Search

To get the distribution network to operate at its optimum performance in an automated distribution system reconfiguration was been proposed and researched. Considering, however, that optimum performance implies minimum loss, no overloading of transformers and cables, correct voltage profile, and absence of phase voltage and current imbalances, network reconfiguration alone is insufficient. It has to be complemented with techniques for phase rearrangement between the distribution transformer banks and the specific primary feeder with a radial structure and dynamic phase and load balancing along a feeder with a radial structure. This paper contributes such a technique at the low-voltage and medium-voltage levels of a distribution network simultaneously with reconfiguration at both levels. While the neural network is adopted for the network reconfiguration problem, this paper introduces a heuristic method for the phase balancing/loss minimization problem. A comparison of the heuristic algorithm with that of the neural network shows the former to be more robust. The approach proposed here, therefore for the combined problem, uses the neural network in conjunction with a heuristic method which enables different reconfiguration switches to be turned on/off and connected consumers to be switched between different phases to keep the phases balanced. An application example of the proposed method using real data is presented. Index Terms--Distribution automation, distribution control, heuristic algorithm, load balancing, neural network, optimal control, phase arrangement, phase current imbalance, phase voltage imbalance, power loss, reconfiguration.

This study was motivated by the report of a survey of herbal remedies used by Fulani herdsmen in the management of cow diarrhoea in Plateau State, Nigeria. The report identified F. platyphylla stem bark amongst major herbs. Activity of aqueous stem extract of F. platyphylla against diarrhoea caused by physiological changes and by pathological infections was herein determined. Thirty albino rats were fasted for 18 hours. They were grouped into six and induced with diarrhoea using castor oil. The first two groups received distilled water (1 ml) and loperamide (5 mg/kg), while other groups were administered plant extract 50, 100, 200 and 400 mg/kg body weight respectively. The severity of diarrhoea was assessed hourly for 4 hrs. Gastrointestinal motility experiment was carried out using atropine sulphate (5 mg/kg). In vitro anti-diarrhoeal test was carried out against E. coli clinical and laboratory isolates versus antibiotics. The extract inhibited defecation moderately, and regulated frequency of wet stool better than loperamide, the lowest dose (50 mg/kg b. w.) competed favourably with the loperamide. This dose produced the most remarkable activity considering the latent period, total stool frequency, purging indices and percentage inhibition of defecation. The dose showed remarkable activity in the propulsion of charcoal meal through gastrointestinal tract as displayed in the inhibition of diarrhoea. The results of in vitro anti-diarrhoeal test against E. coli showed that the plant extract was inactive on the microorganism. The results from the present study validated the anti-diarrhoeal potential of F. platyphylla via its physiological action. [ABSTRACT FROM AUTHOR]

In this paper, Neural Network (NN) approach is developed and utilised to detect winding faults in an electrical machine using the samples data of electrical machine in both the healthy and different fault conditions (i.e. shorted-turn fault, phase-to-ground fault and coil-to-coil fault). This is done by interfacing a data acquisition device connected to the machine with a computer in the laboratory. Thereafter, a two-layer feed-forward network with Levenberg–Marquardt back-propagation algorithm is created with the collected input dataset. The NN model developed was tested with both the healthy and the four different fault conditions of the electrical machine. The results from the NN approach was also compared with other results obtained by determining the fault index (FI) of an electrical machine using signal processing approach. The results show that the NN approach can identify each of the electrical machine condition with high accuracy. The percentage accuracy for healthy (normal), shorted-turn, phase-to-ground and coil-to-coil fault conditions are 99, 99.6, 100 and 100% respectively. [ABSTRACT FROM AUTHOR]

Additional heat produced in induction machines due to stray load losses could influence the plant rating, winding insulation design, operating limit, and the machine protection design. Quantifying this additional heat and stray load losses accurately and, hence, investigating the extent of some of these influences are the concerns of this paper. Two experimentally verified models, electrical and thermal, are presented. Results of a practical exercise on the measurement of stray load losses by different test methods are reported. The study, thereafter, gives insight into the relationship between stray load losses and the influences mentioned above and contribute results, which are useful to the design and operation of this machine and its protection. Index Terms--Induction machines, induction motor protection, induction motors, losses, modeling.

The enhancement of the operability range of a stand-alone single-phase induction generator scheme with an inverter-battery system connected to the auxiliary winding is the theme of this paper. The reactive power requirement of the load connected to the main winding is met by the inverter system operating with either of two proposed pulsewidth modulation techniques, in the process of which the load voltage and frequency are regulated. The proposed schemes have potential application as power sources for autonomous systems and for utility interface to single-phase power system grids. Simulation and calculation results of the generator system connected to an impedance and motor loads, confirmed with some experimental results, are also set forth to validate some of the conclusions of the paper. Index Terms--Battery, dc-ac inverter, induction generator, pulsewidth modulation.

Pipelines installed in the energy utility corridor with alternating current (AC) or direct current (DC) sources have attendant problem of induced corrosion. In the past years, AC or DC induced corrosion of metallic pipelines has been a major challenge facing pipeline utilities. Nevertheless, considerable research studies have been conducted to appraise the impact of both corrosion types on metallic pipelines. While the mechanism of DC induced corrosion is well established with a level of accuracy, the corrosion due to AC has not been fully covered in the literature. This paper presents a comprehensive review of the research trends in this domain with much emphasis on the corrosion caused by AC. Some of the technical and laboratory research works conducted are also covered. A vision for future research is also identified which may be useful for further studies. The series of investigations conducted revealed that the corrosion of pipelines with a coating defect becomes significant as the AC density increases. In extreme cases, corrosion damage is expected if the AC density increases beyond a certain limit. Furthermore, the proposed cathodic protection potential for protecting pipelines against corrosion is not efficient enough when the pipe is exposed to interference caused by AC. Consequently, research studies and field implementations focusing on the combined effect of AC and DC on pipelines with multilayer soil analysis would give promote understanding of the problem. [ABSTRACT FROM AUTHOR]

Summary: Voltage stability has of recent been a subject of growing concern to power system utilities. In this paper, 2 techniques, one based on topological structure of power networks and the other on the conventional power flow solution, are proposed for voltage stability analysis. The network structural characteristics theory participation factor proposed is formulated to identify the weak bus of the system. The voltage stability enhancement is achieved through the incorporation of power electronic–based thyristor‐controlled series compensator device. This is done by modifying the admittance matrix and network structural characteristics theory participation factor formulated to incorporate the effect of variable reactance of thyristor‐controlled series compensator device. The second suggested approach based on power flow is also investigated. The results of both techniques are compared with the conventional approaches. The results of simulations obtained show that voltage stability enhancement can significantly be achieved from the network structural point of view, as it saves time and reduces system computational burden. [ABSTRACT FROM AUTHOR]

The introduction of new operation enhancement technologies plus increasing application of power electronics, coupled with the continuous increase in load demand, has increased the risk of power networks to voltage instability and susceptibility to voltage collapse. This frequent occurrence of voltage collapse in modern power system has been a growing concern among power system utilities. This paper proposes alternative techniques for the identification of critical nodes that are liable to voltage instability in a power system. The first method is based on the critical mode corresponding to the smallest eigenvalues, while the second technique is based on the centrality measure to identify the most influential node of the networks. The eigenvector centrality measure is formulated from the response matrices of both the load and generator nodes of the networks. The effectiveness of the suggested approaches is tested using the IEEE 30-bus and the Southern Indian 10-bus power networks. The results are compared with the techniques based on the traditional power flow. The whole procedure of the results involved in the identification of critical nodes through the proposed methods is totally non-iterative and thereby saves time and requires less computational burden. [ABSTRACT FROM AUTHOR]

In power system, utility engineers are often faced with the challenge of reinforcing weak power networks without adding any new infrastructures. This paper analyses the topological structure of a topologically weak network and then institutes a way of reinforcing the network through restructuring. The proposed scheme explores the concept of network structural characteristics of power networks in conjunction with the shortest electrical distance from graph theory. The branch impedances of new sets of candidate transmission lines that could possibly reinforce the existing structurally weak network are determined. The standard IEEE 5-bus and 30-bus test systems are used to illustrate the effectiveness of the proposed scheme. The results obtained show that the proposed approach is generally useful in power system network design, planning and efficient operation. [ABSTRACT FROM AUTHOR]

This paper proposes two techniques for the identification of critical buses in a power system. The technique of Network Structural Theory Participation Factor (NSTPF) depends on the network structural interconnection of buses as captured by the admittance matrix of the system and is formulated based on the fundamental circuit theory law using eigenvalue decomposition method. Another power flow based technique which depends on the system maximum loadability, the system step size among other factors is also proposed. Traditional power flow based techniques are used as benchmarks to determine the significance of the proposed methods. To ensure voltage stability enhancement, STATCOM FACTS device is installed at the selected weak load buses of the practical Nigerian 24 bus and IEEE 30 bus test systems. The results of the simulation obtained show that, the suggested approach of NSTPF is more suitable in the identification of weak buses that are liable to voltage instability in power systems as it requires less computational burden and also saves time compared to techniques based on power flow solutions. [ABSTRACT FROM AUTHOR]

Metallic pipelines have attendant problems of alternating current (AC) assisted corrosion when installed in the utility corridor with high voltage transmission lines. Research studies in the past and recent years have shown that this corrosion is a primary function of the AC density through the pipe coating defect. While several other AC corrosion risk assessment indices have been proposed, the AC density is regarded as a valuable parameter in assessing pipeline corrosion risk due to AC interference. Also, there exists a threshold value which, if exceeded, guarantees the possibility of pipeline corrosion damage. However, for buried pipelines, monitoring these AC corrosion assessment indices is a major challenge. Therefore, to avoid severe corrosion damage to such pipelines, a corrosion assessment for evaluating the corrosion risk of the pipelines due to AC interference is presented in this paper. The assessment was demonstrated on a buried pipeline in one of the Rand Water sites, South Africa where AC interference is frequent. The overall simulation results yield useful information which may be essential for pipeline operators, most especially Rand Water, South Africa and corrosion engineers for AC corrosion assessment of metallic pipelines installed near transmission lines. The analysis presented in this paper may also be used for the evaluation of a safe position for installing new pipelines near existing power lines right-of-way. [ABSTRACT FROM AUTHOR]

This paper presents an alternative approach of Inherent Structural Characteristics Theory (ISCT), for solving loss allocation to network participants as well as generation-to-load matching problems in a deregulated environment. The mathematical formulations of ISCT, based on the fundamental circuit theory laws, are revisited. A Generation-to-Load Allocation Coefficient (GLAC) matrix for solving generation-to-load allocation and network loss allocation to load problems, for efficient transmission pricing, is formulated. The allocation of real and reactive power contributions, by individual generator, required to serve the network demands is also determined on the basis of the GLAC matrix. Total network losses are determined and allocated to individual network loads based on GLAC matrix. The approach is demonstrated using the standard IEEE 30 bus network. The results obtained are compared with that obtained using graph theory approach based on the solved power flow. The comparison of the results shows that the ISCT approach is reasonable and it is a good signal, which could be useful for pricing of electricity by the market regulators. [ABSTRACT FROM AUTHOR]

Electrical machines are useful in nuclear power plants, military applications, domestic appliances and industrial utilities. The relevant literature indicates that the induction machine takes about ninety percent of all electrical machine globally used in the industry. The risk of the failure of this machine can be avoided if the proper diagnostic scheme is designed and implemented to detect failure/impending faults at an incipient stage. This paper describes Discrete Wavelet Transform (DWT) based diagnosis technique that analyses stator currents of induction machine under healthy and faulty conditions. This enables the extraction of harmonic components caused by each signal for further analysis. On one hand, the maximum energy for each signal gives information about the time a certain fault occurs in the machine and the time it starts deviating from the normal (healthy) state. On the other hand, a Fault Index (FI) is generated for each situation in order to classify the state of the machine into normal, medium or high. The colours; green, yellow and red are used to represent the normal, medium and high states respectively. Should the faults at medium state are not detected on time, it may lead a more serious fault (high state). Thus, this technique is robust to identify a fault of an induction machine at the incipient state with a very minimal time. [ABSTRACT FROM AUTHOR]

Incipient detection and diagnosis of stator winding shorted-turn faults in induction machines is essential for reliable and economical operations in industries. The problem of detecting shorted-turn faults in stator windings has been difficult. Although, from the supply currents, major winding faults can easily be detected, minor faults with less than five per cent of winding turns are not easily detectable. If not detected early, such faults can lead to major winding faults which may further lead to the disruption of the machine and causes production shutdowns. This paper describes the discrete wavelet transform (DWT) based diagnosis technique that analyses stator currents under faulty (stator shorted-turn) and healthy conditions. The developed technique depends on the band pass filtering carried out by the DWT, facilitating the extraction of the harmonic components produced by the shorted-turn faults. The discrepancies energy spectrum for three frequencies from the residual of de-noising analysis enables us to classify the fault index. From 38 seconds, the shorted turn begins to show significant difference in the energy spectrum, and if this is not detected in time, it may lead to a more serious fault. [ABSTRACT FROM AUTHOR]

The currents owing through a transmission line produce a rotating magnetic field of vertical and horizontal components which are orthogonal in space and vary with time. Buried and aerial metallic pipelines that run parallel to or are placed in the vicinity of overhead AC high voltage transmission lines are affected by this field resulting in an induced voltage on the pipelines. Several related studies and safety standards dealing with this problem have been published. Nevertheless on a multi-circuit line, the issue of current phase shift variation has not been fully covered yet. This paper provides a detailed analysis of the effect of current phase shifts on the magnetic field distribution and polarization pattern around power lines using analytical approach from electromagnetic field theory. In this study, not only the variation of the filed distribution with phase arrangements and phase shifts is further established, but also the characteristic nature of the variation of the field distributions for six phase arrangements is examined in more detail. The results show that the magnetic field distribution at the ground level and the spatial distribution of the magnetic field polarization ratio vary significantly with the phase sequence arrangement as well as the current phase shifts between the two circuits. The field polarization differs at different locations. The information from the results can be useful for consideration in designing an effective AC mitigation technique and in placing pipelines in the utility corridor with power lines. Pipelines should be placed in a region of minimum field intensity within the right-of-way of the line, in order to have minimal induction on the pipeline in normal operating conditions of the line. [ABSTRACT FROM AUTHOR]

Electrical power grids are often susceptible to voltage instability and have been a growing concern. In this study, the authors propose techniques based on network response structural characteristics for voltage stability assessment and for the identification of important nodes in electrical power grids. First, the network response structural characteristic indices (NRSCIs) which are inherent in the conventional power grids in terms of the Kirchhoff matrix is formulated. The eigenvalue decomposition (ED) technique is then applied to a submatrix of the Kirchhoff matrix to determine the topological strength of the electrical network graph. The vertex (node) that has a minimum eigenvalue is taken as the critical mode, from which its contributions to the entire graph is identified using the proposed network response structural characteristics theory participation factor (NRSCTPF). To demonstrate the magnitude of the concept formulated, the known degree centrality is modified in terms of the established NRSCI, which are then used to determine the important nodes of the network graph. The results obtained show that the proposed NRSCTPF and the degree centrality based on the NRSCI can be used for voltage stability assessment and identification of important nodes. The proposed approach is also less computationally intensive compared with the traditional approach. [ABSTRACT FROM AUTHOR]

In this study, the antidiarrheal, cytotoxic and genotoxic properties of sorghum, millet and corn steep liquors as well as mistletoe extract in wistar rats were investigated. Comparative analysis of antidiarrheal potentials of sorghum, millet and steep liqours with standard drug (loperamide) and oral rehydration solution (ORS) in a castor oil-induced diarrheal model was carried out. Blood was examined for serum biochemical parameters and genotoxic effects were investigated using micronucleus test. In the antidiarrheal test, the test agents showed action which was significant (P<0.05). Mistletoe extract exerted maximum inhibition (55.56 %) against defecation, whereas 44.44 % and 59.26 % inhibitions were obtained for ORS and loperamide respectively. The genotoxicity studies of these steep liquors and mistletoe extract revealed damage to the genetic material and alteration of the activities of some marker enzymes, which is indicative of tissue damage. Although sorghum, millet and corn steep liquors, as well as mistletoe extract have anti-diarrheal activities, their indiscriminate usage, at high concentrations should be discouraged. [ABSTRACT FROM AUTHOR]

This study investigated the nutritional value of pre-treated rice and wheat bran wastes as feed formulation in experimental rats. Aspergillus niger KM isolated from decomposing organic matter was tested for cellulase assay. The lignocellulosic agricultural residues (wheat bran and rice bran) were pretreated with ammonia and diluted sulfuric acid after which solid substrate fermentation with Aspergillus niger KM was carried out. Determination of reducing sugar was carried out and the fermented residues were included as components in feed formulation and were fed to different groups of rats for four weeks. The proximate analysis of the feed formulation showed that the NH3 pretreated feeds gave higher protein content of 21.94%, relative to the control or other groups. Growth performances of animals fed with NH3 pretreated wheat bran significantly increased from 158.25 to 201.66 g throughout the feeding periods. Evaluation of the various feeds' effect on tissue marker enzymes revealed inconsistent alterations relative to the control. Bioconverted wheat or rice bran has nutritive value to support animal growth and could be explored in animal feed preparation. [ABSTRACT FROM AUTHOR]

In this study, the antidiarrheal, cytotoxic and genotoxic properties of sorghum, millet and corn steep liquors as well as mistletoe extract in wistar rats were investigated. Comparative analysis of antidiarrheal potentials of sorghum, millet and steep liqours with standard drug (loperamide) and oral rehydration solution (ORS) in a castor oil-induced diarrheal model was carried out. Blood was examined for serum biochemical parameters and genotoxic effects were investigated using micronucleus test. In the antidiarrheal test, the test agents showed action which was significant (P<0.05). Mistletoe extract exerted maximum inhibition (55.56 %) against defecation, whereas 44.44 % and 59.26 % inhibitions were obtained for ORS and loperamide respectively. The genotoxicity studies of these steep liquors and mistletoe extract revealed damage to the genetic material and alteration of the activities of some marker enzymes, which is indicative of tissue damage. Although sorghum, millet and corn steep liquors, as well as mistletoe extract have anti-diarrheal activities, their indiscriminate usage, at high concentrations should be discouraged. [ABSTRACT FROM AUTHOR]

In the food and beverage industry, where growing, processing, packaging, distribution, storage, preparation, serving and disposing of food is the order of the day; energy consumption becomes an important input. Various energy models have been developed since the early 1970s, the period when energy caught the attention of policymakers due to the sudden price increase. Among the models are the index decomposition analysis (IDA), artificial neural network (ANN) and data envelopment analysis (DEA). The purpose of this study is to combine the strengths of these models, i.e., IDA, ANN and DEA, to allow biases in one model to offset biases in the other, so as to examine the effectiveness of energy management policies in a particular food and beverage industry. The integrated model applied to the food and beverage revealed that approximately 11% of energy consumed could be saved. [ABSTRACT FROM AUTHOR]

Abstract: The electrical network system is to ensure that an adequate supply is available to meet the estimated load of the consumers in both the near and more distant future. In order to avoid excessive voltage drop and minimize loss, it may be economical to install apparatus to balance or partially balance the loads. It is believed that the technology to achieve an automatic load balancing lends itself readily for the implementation of different types of algorithms for automatically rearranging the connection of consumers on the low voltage end of a feeder for optimal performance. In this paper the combination of the fuzzy logic, which addresses the linear solution, with Newtown Raphson as optimization method for the nonlinear behavior of the load is developed. A study case is presented for a radial feeder of 150 loads. [Copyright &y& Elsevier]

The energy of traditional continuous Hopfield neural networks (CHNN) only decreases with time, so it cannot jump out of local minima. By adding an extra self-feedback to every neuron of CHNN, the energy of CHNN will not always decrease, but can increase or maintain. The energy increasing may lead to avoiding the local optimal values. The conditions under which the CHNN energy increases, decreases or maintains are given, respectively. An adding decaying self-feedback CHNN (ADSCHNN) is presented and approved. Furthermore, the ADSCHNN is applied to the solution of the traveling salesman problem (TSP) and a comparison between chaotic simulated annealing (CSA) and ADSCHNN in the same energy function is conducted. ADSCHNN also is compared with other methods. Simulations results show that the ADSCHNN outperformed other methods and obtained the local optimal solution or the global optimal solution. [ABSTRACT FROM AUTHOR]

In this paper, a stand-alone application with graphical user interface (GUI) developed for monitoring AC induced corrosion expectancies of buried pipelines near a high voltage AC transmission line is presented. A Rand water site, South Africa, was used as a case study. The interface was based on estimating the AC induced corrosion risk assessment indices for buried pipelines near existing overhead high voltage transmission lines using Carson's concept of mutual impedances between both the pipeline and transmission circuits. The GUI was developed using MATLAB software and have been tested to process user input data from field measurements in such site. The developed application permits the evaluation of the AC induced corrosion risk assessment indices and may be particularly useful in the analysis of AC induced potential on buried pipelines. [ABSTRACT FROM AUTHOR]

Background: Propolis is a bee (Apis mellifera) product of plant origin with varied chemical composition depending on the ecology of the botanical origin. It has been reported in literature to possess various therapeutic effects both traditionally, clinical trial, and animal study., Objectives: In the present study bioactive principle in methanol extract of Nigerian bee (A. mellifera) propolis was determined by gas chromatography-mass spectrometry (GC/MS) study., Materials and Methods: The methanol extract of Nigerian bee (A. mellifera) propolis was characterized for its chemical composition by preliminary phytochemicals screening and GC/MS analysis using standard procedures and methods., Results: Phytochemical screening revealed the presence of flavonoids, saponins, alkaloids, tannins, cardiac glycosides, anthraquinones phlobatannins, and steroids while GC/MS chromatogram revealed nineteen peaks representing 60 different chemical compounds. The first compounds identified with less retention time (RT) (13.33s) were methyl tetradecanoate, tridecanoic acid, methyl ester, decanoic acid, methyl ester while squalene, all-trans-squalene, 2,6,10-dodecatrien-1-ol, 3,7,11-trimethyl-, (E,E)- and farnesol isomer a took longest RT (23.647s) to identify. Methyl 14-methylpentadecanoate, hexadecanoic acid methyl ester, methyl isoheptadecanoate, and methyl tridecanoate were the most concentrated constituent as revealed by there peak height (26.01%) while eicosanoic acid was the least concentrated (peak height 0.81%) constituent of Nigerian bee propolis., Conclusion: The presence of these chemical principles is an indication that methanol extract of Nigeria bee propolis, if properly screened could yield a drug of pharmaceutical importance.