Pitshou Bokoro | University of Johannesburg, South Africa (original) (raw)

Papers by Pitshou Bokoro

Research paper thumbnail of The Impact of Market-Based Policies on Access to Electricity and Sustainable Development in Sub-Saharan Africa

Studies in systems, decision and control, Sep 19, 2023

Research paper thumbnail of A Comprehensive Summary of the Contributions and the Quintessence of This Book

Studies in systems, decision and control, Sep 19, 2023

Research paper thumbnail of A Review of Leakage Current-based Condition Monitoring Techniques of Metal Oxide Surge Arresters

Research paper thumbnail of Performance Analysis of Double Arrester Protection Configuration of Pole Mounted Transformers using Probabilistic Risk Evaluation

Research paper thumbnail of Dual Extended State Observer Based Feedback Linearizing Control for Magnetic Levitation System with Mismatched Disturbances and Uncertainties

Research paper thumbnail of Dual-Extended State Observer-Based Feedback Linearizing Control for a Nonlinear System with Mismatched Disturbances and Uncertainties

Energies, Mar 30, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Statistical Analysis of Varistor Capacitance under Slow-Front Overvoltages

IECON 2022 – 48th Annual Conference of the IEEE Industrial Electronics Society, Oct 17, 2022

Research paper thumbnail of An Assessment of Failure Rate of Pole-Mounted Transformers Using Probabilistic Risk Evaluation of Lightning Arresters

IECON 2022 – 48th Annual Conference of the IEEE Industrial Electronics Society, Oct 17, 2022

Research paper thumbnail of Improving Electricity Supply Reliability: A Case Study of Remote Communities of Limpopo in South Africa

Studies in systems, decision and control, Sep 19, 2023

Research paper thumbnail of Power Loss Minimization through Reconfiguration Using BPSO-Based Technique

Electric Power Components and Systems

Research paper thumbnail of Effect of electro-thermally induced degradation on the capacitance of metal oxide varistors

In this study, changes in the capacitance of MOV-based arresters resulting from thermal stresses ... more In this study, changes in the capacitance of MOV-based arresters resulting from thermal stresses are analysed. Low-voltage MOV samples are artificially degraded at different thermal stresses, while the simultaneously applied ac field was kept constant. Prior to ANOVA being applied, the change in capacitance measured at room temperature, before and after degradation process, is tested for compliance with normality using Anderson-Darling test. Results show significant reduction in capacitance after electro-thermal degradation.

Research paper thumbnail of Coordinated Control of Wind Energy Conversion System during Unsymmetrical Fault at Grid

Energies, Jul 4, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of On-line monitoring of metal-oxide surge arresters using improved equivalent model with evolutionary optimisation algorithm

A resistive-current extraction algorithm to assist with on-line monitoring of surge arresters is ... more A resistive-current extraction algorithm to assist with on-line monitoring of surge arresters is proposed in this paper. The algorithm is based on the improved equivalent model for surge arresters and combines evolutionary optimisation with the base-frequency approximating method. A genetic algorithm is used to obtain the optimal capacitance such that the phase shift between the base-components of the branch voltage and current is minimised thereby yielding a good approximation of the resistive current. In this paper, the algorithm is implemented and tested using Matlab/Simulink. Results indicate that the proposed algorithm is able to efficiently and accurately obtain the resistive component of the leakage current, using the improved equivalent model, under both ideal and distorted supply conditions.

Research paper thumbnail of Islanding Detection with Reduced Non-Detection Zones and Restoration by Reconfiguration

Energies, Mar 27, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Investigation of Very Fast-Front Transient Overvoltages for Selection and Placement of Surge Arresters

An analysis of very fast front transient overvoltages, generated as a result of induced effects o... more An analysis of very fast front transient overvoltages, generated as a result of induced effects of lightning, across a photovoltaic plant is investigated. The EMTP-RV version 3.3 computer software platform is used to simulate surge voltage magnification. Selection and placement of surge arresters for effective protection of power transformers are conducted. Results show that selected arresters placed on bus 4 and coordinated with those placed on bus 5 and 3 ensure surge amplitude reduction of 33% on bus 4.

Research paper thumbnail of Assessing the Significance of Electro-Thermal Stress on Varistor Arresters Using Kruskal-Wallis H-Test

In this study, the effect of electro-thermal stresses on the microstructure of low-voltage zinc o... more In this study, the effect of electro-thermal stresses on the microstructure of low-voltage zinc oxide varistors is experimentally investigated. Accelerated ageing tests, based on continuous ac voltage stress at several thermal points, are conducted prior to linear intercept on scanning electro microscopy-based micrographs. The Kruskal-Wallis H-test is used to assess the extent of microstructural changes in the tested varistor arresters. Results obtained show significant change in the microstructure of the varistor arresters as a result of electro-thermal treatment.

Research paper thumbnail of Microstructure observation of zinc oxide exposed to thermal and ac field stresses

In this work, ac field and thermal stresses of magnitude and duration 0.76 V1mA/85°C/48 hours is ... more In this work, ac field and thermal stresses of magnitude and duration 0.76 V1mA/85°C/48 hours is used to implement accelerated degradation on commercially-sourced Zinc oxide (ZnO) varistors. The following parameters are measured and analysed before and after degradation test: the average size of ZnO grains using linear intercept method on Scanning Electron Microscopy (SEM) micrograps, microstructure phase composition using X-ray diffractometer (XRD) and Energy Dispersion Spectroscopy (EDS) techniques, and (V — I) characteristic curve using the Keithley 2401 source-meter. The degradation rate and the non-linear coefficient of the tested samples are derived from the (V — I) characteristic. The results obtained indicate an increase of ZnO grain average size from 5.7749 μm to 6.8753 μm, a decrease from 23.6 to 16.1 of the coefficient of non-linearity and a higher degradation rate of 32.6923 μAh−1/2 for degraded or failed varistor samples.

Research paper thumbnail of Distributed Hybrid Power-Sharing Control Strategy within Islanded Microgrids

Research paper thumbnail of Development and performance evaluation of a single stage travelling-wave thermo-acoustic generator

Thermo-acoustic systems are being considered as a potential solution for electricity generation. ... more Thermo-acoustic systems are being considered as a potential solution for electricity generation. This work describes the construction of a single stage travelling-wave thermo-acoustic generator. Secondly, an experimental investigation into the effect of the heat source on the potential of the device for electricity generation is performed. The magnitude of the sound generated by the engine, the onset time and the magnitude of electricity generated by the linear alternator have been considered as performance indicators for the device developed. This paper provides clarity on the potential for thermo-acoustic system for sound-to-electricity conversion. Clear trends showing the effect of inputs parameters on device performance have been disclosed. The minimum/maximum amount of heat that has produced a sound was 339/634° C corresponding to sound of 114.0/114.13 dB and a voltage of 278/319 mV. Although the efficiency of the sound-to-electricity conversion was low, this work proves the viability of thermo-acoustic as the alternative solution for electricity generation.

Research paper thumbnail of Durability Analysis of Metal Oxide Varistor under Direct Current Switching Surges

2020 International SAUPEC/RobMech/PRASA Conference, 2020

The circuit-break switch of a direct current (DC) system will have to dissipate any stored residu... more The circuit-break switch of a direct current (DC) system will have to dissipate any stored residual line inductance energy during the switch-off period. Therefore, it is common to make use of a metal oxide varistor (MOV) mounted in parallel with a DC switch, in order to prevent arc damage by absorbing and transferring stored residual line inductance energy around the switch. However, the parallel-connected surge protecting MOV should not fail before the expected lifetime operation of the DC switch. Under repeated DC switching surge conditions, a zinc oxide (ZnO) based varistor degrades and its energy absorption capability reduces over time. Fast consecutive switch-off operations are not common in circuit-break DC switch applications, thereby allowing sufficient time for excess absorbed energy by the MOV to be dissipated as heat to ambiance. However, it is not well understood how varistor DC switching surge durability could be modeled, for this specific type of energy handling capability (EHC). In this work, a novel method to model the MOV durability or resiliency to DC switching surges with time intervals in-between for sufficient cooling is proposed. The obtained model will then serve as an average numerical durability indicator that could assist designers in predicting the expected lifetime of the parallel connected surge protecting MOV. It will also be a more effective way of comparing this specific type of degradation or EHC between different manufacturers with similar specifications.

Research paper thumbnail of The Impact of Market-Based Policies on Access to Electricity and Sustainable Development in Sub-Saharan Africa

Studies in systems, decision and control, Sep 19, 2023

Research paper thumbnail of A Comprehensive Summary of the Contributions and the Quintessence of This Book

Studies in systems, decision and control, Sep 19, 2023

Research paper thumbnail of A Review of Leakage Current-based Condition Monitoring Techniques of Metal Oxide Surge Arresters

Research paper thumbnail of Performance Analysis of Double Arrester Protection Configuration of Pole Mounted Transformers using Probabilistic Risk Evaluation

Research paper thumbnail of Dual Extended State Observer Based Feedback Linearizing Control for Magnetic Levitation System with Mismatched Disturbances and Uncertainties

Research paper thumbnail of Dual-Extended State Observer-Based Feedback Linearizing Control for a Nonlinear System with Mismatched Disturbances and Uncertainties

Energies, Mar 30, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Statistical Analysis of Varistor Capacitance under Slow-Front Overvoltages

IECON 2022 – 48th Annual Conference of the IEEE Industrial Electronics Society, Oct 17, 2022

Research paper thumbnail of An Assessment of Failure Rate of Pole-Mounted Transformers Using Probabilistic Risk Evaluation of Lightning Arresters

IECON 2022 – 48th Annual Conference of the IEEE Industrial Electronics Society, Oct 17, 2022

Research paper thumbnail of Improving Electricity Supply Reliability: A Case Study of Remote Communities of Limpopo in South Africa

Studies in systems, decision and control, Sep 19, 2023

Research paper thumbnail of Power Loss Minimization through Reconfiguration Using BPSO-Based Technique

Electric Power Components and Systems

Research paper thumbnail of Effect of electro-thermally induced degradation on the capacitance of metal oxide varistors

In this study, changes in the capacitance of MOV-based arresters resulting from thermal stresses ... more In this study, changes in the capacitance of MOV-based arresters resulting from thermal stresses are analysed. Low-voltage MOV samples are artificially degraded at different thermal stresses, while the simultaneously applied ac field was kept constant. Prior to ANOVA being applied, the change in capacitance measured at room temperature, before and after degradation process, is tested for compliance with normality using Anderson-Darling test. Results show significant reduction in capacitance after electro-thermal degradation.

Research paper thumbnail of Coordinated Control of Wind Energy Conversion System during Unsymmetrical Fault at Grid

Energies, Jul 4, 2022

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of On-line monitoring of metal-oxide surge arresters using improved equivalent model with evolutionary optimisation algorithm

A resistive-current extraction algorithm to assist with on-line monitoring of surge arresters is ... more A resistive-current extraction algorithm to assist with on-line monitoring of surge arresters is proposed in this paper. The algorithm is based on the improved equivalent model for surge arresters and combines evolutionary optimisation with the base-frequency approximating method. A genetic algorithm is used to obtain the optimal capacitance such that the phase shift between the base-components of the branch voltage and current is minimised thereby yielding a good approximation of the resistive current. In this paper, the algorithm is implemented and tested using Matlab/Simulink. Results indicate that the proposed algorithm is able to efficiently and accurately obtain the resistive component of the leakage current, using the improved equivalent model, under both ideal and distorted supply conditions.

Research paper thumbnail of Islanding Detection with Reduced Non-Detection Zones and Restoration by Reconfiguration

Energies, Mar 27, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Investigation of Very Fast-Front Transient Overvoltages for Selection and Placement of Surge Arresters

An analysis of very fast front transient overvoltages, generated as a result of induced effects o... more An analysis of very fast front transient overvoltages, generated as a result of induced effects of lightning, across a photovoltaic plant is investigated. The EMTP-RV version 3.3 computer software platform is used to simulate surge voltage magnification. Selection and placement of surge arresters for effective protection of power transformers are conducted. Results show that selected arresters placed on bus 4 and coordinated with those placed on bus 5 and 3 ensure surge amplitude reduction of 33% on bus 4.

Research paper thumbnail of Assessing the Significance of Electro-Thermal Stress on Varistor Arresters Using Kruskal-Wallis H-Test

In this study, the effect of electro-thermal stresses on the microstructure of low-voltage zinc o... more In this study, the effect of electro-thermal stresses on the microstructure of low-voltage zinc oxide varistors is experimentally investigated. Accelerated ageing tests, based on continuous ac voltage stress at several thermal points, are conducted prior to linear intercept on scanning electro microscopy-based micrographs. The Kruskal-Wallis H-test is used to assess the extent of microstructural changes in the tested varistor arresters. Results obtained show significant change in the microstructure of the varistor arresters as a result of electro-thermal treatment.

Research paper thumbnail of Microstructure observation of zinc oxide exposed to thermal and ac field stresses

In this work, ac field and thermal stresses of magnitude and duration 0.76 V1mA/85°C/48 hours is ... more In this work, ac field and thermal stresses of magnitude and duration 0.76 V1mA/85°C/48 hours is used to implement accelerated degradation on commercially-sourced Zinc oxide (ZnO) varistors. The following parameters are measured and analysed before and after degradation test: the average size of ZnO grains using linear intercept method on Scanning Electron Microscopy (SEM) micrograps, microstructure phase composition using X-ray diffractometer (XRD) and Energy Dispersion Spectroscopy (EDS) techniques, and (V — I) characteristic curve using the Keithley 2401 source-meter. The degradation rate and the non-linear coefficient of the tested samples are derived from the (V — I) characteristic. The results obtained indicate an increase of ZnO grain average size from 5.7749 μm to 6.8753 μm, a decrease from 23.6 to 16.1 of the coefficient of non-linearity and a higher degradation rate of 32.6923 μAh−1/2 for degraded or failed varistor samples.

Research paper thumbnail of Distributed Hybrid Power-Sharing Control Strategy within Islanded Microgrids

Research paper thumbnail of Development and performance evaluation of a single stage travelling-wave thermo-acoustic generator

Thermo-acoustic systems are being considered as a potential solution for electricity generation. ... more Thermo-acoustic systems are being considered as a potential solution for electricity generation. This work describes the construction of a single stage travelling-wave thermo-acoustic generator. Secondly, an experimental investigation into the effect of the heat source on the potential of the device for electricity generation is performed. The magnitude of the sound generated by the engine, the onset time and the magnitude of electricity generated by the linear alternator have been considered as performance indicators for the device developed. This paper provides clarity on the potential for thermo-acoustic system for sound-to-electricity conversion. Clear trends showing the effect of inputs parameters on device performance have been disclosed. The minimum/maximum amount of heat that has produced a sound was 339/634° C corresponding to sound of 114.0/114.13 dB and a voltage of 278/319 mV. Although the efficiency of the sound-to-electricity conversion was low, this work proves the viability of thermo-acoustic as the alternative solution for electricity generation.

Research paper thumbnail of Durability Analysis of Metal Oxide Varistor under Direct Current Switching Surges

2020 International SAUPEC/RobMech/PRASA Conference, 2020

The circuit-break switch of a direct current (DC) system will have to dissipate any stored residu... more The circuit-break switch of a direct current (DC) system will have to dissipate any stored residual line inductance energy during the switch-off period. Therefore, it is common to make use of a metal oxide varistor (MOV) mounted in parallel with a DC switch, in order to prevent arc damage by absorbing and transferring stored residual line inductance energy around the switch. However, the parallel-connected surge protecting MOV should not fail before the expected lifetime operation of the DC switch. Under repeated DC switching surge conditions, a zinc oxide (ZnO) based varistor degrades and its energy absorption capability reduces over time. Fast consecutive switch-off operations are not common in circuit-break DC switch applications, thereby allowing sufficient time for excess absorbed energy by the MOV to be dissipated as heat to ambiance. However, it is not well understood how varistor DC switching surge durability could be modeled, for this specific type of energy handling capability (EHC). In this work, a novel method to model the MOV durability or resiliency to DC switching surges with time intervals in-between for sufficient cooling is proposed. The obtained model will then serve as an average numerical durability indicator that could assist designers in predicting the expected lifetime of the parallel connected surge protecting MOV. It will also be a more effective way of comparing this specific type of degradation or EHC between different manufacturers with similar specifications.