A model for long air gap discharge using an equivalent electricalnetwork

In this paper, an attempt of the whole discharge model is proposed. This model is based on an equivalent electrical network, the parameters of which are determined from electromagnetic field and gas discharge theories. It uses the fact that the discharge channel may be likened to a long conductor and employs a typical LCR representation for a single conductor line. For all phases of the discharge, the same circuit is used in modeling the change of stage with variable resistances and inductances. For a given shape and electrode configuration, the model allows us to determine the currents of the leader and the return stroke, the corresponding charge, the potential drop along the leader channel, the power and energy injected into the gap and the leader propagation velocities. The obtained results are found to be in accordance with the experimental ones obtained for discharges in long air gaps, created in laboratory     

Using mucuna and P fertilizer to increase maize grain yield and N fertilizer use efficiency in the coastal savanna of Togo

To reduce severe soil degradation associated with agriculture an intensified land-use system is being promoted in West African countries. Most soils of the West African savanna zones are so poor that the efficiency of mineral fertilizers, if applied, is very low. For this reason and because of their high cost and unavailability, many small-scale farmers are reluctant to apply fertilizer. This work investigates a fertilizer management strategy using integrated soil fertility management with a leguminous cover crop (mucuna) so as to improve the soil fertility and increase the use efficiency of fertilizer. The experiment was conducted in the coastal savanna of Togo at Djaka Kopé. The aim was to evaluate the effectiveness of mucuna short fallow (MSF) in increasing maize grain yield through an improved use efficiency of mineral fertilizer. A 2-year maize–mucuna relay intercropping system was compared with continuous sole maize cropping. Fertilizer treatments were factorial combinations of 0, 50 and 100 kg nitrogen (N) ha^–1 and 0, 20 and 40 kg phosphorus (P) ha^–1. While maize grain yield was significantly increased by N fertilization, P did not show any important effect on grain yield. With no N and P applied, grain yield after MSF was on average 40% (572 kg ha^–1) higher than without. The response to N was much greater than the response to MSF, indicating that N was undoubtedly the key element for maize yield building. P fertilization and MSF together positively influenced the apparent N recovery fraction (NRF). N uptake alone did not reflect on its own the yield obtained, and the relationship between grain yield and N uptake is shifted by MSF, with the grain yield increase per unit of N uptake being higher with than without MSF. Combining MSF and P fertilization may therefore lead to improved N use efficiency, making the application of fertilizer N (lower rates) more attractive to small-scale farmers.     

Millet nutrient use efficiency as affected by natural soil fertility,mineral fertilizer use and rainfall in the West African Sahel

Field experiments were designed to investigate the effectiveness of integrated soil fertility management (ISFM), comparing fertilizer use efficiency and its impact on millet, cultivated close to the homestead (“infields”) and away from the homestead (“outfields”). Millet yields and response to N (0, 30, and 60 kg ha⁻¹) and P (0, 15, and 30 kg ha⁻¹) were determined on nine infields and nine outfields over a period of 3 years (from 1999 to 2001) in the southern Sahel of Niger. Rainfall was 650, 470, and 370 mm during the three successive years, interaction between decreasing rainfall and millet yield performance was also analyzed. While soil organic carbon (1.5 g kg⁻¹ on outfields and 1.6 g kg⁻¹ on infields) and pH-H₂O (4.8 on outfields and 5.1 on infields) were comparable, total-N, plant available P (measured as P-Olsen and P-Bray), and exchangeable Ca, K, and Mg levels were higher on infields as compared to outfields. Without fertilizer, average grain yield (GY) and stover yield obtained on infields were three times as high as on outfields. GY across years and fertilizer treatments was higher on infields as compared to outfields (P < 0.001). Average yield was 800 kg ha⁻¹ on outfields and 1,360 kg ha⁻¹ on infields (P < 0.001). On outfields, average GY was stagnant over the 3-year experimental period. Despite declining rainfall, millet GY across all treatments gradually increased over time on infields (P < 0.001). P fertilization alone resulted on both field types to steadily and substantial yield increases while yield response to N fertilization was only obvious when fertilizer P was applied. With no fertilizer applied, N uptake on infields (19 kg N ha⁻¹) was more than twice as high as on outfields (7 kg ha⁻¹), and P uptake was four times higher on infields (3 kg ha⁻¹) than on outfields (0.8 kg ha⁻¹). Indigenous soil N supply was on average 24 kg N ha⁻¹ on outfields and 46 kg N ha⁻¹ on infields. Average value for indigenous soil P supply was 4 kg P ha⁻¹ on infields and 2 kg ha⁻¹ on outfields. Apparent recovery of fertilizer N applied varied considerably among treatments and ranged from 17 to 23% on outfields and 34 to 37% on infields (P < 0.001). Average apparent recovery of fertilizer P applied was significantly higher (P < 0.001) on infields (31%) than on outfields (18%) over the 3-year growing period, illustrating ISFM-induced positive effect on millet nutrient N and P use. Results indicate higher inherent soil fertility, underline ISFM-induced drought tolerance of soils on infields as compared to outfields, and highlight the crucial role of fertilizer P (especially on outfields) for millet production. These call for site-specific nutrient management and support, even under low rainfall conditions, the potential value of fertile infields for efficient and productive external input use and sustainable millet production in West African Sahel.     

Fatty acids composition as a means to estimate the high heating value (HHV) of vegetable oils and biodiesel fuels

High heating value (HHV) is an important property which characterises the energy content of a fuel such as solid, liquid and gaseous fuels. The previous assertion is particularly important for vegetable oils and biodiesels fuels which are expected to replace fossil oils. Estimation of the HHV of vegetable oils and biodiesels by using their fatty acid composition is the aim of this paper. The comparison between the HHVs predicted by the method and those obtained experimentally gives an average bias error of −0.84% and an average absolute error of 1.71%. These values show the utility, the validity and the applicability of the method to vegetable oils and their derivatives.     

Effect of Exposure to Electrical Discharge on Transformer Oil Properties

Petroleum based oils, the so-called mineral oils, are used for impregnating solid insulations or filling products of very large number of electric materials： transformers, reactors, cables, bushings, c...     

Oil prices and the South African economy: A macro–meso–micro analysis

Three levels of analysis are used to track the channels by which South Africa and its people are impacted by an increase of oil prices, namely the macro-economic level, the meso-economic level and the micro-economic/household level. The paper uses an economy and energy integrated approach to quantify these different channels. The approach combines a household survey dataset and an input–output dataset to implement the models. Results indicate that the impacts on the macroeconomy are negative, with gross domestic product falling and the current account balance worsening. All of the industries falling into the high intensive oil – use group witness an increase of their input cost that is above the economy – wide average. The impact of doubling paraffin prices results in poor households in rural areas and among the “Black” population, in particular, witnessing an increase of their cost of living which is much higher than their corresponding highest expenditure quintile groups. An increase of transport fuel hits the richer households much harder. The distributional impacts of rising transport cost as a consequence of high oil and oil-products prices shows that median quintile expenditure groups observe the highest impact both in urban and rural areas and especially among the “Black” population.     

Application of Dynamic Model to Flashover of Ice-covered Insulators

The purpose of this paper is to study the effect of insulator dimensions as well as applied water conductivity on flashover voltage under icing conditions, using a dynamic arc model. The electrical performance of several insulators with various diameters and dry arcing distances were evaluated using this model. Moreover, in order to assess the influence of meteorological variables, different applied water conductivities were considered for the laboratory experiments. The model was found to be in good agreement with the experimental results. The results obtained indicate that flashover prediction is possible under ac voltage, using the proposed model. This contribution is also intended to provide a fresh perspective by contributing an innovative approach to this domain of research.