E.L. da Silva

Transmission network expansion planning under an improved genetic algorithm

This paper describes the application of an improved genetic algorithm (IGA) to deal with the solution of the transmission network expansion planning (TNEP) problem. Genetic algorithms (GAs) have demonstrated the ability to deal with nonconvex, nonlinear, integer-mixed optimization problems, like the TNEP problem, better than a number of mathematical methodologies. Some special features have been added to the basic genetic algorithm (GA) to improve its performance in solving the TNEP problem for three real-life, large-scale transmission systems. Results obtained reveal that GAs represent a promising approach for dealing with such a problem. In this paper, the theoretical issues of GA applied to this problem are emphasized.

Transmission network expansion planning under a Tabu Search approach

This paper describes an implementation of Tabu Search to cope with long-term transmission network expansion planning problems. Tabu Search is a metaheuristic proposed in 1989 to be applied to combinatorial problems. To assess the potential of our approach we test it with two cases of transmission network expansion planning. The results obtained by our approach let us to conclude that TS is a robust and promising technique to be applied in this problem.

Solving the hydro unit commitment problem via dual decomposition and sequential quadratic programming

This paper presents an algorithm that achieves the hydro unit commitment in hydrothermal systems. This problem is difficult to solve since several constraints with continuous and discrete variables exist, including hydraulic coupling, storage and released flow limits of the reservoirs, and unit forbidden operation zones. The forbidden zones cause a noncontinuous operation of the generating units, making the solution of the problem more difficult, due to the associated combinatorial nature. Moreover, there exists the presence of nonlinear functions that represent the tailrace level, the hydraulic losses, and the unit efficiency. To solve a problem that contains all of these characteristics is a challenging task. Within this scenario, an algorithm is presented that makes use of Lagrangian relaxation, in which some variables are artificially duplicated in order to separate the problem into simpler subproblems. The idea is to relax the spatial and temporal coupling present in the constraints associated with the forbidden zones. In order to solve the subproblems of nonlinear continuous nature that result from the relaxation, this paper presents a sequential quadratic programming algorithm. To update the Lagrange multipliers, an algorithm based on the Bundle Method is used. We assess our approach on a real-life hydroelectric configuration, proving the conceptual and practical feasibility of the proposed algorithm.

Generation maintenance scheduling considering transmission constraints

This paper describes a new approach for establishing power systems scheduled generators outages for maintenance purposes. The time frame considered refers to power systems short-term operations planning horizon (i.e. one month ahead). The papers main contribution is focused on modeling grid operational constraints, which are dealt with by a DC optimal power flow. The resulting large-scale optimization problem is solved by mixed-integer programming techniques aided by Benders decomposition strategy. The obtained results clearly show that representing transmission influence is essential for the establishment of a sound set of scheduled outages for the systems generators, especially in the case of hydrothermal systems.

A reliable approach for solving the transmission network expansion planning problem using genetic algorithms

Abstract This paper presents a reliable approach for solving the transmission network expansion planning (TNEP) problem through a genetic algorithm (GA). GAs have demonstrated the ability to deal with non-convex, non-linear, integer-mixed optimization problems, such as the TNEP problem, better than a number of mathematical methodologies. The procedure presented consists on finding unfeasible solutions for the problem through the GA. These solutions are used for predicting the cost of the optimum solution using a ‘loss of load limit curve’, of the transmission system. Once this cost is estimated, the optimum solution can be found by performing a local search starting from the unfeasible solutions that have costs close to the estimated cost. This approach makes the GA more robust and reliable for solving the problem for different transmission systems.

Practical Cost-Based Approach for the Voltage Ancillary Service

The restructuring and deregulation of the electricity sector most noticeably involves the introduction of competition into energy supply. In parallel with this, however, there is an increasing desire amongst transmission system operators, generators, and consumers for commercial principles to be applied to transmission services, including the provision of voltage support and reactive power control. The identification of the costs of providing such services is an important first step towards developing a transmission services market. Implementing a payment structure based on the remuneration of incurred costs can be an attractive option to commercial power sector players, who wish such costs to be recoverable at an appropriate rate of retum, and system operators, who need to be assured of the availability of the necessary services. This paper addresses both the principles and practical issues involved in developing cost-based payments for reactive power, with reference to the ongoing restructuring of the Brazilian power sector.

Dietary intake and oxidative stress in breast cancer: before and after treatments

OBJECTIVE The aim of this study was to investigate changes in dietary intake, anthropometric parameters and markers of oxidative stress in 40 women who underwent surgery, chemotherapy or radiation therapy for breast cancer. METHODS Pretreatment and post-treatment measurements included data collected through a food frequency questionnaire, weight and height to calculate the body mass index (BMI) and oxidative stress markers assessed from blood reduced glutathione (GSH), serum antioxidant capacity (AC), plasma thiobarbituric acid reactive substances (TBARS), serum lipid hydroperoxides (LH) and plasma carbonyls. Differences were compared using paired Students t-test or paired Wilcoxons test. RESULTS A significant increase (P < 0.05) in the intake of the food groups: meat and eggs, dairy products, beans, oils and fats, as well as food from the subgroups: red meat, milk and other dairy products rich in fat, fruit rich in vitamin C and vegetable fats was found after treatments. There was a significant increase in body weight (P < 0.05), BMI (P < 0.05), levels of TBARS (P < 0.0001), LH (P < 0.005) and carbonyls (P < 0.0001) and a significant decrease of levels of AC (P < 0.005) and GSH (P < 0.0001). CONCLUSION Breast cancer diagnosis and treatments were associated with dietary intake changes and increased body weight, BMI and oxidative stress. These potential changes have important implications for preventive nutrition counseling.

Nodal price control: a mechanism for transmission network cost allocation

This paper presents an approach for the allocation of transmission network costs by controlling the nodal electricity prices. The proposed approach introduces generation and nodal injection penalties into the traditional economic dispatch so as to create nodal price differences that recover the required transmission revenue from the resulting congestion rent. As a consequence, the new electricity prices reflect not only the marginal costs of production subject to transmission constraints but also the capital costs of the network. This is the approach commonly adopted with most commodities whose price includes the unit cost of the good itself as well as the transportation cost from the production centers to the final consumer.

Modeling competition in transmission expansion

The transmission network plays a key role in allowing access to the most efficient generators to all consumers. In most cases, the new transmission projects are defined by a system operator, which focuses on improving the bulk systems reliability and reducing short-term operating problems. Because electricity market participants are prevented from investing in transmission facilities that may benefit them, transmission expansion may not have been sufficient to stimulate competition within the market. In this paper, we show formally through a mathematical formulation based on the Lagrangian relaxation technique that the investment in transmission capacity can be a profitable activity, therefore the introduction of competition in the transmission expansion could be possible. Such a competitive expansion of transmission capacity would allow the participants to improve the efficiency of the electricity market.

Influence of the traditional Brazilian drink Ilex paraguariensis tea on glucose homeostasis

In this study we examined the acute in vivo effect and short- and long-term in vitro effects of samples from native and commercial Ilex paraguariensis on glucose homeostasis. Also, the potential effect of I. paraguariensis on serum insulin secretion was investigated. The chemical identification and quantification of methyl xanthines and polyphenols in CH₂Cl₂, EtOAc and n-BuOH fractions of native I. paraguariensis as well as infusions of green and roasted I. paraguariensis from a commercial source was verified by high-performance liquid chromatography. The results for the serum glucose-lowering indicated that both fractions and both infusions were able to improve significantly the oral glucose tolerance curve. Additionally, both the EtOAc and n-BuOH fractions induced-insulin secretion, but EtOAc induced an early (at 15 min) and late (at 60 min) biphasic peak of insulin secretion similar to glipizide stimulatory effect. Both fractions increased liver glycogen content compared with fasted normal rats. Also, EtOAc and n-BuOH fractions inhibited in vitro disaccharidases activities after an acute treatment. The maximum inhibitory effect of the EtOAc and n-BuOH fractions on maltase activity (at 5 min) was around 35%. The evident reduction of protein glycation by glucose or fructose with EtOAc and n-BuOH fractions increased from 7 to 28 days of in vitro incubation. Inhibition of bovine serum albumin glycation by glucose and fructose, by around 50% and 90%, respectively, was observed. Additionally, the green and roasted mate infusions reduced the formation of AGEs in a characteristic long-term effect. In conclusion, this study shows that I. paraguariensis has an anti-hyperglycemic potential role able to improve the diabetic status and is probably a source of multiple hypoglycemic compounds.