26T12:22:02Z
- Subjects: Electric power-plants , Load forecasting , Electric power systems , Electric power distribution , Load dispatching
- Type: Thesis
- Identifier: uj:8174 , http://hdl.handle.net/10210/2179
- Description: D.Phil , The prediction of the expected transmission network loads as required for transmission network power flow studies, has become very important and much more complex than ten to twenty years ago. Therefore a single forecast is no longer the answer to the problem. The modelling of different long-term electrical forecasts makes it possible to compare a number of different forecasts. The modelling provides the further option that each expected load can be entered as a range and then the developed balancing algorithm checks for consensus (feasibility). If feasibility exists, then the different forecasts are reconciled (a feasible solution is determined). Factors such as international and national market trends, economical cycles, different weather patterns, climate cycles and demographic changes are studied. The factors that have significant impact on the transmission electrical loads are integrated in ten different forecasts. It thus gives more insight into the electrical industry and makes the forecast results more informative and therefore reduces the uncertainty in the future expected loads.
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Determination and dynamic compensation of fictitious power in electric power systems
- Enslin, Johan Heinrich Richter
- Authors: Enslin, Johan Heinrich Richter
- Date: 2014-09-23
- Subjects: Power electronics , Electric power systems
- Type: Thesis
- Identifier: uj:12357 , http://hdl.handle.net/10210/12142
- Description: D.Ing. (Electrical & Electronic Engineering) , Please refer to full text to view abstract
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- Authors: Enslin, Johan Heinrich Richter
- Date: 2014-09-23
- Subjects: Power electronics , Electric power systems
- Type: Thesis
- Identifier: uj:12357 , http://hdl.handle.net/10210/12142
- Description: D.Ing. (Electrical & Electronic Engineering) , Please refer to full text to view abstract
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Power transmission lines fault detecting and locating using artificial neural networks
- Pouabe Eboule, Patrick Serge
- Authors: Pouabe Eboule, Patrick Serge
- Date: 2017
- Subjects: Electric power systems , Fault location (Engineering) , Neural networks (Computer science) , Electric lines
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/262634 , uj:27729
- Description: Abstract: Please refer to full text to view abstract , M.Tech.
- Full Text:
- Authors: Pouabe Eboule, Patrick Serge
- Date: 2017
- Subjects: Electric power systems , Fault location (Engineering) , Neural networks (Computer science) , Electric lines
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/262634 , uj:27729
- Description: Abstract: Please refer to full text to view abstract , M.Tech.
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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)
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- 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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Harmonic impedance estimation of a power system implementing frequency domain measurement techniques
- Authors: Venter, Fredrik Hendrik
- Date: 2012-08-13
- Subjects: Harmonics (Electric waves) , Electric power systems
- Type: Thesis
- Identifier: uj:9129 , http://hdl.handle.net/10210/5585
- Description: M.Ing. , The increased used of non-linear loads within the power system during recent years have resulted in deviations from the perfect sinusoidal voltage and current waveform. This deviation from the perfect sinusoidal waveform can be expressed according to Fourier analysis by a set of co-sinusoidal waveforms having frequencies, which are a multiple of the fundamental frequency, referred to as harmonics. Non-linear loads are generally characterised by harmonic currents. It is therefore often preferred to express the harmonic emission limits in terms of harmonic currents rather than harmonic voltages. In order to translate the harmonic currents into harmonic voltages the harmonic impedance of the power system must be known. The power system's harmonic impedance can be assessed via computational, simulation and measurement techniques. The study will concentrate on the estimation of the harmonic impedance of a 33kV power system by implementing two online frequency domain measurement techniques. Both techniques are applied at the point of delivery of a dominant nonlinear load during normal and energisation load conditions with its power factor correction capacitor bank in and out off service. The estimated harmonic impedance is then compared with the calculated and simulated harmonic impedance.
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Harmonic impedance estimation of a power system implementing frequency domain measurement techniques
- Authors: Venter, Fredrik Hendrik
- Date: 2012-08-13
- Subjects: Harmonics (Electric waves) , Electric power systems
- Type: Thesis
- Identifier: uj:9129 , http://hdl.handle.net/10210/5585
- Description: M.Ing. , The increased used of non-linear loads within the power system during recent years have resulted in deviations from the perfect sinusoidal voltage and current waveform. This deviation from the perfect sinusoidal waveform can be expressed according to Fourier analysis by a set of co-sinusoidal waveforms having frequencies, which are a multiple of the fundamental frequency, referred to as harmonics. Non-linear loads are generally characterised by harmonic currents. It is therefore often preferred to express the harmonic emission limits in terms of harmonic currents rather than harmonic voltages. In order to translate the harmonic currents into harmonic voltages the harmonic impedance of the power system must be known. The power system's harmonic impedance can be assessed via computational, simulation and measurement techniques. The study will concentrate on the estimation of the harmonic impedance of a 33kV power system by implementing two online frequency domain measurement techniques. Both techniques are applied at the point of delivery of a dominant nonlinear load during normal and energisation load conditions with its power factor correction capacitor bank in and out off service. The estimated harmonic impedance is then compared with the calculated and simulated harmonic impedance.
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Condition monitoring of transformer’s bushings using computational intelligence
- Authors: Maumela, Joshua Tshifhiwa
- Date: 2014-04-16
- Subjects: Electric insulators and insulation , Electric power systems , Intelligent agents (Computer software) , Computational intelligence
- Type: Thesis
- Identifier: uj:10800 , http://hdl.handle.net/10210/10307
- Description: M.Ing. (Electrical and Electronic Engineering) , Dissolved Gas-in-oil analysis (DGA) is used to monitor the condition of bushings on large power transformers. There are different techniques used in determining the conditions from the data collected, but in this work the Artificial Intelligence techniques are investigated. This work investigates which gases in DGA are related to each other and which ones are important for making decisions. When the related and crucial gases are determined, the other gases are discarded thereby reducing the number of attributes in DGA. Hence a further investigation is done to see how these new datasets influence the performance of the classifiers used to classify the DGA of full attributes. The classifiers used in these experiments were Backpropagation Neural Networks (BPNN) and Support Vector Machines (SVM) whereas the Principal Component Analysis (PCA), Rough Set (RS), Incremental Granular Ranking (GR++) and Decision Trees (DT) were used to reduce the attributes of the dataset. The parameters used when training the BPNN and SVM classifiers are kept fixed to create a controlled test environment when investigating the effects of reducing the number of gases. This work further introduced a new classifier that can handle high dimension dataset and noisy dataset, Rough Neural Network (RNN). This classifier was tested when trained using the full dataset and how it is affected by reducing the number of gases used to train it. The results in these experiments showed that ethane and total combustible gases attributes are core attributes chosen by the four algorithms as gases needed for decision making. The average results of the classification performance showed that the reduction of attributes helps improve the performance of classifiers. Hence the science of transformer condition monitoring can be derived from studying the relations and patterns created by the different gases attributes in DGA. This statement is supported by the classification improvements where the RNN classifier had 99.7% classification accuracy when trained using the three attributes determined by the PCA.
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- Authors: Maumela, Joshua Tshifhiwa
- Date: 2014-04-16
- Subjects: Electric insulators and insulation , Electric power systems , Intelligent agents (Computer software) , Computational intelligence
- Type: Thesis
- Identifier: uj:10800 , http://hdl.handle.net/10210/10307
- Description: M.Ing. (Electrical and Electronic Engineering) , Dissolved Gas-in-oil analysis (DGA) is used to monitor the condition of bushings on large power transformers. There are different techniques used in determining the conditions from the data collected, but in this work the Artificial Intelligence techniques are investigated. This work investigates which gases in DGA are related to each other and which ones are important for making decisions. When the related and crucial gases are determined, the other gases are discarded thereby reducing the number of attributes in DGA. Hence a further investigation is done to see how these new datasets influence the performance of the classifiers used to classify the DGA of full attributes. The classifiers used in these experiments were Backpropagation Neural Networks (BPNN) and Support Vector Machines (SVM) whereas the Principal Component Analysis (PCA), Rough Set (RS), Incremental Granular Ranking (GR++) and Decision Trees (DT) were used to reduce the attributes of the dataset. The parameters used when training the BPNN and SVM classifiers are kept fixed to create a controlled test environment when investigating the effects of reducing the number of gases. This work further introduced a new classifier that can handle high dimension dataset and noisy dataset, Rough Neural Network (RNN). This classifier was tested when trained using the full dataset and how it is affected by reducing the number of gases used to train it. The results in these experiments showed that ethane and total combustible gases attributes are core attributes chosen by the four algorithms as gases needed for decision making. The average results of the classification performance showed that the reduction of attributes helps improve the performance of classifiers. Hence the science of transformer condition monitoring can be derived from studying the relations and patterns created by the different gases attributes in DGA. This statement is supported by the classification improvements where the RNN classifier had 99.7% classification accuracy when trained using the three attributes determined by the PCA.
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Controlled power flow capacitive divider for electric power tapping
- Jimoh, A. A., Munda, J., Britten, A. C., Nicolae, Dan-Valentin
- Authors: Jimoh, A. A. , Munda, J. , Britten, A. C. , Nicolae, Dan-Valentin
- Date: 2006
- Subjects: Electric power systems , Capacitance meters
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/15982 , uj:15724 , ISBN: 1-4244-0121-6 , Citation: Jimoh, A.A. et al. 2006. Controlled power flow capacitive divider for eletric power tapping. In: Proceedings of the 12th International Power Electronics and Motion Control Conference, 30 August-1st September, 2006, Portoroz. DOI: 10.1109/EPEPEMC.2006.4778611-1477
- Description: Abstract: Capacitive divider systems for tapping electric power from high voltage transmission lines are known to exhibit certain detrimental problems of stability, sub-resonance harmonic oscillations, and ferroresonance when coupled with non-linear loads. On the other hand, they can improve reactive power flow, power factor and contribute to improved harmonic filtration of the larger power system. This paper, therefore, proposes a controlled power flow conditioner as an essential integral component of a capacitive divider system to control power transfer between the high voltage transmission line, capacitive divider system, and the load. The ultimate objective of this conditioner is to mitigate or minimize the attendant problems associated with coupling the system to the load, and optimize the derivable benefits to the larger network.
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- Authors: Jimoh, A. A. , Munda, J. , Britten, A. C. , Nicolae, Dan-Valentin
- Date: 2006
- Subjects: Electric power systems , Capacitance meters
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/15982 , uj:15724 , ISBN: 1-4244-0121-6 , Citation: Jimoh, A.A. et al. 2006. Controlled power flow capacitive divider for eletric power tapping. In: Proceedings of the 12th International Power Electronics and Motion Control Conference, 30 August-1st September, 2006, Portoroz. DOI: 10.1109/EPEPEMC.2006.4778611-1477
- Description: Abstract: Capacitive divider systems for tapping electric power from high voltage transmission lines are known to exhibit certain detrimental problems of stability, sub-resonance harmonic oscillations, and ferroresonance when coupled with non-linear loads. On the other hand, they can improve reactive power flow, power factor and contribute to improved harmonic filtration of the larger power system. This paper, therefore, proposes a controlled power flow conditioner as an essential integral component of a capacitive divider system to control power transfer between the high voltage transmission line, capacitive divider system, and the load. The ultimate objective of this conditioner is to mitigate or minimize the attendant problems associated with coupling the system to the load, and optimize the derivable benefits to the larger network.
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Non linear load identification
- Du Toit, Jacobus Petrus Verster
- Authors: Du Toit, Jacobus Petrus Verster
- Date: 2015-03-02
- Subjects: Harmonics (Electric waves) , Electric power systems , Wavelets (Mathematics)
- Type: Thesis
- Identifier: uj:13376 , http://hdl.handle.net/10210/13388
- Description: M.Ing. , With the increased use of nonlinear loads such as variable speed motor drives and rectifiers, the voltages and currents on the power system grid are no longer sinusoidal. These non-sinusoidal waveforms cannot be analyzed by conventional power theories and the usual recourse is to decompose the nonlinear waveform into a set of harmonics. Harmonic voltage and current components are detrimental to the power system and may cause additional losses, or premature failure of equipment, and as such they have a definite influence on the quality of supply. This thesis shows the limitations and potential pitfalls of harmonic decomposition and other power theories, and examines various methods used for identifying, quantifying and modelling nonlinear loads. The aim of the thesis is to evaluate methods for attaching a specific disturbance or non-linearity on the voltage waveform to a specific load connected at the point of common coupling. The power theories examined include the total complex power, the IEEE working group definitions of apparent power, true power factor and harmonic adjusted power factor. Some new techniques for estimating the degree to which a load is disturbing the voltage at the point of common coupling is introduced, including the calculation of correlation indices, and the the use of wavelets.
- Full Text:
- Authors: Du Toit, Jacobus Petrus Verster
- Date: 2015-03-02
- Subjects: Harmonics (Electric waves) , Electric power systems , Wavelets (Mathematics)
- Type: Thesis
- Identifier: uj:13376 , http://hdl.handle.net/10210/13388
- Description: M.Ing. , With the increased use of nonlinear loads such as variable speed motor drives and rectifiers, the voltages and currents on the power system grid are no longer sinusoidal. These non-sinusoidal waveforms cannot be analyzed by conventional power theories and the usual recourse is to decompose the nonlinear waveform into a set of harmonics. Harmonic voltage and current components are detrimental to the power system and may cause additional losses, or premature failure of equipment, and as such they have a definite influence on the quality of supply. This thesis shows the limitations and potential pitfalls of harmonic decomposition and other power theories, and examines various methods used for identifying, quantifying and modelling nonlinear loads. The aim of the thesis is to evaluate methods for attaching a specific disturbance or non-linearity on the voltage waveform to a specific load connected at the point of common coupling. The power theories examined include the total complex power, the IEEE working group definitions of apparent power, true power factor and harmonic adjusted power factor. Some new techniques for estimating the degree to which a load is disturbing the voltage at the point of common coupling is introduced, including the calculation of correlation indices, and the the use of wavelets.
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Power transformer failure management on the Eskom distribution network in Limpopo
- Authors: Sako, Maite Martha
- Date: 2016
- Subjects: Eskom (Firm( , Electronic transformers , Electric power distribution , Electric power systems
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/242337 , uj:24992
- Description: M.Ing. (Engineering Management) , Abstract: Electricity is a crucial key component in the everyday life influencing the economy, safety, health, productivity and comfort of the people. Power utilities continue to make the continuity of electricity supply to the consumers their first priority. Power transformers are the crucial part of the power system network because they regulate the voltage either up or down on the electrical network for safe use by the consumers. Their reliable operation on the network is very critical because it directly impacts the reliability and stability of the entire electrical network connected to it. One of the major challenges power utilities face is the failure of substation power transformers on the distribution network. Sudden failures of these transformers cause the interruption of supply to the customers. For the utility, it causes high transformer repair costs and revenue loss. The power utility is also forced to replace the failed power transformers in order to reduce the outage time for the affected customers. Although power transformers have become the heart of the distribution network, the success rate for these transformers to complete their full life cycle is not a guarantee. The performance of the power transformers on the Limpopo distribution network has not reached the projected target set by the plant performance department in the past four years and this is cause for great concern. There was a number of power transformer failures recorded in the substations. After investigations were conducted, it was found that the major causes for these failures were aging, overloading, improper maintenance schedule, internal faults and insufficient security measures in substations in remote areas. This dissertation looks at the methodologies that are currently being implemented to ensure that the installed substation power transformers approach or complete their full life cycle. It further proposes the improvement of the methodologies currently being implemented. The conclusion reached in this study is that in order for the substation power transformer failures on the Eskom distribution network in Limpopo to decrease, the methods that can alleviate the problem include: installation of an online monitoring system on the power transformers; improvement of the maintenance schedule; installation of a backup transformers in single transformer substations; improvement of the security measures in substations that are located in remote areas; putting asset replacement plans in place for transformers that are approaching their...
- Full Text:
- Authors: Sako, Maite Martha
- Date: 2016
- Subjects: Eskom (Firm( , Electronic transformers , Electric power distribution , Electric power systems
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/242337 , uj:24992
- Description: M.Ing. (Engineering Management) , Abstract: Electricity is a crucial key component in the everyday life influencing the economy, safety, health, productivity and comfort of the people. Power utilities continue to make the continuity of electricity supply to the consumers their first priority. Power transformers are the crucial part of the power system network because they regulate the voltage either up or down on the electrical network for safe use by the consumers. Their reliable operation on the network is very critical because it directly impacts the reliability and stability of the entire electrical network connected to it. One of the major challenges power utilities face is the failure of substation power transformers on the distribution network. Sudden failures of these transformers cause the interruption of supply to the customers. For the utility, it causes high transformer repair costs and revenue loss. The power utility is also forced to replace the failed power transformers in order to reduce the outage time for the affected customers. Although power transformers have become the heart of the distribution network, the success rate for these transformers to complete their full life cycle is not a guarantee. The performance of the power transformers on the Limpopo distribution network has not reached the projected target set by the plant performance department in the past four years and this is cause for great concern. There was a number of power transformer failures recorded in the substations. After investigations were conducted, it was found that the major causes for these failures were aging, overloading, improper maintenance schedule, internal faults and insufficient security measures in substations in remote areas. This dissertation looks at the methodologies that are currently being implemented to ensure that the installed substation power transformers approach or complete their full life cycle. It further proposes the improvement of the methodologies currently being implemented. The conclusion reached in this study is that in order for the substation power transformer failures on the Eskom distribution network in Limpopo to decrease, the methods that can alleviate the problem include: installation of an online monitoring system on the power transformers; improvement of the maintenance schedule; installation of a backup transformers in single transformer substations; improvement of the security measures in substations that are located in remote areas; putting asset replacement plans in place for transformers that are approaching their...
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Quality principles and supplier selection during electricity network construction projects : a comparative study
- Authors: Ramohlale, Ntjana George
- Date: 2015
- Subjects: Construction projects - Management , Electric power systems , Contractors
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/56966 , uj:16362
- Description: Abstract: Quality principles and supplier selection play an important role in projects especially where the customer is planning to outsource the work to an external organisation. The application of quality principles will help ensure that work that is going to be carried out is planned well in advance and the necessary measures are put in place to ensure that it is carried out as required. Supplier selection is a process where potential suppliers and contractors are invited to submit their information in order to be considered for work that the customer has. With the invitation, requirements will be attached and they need to show that they are capable of turning those requirements to actual output. The customer will have pre-defined criteria that will be used for evaluations and the best capable supplier or contractor will then be selected to execute the job. It has been realised that as much as quality principles are defined and the supplier selection process is adopted on projects, failure can still be experienced. This research looked at two industry cases in the construction of electricity networks. One project was for the construction of four 132kV lines and the other project focused on the relocation of lines which were in the way of some township development. The study adopted a questionnaire as a data collection tool, which was sent to the team members of both projects to complete. The results show that much as the customer was the same organisation with projects in different locations, there were slight differences in the way the projects were handled. From both projects, team members were aware of the level of quality required, requirements were put in place and the evaluation criteria used for the selection of contractors were utilised. The differences that led to project ABC failing and project XYZ being a success, were in the implementation of contract quality plans that were agreed upon before work commenced and in the performance monitoring as work was being executed. Project ABC failed due to lack of experience in enforcing what was agreed upon and not monitoring performance as stated within inspection and test plans. , M.Phil. (Engineering Management)
- Full Text:
- Authors: Ramohlale, Ntjana George
- Date: 2015
- Subjects: Construction projects - Management , Electric power systems , Contractors
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/56966 , uj:16362
- Description: Abstract: Quality principles and supplier selection play an important role in projects especially where the customer is planning to outsource the work to an external organisation. The application of quality principles will help ensure that work that is going to be carried out is planned well in advance and the necessary measures are put in place to ensure that it is carried out as required. Supplier selection is a process where potential suppliers and contractors are invited to submit their information in order to be considered for work that the customer has. With the invitation, requirements will be attached and they need to show that they are capable of turning those requirements to actual output. The customer will have pre-defined criteria that will be used for evaluations and the best capable supplier or contractor will then be selected to execute the job. It has been realised that as much as quality principles are defined and the supplier selection process is adopted on projects, failure can still be experienced. This research looked at two industry cases in the construction of electricity networks. One project was for the construction of four 132kV lines and the other project focused on the relocation of lines which were in the way of some township development. The study adopted a questionnaire as a data collection tool, which was sent to the team members of both projects to complete. The results show that much as the customer was the same organisation with projects in different locations, there were slight differences in the way the projects were handled. From both projects, team members were aware of the level of quality required, requirements were put in place and the evaluation criteria used for the selection of contractors were utilised. The differences that led to project ABC failing and project XYZ being a success, were in the implementation of contract quality plans that were agreed upon before work commenced and in the performance monitoring as work was being executed. Project ABC failed due to lack of experience in enforcing what was agreed upon and not monitoring performance as stated within inspection and test plans. , M.Phil. (Engineering Management)
- Full Text:
A strategy for electrical load management in the South African mining industry
- Authors: Boake, Ian Gordon
- Date: 2009-02-26T12:16:21Z
- Subjects: Electric power-plants , Electric power systems , Mineral industries , South African power supply
- Type: Thesis
- Identifier: uj:8145 , http://hdl.handle.net/10210/2152
- Description: D.Ing , It is every person’s social responsibility to ensure that electrical energy is used as efficiently as possible. This is as a result of the considerable fossil fuels that are currently required to generate electricity. These fuels are available in limited supply on Earth and result in air pollution when consumed in the electrical energy generation process. Moreover, as scarcity increases, not just in fuel reserves, but also in electricity infrastructure such as servitudes, generation capacity etc, the costs of electricity also rises. This then brings about an opportunity to reduce input costs if the electrical energy is utilized as efficiently as possible. This can however only be done by the application of a suitable strategy. This thesis develops an electrical load management (ELM) strategy which may be effective in reducing input costs, by reducing electrical energy costs. This strategy has it’s foundation in tried-and-tested ELM strategies (albeit called by other names such as demand-side management (DSM) and Energy Management (EM)) developed by the world’s foremost utility research organization called EPRI over a number of decades, thereby ensuring, to some extent, the success of the proposed strategy. The strategy has been tested, in its constituent parts, in a real world environment in the South African mining industry. The examples of the sub-elements that have been tested in the industry are the artificial neural network (ANN) for short-term forecasting; the statistical regression technique for short-term load forecasting; the analysis of the external factors affecting the electricity supply industry and also the comparison of electricity tariffs in the mining industry. The validity of the strategy is further enhanced by the involvement of Technology Managers within the mining industry which have been involved with ELM in the mining industry for a number of years. Their input was solicited via an in-depth survey which was conducted in this industry. This survey represents the ELM strategy currently in existence of: - 62 shafts or open pit operations, 44 process plants and 5 smelter operations. The largest mining groups in South Africa were involved in this survey so that this survey represents: amongst others, 40% of the gold mining industry, 62% of the platinum mining industry and 95% of the diamond mining industry. The collective experience represented by the survey is equivalent to 67 man-years in ELM in the mining industry. Electricity tariffs are the means by which benefits for electrical load management are obtained. It thus warranted an analysis of all the factors affecting the electricity tariffs and in particular the factors affecting the price of electricity. To this end the Electricity Supply Industry (ESI) was analyzed in-depth and proactively to identify the external factors which may affect the price of electricity. Production intrusions may not be tolerated in the mining industry and as these intrusions have been the major cause for abandoning such ELM strategies previously, an electrical load model with production correlation was developed in this research which affords production a very high priority in the ELM strategy. Moreover, this load model, which is a key element of the ELM strategy in this thesis, forecasts the electrical efficiency of a mine in the near future. The effect of this efficiency forecast is to give management a real-time and proactive tool by which to make decisions. This approach avoids potentially large inefficiencies on the overall mine load such as when the electrical efficiency was only checked at the end of each month. This model may be used either in real-time control mode or in simulation mode to test various ELM initiatives before they are implemented. The model has either a statistical-regression based load-forecasting algorithm or an Artificial Neural Network (ANN) load-forecasting algorithm at its core. The choice of which forecasting methodology is used is determined by the value of the Pearson’s rank correlation coefficient for a set of test data. The latest prevailing ELM technologies have also been incorporated into a matrix for easy identification. The matrix should assist with the implementation of this ELM strategy. Not all of the technologies found in the matrix result in control of the mining load for ELM initiatives such as: “peak-clipping”, “load-shifting” or “valley-filling”. Some of these technologies result in “conservation” of the electrical energy by the application of newer and more efficient techniques to perform the necessary activities found on a typical mine (drilling, ventilation, cooling etc.). A complete strategy for ELM in the South African mining industry is thus developed in this thesis which overcomes two of the most serious pitfalls associated with previous strategies. These pitfalls being, the inadequate focus on production in those strategies and also the lack of real-time, efficiency-forecasting of the overall mine load. The strategy also focuses the potential Electrical Load Manager on the key steps of this process, by means of an intuitive, step-by-step approach. It is grounded in the demand-side management (DSM) experiences of the past, enhanced by actual case studies of the sub-elements in the mining industry and has been ratified by the involvement of very experienced Technology Managers active in ELM in South African mining industry.
- Full Text:
- Authors: Boake, Ian Gordon
- Date: 2009-02-26T12:16:21Z
- Subjects: Electric power-plants , Electric power systems , Mineral industries , South African power supply
- Type: Thesis
- Identifier: uj:8145 , http://hdl.handle.net/10210/2152
- Description: D.Ing , It is every person’s social responsibility to ensure that electrical energy is used as efficiently as possible. This is as a result of the considerable fossil fuels that are currently required to generate electricity. These fuels are available in limited supply on Earth and result in air pollution when consumed in the electrical energy generation process. Moreover, as scarcity increases, not just in fuel reserves, but also in electricity infrastructure such as servitudes, generation capacity etc, the costs of electricity also rises. This then brings about an opportunity to reduce input costs if the electrical energy is utilized as efficiently as possible. This can however only be done by the application of a suitable strategy. This thesis develops an electrical load management (ELM) strategy which may be effective in reducing input costs, by reducing electrical energy costs. This strategy has it’s foundation in tried-and-tested ELM strategies (albeit called by other names such as demand-side management (DSM) and Energy Management (EM)) developed by the world’s foremost utility research organization called EPRI over a number of decades, thereby ensuring, to some extent, the success of the proposed strategy. The strategy has been tested, in its constituent parts, in a real world environment in the South African mining industry. The examples of the sub-elements that have been tested in the industry are the artificial neural network (ANN) for short-term forecasting; the statistical regression technique for short-term load forecasting; the analysis of the external factors affecting the electricity supply industry and also the comparison of electricity tariffs in the mining industry. The validity of the strategy is further enhanced by the involvement of Technology Managers within the mining industry which have been involved with ELM in the mining industry for a number of years. Their input was solicited via an in-depth survey which was conducted in this industry. This survey represents the ELM strategy currently in existence of: - 62 shafts or open pit operations, 44 process plants and 5 smelter operations. The largest mining groups in South Africa were involved in this survey so that this survey represents: amongst others, 40% of the gold mining industry, 62% of the platinum mining industry and 95% of the diamond mining industry. The collective experience represented by the survey is equivalent to 67 man-years in ELM in the mining industry. Electricity tariffs are the means by which benefits for electrical load management are obtained. It thus warranted an analysis of all the factors affecting the electricity tariffs and in particular the factors affecting the price of electricity. To this end the Electricity Supply Industry (ESI) was analyzed in-depth and proactively to identify the external factors which may affect the price of electricity. Production intrusions may not be tolerated in the mining industry and as these intrusions have been the major cause for abandoning such ELM strategies previously, an electrical load model with production correlation was developed in this research which affords production a very high priority in the ELM strategy. Moreover, this load model, which is a key element of the ELM strategy in this thesis, forecasts the electrical efficiency of a mine in the near future. The effect of this efficiency forecast is to give management a real-time and proactive tool by which to make decisions. This approach avoids potentially large inefficiencies on the overall mine load such as when the electrical efficiency was only checked at the end of each month. This model may be used either in real-time control mode or in simulation mode to test various ELM initiatives before they are implemented. The model has either a statistical-regression based load-forecasting algorithm or an Artificial Neural Network (ANN) load-forecasting algorithm at its core. The choice of which forecasting methodology is used is determined by the value of the Pearson’s rank correlation coefficient for a set of test data. The latest prevailing ELM technologies have also been incorporated into a matrix for easy identification. The matrix should assist with the implementation of this ELM strategy. Not all of the technologies found in the matrix result in control of the mining load for ELM initiatives such as: “peak-clipping”, “load-shifting” or “valley-filling”. Some of these technologies result in “conservation” of the electrical energy by the application of newer and more efficient techniques to perform the necessary activities found on a typical mine (drilling, ventilation, cooling etc.). A complete strategy for ELM in the South African mining industry is thus developed in this thesis which overcomes two of the most serious pitfalls associated with previous strategies. These pitfalls being, the inadequate focus on production in those strategies and also the lack of real-time, efficiency-forecasting of the overall mine load. The strategy also focuses the potential Electrical Load Manager on the key steps of this process, by means of an intuitive, step-by-step approach. It is grounded in the demand-side management (DSM) experiences of the past, enhanced by actual case studies of the sub-elements in the mining industry and has been ratified by the involvement of very experienced Technology Managers active in ELM in South African mining industry.
- Full Text:
A comprehensive study of power system harmonics
- Kasemuana Matototo, Seraphin
- Authors: Kasemuana Matototo, Seraphin
- Date: 2014-04-16
- Subjects: Electric power systems , Harmonics (Electric waves) , Electric power distribution , Electric networks
- Type: Thesis
- Identifier: uj:10802 , http://hdl.handle.net/10210/10309
- Description: M.Tech. (Electrical and Electronic Engineering) , With the increasing use of nonlinear loads in power systems, harmonic pollution becomes more frequent with disastrous consequences on the electrical network and other loads. Harmonic currents cause problems such as system resonance, protective relays and switchgear malfunction, communication interference, incorrect meter, equipment and process failure, over heating of transmission and distribution systems, insulation degradation and power transformer failure. It appears therefore absolutely essential to determine the current profile of the loads connected to the same Point of Common Coupling (PCC). This study aims to assess a distorted power system in order to determine the characteristics components of distorted waveforms (DC components, fundamental and harmonics components), and to quantify the respective distortion contributions in the power network. The numerical method is applied to analyse the current waveforms captured with the aid of the digital scope meter (DSO) 1200 series at different sections of the network. The power network under study is designed, constructed and analysed with the MatLab/Simulink 7.0 package. In both methods, the Individual Harmonic Distortion (IHD) and the current total harmonic distortion (ITHD) for the line, the non-linear and linear loads are computed for the harmonic components 5th, 7th, 11th and 13th. The results showed that for the analysis of the power system, numerical analysis based on the resultant harmonic curve method and the MatLab/Simulink as applied to the network all converged to highlight that harmonic components appear both on the line, the PCC and the linear load. This is due to the fact that the converter characteristic harmonics (5th, 7th, 11th, 13th…) are found in the network components (line, PCC, linear load…). The resultant harmonic curve method indicated a randomly distributed percentage IHD in different sections of the network for harmonic orders higher than 7th, whereas the Matlab/Simulink results normally show a non-uniform decay pattern of the IHD as the harmonic order increases within the respective section of the network.
- Full Text:
- Authors: Kasemuana Matototo, Seraphin
- Date: 2014-04-16
- Subjects: Electric power systems , Harmonics (Electric waves) , Electric power distribution , Electric networks
- Type: Thesis
- Identifier: uj:10802 , http://hdl.handle.net/10210/10309
- Description: M.Tech. (Electrical and Electronic Engineering) , With the increasing use of nonlinear loads in power systems, harmonic pollution becomes more frequent with disastrous consequences on the electrical network and other loads. Harmonic currents cause problems such as system resonance, protective relays and switchgear malfunction, communication interference, incorrect meter, equipment and process failure, over heating of transmission and distribution systems, insulation degradation and power transformer failure. It appears therefore absolutely essential to determine the current profile of the loads connected to the same Point of Common Coupling (PCC). This study aims to assess a distorted power system in order to determine the characteristics components of distorted waveforms (DC components, fundamental and harmonics components), and to quantify the respective distortion contributions in the power network. The numerical method is applied to analyse the current waveforms captured with the aid of the digital scope meter (DSO) 1200 series at different sections of the network. The power network under study is designed, constructed and analysed with the MatLab/Simulink 7.0 package. In both methods, the Individual Harmonic Distortion (IHD) and the current total harmonic distortion (ITHD) for the line, the non-linear and linear loads are computed for the harmonic components 5th, 7th, 11th and 13th. The results showed that for the analysis of the power system, numerical analysis based on the resultant harmonic curve method and the MatLab/Simulink as applied to the network all converged to highlight that harmonic components appear both on the line, the PCC and the linear load. This is due to the fact that the converter characteristic harmonics (5th, 7th, 11th, 13th…) are found in the network components (line, PCC, linear load…). The resultant harmonic curve method indicated a randomly distributed percentage IHD in different sections of the network for harmonic orders higher than 7th, whereas the Matlab/Simulink results normally show a non-uniform decay pattern of the IHD as the harmonic order increases within the respective section of the network.
- Full Text:
Another case of discrepancies when evaluating power theories using real data
- Cornelius, Jurgens J. J., Janse van Rensburg, J. F., Nicolae, Dan-Valentin
- Authors: Cornelius, Jurgens J. J. , Janse van Rensburg, J. F. , Nicolae, Dan-Valentin
- Date: 2014
- Subjects: Electric power systems , Electric power transmission
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/17548 , uj:15899 , ISBN: 978-1-4673-6487-4 , Citation: Cornelius, J.J.J., Janse van Rensburg, J.F. & Nicolae, D.V. 2014. Another case of Discrepancies when evaluating power theories using real data. International Conference on Harmonics and quality of power, 25-28 May 2014, Bucharest, Romania. DOI:10.1109/ICHQP.2014.6842839 /9781497394874
- Description: Abstract: Most non-sinusoidal power theories have been developed from theoretical techniques, as well as relying on hypothetical and experimental networks to highlight the advantages of each. The drawback of the power theories is that no single one has been universally accepted as a benchmark for other developments. This paper will however show this weakness by means of evaluating two power theories in the time domain, using real recorded data.
- Full Text:
- Authors: Cornelius, Jurgens J. J. , Janse van Rensburg, J. F. , Nicolae, Dan-Valentin
- Date: 2014
- Subjects: Electric power systems , Electric power transmission
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/17548 , uj:15899 , ISBN: 978-1-4673-6487-4 , Citation: Cornelius, J.J.J., Janse van Rensburg, J.F. & Nicolae, D.V. 2014. Another case of Discrepancies when evaluating power theories using real data. International Conference on Harmonics and quality of power, 25-28 May 2014, Bucharest, Romania. DOI:10.1109/ICHQP.2014.6842839 /9781497394874
- Description: Abstract: Most non-sinusoidal power theories have been developed from theoretical techniques, as well as relying on hypothetical and experimental networks to highlight the advantages of each. The drawback of the power theories is that no single one has been universally accepted as a benchmark for other developments. This paper will however show this weakness by means of evaluating two power theories in the time domain, using real recorded data.
- Full Text:
Impact of the converter operating modes on line current harmonic generation
- Authors: Bokoro, Ntambu Pitshou
- Date: 2012-06-04
- Subjects: Electric power systems , Harmonics (Electric waves) , Electric networks
- Type: Thesis
- Identifier: uj:2333 , http://hdl.handle.net/10210/4790
- Description: M.Ing. , Line commutated thyristor converters are proven to be natural line harmonic currentgenerating sources regardless of their operating modes. The quality of harmonic current components induced back to the lines is commonly described to be similar under both states of operation. This however does not seem to be quite obvious as far as the aggregate harmonic current contribution to the phase inputs per operating region of thyristor converters. It becomes thus important to examine the degree of association between thyristor converter operating states and the magnitude of current harmonic pollution induced back to the input lines to subsequently establish the most current harmonic polluting region of operation. For the purpose of this study, the Nyquist-Shannon theorem, best known as the sampling theorem, whereby the converter output signal or waveform is sampled by the switching function to reconstruct the input waveform, is numerically applied in conjunction with the MatLab/Simulink 7.0 which enables the simulation of the two-quadrant operation of direct current variable speed drive (DC VSD) and that of high voltage direct current link (HVDC) converter station operation, as well as physical measurements on the twoquadrant operation of the DC VSD (Saftronics DC2L) with the aid of the digital scope meter (DSO)1200 series. However, numerical analysis based on the sampling theorem, practical measurements obtained and the MatLab/Simulink simulations indicate that the converter operating states cause a randomly distributed harmonic current generation trend in the input lines as the firing angle is increased and the most harmonic current contribution cannot be attributed to a specific region of the controlled converter firing angle.
- Full Text:
- Authors: Bokoro, Ntambu Pitshou
- Date: 2012-06-04
- Subjects: Electric power systems , Harmonics (Electric waves) , Electric networks
- Type: Thesis
- Identifier: uj:2333 , http://hdl.handle.net/10210/4790
- Description: M.Ing. , Line commutated thyristor converters are proven to be natural line harmonic currentgenerating sources regardless of their operating modes. The quality of harmonic current components induced back to the lines is commonly described to be similar under both states of operation. This however does not seem to be quite obvious as far as the aggregate harmonic current contribution to the phase inputs per operating region of thyristor converters. It becomes thus important to examine the degree of association between thyristor converter operating states and the magnitude of current harmonic pollution induced back to the input lines to subsequently establish the most current harmonic polluting region of operation. For the purpose of this study, the Nyquist-Shannon theorem, best known as the sampling theorem, whereby the converter output signal or waveform is sampled by the switching function to reconstruct the input waveform, is numerically applied in conjunction with the MatLab/Simulink 7.0 which enables the simulation of the two-quadrant operation of direct current variable speed drive (DC VSD) and that of high voltage direct current link (HVDC) converter station operation, as well as physical measurements on the twoquadrant operation of the DC VSD (Saftronics DC2L) with the aid of the digital scope meter (DSO)1200 series. However, numerical analysis based on the sampling theorem, practical measurements obtained and the MatLab/Simulink simulations indicate that the converter operating states cause a randomly distributed harmonic current generation trend in the input lines as the firing angle is increased and the most harmonic current contribution cannot be attributed to a specific region of the controlled converter firing angle.
- Full Text:
Gemultiplekseerde differensierende optieseveselsensor vir die meting van elektriese stroom in hoogspanningslyne
- Authors: Theron, David Cornelius
- Date: 2014-02-12
- Subjects: Optical fiber detectors , Electric current converters , Electric power systems
- Type: Thesis
- Identifier: uj:3913 , http://hdl.handle.net/10210/9277
- Description: M.Ing. , Please refer to full text to view abstract
- Full Text:
- Authors: Theron, David Cornelius
- Date: 2014-02-12
- Subjects: Optical fiber detectors , Electric current converters , Electric power systems
- Type: Thesis
- Identifier: uj:3913 , http://hdl.handle.net/10210/9277
- Description: M.Ing. , Please refer to full text to view abstract
- Full Text:
'n Hibriede vervormingskompensator, beheer deur 'n kunsmatige neurale netwerk
- Authors: Pretorius, Robert W.
- Date: 2014-03-10
- Subjects: Power electronics , Electric power systems , Neural networks (Computer science)
- Type: Thesis
- Identifier: uj:4245 , http://hdl.handle.net/10210/9603
- Description: M.Ing. (Electrical and Electronics) , The increased use of power electronic equipment in power networks prompted the development of various topologies to compensate for the distortion in the power networks. The various compensator topologies employ a vast range of converters for the compensation of the different non-active power components. The compensators are either designed to eliminate a specific non-active power component, or a combination of converters is used to simultaneously compensate for several non-active components. The choice of compensator depends largely on the type of load, the distortion levels in the power network, the effectiveness of the compensator and very importantly, the cost implications for the user. Under constant load conditions a particular compensator would suffice. It is however not the case when the load and the accompanied distortion varies with time, which is the case with present non-linear, dynamic high power loads on the network. In these cases,. a need for another compensator or compensation strategy, that is more effective in compensating the changing load condition, exists. It would therefore be advantageous to construct a single compensator from various converters -the hybrid compensator -, so as to enable the user to compensate effectively at all times the distortion caused by his load. In order to be able to operate such a hybrid compensator cost-effectively an intelligent control system capable of constantly monitoring the load and updating the compensation strategy, is needed. Keeping in mind that, with the technology available today, compensators can effectively operate for periods in excess of twenty years, it makes sound economical sense to operate the compensator as cost-optimally as possible. This dissertation investigates the development of an artificial neural network based controller for the cost-optimal control of a hybrid compensator. The hybrid compensator considered consists of the following: A 21 kVAR three phase FF-TCR compensator with LC-fiIters tuned at the 5th, 7th,11th and 13th harmonic frequencies and a 6 kVA three-phase dynamic power filter. The hybrid compensator is to be applied for the compensation of a 25 KVA non-linear load (Inductively loaded controlled rectifier). The above mentioned compensators have been modelled to agree with experimental pilot plants. The complete system with low-level controllers was simulated with EMTP (The Electromagnetic Transients Program). This simulation was used to verify the intelligent controller operation. The neural network based controller that is investigated, consists of a Backpropagation-trained neural network, that continuously analyses the load conditions, considers the operational characteristics and losses of the hybrid compensator and proposes a cost-optimal compensation strategy for the hybrid compensator. The modelling of the hybrid compensator's operational losses and characteristics to enable the cost-effective operation thereof is discussed. Special attention is given to the modelling of the cost-effective control strategy, in the training data used for the training of the neural network controller. The training of the neural network controller, and an evaluation of its behaviour when applied to two different hybrid compensator structures, is also given.
- Full Text:
- Authors: Pretorius, Robert W.
- Date: 2014-03-10
- Subjects: Power electronics , Electric power systems , Neural networks (Computer science)
- Type: Thesis
- Identifier: uj:4245 , http://hdl.handle.net/10210/9603
- Description: M.Ing. (Electrical and Electronics) , The increased use of power electronic equipment in power networks prompted the development of various topologies to compensate for the distortion in the power networks. The various compensator topologies employ a vast range of converters for the compensation of the different non-active power components. The compensators are either designed to eliminate a specific non-active power component, or a combination of converters is used to simultaneously compensate for several non-active components. The choice of compensator depends largely on the type of load, the distortion levels in the power network, the effectiveness of the compensator and very importantly, the cost implications for the user. Under constant load conditions a particular compensator would suffice. It is however not the case when the load and the accompanied distortion varies with time, which is the case with present non-linear, dynamic high power loads on the network. In these cases,. a need for another compensator or compensation strategy, that is more effective in compensating the changing load condition, exists. It would therefore be advantageous to construct a single compensator from various converters -the hybrid compensator -, so as to enable the user to compensate effectively at all times the distortion caused by his load. In order to be able to operate such a hybrid compensator cost-effectively an intelligent control system capable of constantly monitoring the load and updating the compensation strategy, is needed. Keeping in mind that, with the technology available today, compensators can effectively operate for periods in excess of twenty years, it makes sound economical sense to operate the compensator as cost-optimally as possible. This dissertation investigates the development of an artificial neural network based controller for the cost-optimal control of a hybrid compensator. The hybrid compensator considered consists of the following: A 21 kVAR three phase FF-TCR compensator with LC-fiIters tuned at the 5th, 7th,11th and 13th harmonic frequencies and a 6 kVA three-phase dynamic power filter. The hybrid compensator is to be applied for the compensation of a 25 KVA non-linear load (Inductively loaded controlled rectifier). The above mentioned compensators have been modelled to agree with experimental pilot plants. The complete system with low-level controllers was simulated with EMTP (The Electromagnetic Transients Program). This simulation was used to verify the intelligent controller operation. The neural network based controller that is investigated, consists of a Backpropagation-trained neural network, that continuously analyses the load conditions, considers the operational characteristics and losses of the hybrid compensator and proposes a cost-optimal compensation strategy for the hybrid compensator. The modelling of the hybrid compensator's operational losses and characteristics to enable the cost-effective operation thereof is discussed. Special attention is given to the modelling of the cost-effective control strategy, in the training data used for the training of the neural network controller. The training of the neural network controller, and an evaluation of its behaviour when applied to two different hybrid compensator structures, is also given.
- Full Text:
Utilizing IEC61850 standard and the generic object orientated substation event in modern protection and control devices
- Authors: Motsei, Tumelo Timoty
- Date: 2016
- Subjects: Electric power systems , Electric power systems - Protection , Electric power systems - Control , Computer network protocols
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/243029 , uj:25083
- Description: M.Ing. (Engineering Management) , Abstract: The research is about the comparative study between IEC61850 and the conventional DNP3 protocol in as far as the practicability of their application in the modern substation environment is concerned. IEC61850 is a fairly new international standard and technology that entails numerous progressions to traditional Substation Automation Systems (SAS). Currently in South Africa, the major electricity supply utility, Eskom, has predominantly employed Distributed Network Protocol 3 (DNP3) technology for communicating data between protection and control devices. This protocol does not possess all the desirable attributes for use in the Smart Grid (The world is shifting towards smart grid operations). For instance, with IEC61850 the secondary power circuits are simplified by replacing clusters of wires in a substation with a simpler piece of equipment called a process bus. Faster performance speeds can then consequently be realized using Ethernet and Generic Object Orientated Substation Event (GOOSE) messaging in the new substation network which in turn results in a more reliable power system. It is often a challenging task to evaluate the feasibility of the new technology such as IEC61850 when there are only few known cases of its implementation. There are numerous suggestions as to how IEC61850 should be implemented in the industries however; there is currently no one procedure that has been proven to be the best. In the face of this, IEC61850 has proven to be the future of communications in the power system protection environment. The numerous benefits of IEC61850 overshadow the currently utilized traditional protocols such as DNP3. The Design alternatives analysis is thus conducted in this research to determine if power utilities can do away with the traditional DNP3 platforms in the name of introducing the revolutionary IEC61850 technology in their plants. A Monte Carlo approach is employed for comprehensive analysis of the design alternatives. All the inputs to Monte Carlo analysis are evaluated using the Simple Additive Weighting (SAW) strategy as a deterministic model within Monte Carlo to evaluate the probability of IEC61850 being the most preferred technology over DNP3. The inputs to Monte Carlo analysis are the weights of the technology selection criteria. The weights are computed from randomized judgement/comparison matrices using a Visual Basic (VBA) code in Excel. The design alternatives base rates within SAW analysis are determined through application of theory and laboratory experiments results. Intelligent Electronic Devices (IEDs) were used in the laboratory to evaluate the performance and characteristics of both IEC61850 and DNP3 technologies. The whole Monte Carlo procedure from determination of criteria comparison matrices to determining the probability of IEC61850 being the most preferred technology, is carried out by a VBA code complied in Microsoft Excel. About 100 seven-criterion comparison matrices were generated within Microsoft Excel for the purpose of this study. After performing Monte Carlo analysis it was observed that the probability of IEC61850 being the most preferred technology in the industry was 0.46 for a worst case scenario whereby the flexible base rates in SAW analysis were maximized in favour of the DNP3 technology. For any other worst case scenarios studied in this research, IEC61850 proved to be more beneficial than DNP3 technology with a probability between 0.52 and 0.59. The selection criteria which allowed flexible base rates were; ease of system configuration, space saving and system scalability. The base rates for the performance speed, technology system effectiveness, reliability of the system, and purchase costs were fixed.
- Full Text:
- Authors: Motsei, Tumelo Timoty
- Date: 2016
- Subjects: Electric power systems , Electric power systems - Protection , Electric power systems - Control , Computer network protocols
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/243029 , uj:25083
- Description: M.Ing. (Engineering Management) , Abstract: The research is about the comparative study between IEC61850 and the conventional DNP3 protocol in as far as the practicability of their application in the modern substation environment is concerned. IEC61850 is a fairly new international standard and technology that entails numerous progressions to traditional Substation Automation Systems (SAS). Currently in South Africa, the major electricity supply utility, Eskom, has predominantly employed Distributed Network Protocol 3 (DNP3) technology for communicating data between protection and control devices. This protocol does not possess all the desirable attributes for use in the Smart Grid (The world is shifting towards smart grid operations). For instance, with IEC61850 the secondary power circuits are simplified by replacing clusters of wires in a substation with a simpler piece of equipment called a process bus. Faster performance speeds can then consequently be realized using Ethernet and Generic Object Orientated Substation Event (GOOSE) messaging in the new substation network which in turn results in a more reliable power system. It is often a challenging task to evaluate the feasibility of the new technology such as IEC61850 when there are only few known cases of its implementation. There are numerous suggestions as to how IEC61850 should be implemented in the industries however; there is currently no one procedure that has been proven to be the best. In the face of this, IEC61850 has proven to be the future of communications in the power system protection environment. The numerous benefits of IEC61850 overshadow the currently utilized traditional protocols such as DNP3. The Design alternatives analysis is thus conducted in this research to determine if power utilities can do away with the traditional DNP3 platforms in the name of introducing the revolutionary IEC61850 technology in their plants. A Monte Carlo approach is employed for comprehensive analysis of the design alternatives. All the inputs to Monte Carlo analysis are evaluated using the Simple Additive Weighting (SAW) strategy as a deterministic model within Monte Carlo to evaluate the probability of IEC61850 being the most preferred technology over DNP3. The inputs to Monte Carlo analysis are the weights of the technology selection criteria. The weights are computed from randomized judgement/comparison matrices using a Visual Basic (VBA) code in Excel. The design alternatives base rates within SAW analysis are determined through application of theory and laboratory experiments results. Intelligent Electronic Devices (IEDs) were used in the laboratory to evaluate the performance and characteristics of both IEC61850 and DNP3 technologies. The whole Monte Carlo procedure from determination of criteria comparison matrices to determining the probability of IEC61850 being the most preferred technology, is carried out by a VBA code complied in Microsoft Excel. About 100 seven-criterion comparison matrices were generated within Microsoft Excel for the purpose of this study. After performing Monte Carlo analysis it was observed that the probability of IEC61850 being the most preferred technology in the industry was 0.46 for a worst case scenario whereby the flexible base rates in SAW analysis were maximized in favour of the DNP3 technology. For any other worst case scenarios studied in this research, IEC61850 proved to be more beneficial than DNP3 technology with a probability between 0.52 and 0.59. The selection criteria which allowed flexible base rates were; ease of system configuration, space saving and system scalability. The base rates for the performance speed, technology system effectiveness, reliability of the system, and purchase costs were fixed.
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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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EMI mitigation in AC-DC transfer measurement system
- Hlakola, Mmatselagale Marcus
- Authors: Hlakola, Mmatselagale Marcus
- Date: 2016
- Subjects: Electric power distribution - Direct current , Electric power distribution - Alternating current , Electric current converters , Electric power systems
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/225262 , uj:22747
- Description: Abstract: The AC-DC transfer measurement system constitutes a primary establishment for AC voltage, power and energy measurements. This is achieved by comparing the RMS of an AC signal with a DC reference using a thermal converter. The mathematical modelling was developed for a better description of the thermal RMS-DC converter’s operation and performance. The theoretical and simulation analysis was carried out to outline the factors influencing the transfer characteristics of the converter in AC and DC regimes. Since any system of electric and/or electronic instruments can experience undesired electrical signals ground currents resulting in annoying and often subtle measurement errors, remedial measures of controlling electromagnetic interference (EMI) are desired and essential. The generation and emission of unwanted electrical noise often result in performance degradation and failures of electronic systems. It is then necessary to find a mitigation technique to overcome this problem and avoid costly systems failures in industry. A literature review of the EMI modelling research was carried out as the main foundation for understanding noise management in AC measurement systems. EMI generation and propagation paths have been outlined. The AC-DC transfer measurement system was analysed for possible EMI sources. Based on the analysis, a microcontroller-driven GPIB isolator device was designed and prototyped to prevent the ground loops occurrence between the measurement circuit and the control-plane circuit of the AC-DC transfer measurement system. Various methods of reducing and controlling unwanted signals in the measurement circuit have been explained. , M.Phil. (Electrical and Electronic Engineering)
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- Authors: Hlakola, Mmatselagale Marcus
- Date: 2016
- Subjects: Electric power distribution - Direct current , Electric power distribution - Alternating current , Electric current converters , Electric power systems
- Language: English
- Type: Masters (Thesis)
- Identifier: http://hdl.handle.net/10210/225262 , uj:22747
- Description: Abstract: The AC-DC transfer measurement system constitutes a primary establishment for AC voltage, power and energy measurements. This is achieved by comparing the RMS of an AC signal with a DC reference using a thermal converter. The mathematical modelling was developed for a better description of the thermal RMS-DC converter’s operation and performance. The theoretical and simulation analysis was carried out to outline the factors influencing the transfer characteristics of the converter in AC and DC regimes. Since any system of electric and/or electronic instruments can experience undesired electrical signals ground currents resulting in annoying and often subtle measurement errors, remedial measures of controlling electromagnetic interference (EMI) are desired and essential. The generation and emission of unwanted electrical noise often result in performance degradation and failures of electronic systems. It is then necessary to find a mitigation technique to overcome this problem and avoid costly systems failures in industry. A literature review of the EMI modelling research was carried out as the main foundation for understanding noise management in AC measurement systems. EMI generation and propagation paths have been outlined. The AC-DC transfer measurement system was analysed for possible EMI sources. Based on the analysis, a microcontroller-driven GPIB isolator device was designed and prototyped to prevent the ground loops occurrence between the measurement circuit and the control-plane circuit of the AC-DC transfer measurement system. Various methods of reducing and controlling unwanted signals in the measurement circuit have been explained. , M.Phil. (Electrical and Electronic Engineering)
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