Synchronous Generator Excitation Chatter-Free Sliding Mode Controller

A chatter-free sliding mode controller (SMC) for synchronous generator excitation is presented in this paper. A linearized model of a single machine connected to an infinite bus is employed to design a variable-structure controller which not only stabilizes the system, but also ensures that this is maintained in the face of system parameter variations. Validating the robustness feature of an SMC, simulation results that show the dynamic performance of the system under both constant excitation and SMC-controlled excitation are presented

An Electronic Protection Unit for Diesel Engine Standby Generators

Today diesel engine-driven standby generators for backup power supply have been adopted for residential, commercial, and industrial use--especially in some developing countries where power from the utility company is highly erratic. Although many of these generators function well in operation, certain engine conditions, such as low oil pressure, high oil and water temperature, abnormally high speed, etc., could lead to malfunction, failure, or complete breakdown of the engine. Therefore, the focus of this work is to present the implementation of a simple, but effective electronic protection unit (EPU) capable of mitigating the adverse effect which may arise as a result of these conditions. It is composed of two major sub-circuits-the main protective sub-circuit and the timing sub-circuit-realized using a combination of passive and active components. Unlike the common electrical relay-based protection system, this unit has an additional advantage of being able to keep the faultindicating system of the generator working even after engine shutdown, thereby facilitating fault tracking. The unit has been tested on a diesel engine-driven generator and found to function satisfactorily. The test results are shown

Semi analytic method for solving infectious disease model

In this paper, we present a deterministic model that captures the essential dynamics of infectious diseases. Differential Transform Method (DTM) is applied to attempt the series solution of the model. The efficiency of the DTM in solving the model is confirmed by classical fourth-order Runge-Kutta method implemented in Maple 18. The comparisons between the DTM and Runge-Kutta (RK4) solutions were made and there exists positive correlation between the results obtained by the two methods. The outcome of comparison between the DTM and RK4 validates the potential of the DTM in coping with the analysis of modern epidemics

Review of lightning protection standard in building structures in Nigeria.

A lightning protection system performs a simple task. It provides a specified path on which lightning can travel. When a building structure is equiped with a lightning protection system, the distructive power of the lightning strike is directed safely into the ground, leaving structures and equipment unharmed. This paper provides a comprehensive guidance for selection and installation of protection devices for building structures

ON THE GLOBAL STABILITY OF CHOLERA MODEL WITH PREVENTION AND CONTROL

In this study, a system of first order ordinary differential equations is used to analyse the dynamics of cholera disease via a mathematical model extended from Fung (2014) cholera model. The global stability analysis is conducted for the extended model by suitable Lyapunov function and LaSalle’s invariance principle. It is shown that the disease free equilibrium (DFE) for the extended model is globally asymptotically stable if Rq0 1 for the extended model or R0 > 1 for the original model and the disease persists at a positive level though with mild waves (i.e few cases of cholera) in the case of Rq0 > 1. Numerical simulations for strong, weak, and no prevention and control measures are carried out to verify the analytical results and Maple 18 is used to carry out the computations

Partial Purification and Characterization of Cellulase from the haemolymph of the African Giant Land Snail (Archachatina marginata)

The aim of this study is to partially purify and characterize the cellulase extracted from the snail haemolymph of the African giant land snail of the species, Archachatina marginata. The protein concentration of the haemolymph was found to be 168 mg mLG1 and the specific activity of the crude cellulase was found to be 0.007 U mgG1 protein using Carboxymethyl-cellulose (CMC) as the substrate. The partial purification on Sephadex G-200 produced two activity peaks. The molecular weights of the two cellulase fractions were estimated to be 112,202 and 67,000. The Michealis Menten constant (km) for cellulase was 4.3 and 2.8 mg mLG1 for the higher and lower molecular weight fractions, respectively. The multiplicity of cellulase complexes indicated that the haemolymph of A. marginata may convert derived cellulose in foodstuffs such as garlic, mushrooms and domestic wastes into sources of fuel. It is suggested that the enzyme can be used to produce value-added products, such as ethanol, citric acid, amino acids and vitamins including primary metabolites from cellulosic wastes

Duration of homelessness and its relationship to use of hospital and emergency department services in Helsinki, Finland

Aims: Homelessness is associated with poor health outcomes and increased use of hospital and emergency department (ED) services. Little is known about the duration of homelessness in relation to health care service use. The aim of this study was to examine the use of hospital and ED services among the homeless in Helsinki, Finland, and for the first time, to examine the relationship between service use and duration of homelessness. Methods: Six hundred and eighty-three persons staying at least one night in a shelter between September 2009 and September 2010 were followed until the end of 2014. Using negative binominal regression analysis we calculated the use of hospital and ED services and compared the use with that of a matched control group (N = 1361). We also analyzed service use in relation to the time spent homeless during follow-up. Results: The mean time spent homeless during the follow-up was 8.5 months, one third was temporarily homeless (less than 2% of the follow-up time), but recurrent episodes of homelessness were also common. The study group’s incidence rate ratios for medical-surgical hospital days was 6.23 (95% CI: 4.73 to 8.21), for psychiatric hospital days 43.11 (95% CI: 23.02 to 80.74) and for ED visits 10.21 (95% CI: 8.77 to 11.90), compared with controls. The number of medical-surgical hospital days and ED visits/person-year increased as homelessness was prolonged, but the pattern was opposite for psychiatric hospital days. Conclusions: Homeless persons are heavy users of hospital and ED services, and there is also increased use among those temporarily homeless.</p

Design and Construction of an Automatic Transfer Switch for a Single Phase Power Generator

An Automatic Transfer Switch (ATS) for a single phase power generator has been designed to enable the automatic operation and transfer of power supply between a public utility supply and a power generator. The ATS, which is a switchgear control system, provides a functional system that provides an automatic switching of power supply between a primary source (public utility) and a secondary power source (generator). The methods employed in designing the ATS involve the use of electromechanical type relays, contactors, voltage monitoring relays and delay timer relays as main components of the system. Incorporated in the ATS is a digital multimeter (DMM) made up of a 12V d.c and a 5V d.c power supply unit, precision rectifier unit, current transformer and Microcontroller (PIC 16F877) to convert the measured analogue alternating current(a.c). voltage and current quantities to digital values for display on the liquid crystal display (LCD). The result of the automatic transfer switch demonstrates its ability to perform automatic power change over activities easily and with little or no human interactio

Partial Purification and Characterization of Cellulase from the Haemolymph of the African Giant Land Snail (Archachatina marginata)

The aim of this study is to partially purify and characterize the cellulase extracted from the snail haemolymph of the African giant land snail of the species, Archachatina marginata. The protein concentration of the haemolymph was found to be 168 mg mLG1 and the specific activity of the crude cellulase was found to be 0.007 U mgG1 protein using Carboxymethyl-cellulose (CMC) as the substrate. The partial purification on Sephadex G-200 produced two activity peaks. The molecular weights of the two cellulase fractions were estimated to be 112,202 and 67,000. The Michealis Menten constant (km) for cellulase was 4.3 and 2.8 mg mLG1 for the higher and lower molecular weight fractions, respectively. The multiplicity of cellulase complexes indicated that the haemolymph of A. marginata may convert derived cellulose in foodstuffs such as garlic, mushrooms and domestic wastes into sources of fuel. It is suggested that the enzyme can be used to produce value-added products, such as ethanol, citric acid, amino acids and vitamins including primary metabolites from cellulosic wastes