Large fires have an effect of suppressing Very or Ultra High Frequency (VHF/UHF) radio wave signals strength which consequently impact negatively on the efficiency of radio communications at the frequency ranges. Mobi...Large fires have an effect of suppressing Very or Ultra High Frequency (VHF/UHF) radio wave signals strength which consequently impact negatively on the efficiency of radio communications at the frequency ranges. Mobile hand-held radio operating at the frequency ranges is a major communication tool during fire suppression;therefore inefficient radio communication systems put lives of fire fighters at risk. One of the causes of signal attenuation in fire environment is plume ionization. Plume species which include graphitic carbon, alkalis and thermally excited radicals such as methyl are responsible for ionization. As atmospheric pressure ionized medium (combustion plasma), sugarcane fire has momentum transfer electron-neutral collision frequency much higher than plasma frequency, hence propagation of VHF/UHF radio waves through such a medium is predicted to suffer a significant attenuation and phase shift. Radiowave propagation measurements were carried out in a moderate intensity prescribed sugarcane fire at 151 MHz frequency over a 590 m path using a radiowave interferometer. The radio wave interferometer measured signal attenuation of 0.43 dB through the fire with maximum temperature and flame depth of 1154 K and 8.7 m, respectively.展开更多
A significant number of fire-induced power disruptions are observed in several countries every year. The faults are normally phase-to-phase short circuiting or conductor-to-ground discharges at mid-span region of the ...A significant number of fire-induced power disruptions are observed in several countries every year. The faults are normally phase-to-phase short circuiting or conductor-to-ground discharges at mid-span region of the high-voltage transmission system. In any case, the wildfire plumes provide a conductive path. The electrical conductivity is due to intense heat in combustion zone of the fire which creates ion and electrons from flame inherent particulates. Increase in the ion concentration increases the electrical conductivity of the fire plume. The main purpose of this study was to measure dielectric breakdown electric field for vegetation and hydrocarbon flames. The experimental data is needed for validation of simulation schemes which are necessary for evaluation of power grid systems reliability under extreme wildfire weather conditions. In this study, hydrocarbon and vegetation fuels were ignited in a cylindrically shaped steel burner which was fitted with type-K thermocouples to measure flame temperature. The fuels consisted of dried weeping wattle (Peltophorum africanum) litter, butane gas and candle wax. Two pinned copper electrodes supported by retort stands were mounted to the burner and energized to a high voltage. This generated a strong electric field sufficient to initiate dielectric breakdown in the flames. Breakdown electric field strength (Ecrit) obtained from the experiment decreased from 10.5 to 6.9 kV/cm for the flames with temperature range of 1003 to 1410 K, respectively.展开更多
The compulsion to provide reliable electric power for sustenance of socio-economic development is vital for most of southern Africa states. The demand for the resource in the region is anticipated to escalate in the n...The compulsion to provide reliable electric power for sustenance of socio-economic development is vital for most of southern Africa states. The demand for the resource in the region is anticipated to escalate in the next couple of decades. However, there is a deleterious effect of fire-induced power disruption which is observed in many countries. The mechanism through which the disruption occurs is currently a subject of current research in electric power distribution. It has been observed that streamer initiated conduction channel provides a means of high voltage electric power flashover. The main purpose of this study is to determine the empirical expression for breakdown electric field strength of vegetation fires. The breakdown field was measured from vegetation fuel (Peltophorum africanum) flames at different combustion temperatures. The data is essential for validation of simulation schemes which are necessary for evaluation of power grid systems reliability under extreme wildfire weather conditions. In this study, Peltophorum africanum fuels were ignited in a cylindrically shaped steel burner which was fitted with a Type-K thermocouple to measure flame temperature. The fuels consisted of dried fine twig (≤0.8 mm Ø) and limb wood (≥10 mm Ø) litter. Two copper pinned-electrodes supported by retort stands were mounted to the burner and energized to a high voltage. This generated a strong electric field sufficient to initiate dielectric breakdown in the flames. The measured electric field strength was plotted against flame temperatures and fit with a non-linear relation to give the empirical relation.展开更多
A fuel bed was constructed where various vegetation species could be used as combustion fuel. The fuel bed was equipped with a thermocouple to measure fire temperature and a two-port automatic network analyser to meas...A fuel bed was constructed where various vegetation species could be used as combustion fuel. The fuel bed was equipped with a thermocouple to measure fire temperature and a two-port automatic network analyser to measure microwave scattering parameters in flame medium. The parameters are then used to determine microwave propagation characteristics in fire. The measurements have implications on radio wave communication during wildfire suppression and in remote sensing. The attenuation data also provide an estimation of vegetation fire ionisation and conductivity. Eucalyptus litter fire with a maximum flame temperature of 976 K was set on the fuel bed and X-band microwaves (7.00 - 9.50 GHz) were caused to propagate through the flame. Attenuation of 0.35 - 0.90 dB was measured for microwaves in the frequency range. For the low intensity fire, conductivity was measured to range from 0.00021 - 0.00055 mho/m and electron density was to be the range of 1.83 - 2.24 × 1015 m-3.展开更多
文摘Large fires have an effect of suppressing Very or Ultra High Frequency (VHF/UHF) radio wave signals strength which consequently impact negatively on the efficiency of radio communications at the frequency ranges. Mobile hand-held radio operating at the frequency ranges is a major communication tool during fire suppression;therefore inefficient radio communication systems put lives of fire fighters at risk. One of the causes of signal attenuation in fire environment is plume ionization. Plume species which include graphitic carbon, alkalis and thermally excited radicals such as methyl are responsible for ionization. As atmospheric pressure ionized medium (combustion plasma), sugarcane fire has momentum transfer electron-neutral collision frequency much higher than plasma frequency, hence propagation of VHF/UHF radio waves through such a medium is predicted to suffer a significant attenuation and phase shift. Radiowave propagation measurements were carried out in a moderate intensity prescribed sugarcane fire at 151 MHz frequency over a 590 m path using a radiowave interferometer. The radio wave interferometer measured signal attenuation of 0.43 dB through the fire with maximum temperature and flame depth of 1154 K and 8.7 m, respectively.
文摘A significant number of fire-induced power disruptions are observed in several countries every year. The faults are normally phase-to-phase short circuiting or conductor-to-ground discharges at mid-span region of the high-voltage transmission system. In any case, the wildfire plumes provide a conductive path. The electrical conductivity is due to intense heat in combustion zone of the fire which creates ion and electrons from flame inherent particulates. Increase in the ion concentration increases the electrical conductivity of the fire plume. The main purpose of this study was to measure dielectric breakdown electric field for vegetation and hydrocarbon flames. The experimental data is needed for validation of simulation schemes which are necessary for evaluation of power grid systems reliability under extreme wildfire weather conditions. In this study, hydrocarbon and vegetation fuels were ignited in a cylindrically shaped steel burner which was fitted with type-K thermocouples to measure flame temperature. The fuels consisted of dried weeping wattle (Peltophorum africanum) litter, butane gas and candle wax. Two pinned copper electrodes supported by retort stands were mounted to the burner and energized to a high voltage. This generated a strong electric field sufficient to initiate dielectric breakdown in the flames. Breakdown electric field strength (Ecrit) obtained from the experiment decreased from 10.5 to 6.9 kV/cm for the flames with temperature range of 1003 to 1410 K, respectively.
文摘The compulsion to provide reliable electric power for sustenance of socio-economic development is vital for most of southern Africa states. The demand for the resource in the region is anticipated to escalate in the next couple of decades. However, there is a deleterious effect of fire-induced power disruption which is observed in many countries. The mechanism through which the disruption occurs is currently a subject of current research in electric power distribution. It has been observed that streamer initiated conduction channel provides a means of high voltage electric power flashover. The main purpose of this study is to determine the empirical expression for breakdown electric field strength of vegetation fires. The breakdown field was measured from vegetation fuel (Peltophorum africanum) flames at different combustion temperatures. The data is essential for validation of simulation schemes which are necessary for evaluation of power grid systems reliability under extreme wildfire weather conditions. In this study, Peltophorum africanum fuels were ignited in a cylindrically shaped steel burner which was fitted with a Type-K thermocouple to measure flame temperature. The fuels consisted of dried fine twig (≤0.8 mm Ø) and limb wood (≥10 mm Ø) litter. Two copper pinned-electrodes supported by retort stands were mounted to the burner and energized to a high voltage. This generated a strong electric field sufficient to initiate dielectric breakdown in the flames. The measured electric field strength was plotted against flame temperatures and fit with a non-linear relation to give the empirical relation.
文摘A fuel bed was constructed where various vegetation species could be used as combustion fuel. The fuel bed was equipped with a thermocouple to measure fire temperature and a two-port automatic network analyser to measure microwave scattering parameters in flame medium. The parameters are then used to determine microwave propagation characteristics in fire. The measurements have implications on radio wave communication during wildfire suppression and in remote sensing. The attenuation data also provide an estimation of vegetation fire ionisation and conductivity. Eucalyptus litter fire with a maximum flame temperature of 976 K was set on the fuel bed and X-band microwaves (7.00 - 9.50 GHz) were caused to propagate through the flame. Attenuation of 0.35 - 0.90 dB was measured for microwaves in the frequency range. For the low intensity fire, conductivity was measured to range from 0.00021 - 0.00055 mho/m and electron density was to be the range of 1.83 - 2.24 × 1015 m-3.
