Energy assessment of e-motorcycles as a clean transport mode for passenger mobility: A case of Ilala District, Dar es Salaam

Electric motorcycles or e-motorcycles is a clean mode of road transport that present a prominent solution toward decarbonizing cities. Despite of e-motorcycles being cleaner than gasoline ones, at the moment, there is missing information whether it is feasible to replace gasoline motorcycles with e-motorcycles used for business transport purposes. This paper, therefore, presents the results comparing energy usage when using e-motorcycles and when using the gasoline motorcycles.  The energy demand for driving passengers using an e-motorcycle in the precarious routes originated from Gongo la Mboto bus stop to Segerea bus stop, Buguruni Malapa, Gerezani bus stop, Kivukoni bus stop, and Buza bus stop has been estimated. In each route, the energy has been estimated in one and four round-trips. The results reveal that the brushless direct current motor (BLDC) rated 2.5 kW is suitable for driving two passengers while consuming about 0.05 kWh/km at 50 km/h for the distance of 36 km. Increase in route length exhibit the uptrend in total energy required (Etotal). The maximum Etotal for one and four round-trips are 2.5 kWh and 10.0 kWh, respectively, for a route of 36 km length. Considering the energy demand of 2.5 kWh for one round-trip of 36 km, a battery pack of 45 Ah 60 V is found suitable to power the e-motorcycle per charge without compromising the design in terms of weight and size. Consequently, this yields to a saving of about 6.4 kWh, which is around 72 % of the energy that could be used by its gasoline counterpart. This means an e-motorcycle of this power rating could save 0.18 kWh/km, equivalent to 0.02 L/km. Moreover, e-motorcycle could cost 24.3 Tsh/km compared to 754.8 Tsh/km for its gasoline counterpart, and save around 97 % of the fuel cost. These results indicate that an e-motorcycle can outperform its gasoline counterpart. These findings play vital roles in designing energy storage systems and charging infrastructure that could offer a reliable service to end-users and assist to accelerate e-motorcycle adoption

Effect of HV Impulses on Partial Discharge Activity in Oil-Impregnated Paper Insulation

High voltage (HV) transients in electrical power systems are mainly caused by lightning strikes and switching operations.  The high voltage transient from its point of origin can propagate in either direction in the electrical power transmission line, and if its magnitude would be below the Basic Insulation Level (BIL) of the equipment for impulse voltage, it can reach the terminals of the equipment without being dissipated by surge arresters.  The dielectric properties of a particular insulation at the instant of interaction with a high voltage transient would determine the level of the degradation of the electrical insulation caused by the high voltage transient. This thesis suggests on-line diagnostic techniques for monitoring the oil-impregnated paper condenser bushings by utilizing the naturally occurring HV transients in electrical power systems. The aim of the first experiment was to investigate the partial discharge (PD) characteristics of the PD defects which are likely to be found in oil-imregnated paper condenser bushings. In order to understand the condition at which the HV impulses would cause the change in phase resolved partial discharge (PRPD) patterns, four more experiments were performed. The second experiment was set in such a way that the effect of HV impulses alone could be investigated. On the other hand, the third experiment was set to examine the effect of PD-ageing at elevated AC voltage. The fourth experiment aimed in investigating the effect of combined PD-ageing at elevated AC voltage and the HV impulses. In order to investigate how different electrical stresses affect the dielectric properties of the oil-impreganted paper insulation, the fifth experiment about the dielectric spectroscopy (DS) in frequency domain was performed. The measurement results presented in this thesis show that high voltage impulses can have a large impact on the behavior of PRPD patterns if the test sample is aged by partial discharges, but a smaller impact when the test sample is unaged. The measurement results also show that the degradation of the oil-impregnated papers is much faster when the oil-impregnated papers are suffered from the combination of the HV impulses and the PD activity at elevated AC voltage than when they are suffered from the PD activity at elevated AC voltage alone.QC 20121115</p

Effect of HV Impulses on Partial Discharge Activity in Oil-Impregnated Paper Insulation

High voltage (HV) transients in electrical power systems are mainly caused by lightning strikes and switching operations.  The high voltage transient from its point of origin can propagate in either direction in the electrical power transmission line, and if its magnitude would be below the Basic Insulation Level (BIL) of the equipment for impulse voltage, it can reach the terminals of the equipment without being dissipated by surge arresters.  The dielectric properties of a particular insulation at the instant of interaction with a high voltage transient would determine the level of the degradation of the electrical insulation caused by the high voltage transient. This thesis suggests on-line diagnostic techniques for monitoring the oil-impregnated paper condenser bushings by utilizing the naturally occurring HV transients in electrical power systems. The aim of the first experiment was to investigate the partial discharge (PD) characteristics of the PD defects which are likely to be found in oil-imregnated paper condenser bushings. In order to understand the condition at which the HV impulses would cause the change in phase resolved partial discharge (PRPD) patterns, four more experiments were performed. The second experiment was set in such a way that the effect of HV impulses alone could be investigated. On the other hand, the third experiment was set to examine the effect of PD-ageing at elevated AC voltage. The fourth experiment aimed in investigating the effect of combined PD-ageing at elevated AC voltage and the HV impulses. In order to investigate how different electrical stresses affect the dielectric properties of the oil-impreganted paper insulation, the fifth experiment about the dielectric spectroscopy (DS) in frequency domain was performed. The measurement results presented in this thesis show that high voltage impulses can have a large impact on the behavior of PRPD patterns if the test sample is aged by partial discharges, but a smaller impact when the test sample is unaged. The measurement results also show that the degradation of the oil-impregnated papers is much faster when the oil-impregnated papers are suffered from the combination of the HV impulses and the PD activity at elevated AC voltage than when they are suffered from the PD activity at elevated AC voltage alone.QC 20121115</p

The Effect of HV Impulses on Partial Discharge Activity and on the Dielectric Response in Oil-impregnated Paper Insulation

This work investigates how HV impulses affect the behavior of partial discharge (PD) activity and the low voltage dielectric response of oil-impregnated paper insulation. It also investigates how the change in the PD activity is related to the degradation level of oil-impregnated paper insulation. In order to accomplish these objectives, the ageing were done under three different electrical stress conditions, i.e. HV impulses following an early stage 50 Hz AC PD activity, a prolonged PD activity at a 50 Hz AC stress alone, and a combination of HV impulses and a prolonged PD activity at a 50 Hz AC stress. In order to predict the level of deterioration caused by each ageing stress condition, the dielectric spectroscopy (DS) measurements in a frequency range of 1.0 mHz to 1.0 kHz were performed before and after subjecting a test object to each of the ageing stress conditions.      The investigations were mainly done on the test samples consisting of a cavity deliberately introduced between the layers of oil-impregnated paper. Additionally, the investigation about the effect of HV impulses alone on the DS results was done on aged oil-impregnated paper transformer bushing.      The PD experimental results presented in this thesis indicate that HV impulses below the impulse breakdown stress following an early stage AC PD activity will neither cause a significant change in phase resolved partial discharge (PRPD) patterns nor damage oil-impregnated paper insulation to a level that can be noticed with visual observations. On the other hand, a prolonged PD activity at a 50 Hz AC stress can cause the change in PRPD patterns by decreasing the total PD charge and the number of PD pulses, but cannot quickly damage the oil-impregnated paper insulation as it would do when it is combined with HV impulses. In addition to that, the results show that the combination of both, HV impulses and a prolonged PD activity at a 50 Hz AC stress can cause a high drop in the PD parameters (total PD charge and number of PD pulses).       The DS results show that HV impulses below the impulse breakdown stress following an early stage 50 Hz AC PD activity will not cause a significant increase in the real part of the complex capacitance and in the dissipation factor as they will do when they are combined with a prolonged PD activity at a 50 Hz AC stress. Further, the dielectric spectroscopy results obtained every three hours during the ageing of oil-impregnated paper insulation by a prolonged PD activity at an AC stress show that the dissipation factor will increase, but the PD parameters (total PD charge and the repetition rate) will decrease with time of PD application. For a case of the aged oil-impregnated paper transformer bushing, HV impulses of amplitudes up to 200 kV did not result in the change in the dissipation factor curve before removing insulating oil from the bushing. However, after removing about 2.5 liters of insulating oil from the bushing, HV impulses resulted in the change in the dissipation factor curve. The magnitudes of the dissipation factor curves appeared to be much higher in the middle frequencies region, i.e. the frequencies between 10 mHz and 100 Hz. After refilling the bushing with the same insulating oil, the loss peak shifted towards the higher frequencies.      To understand how the ageing by-products initiated by PDs in the small cavity can modify the geometry of oil-impregnated paper insulation; the model of oil-impregnated paper insulation, comprising of a small cavity, was implemented in Finite Element Method (FEM) software (COMSOL Multiphysics 4.2a). The comparison between the simulation and experimental results show that PD by-products will result in two zones, i.e. aged and unaged zones, and the aged zone will grow with time of PD application; thereby increasing the dissipation factor. On the other hand, in order to interpret  the change in the dissipation factors for the dielectrics in aged oil-impregnated paper transformer bushing after had been exposed to HV impulses, a model of a part of the condenser body (oil-paper insulation) was also implemented in the FEM software (COMSOL Multiphysics 4.2a). To model a condition of low insulating oil level in the bushing, a part of oil subdomains was replaced with the air dielectric properties. A comparison between the simulation and experimental dissipation factor curves indicate that HV impulses will produce the by-products (ions), which will increase the conductivity of air when the bushing has low insulating oil level. On refilling the bushing with the same insulating oil, the insulating oil will take these ions and the reactions between the aged insulating oil by-products (such as acids) and the ions, may produce more ions, thereby increasing further the conductivity of the insulating oil.    QC 20140303</p

Effect of HV Impulses on Partial Discharge Activity in Oil-Impregnated Paper Insulation

High voltage (HV) transients in electrical power systems are mainly caused by lightning strikes and switching operations.  The high voltage transient from its point of origin can propagate in either direction in the electrical power transmission line, and if its magnitude would be below the Basic Insulation Level (BIL) of the equipment for impulse voltage, it can reach the terminals of the equipment without being dissipated by surge arresters.  The dielectric properties of a particular insulation at the instant of interaction with a high voltage transient would determine the level of the degradation of the electrical insulation caused by the high voltage transient. This thesis suggests on-line diagnostic techniques for monitoring the oil-impregnated paper condenser bushings by utilizing the naturally occurring HV transients in electrical power systems. The aim of the first experiment was to investigate the partial discharge (PD) characteristics of the PD defects which are likely to be found in oil-imregnated paper condenser bushings. In order to understand the condition at which the HV impulses would cause the change in phase resolved partial discharge (PRPD) patterns, four more experiments were performed. The second experiment was set in such a way that the effect of HV impulses alone could be investigated. On the other hand, the third experiment was set to examine the effect of PD-ageing at elevated AC voltage. The fourth experiment aimed in investigating the effect of combined PD-ageing at elevated AC voltage and the HV impulses. In order to investigate how different electrical stresses affect the dielectric properties of the oil-impreganted paper insulation, the fifth experiment about the dielectric spectroscopy (DS) in frequency domain was performed. The measurement results presented in this thesis show that high voltage impulses can have a large impact on the behavior of PRPD patterns if the test sample is aged by partial discharges, but a smaller impact when the test sample is unaged. The measurement results also show that the degradation of the oil-impregnated papers is much faster when the oil-impregnated papers are suffered from the combination of the HV impulses and the PD activity at elevated AC voltage than when they are suffered from the PD activity at elevated AC voltage alone.QC 20121115</p

Review of Partial Discharge Activity Considering Very-Low Frequency and Damped Applied Voltage

When detecting the presence of partial discharge (PD) activity in the insulation system in high-voltage equipment, the excitation voltages at variable frequency have been widely used instead of power-frequency (50/60 Hz) sinusoidal voltage in order to reduce the charging power. This work reviews the relevant research on PD activity at very low frequency (VLF) method, including sinusoidal or cosine-rectangular voltage shape, and damped AC (DAC) method. Based on the research history and development status, some major PD characteristics, such as PD inception voltage (PDIV), PD amplitude, PD charge, PD phase-resolved pattern, and several hot issues, such as surface charge decay and statistical time lag, have been discussed. Moreover, the advantages, disadvantages, and applied conditions of two reviewed methods has been summarized. Finally, the prospects have been made on the main development trends of this research field in the future.DC systems, Energy conversion & Storag

Effect of Dielectric Material on Decay of Surface Charge Deposited by Corona Discharge

This work investigates the effect of different dielectric barriers on coronadischarge in the needle-plane geometry, where a layer of dielectric material was placedover the surface of the plane electrode. Different dielectric materials used werepolytetrafluoroethylene (PTFE), polyethylene (PE), polycarbonate (PC), polyvinylchloride(PVC), epoxy and pressboard. The discharges were generated by the application ofperiodic negative step voltage pulses. The results show that the evolution of coronapulses over time depends on the dielectric properties of the barriers. Unlike pressboardwith a higher conductivity, the dielectric materials with a lower conductivity such as PTFEand PE would have more surface charges deposited on its surface during the firstcharging period of 100 ms, and the charges would not disappear during the relaxationperiod of 10 s, therefore, the discharge activities can be reduced significantly after thefirst charging period.QC 20150518</p