Power sensitivity and algebraic technique for evaluation of penetration level of photovoltaic on DC link of VSC HVDC transmission

Abstract: With the increased advent of VSC HVDC with long DC transmission link in power systems, situations have arisen and will be even more frequent in the future, where several distributed generation will be connected on the DC-link for more power transfer capability. As penetration level increases, there is need to predict the limit before violation of voltage and power instability on the DC transmission link and ensure that it does not interfere with the main VSC HVDC system control. In this paper, power sensitivity and algebraic technique is proposed to predict the maximum DG penetration that can be accepted at a particular location on the dc link of VSC HVDC transmission system before violation of voltage and power stabilit

Forests, farms, and fallows: The dynamics of tree cover transition in the southern part of the uluguru mountains, Tanzania

Forests and woodlands remain under threat in tropical Africa due to excessive exploitation and inadequate management interventions, and the isolated success stories of tree retention and tree cover transition on African agricultural land are less well documented. In this study, we characterize the status of tree cover in a landscape that contains forest patches, fallows, and farms in the southern part of Uluguru Mountains. We aimed to unveil the practices of traditional tree fallow system which is socially acceptable in local settings and how it provides a buffering effects to minimize forest disturbances and thus represents an important step towards tree cover transition. We assessed land cover dynamics for the period of 1995 to 2020 and compared tree stocking for forest patches, fallows, and farms. We found that tree biomass carbon stocks were 56 ± 5 t/ha in forest patches, 33 ± 7 t/ha in fallows, and 9 ± 2 t/ha on farms. In terms of land cover, farms shrank at intensifying rates over time for the entire assessment period of 1995–2020. Forest cover decreased from 1995–2014, with the reduction rate slowing from 2007–2014 and the trend reversing from 2014–2020, such that forest cover showed a net increase across the entire study period. Fallow consistently and progressively increased from 1995–2020. We conclude that traditional tree fallows in the study site remain a significant element of land management practice among communities, and there appears to be a trend towards intensified tree-based farming. The gains in fallowed land represent an embracing of a traditional land management system that supports rotational and alternate uses of cropping space as well as providing a buffering effect to limit over-exploitation of forests. In order to maximize tree cover and carbon stocks in the farm landscape, this well-known traditional tree fallow system can be further optimized through the incorporation of additional innovations

Experimental Validation of Synchronous Machine Saturated Models

The need of refined models of synchronous machines is felt in industry to day due to several factors: more economical machine design resulting in a decrease of security and stability margins of operations; increased power system complexity often requiring the synchronous unit to work under severe dynamic conditions and, finally, present day computer aided techniques of analysis removing the need of simplifying modelling assumptions

Simulation and Control Techniques of FACTS

Advanced series compensation allows to continuously modify the flexible reactance of tie-lines between interconnected areas. This paper is dealing with with modelling and simulation of FACTS using well known softwares

mpact of forestland tenure changes on forest cover, stocking and tree species diversity in Amani nature reserve, Tanzania

The aim of the present study was to evaluate the impact of changes from private to state tenure on forest resources for three blocks in Amani Nature Reserve. The resource changes were determined in terms of forest cover, forest stocking and tree species diversity over a period of six to eight years. When considering the three blocks as one entity one may in general maintain that there have been positive changes regarding forest cover. There were differences between the blocks, however. The proportions of dense and semi-closed forest increased by around 14% in the former tea company block, remained unchanged in the former farmland and decreased by around 12% in the former sisal company block. The changes in stocking parameters and tree species diversity were mainly positive, but none were statistically significant. Although the results were somewhat ambiguous evidence of positive impacts as a result of the tenure changes was identified. This is in line with the main aim of establishing nature reserves focusing on conservation values. More research, however, is required regarding impacts of tenure changes on livelihood for those living adjacent to the nature reserve

Changing climate patterns risk the spread of Varroa destructor infestation of African honey bees in Tanzania

Background Climate change creates opportune conditions that favour the spread of pests and diseases outside their known active range. Modelling climate change scenarios is oftentimes useful tool to assess the climate analogues to unveil the potential risk of spreading suitability conditions for pests and diseases and hence allows development of appropriate responses to address the impending challenge. In the current study, we modelled the impact of climate change on the distribution of Varroa destructor, a parasitic mite that attacks all life forms of honey bees and remains a significant threat to their survival and productivity of bee products in Tanzania and elsewhere. Methods The data about the presence of V. destructor were collected in eight regions of Tanzania selected in consideration of several factors including potentials for beekeeping activities, elevation (highlands vs. lowlands) and differences in climatic conditions. A total of 19 bioclimatic datasets covering the entire country were used for developing climate scenarios of mid-century 2055 and late-century 2085 for both rcp4.5 and rcp8.5. We thereafter modelled the current and future risk distribution of V. destructor using MaxEnt. Results The results indicated a model performance of AUC = 0.85, with mean diurnal range in temperature (Bio2, 43.9%), mean temperature (Bio1, 20.6%) and mean annual rainfall (Bio12, 11.7%) as the important variables. Future risk projections indicated mixed responses of the potential risk of spreads of V. destructor, exhibiting both decrease and increases in the mid-century 2055 and late-century 2085 on different sites. Overall, there is a general decline of highly suitable areas of V. destructor in mid- and late-century across all scenarios (rcp4.5 and rcp8.5). The moderately suitable areas indicated a mixed response in mid-century with decline (under rcp4.5) and increase (under rcp8.5) and consistent increase in late century. The marginally suitable areas show a decline in mid-century and increase in late-century. Our results suggest that the climate change will continue to significantly affect the distribution and risks spread of V. destructor in Tanzania. The suitability range of V. destructor will shift where highly suitable areas will be diminishing to the advantage of the honey bees’ populations, but increase of moderately suitable sites indicates an expansion to new areas. The late century projections show the increased risks due to surge in the moderate and marginal suitability which means expansion in the areas where V. destructor will operate. Conclusion The current and predicted areas of habitat suitability for V. destructor’s host provides information useful for beekeeping stakeholders in Tanzania to consider the impending risks and allow adequate interventions to address challenges facing honey bees and the beekeeping industry. We recommend further studies on understanding the severity of V. destructor in health and stability of the honey bees in Tanzania. This will provide a better picture on how the country will need to monitor and reduce the risks associated with the increase of V. destructor activities as triggered by climate change. The loss of honey bees’ colonies and its subsequent impact in bees’ products production and pollination effect have both ecological and economic implications that need to have prioritization by the stakeholders in the country to address the challenge of spreading V. destructor

Allanblackia, Butterflies and Cardamom: sustaining livelihoods alongside biodiversity conservation on the forest-agroforestry interface in the East Usambara Mountains, Tanzania

Win–win outcomes for biodiversity conservation and poverty reduction are the holy grail of integrating conservation and development and are rarely met. Domestication of valued local species and introduction of high valued crops can help prevent depletion of wild resources. We compared three commodities from the forest–agroforestry interface of the East Usambara Mountains in Tanzania at different stages of domestication: (a) Allanblackia stuhlmannii, a local tree with valuable edible kernel oil; (b) butterflies, with an international market chain for pupae sold to butterfly gardens and (c) cardamom (Elettaria cardamomum), an introduced shade tolerant spice from India with established global markets. Data on production systems, institutional set-up and profitability were collected through focus group discussions, interviews with key individual informants and literature review. Cardamom has become a major support for rural livelihoods, generating 9 million USD for 750 tons of product in the area, or 850 USD per year for 10,600 households. Allanblackia and butterflies generate only 1% of that income for the landscape. For Allanblackia (around 20 USD per year for 5000 households), the transition from a forest product collected from the wild to being an agroforestry commodity is in an early but critical stage, where the slow growth of the trees and inadequate research attention to production systems, as well as modest farm gate price, currently limit farmer interest but are the focus of ongoing research. Butterflies (approximately 200 USD per year for 350 households) have had the fastest domestication pathway, with continuous innovation into new products and use, linked to international markets. There is gender-sensitive integration with household tasks and compatibility with homegarden agroforestry systems, while due attention is given to institutional arrangements of its local business scheme. Cardamom's economic success has made it a ‘villain’ to forests conservation, as forest transformation to cardamom agroforestry retains only half of the forest trees, and is a step towards further change. Differences in institutional settings of these three domestication pathways relate to their potential to reconcile biodiversity and livelihood concerns and suggest that a socio-ecological system approach to domestication is a prerequisite for a biological–technical one to achieve societal goals

mpact of forestland tenure changes on forest cover, stocking and tree species diversity in Amani nature reserve, Tanzania

The aim of the present study was to evaluate the impact of changes from private to state tenure on forest resources for three blocks in Amani Nature Reserve. The resource changes were determined in terms of forest cover, forest stocking and tree species diversity over a period of six to eight years. When considering the three blocks as one entity one may in general maintain that there have been positive changes regarding forest cover. There were differences between the blocks, however. The proportions of dense and semi-closed forest increased by around 14% in the former tea company block, remained unchanged in the former farmland and decreased by around 12% in the former sisal company block. The changes in stocking parameters and tree species diversity were mainly positive, but none were statistically significant. Although the results were somewhat ambiguous evidence of positive impacts as a result of the tenure changes was identified. This is in line with the main aim of establishing nature reserves focusing on conservation values. More research, however, is required regarding impacts of tenure changes on livelihood for those living adjacent to the nature reserve

Is conservation agriculture ‘climate-smart’ for maize farmers in the highlands of Tanzania?

Conservation agriculture (CA) is promoted extensively to increase the productivity and environmental sustainability of maize production systems across sub-Saharan Africa and is often listed as a climate-smart agriculture (CSA) practice. However, the impacts of CA on food security, resilience/adaptive capacity and climate change mitigation are location-dependent and it is unknown whether CA can simultaneously address CSA’s multiple objectives. Here we evaluate four variations of CA: reduced tillage plus mulch (mulch), reduced tillage plus mulch and leguminous cover crop (Lablab), reduced tillage plus mulch and leguminous trees (CAWT), and reduced tillage plus mulch and nitrogen fertilizer (CA + F)—for their effect on CSA-relevant outcomes in highland Tanzania maize production. By comparison to conventional practice in the region, intensification of maize production by Lablab, CAWT, and CA + F significantly increases yields by 40, 89 and 77 %, respectively. Likewise, rainfall use efficiency was highest in these three treatments and significantly greater than conventional practices in 7 of 12 comparisons. Seasonal and annual greenhouse gas fluxes were similar across all treatments; however, yield-scaled global warming potential (Mg CO2 eq Mg grain−1) was lower in CAWT (2.1–3.1) and CA + F (1.9–2.3) than conventional practice (1.9–8.3), averaging 62 and 68 % of the emission intensity of conventional practice, respectively. The findings demonstrate that CA can deliver benefits consistent with the objectives of CSA for farmers in this region, particularly when soil nitrogen limitation is alleviated, providing other constraints to adoption are removed