Current harmonic compensation of nonlinear loads in a three phase, four wire system
- Authors: Mtakati, Sibulele Morgen
- Date: 2023-12
- Subjects: Electric utilities -- Quality control , Electric power systems , Electric power system stability
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/66581 , vital:75607
- Description: Nonlinear loads, in low voltage distribution networks, inject current harmonics which affect the quality of supply voltages. In this work, the power usage of a university student residential complex was logged over a four day period for analysis of harmonic currents injected by nonlinear loads. Student residents use nonlinear loads such as lighting, televisions, computer power supplies, and other household appliances. The harmonic analysis was performed on the quality of voltages in the university’s distribution network, the level of current distortion in the load current and the contribution of triplen harmonics to the neutral current. Standards such as the NRS048-2 (2007), IEEE-519 (2014) and IEC61000-3-2 (2009) are helpful in regulating harmonic levels in the distribution network, however, they cannot guarantee good quality supply. This work further investigates two methods of current harmonic cancellation, i.e. a shunt passive and an active current harmonic cancellation technique. A passive power filter was designed, built, and evaluated for a given nonlinear load to provide selective filtering of the dominant current harmonics. A four branch, shunt, passive filter was considered in this work for implementation in a three phase four wire distribution network due to its attractive possibility to be tuned to two different harmonic components with a minimum number of passive elements. While passive filters may be inexpensive, they suffer from several disadvantages, such as providing fixed compensation, performance that is source impedance dependent, has an inherent risk of system resonance and detuning due to ageing and component variation. To overcome the disadvantages of passive filters, a shunt connected active power filter was designed, built and evaluated to provide adjustable, wide bandwidth and dynamic correction to nonlinear loads for the compensation of harmonic currents, reactive power, and neutral currents. The controller used was an indirect FFT-based technique with a second order generalized integrator (SOGI) filter for voltage synchronization. It was digitally implemented in an FPGA programmed in VHDL to allow for fast parallel processing of input variables. , Thesis (MEng) -- Faculty of Engineering, the Built Environment, and Technology, School of Engineering, 2023
- Full Text:
- Date Issued: 2023-12
- Authors: Mtakati, Sibulele Morgen
- Date: 2023-12
- Subjects: Electric utilities -- Quality control , Electric power systems , Electric power system stability
- Language: English
- Type: Master's theses , text
- Identifier: http://hdl.handle.net/10948/66581 , vital:75607
- Description: Nonlinear loads, in low voltage distribution networks, inject current harmonics which affect the quality of supply voltages. In this work, the power usage of a university student residential complex was logged over a four day period for analysis of harmonic currents injected by nonlinear loads. Student residents use nonlinear loads such as lighting, televisions, computer power supplies, and other household appliances. The harmonic analysis was performed on the quality of voltages in the university’s distribution network, the level of current distortion in the load current and the contribution of triplen harmonics to the neutral current. Standards such as the NRS048-2 (2007), IEEE-519 (2014) and IEC61000-3-2 (2009) are helpful in regulating harmonic levels in the distribution network, however, they cannot guarantee good quality supply. This work further investigates two methods of current harmonic cancellation, i.e. a shunt passive and an active current harmonic cancellation technique. A passive power filter was designed, built, and evaluated for a given nonlinear load to provide selective filtering of the dominant current harmonics. A four branch, shunt, passive filter was considered in this work for implementation in a three phase four wire distribution network due to its attractive possibility to be tuned to two different harmonic components with a minimum number of passive elements. While passive filters may be inexpensive, they suffer from several disadvantages, such as providing fixed compensation, performance that is source impedance dependent, has an inherent risk of system resonance and detuning due to ageing and component variation. To overcome the disadvantages of passive filters, a shunt connected active power filter was designed, built and evaluated to provide adjustable, wide bandwidth and dynamic correction to nonlinear loads for the compensation of harmonic currents, reactive power, and neutral currents. The controller used was an indirect FFT-based technique with a second order generalized integrator (SOGI) filter for voltage synchronization. It was digitally implemented in an FPGA programmed in VHDL to allow for fast parallel processing of input variables. , Thesis (MEng) -- Faculty of Engineering, the Built Environment, and Technology, School of Engineering, 2023
- Full Text:
- Date Issued: 2023-12
Impact of intergrating teebus hydro power on the unbalanced distribution MV network
- Authors: Mthethwa, Lindani
- Date: 2018
- Subjects: Electric power systems , Renewable energy sources Hydroelectric power plants
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/33054 , vital:32512
- Description: Small hydro power sources have been identified as one of the renewable energy technologies that the South African government is focusing on in order to generate more electricity from renewable/independent resources. Due to the low carbon output of most renewable energy technologies and the carbon intensive power generation technologies that are currently being used in South Africa e.g. Hydro, coal, gas, and etc. further pressure is increasing to incorporate cleaner forms of generation. In 2002 a study focusing on the hydropower potential was compiled providing an assessment according to conventional and unconventional possibilities for all the provinces. Nowadays, the power electricity demand is growing fast and one of the main tasks for power engineers is to generate electricity from renewable energy sources to overcome this increase in the energy consumption and at the same time reduce environmental impact of power generation. Eskom Distribution Eastern Cape Operating Unit (ECOU) was requested to investigate the feasibility of connecting a small hydro power scheme located in the Teebus area in the Eastern Cape. The Eastern Cape in particular, was identified as potentially the most productive area for small hydroelectric development in South Africa for both the grid connected and off grid applications. These network conditions are in contrast to the South African electricity network where long radial feeders with low X/R ratios and high resistance, spanning large geographic areas, give rise to low voltages on the network. Practical simulation networks have been used to test the conditions set out in the South African Grid Code/NERSA standard and to test the impact of connecting small hydro generation onto the unbalanced distribution network. These networks are representative of various real case scenarios of the South African distribution network. Most of the findings from the simulations were consistent with what was expected when comparing with other literatures. From the simulation results it was seen that the performance of the variable speed generators were superior to that of the fixed speed generators during transient conditions. It was also seen that the weakness of the network had a negative effect on the stability of the system. It is also noted that the stability studies are a necessity when connecting the generators to a network and that each case should be reviewed individually. The fundamental cause of voltage instability is identified as incapability of combined distribution and generation system to meet excessive load demand in either real power or reactive power form.
- Full Text:
- Date Issued: 2018
- Authors: Mthethwa, Lindani
- Date: 2018
- Subjects: Electric power systems , Renewable energy sources Hydroelectric power plants
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: http://hdl.handle.net/10948/33054 , vital:32512
- Description: Small hydro power sources have been identified as one of the renewable energy technologies that the South African government is focusing on in order to generate more electricity from renewable/independent resources. Due to the low carbon output of most renewable energy technologies and the carbon intensive power generation technologies that are currently being used in South Africa e.g. Hydro, coal, gas, and etc. further pressure is increasing to incorporate cleaner forms of generation. In 2002 a study focusing on the hydropower potential was compiled providing an assessment according to conventional and unconventional possibilities for all the provinces. Nowadays, the power electricity demand is growing fast and one of the main tasks for power engineers is to generate electricity from renewable energy sources to overcome this increase in the energy consumption and at the same time reduce environmental impact of power generation. Eskom Distribution Eastern Cape Operating Unit (ECOU) was requested to investigate the feasibility of connecting a small hydro power scheme located in the Teebus area in the Eastern Cape. The Eastern Cape in particular, was identified as potentially the most productive area for small hydroelectric development in South Africa for both the grid connected and off grid applications. These network conditions are in contrast to the South African electricity network where long radial feeders with low X/R ratios and high resistance, spanning large geographic areas, give rise to low voltages on the network. Practical simulation networks have been used to test the conditions set out in the South African Grid Code/NERSA standard and to test the impact of connecting small hydro generation onto the unbalanced distribution network. These networks are representative of various real case scenarios of the South African distribution network. Most of the findings from the simulations were consistent with what was expected when comparing with other literatures. From the simulation results it was seen that the performance of the variable speed generators were superior to that of the fixed speed generators during transient conditions. It was also seen that the weakness of the network had a negative effect on the stability of the system. It is also noted that the stability studies are a necessity when connecting the generators to a network and that each case should be reviewed individually. The fundamental cause of voltage instability is identified as incapability of combined distribution and generation system to meet excessive load demand in either real power or reactive power form.
- Full Text:
- Date Issued: 2018
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