Pitshou Bokoro - Profile on Academia.edu (original) (raw)

Papers by Pitshou Bokoro

Condition assessment of SF6 circuit breakers using analysis of variance (ANOVA)

In this study, the condition of high-voltage three-phase SF6 circuit breakers is assessed using a... more In this study, the condition of high-voltage three-phase SF6 circuit breakers is assessed using analysis of variance-based statistical test. 40 SF6 circuit breakers, with similar technical characteristics and operating conditions, were tested on the field using the SA10 switch analyser. The chi-square test for normality was performed on the measured coil tripping times, before analysis of variance was applied. Results obtained indicate the difference between and within the coil tripping times is not significant.

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

A Comprehensive Summary of the Contributions and the Quintessence of This Book

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

A review of proposed leakage current-based techniques applied in condition monitoring of metal ox... more A review of proposed leakage current-based techniques applied in condition monitoring of metal oxide surge arresters is presented in this study. The fundamental conceptual theories that form the basis of resistive current extraction as well as the challenges associated to the implementation of measurement techniques are evaluated. The problematic influence of system voltage harmonics on reported leakage current assessment methods of gapless metal oxide surge protection units is also examined. It is therefore observed that the proposed methods are not completely reliable, and capacitive current compensation techniques remain the fundamental conceptual theory for future developments of accurate and practical measurement of resistive component without the knowledge of system voltage.

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

This research work presents the nonlinear control framework to estimate and reject the mismatched... more This research work presents the nonlinear control framework to estimate and reject the mismatched lumped disturbances acting on the nonlinear uncertain system. It is an unfortunate fact that the conventional Extended State Observer (ESO) is not capable to estimate the mismatched lumped disturbance and its derivative simultaneously for the systems. Also, the basic ESO is only suitable for systems with Integral Chain Form (ICF) structure. Similarly, the conventional Feedback Linearizing Control (FLC) approach is not robust for stabilizing the systems in the presence of disturbances and uncertainties. Hence, the nonlinear control framework is proposed to overcome the above issues which are composed of, (a) Dual Extended State Observer (DESO), and (b) DESO based FLC. The DESO provides information on the unmeasured state, mismatched disturbance, and its derivative. While the DESO-FLC utilizes the information from DESO to counter the effect of such disturbances and to stabilize the nonlinear systems around the reference point. The detailed closed-loop analysis is presented for the proposed control framework in the presence of lumped disturbances. The performance robustness of the presented design has been validated for the third-order, nonlinear, unstable, and disturbed Magnetic Levitation System (MLS). The results of the DESO-FLC approach are compared with the most popular Linear Quadratic Regulator (LQR) and nonlinear FLC approaches based on the integral error criterion and the average electrical energy consumption.

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

Statistical Analysis of Varistor Capacitance under Slow-Front Overvoltages

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

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

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

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

Power Loss Minimization through Reconfiguration Using BPSO-Based Technique

Electric Power Components and Systems

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.

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

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.

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

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.

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.

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.

Distributed Hybrid Power-Sharing Control Strategy within Islanded Microgrids

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.

Condition assessment of SF6 circuit breakers using analysis of variance (ANOVA)

In this study, the condition of high-voltage three-phase SF6 circuit breakers is assessed using a... more In this study, the condition of high-voltage three-phase SF6 circuit breakers is assessed using analysis of variance-based statistical test. 40 SF6 circuit breakers, with similar technical characteristics and operating conditions, were tested on the field using the SA10 switch analyser. The chi-square test for normality was performed on the measured coil tripping times, before analysis of variance was applied. Results obtained indicate the difference between and within the coil tripping times is not significant.

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

A Comprehensive Summary of the Contributions and the Quintessence of This Book

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

A review of proposed leakage current-based techniques applied in condition monitoring of metal ox... more A review of proposed leakage current-based techniques applied in condition monitoring of metal oxide surge arresters is presented in this study. The fundamental conceptual theories that form the basis of resistive current extraction as well as the challenges associated to the implementation of measurement techniques are evaluated. The problematic influence of system voltage harmonics on reported leakage current assessment methods of gapless metal oxide surge protection units is also examined. It is therefore observed that the proposed methods are not completely reliable, and capacitive current compensation techniques remain the fundamental conceptual theory for future developments of accurate and practical measurement of resistive component without the knowledge of system voltage.

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

This research work presents the nonlinear control framework to estimate and reject the mismatched... more This research work presents the nonlinear control framework to estimate and reject the mismatched lumped disturbances acting on the nonlinear uncertain system. It is an unfortunate fact that the conventional Extended State Observer (ESO) is not capable to estimate the mismatched lumped disturbance and its derivative simultaneously for the systems. Also, the basic ESO is only suitable for systems with Integral Chain Form (ICF) structure. Similarly, the conventional Feedback Linearizing Control (FLC) approach is not robust for stabilizing the systems in the presence of disturbances and uncertainties. Hence, the nonlinear control framework is proposed to overcome the above issues which are composed of, (a) Dual Extended State Observer (DESO), and (b) DESO based FLC. The DESO provides information on the unmeasured state, mismatched disturbance, and its derivative. While the DESO-FLC utilizes the information from DESO to counter the effect of such disturbances and to stabilize the nonlinear systems around the reference point. The detailed closed-loop analysis is presented for the proposed control framework in the presence of lumped disturbances. The performance robustness of the presented design has been validated for the third-order, nonlinear, unstable, and disturbed Magnetic Levitation System (MLS). The results of the DESO-FLC approach are compared with the most popular Linear Quadratic Regulator (LQR) and nonlinear FLC approaches based on the integral error criterion and the average electrical energy consumption.

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

Statistical Analysis of Varistor Capacitance under Slow-Front Overvoltages

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

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

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

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

Power Loss Minimization through Reconfiguration Using BPSO-Based Technique

Electric Power Components and Systems

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.

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

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.

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

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.

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.

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.

Distributed Hybrid Power-Sharing Control Strategy within Islanded Microgrids

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.