1,158 research outputs found
Ecology and control of the trachoma vector Musca sorbens
No full textThe work described in this thesis was conducted In rural Gambia and builds a body of evidence Incriminating the fly Musca sorbens as a vector of the blinding disease, trachoma, which is caused by ocular infection with Chlamydia trachomatis. Literature on hygiene promotion, environmental change and flies and trachoma is reviewed in the context of the SAFE strategy for trachoma control advocated by the World Health Organization M. sorbens was present throughout the year in trachoma endemic communities; was responsible for the majority of fly-eye contacts; C. trachomatis DNA was found on it; and trachoma transmission dropped when they were removed from the environment. In a large cluster-randomised trial communities receiving fly control with insecticide for six months had a mean reduction in trachoma prevalence of 56% (95% Cl 19-93%; P=0.01) compared to controls and 37% (4-70%; P=0.068) fewer new prevalent cases of trachoma. Breeding media choice experiments showed that isolated human faeces were the preferred larval medium for M. sorbens and were capable of supporting the production of large numbers of adults. However, other animal faeces were also able to support M. sorbens development. This suggested that a community-based strategy to reduce the quantity of human faeces on the soil surface by providing latrines would have the effect of reducing the population of M. sorbens, and hence reduce fly-eye contact and trachoma transmission. The provision of latrines gave encouraging results, which were not statistically significant; 30% less active trachoma than controls after six months (-22-81%; P=0.210) and 28% (-5-60%; P=0.146) fewer new prevalent cases. Provision of latrines warrants further investigation as a method to control trachoma, particularly when used in conjunction with other control methods. The potential role of fly control in the SAFE strategy for trachoma control is discussed
On the senior authorship of Musca oleae (Diptera: Tephritidae)
No full textPietro Rossi (1738–1804), Professor at the University of Pisa, in 1790 described the olive fruit
fly Musca oleae in his opus Fauna Etrusca and for the next 121 years, Rossi was considered its
author. During all the 900 century, Gmelin was considered the senior author. In this paper we report that the date of Rossi's Fauna Etrusca has
been found to pre-date Gmelin's 13th Edition for the part that includes Musca oleae. Thus, we conclude that the senior author has to be considered definitively
Rossi and not Gmelin
WT Type 4 Benchmarks for IEC 61400-27-1
No full textSince several years there has been a constant effort at international level for the standardization and the validation of different types of wind turbine (WT) dynamic models. The paper focuses on the IEC 61400-27-1 type 4 model, proposing and fully describing two benchmark systems for the
assessment of dynamic performance. The first system is a simple setup and it is designed to specifically assess the transient response of the WT controls. The second system is based on the IEEE 9-bus test system, and it is a multi-machine configuration allowing for the inclusion of the typical power system dynamics of synchronous machines and corresponding primary regulators. System configurations, models and parameters are designated with the purpose of interoperability and replicability, aiming to models comparison and validation
A novel wide-area control for general application to inverter-based resources in power systems
No full textThe article illustrates the wide-synchronization control, a novel wide-area control for general application to inverter-based resources. The principle is first introduced from a theoretical point of view, including a mathematical proof of the concept, a technological assessment of grid-following and grid-forming converters as actuators, and the examination of the effects of the latencies. The wide-synchronization control is then demonstrated with the application to two case-studies, the standard two-area benchmark system and the large-scale European power system. Analysis and results indicate that the proposed control can remarkably improve the dynamic characteristics of the system, securing a stable operation with a high degree of flexibility and even under critical conditions
Generalized power-angle control for grid-forming converters: A structural analysis
No full textSeveral control schemes have been recently proposed and studied as grid-forming controls for power converters. In all these schemes, the power-angle control loop is the part which defines the fundamental capabilities of the grid-forming control: that control loop governs in fact the inherent synchronization mechanism of the power converter, the power sharing with the other generation sources in the system and the oscillatory characteristics of the converter-based resource. This article introduces a general formulation for the power-angle control characterizing the grid-forming concept for power converters. The generalized power-angle control is based on a polynomial fraction formulation, and it is arranged according to physical requirements and constraints. The structural analysis provides an insight into the capabilities and the design of the power-angle control loop of a grid-forming scheme. The generalized formulation is eventually applied to some common grid-forming controls like the power-synchronization control and the virtual synchronous machine, showing how the proposed generalized power-angle control can effectively realize different control structures
Analysis and simulations of the primary frequency control during a system split in continental europe power system
No full textThe occurrence of system separations in the power system of Continental Europe has been observed in recent decades as a critical event which might cause power imbalances higher than the reference incident specified per system design, representing an actual challenge for the stability and safe operation of the system. This work presents an analysis and simulations of the primary frequency control in the Continental Europe synchronous area in conditions of system separation. The adopted approach is based on fundamental aspects of the frequency-containment reserve process. The analysis takes an actual event into consideration, which determined the separation of the system in January 2021. The main purpose of the work is the development of specific models and simulations able to reproduce the actual split event. Due to specific arrangements discussed in detail, it is possible to obtain a substantial match between the simulations and the frequencies registered after the system split. The work also provides insight into the importance of the temporal sequence of power imbalances and defensive actions in the primary frequency control process. The models developed in the work are finally used to investigate the separation event under different operating conditions, such as missing defensive actions and low inertia scenarios
Frequency Dynamics of the European System during Split Integrating Grid-Forming Capabilities
No full textThe work examines the Continental Europe power system for an actual split event occurred in 2021. The behaviour of the system after the split is first replicated with a specific dynamic simulation model. The validated model is then further developed and extended to investigate the frequency dynamics of the split event, assuming the European system in a scenario characterized by high integration of renewable energy sources interfaced through power converters. The implementation of the non-synchronous generation sources in the simulation model of the system is realized considering two different control concepts for the converters, a grid-following and a grid-forming control. The simulations are performed for different values of relevant parameters for the converters control and different operating conditions for the non-synchronous generation sources. Analysis and results suggest that the integration of non-synchronous generation sources might not necessarily imply only challenges, but rather they can participate in the frequency control and provide an essential contribution to the frequency stability of the system, especially under critical conditions like the system separation
Fundamental Analysis of Grid-Forming Converters Enhanced with Feedforward Controls
No full textThe grid-forming control for power converters can be enhanced by proper feedforward terms included in the active power control loop. Two basic structures are identified, the feedforward angle and the feedforward frequency. The formal analysis of the transfer functions reveals a structural similarity. The two schemes exhibit however a fundamental difference in their transient capabilities. The grid-forming controls are characterized with the introduction of two specific factors, for the direct assessment of the inertia and the damping which can be provided by the grid-forming converter. The sensitivity analysis of the two feedforward schemes indicates that the enhancement of the transient performances of the control results in a reduction of the inertia synthetically provided by the converter. The results show that the feedforward frequency is significantly more sensitive than the feedforward angle to the feedforward term, and that the feedforward frequency presents a suitable range of damping capabilities but limited possibility of improving the inertial capability. The considerations derived in the analytical investigations are finally verified with a simulation-based application case, implementing a detailed EMT model in the Simscape toolbox of Matlab/Simulink
Grid-Following and Grid-Forming MODELS in ATP-EMTP for Power Systems Simulation
No full textThe paper presents the models of grid-following and grid-forming converters in the software ATP-EMTP for power systems simulation. The models are developed using the MODELS language, they are described in details discussing all issues and aspects related to the implementation, and they are also shared as open source models. The models are validated with a simulation-based approach, comparing the results with the models developed in MATLAB/Simulink and in NEPLAN, considering both the phasor RMS and EMT time domains, and thus performing a comprehensive cross-platform and cross-domain validation. In line with the spirit of the ATP software and community, the models of grid-following and grid-forming converters are developed with the purpose of sharing them, and contributing in this way to the creation of a common basis for the integration of these elements into the analysis and simulation of power systems
A Cost-Effective Solution for Clearing High-Impedance Ground Faults in Overhead Low-Voltage Lines
No full textDowned distribution conductors in overhead distribution systems may not be a concern for equipment but greatly challenge the safety of persons, as well as the integrity of properties. Standard overcurrent protective devices may not be able to detect the magnitudes of currents resulting from high-impedance ground faults. Sophisticated relays able to detect high-impedance ground faults have been available to electric utilities. However, their implementation is rather uncommon, especially in developing countries, most likely due to their costs. In this paper, the authors formalize the problem, and propose a possible cost-effective solution for low-voltage overhead lines with neutral wire. This solution consists of a metal hook underneath the line conductors, attached to the pole and connected to the neutral wire. In the case of a falling line, the hook would be contacted and a line-to-neutral short circuit would occur; this would positively activate existing standard overcurrent devices, which can therefore disconnect the supply. Costs related to the installation of the device to existing overhead lines are herein analyzed. The effectiveness of the proposed solutions for two different voltage levels (400 V in European countries and 240 V in the USA) is also discussed
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