Techniques for Ensuring Fault Ride-Through Capability of Grid Connected DFIG-Based Wind Turbine Systems: A Review

Renewable energy sources (RES) are being integrated to electrical grid to complement the conventional sources to meet up with global electrical energy demand. Among other RES, Wind Energy Conversion Systems (WECS) with Doubly Fed Induction Generator (DFIG) have gained global electricity market competitiveness because of the flexible regulation of active and reactive power, higher power quality, variable speed operation, four quadrant converter operation and better dynamic performance. Grid connected DFIG-based WECS are prone to disturbances in the network because of direct connection of stator windings to grid. The ability of the Wind Turbine (WT) to remain connected during grid faults is termed the Fault Ride-Through (FRT) capability. The grid code requirement for integrating the DFIG-based WTs to power networks specified that they must remain connected and support the grid stability during grid disturbances of up to 1500 ms. The use of compensation devices offers the best FRT compliance thereby protecting the DFIG and the converters from voltage fluctuations and over currents during the grid fault. The paper presents a review of techniques employed in ensuring FRT compliance. The article also proposes the state-of-the-art techniques for compensating voltage sag/swell and limiting the fault short-circuit current. Keywords: Renewable energy sources, DFIG, wind turbine system, fault ride-through, grid codes, dual-functional DV

Hydrochemical characterization and evaluation of groundwater quality of zamfara area, northwest, nigeria

This study deals with hydrochemical assessment of groundwater within the lithological framework underlain Zamfara State, Northwestern Nigeria with the aim of ascertaining its suitability for human consumption. Groundwater samples were collected from boreholes tapping the aquifer of the area and analyzed for various physico-chemical parameters, such as total dissolve solids, electrical conductivity (Ec), pH, temperature, Na+, K+, Ca2+, Mg2+, HCO3, Cl-, SO4, NO3, PO4, and trace elements (Mn, Cu, Zn, Fe, Pb and Cr). The results obtained were subjected to multivariate statistical analysis, water quality index method, and hydrochemical variation plots for proper characterization. As far as suitability is concerned most of the studied physic-chemical parameters trace elements (iron, lead and chromium ions) revealed average concentrations lower than the permissible limit set for domestic water use by World Health Organization. However, the compiled overall water quality index for the studied groundwater shows ‘very poor water quality’. Due to the fact that WQI rating reflect the composite influence of different water quality parameters. The result of the multivariate statistical analysis, as applied to the chemical data set of the studied groundwater provides an insight into the underlying controlling hydrochemical processes in the area. Four factors including factor-1 (total hardness, chloride, nitrate, manganese, bicarbonate and alkalinity), factor-2 (TDS, conductivity, total hardness, magnesium and calcium), factor-3 (Temperature, sodium, potassium, copper, zinc, iron and chromium), factor-4 (calcium, magnesium and nitrate) represents the signatures from dissolution of bedrock through which the groundwater passes, ionic mixing, leaching from the lateritic overburden, agricultural activities (fertilizer application) and effluent from waste dumpsites in the study area. The distribution of major ions in the groundwater shows relative abundance of cations: Na++K+ > Ca2+ > Mg2+; while the relative abundance of the anions is: Cl- > HCO3- > SO42-. Groundwater in the aquifer of the study area are majorly of evolved type with mixing of ionic concentrations. Alkali’s are more in abundant to that of alkaline earth, while Cl and HCO3 dominate SO4 and NO3 concentration. The water samples are basically ‘Alkali waters’ with ‘Earth Alkaline’ components that are predominantly HCO3- and Cl-.The relative abundance of the three (3) dominant water types are as thus: Na-HCO3-Cl > Ca-Mg-HCO3-Cl > Na-Ca-Cl. Simple mineral dissolution or mixing processes is mainly responsible for the variation in the hydrochemistry of the groundwater of the study area. &nbsp

Investigating the Role of Diversification on Economic Growth in Nigeria; New Evidence from SVARs

Fluctuations in oil prices have caused economic contractions and challenges to oil-exporting economies. In particular, Nigeria suffers both the previous and current global oil price shocks and this has raised concerns among policymakers, governments, and economic analysts because of the impact of oil and oil prices in Nigeria’s macroeconomic development. However, this paper investigates the role of diversification on economic growth in Nigeria using annual data from 1986 to 2018. The techniques applied showed that only remittances and official development assistance have affected economic growth in the short run. However, the coefficients of one period lagged indicated that the system is capable of adjusting to its long-run equilibrium condition after some shocks in the system.  The findings from variance decomposition indicated that diversification plays a positive role on economic growth in both the short and long-run horizons. By overall implication, the study concludes that diversification has a positive role on Nigeria’s economic growth. Therefore, the study recommends the need for the government to provide active and inclusive policies such as soft loans and commercial agricultural programs to improve its export of agricultural output competitiveness, improve supervisory and regulatory frameworks in the financial sector to ease remittances inflow. For these reasons, diversifying the economy from oil revenue is the ultimate goal for achieving sustainable economic growth and development goals or targets by the year 2030

Phytochemical analysis, proximate composition and antibacterial activities of Ziziphus Species (Z. jujube and Z. spina christi)

Despite tremendous progress in human medicines infectious diseases caused by bacteria, fungi, viruses and parasites are still a major threat to public health. Their impact is particularly large in developing countries due to relative unavailability of medicines and emergence of widespread drugs resistance (Zampini 2009).The aim and objectives of this research work was designed to carried out the Phytochemical analysis, proximate composition and evaluate the antimicrobial activities of the Ziziphus jujube and Ziziphus spina christi leaves against clinical bacterial isolates (Escherichia coli, Staphloccoccus  aureus and Klebsiella  pneumoniae) as they were found out that since ancient times to date, they are used in treating various antimicrobial, ailmentand disorders etc. The results of the research shows that, the effect of antibacterial activities of both aqueous and ethanolic extracts of Ziziphus jujube (e extract conc. aqueous; F=119.37, Bacterial extract conc. aqueous; F=1.00 and extract conc. ethanol; F=15.74, Bacterial extract conc. ethanol; F=0.59) are reciprocal proportional to their counterpart, Ziziphus spina-christi (extract conc. aqueous; F=54.96, Bacterial extract conc. aqueous; F=0.94 and extract conc. ethanol; F=81.11, Bacterial extract conc. ethanol; F=1.37). In sum, the minimum inhibitory concentration of Ziziphus jujube shows that, the aqueous extract has M.I.C at range of 11.7 to 8.7mg/ml on all tested bacteria but the ethanolic extract has M.I.C of 14.8 to 8.2mg/ml range on E.coli, Klepsiella spp and S. aureus. While, the minimum inhibitory concentraton of Ziziphus spina-christi shows that the M.I.C of aqueous extract range of 12.8 to 8.3mg/ml on E. coli, Klepsiella spp and S.aureus. But, Ziziphus spina-christi M.I.C of ethanolic extract is 13.5 to 8.8mg/ml on all the tested bacteria. In sum, Zizuphus spina-christi has lower nutritional content and low MIC ethanolic extract than that of Ziziphus jujube

ANALYSIS OF THE DETERMINANTS OF PROFIT FROM COCOA BEANS MARKETING IN OGUN STATE, NIGERIA

This paper examined the factors that influenced profit from cocoa beans marketing in Ogun State, Nigeria. Fifty (50) cocoa beans marketers were selected using a multi-stage sampling technique. Data were collected with the aid of a structured questionnaire designed to solicit information on the socio-economic characteristics of the cocoa beans marketers, their operating costs and return and problems associated with cocoa beans marketing in the study area. Descriptive statistics, marketing margin analysis, gross margin analysis and the Ordinary Least Square (OLS) regression technique were em-ployed in the analysis of the study data. The study revealed that men (84%) are more involved in co-coa beans marketing than women. Further, the study finds cocoa beans marketing to be a profitable venture in the study area having a gross margin of ₦137,719.27 (US $885.51) per month and a mar-keting margin of N40,600 (US$ 261.94). The percentage marketing margin was 34.73% which implies that the cocoa beans marketers realize a margin of 34.76% of the farm price. The result of the OLS regression analysis revealed that cost of transportation, communication cost, volume of cocoa traded and membership of market union are the significant determinants of the profit margin that accrue to the cocoa beans marketer. The identified constraints to cocoa beans marketing in the study area in-clude low quality of cocoa beans, poor transportation facilities and inadequate capital. The study con-cluded that cocoa beans marketing is economically rewarding in the study area. It recommends that the government should help to provide good transportation facilities. Also, agricultural and commercial banks as well as other micro credit financial institutions should assist in providing credit facility to the marketers as this will enable them expand their scope of marketing and consequently improve their profit margin

Properties of Asphalt Concrete Containing Waste Foundry Sand (WFS) as Filler Material

The high cost of primary construction materials such as cement, and increase in waste generation due to human activities coupled with environmental concerns has led to the incorporation of wide range of waste materials into asphalt concrete. Waste foundry sand (WFS) which is a by-product of ferrous and non-ferrous metal casting industry, has accumulated in stockpiles and landfills, occupying valuable space and causing nuisance in the environment. Consequently, it is imperative to devise a safe and economical solution to manage and utilize the waste. One way of achieving this is by recycling and using it for asphalt concrete production. This study investigated the strength and durability properties of asphalt concrete containing waste foundry sand (WFS) as alternative filler material in asphalt concrete. Marshall design method was adopted for the sample preparation and testing. Fifteen (15) compacted samples were prepared for strength and volumetric properties testing at varying bitumen contents of 4.5%, 5.0%, 5.5%, 6.0% and 6.5%, in accordance with Asphalt Institute and Nigeria General Specification for Road and Bridges to determine optimum bitumen content (OBC). OBC of 5.5% was obtained and used for the asphalt concrete mixes in the study.  Eighteen (18) other briquettes were prepared to determine the optimum WFS content in asphalt concrete necessary for strength and durability of wearing course of flexible pavement. Cement as filler in asphalt concrete was partially replaced with WFS using the obtained OBC in the order of 10%, 20%, 30%, 40%, 50% and 60%. A total of thirty-three (33) standard specimens were prepared. From the Marshall stability-flow and void-density results, the sample prepared with 60% WFS as filler with OBC of 5.5% satisfies the provision of the Nigerian General Specification for Road and Bridges (NGSRB) for use in wearing course of flexible pavement. Based on the analysis of results obtained in this study and a logical comparison made with standard specifications, addition of up to 60% waste foundry sand (WFS) in asphalt concrete would lead to significant conservation of primary construction materials, divert substantial quantities of waste from landfills and present a cheap alternative of filler material necessary for sustainable asphalt concrete construction

Investigating the mineral composition of proceessed cheese, soy and nunu milks consumed in Abuja and Keffi metropolises of Nigeria

Milk and its products are needed for proper body building. Processed cheese, nunu and soy milk consumed within Abuja and Keffi metropolises were analyzed for their mineral contents. X1, Y1, Z1 represents soy milk, nunu and cheese from Abuja metropolis while X2, Y2, Z2 represents sample from Keffi metropolis respectively. Calcium (265.53±0.25 mg/mL), iron (1.19±0.92 mg/mL), potassium (162.77±0.02 mg/mL) were found to be higher in cheese milk (Z1) from Abuja than that (225.82±0.13 mg/mL, 1.05±0.60mg/mL and 130.41±0.04 mg/mL) found in Keffi (Z2) examined respectively, though the amount of sodium present (151.0±0.08 mg/mL) in cheese (Z2) from Keffi is slightly higher than that (150.08±0.01 mg/mL) from Abuja (Z1). Also, Soya milk from Abuja (X1) had highest amount of zinc (0.76±0.00 mg/mL) while that of Keffi (X2) was 0.65±0.3 mg/mL, for magnesium and copper, higher values 18.40±010 mg/mL and 0.25±0.02 mg/mL were recorded for soy milk (X2) from Keffi while soy milk from Abuja (X1) had 17.97±0.20 mg/mL and 0.16±0.01 mg/mL respectively. Chromium was dictated in both cheese samples but not dictated in soya and nunu milks from both metropolises. It is seen from the investigation that cheese had more minerals followed by soya milk. Nunu milk sample had the least quantity of minerals; also all the samples analyzed have minerals present in them. Therefore, they are needed for the proper functioning of the body system Keywords: Analysis, Concentration, Milk, Mineral, Metropolis, Flame Atomic Absorption Spectroscop

Fertility Status of Fadama Soils in Gantsare Village, Wamakko Local Government, Sokoto State As Affected by Cement Dust

A study was conducted in Gantsare village, Wamakko local government, Sokoto state to determine the effect of cement dust emitted from Sokoto cement factory on the fertility of fadama soils. Soil samples were collected in June, 2008 from the eastern, northeastern, and southeastern parts of the village and Girabshi; a nearby village with least effect of the dust. The samples were collected at two depths (0-15 and 15-30 cm) using simple random sampling method. Randomized complete block design (RCBD) was employed, replicated three times, making a total of 24 samples. The samples were analyzed for pH, OC, CEC, total N, available P, exchangeable bases (Ca, Mg, K and Na) and particle size. Almost all parameters determined were found to be statistically significant (P < 0.01). OC was found to be lower in concentration in the areas closer to the factory; eastern part6.25 respectively, likewise CEC and exchangeable bases. The trend in the results observed may be attributed to possible adverse effects of the dust on microbial population, reduction in the availability of some nutrients and a favour on the concentrations of exchangeable bases and CEC. The topsoils showed better results of all the soil chemical properties. The study recommends minimization of the amount of dust reaching agricultural soils and the use of phosphorus and nitrogen fertilizer supplements as soil management practices to enhance soil fertility status and enhance adequate crop yield in the area. Key words:Cement dust, fertility status, fadama soils, soil chemical properties, soil management

Focused antenatal care acceptance in northeastern region of Nigeria: clients' perspective.

Antenatal care is the medical care of the woman during pregnancy to ensure healthy outcomes for both mother and the baby. World Health Organization (WHO) recommended adoption of a new model of ANC known as Focused Ante-Natal Care (FANC), with four clinic visits during pregnancy for all the women in low risk category. Pregnant women who are at low risk of complication form about 75% of all pregnant women Objectives: The objective of the study was to determine acceptance of Focused Antenatal Care among antenatal clinic attendees in health institutions in northeastern Nigeria. Materials And Method: Focused group discussion was used as a qualitative method of data collection in 6 different health facilities. Results: Majority of the clients preferred the FANC to the old method of ANC. Some clients had already started cutting the number of ANC visits in their own way by late presentation during pregnancy. Such practices may contribute negatively to early detection and prevention of diseases during pregnancies. Conclusion: It is therefore highly recommended to fast track governments efforts towards commencement of FANC as recommended by the WHO in all the health facilities in the region in particular and the whole Nigerian nation in general

Ipomea asarifolia (Desr), A Potential Cover Crop for Soil Fertility Improvement in The Sudan Savanna Region, Nigeria

The effect of Ipomea asarifolia on physico - chemical properties of the soils at Usmanu Danfodiyo University, Sokoto main campus, in the Sudan Savanna of Nigeria was investigated. The study determined the effect of the plant on some physical and chemical properties of soils, found out the nutrient retention ability of the plant in the soils and the variation of the effect with distance within the plants’ canopy. A total of 48 samples were collected from four different sites within Usmanu Danfodiyo University main Campus; VC complex area, University stadium area, Behind new library area and opposite IBB centre area and four distances from the plant (control, plant base, 0.5 m and 1 m from the plant base). Samples were collected for use in a randomized complete block design (RCBD) experiment with three replicates. Soil pH, Organic C, CEC, total N, available P, K, Ca and Mg concentrations were determined, particle size analysis was also carried out. The results were subjected to analysis of variance (ANOVA), where significant F values were obtained, the means were separated by Duncan multiple range tests (DMRT). The difference among the sites and the distances were found to be statistically significant (P VC complex area > New library area > IBB centre area. On the other hand, the effect on all the parameters was found to decrease with distance from the plant with the base of the plant having the highest organic C, CEC, total N, available P and exchangeable K, Ca and Mg; 6.83 g kg-1, 5.00 cmol kg-1, 0.42 g kg-1, 10.82 mg kg-1 and 0.26, 0.50 and 0.97 cmol kg-1 respectively, while the control soils had the least values; 3.46 g kg-1, 4.00 cmol kg-1, 0.12 g kg-1, 7.43 mg kg-1, 0.21, 0.38, and 0.45 cmol kg-1 respectively. The effect was attributed to the accumulation of organic matter around the plant and its ability to prevent erosion by both water and wind thus retaining nutrients making it a suitable cover crop for soil fertility improvement