Control/maintenance strategy fault tolerant mode and reliabilityanalysis for hydro power stations

Reliability analysis for hydro power stations for (N+M) and 2N fault tolerant modes (FTM) and their comparison from the standpoint of control and maintenance have been carried out in this paper. It shows that the (N+M) FTM is superior to 2N FTM in reliability and economics in most cases. So, (N+M) FTM is recommended for large power stations, especially for multi-unit plants. A simple method to choose the number of standby controllers is developed by optimizing the (N+M) FTM. The ideas and results proposed in this paper can be used not only for governing systems in hydro power stations but also for other industrial systems     

Axially symmetric compositional simulation of formation tester measurements

This paper describes the development, testing, and successful application of a new compositional code for the numerical simulation of oil-based mud invasion and formation tester measurements that involve arbitrary miscibility between oil-based mud and native oil. The simulator assumes axially symmetric variations of petrophysical properties as well as axially symmetric flow-rate sources and boundary conditions. However, there are no restricting assumptions to the degree of miscibility between the fluids involved in the simulations. We solve the time–space evolution of component concentration with a time-marching implicit pressure explicit concentration (IMPEC) scheme. This method of solution considers the complete equations of state and implements flash calculations to describe the thermo-dynamical evolution of the various compositional phases due to space–time variations of pressure and concentration.Simulations described in this paper consider the process of oil-based mud–filtrate invasion into reservoirs containing mixtures of connate water and oil. Subsequently, we simulate formation tester measurements by enforcing fluid withdrawal through the dual-packer section of the tester. Measurements consist of fluid pressure, fractional flow rates, fluid density, and fluid viscosity. Examples of application include homogenous and multi-layer formations as well as a capillary transition zone. Comparison of simulation results against those obtained with a commercial code confirms the efficiency, accuracy, and reliability of our method of solution.Sensitivity analysis indicate that time evolution of fractional flow rates, fluid density, and fluid viscosity measured with the formation tester remain influenced by the petrophysical properties of the formation, volume of mud–filtrate invasion, and by saturation-dependent rock–fluid properties (relative permeability and capillary pressure). The simulations described in this paper provide suitable guidelines for the acquisition of clean samples of in-situ formation fluids in the presence of invasion and heterogeneous conditions of petrophysical and rock–fluid properties.     

Frequency Dependence of Fading Statistics for Ultrawideband Systems

The variation of channel fading and dispersion statistics between the ultrawideband (UWB) channel subbands is characterized experimentally. Within the FCC-allocated UWB frequency range (3.1-10.6 GHz), the multipath characteristics in various subbands are found to be highly dissimilar. It is demonstrated that the higher subbands suffer greater attenuation, and the rms delay spread varies significantly with the center frequency. The impact of this variation on multiband-OFDM UWB system performance is evaluated, and a large performance variation across the band is reported     

A modified method of estimating Ångström’s turbidity coefficient for solar radiation models

The method by Pinazo et al. (Pinazo JM, Cañada J, Boscá JV. A new method to determine Ångström’s turbidity coefficient: its application for Valencia. Solar Energy 1995;54(4):219–226) to determine the Ångström turbidity coefficient is modified. Two new correlations are developed that link Pinazo’s method with model ‘C’ by Iqbal (Iqbal M. An introduction to solar radiation. New York: Academic Press, 1983), and are derived using measured horizontal visibility data. The modified model is used to compute Ångström turbidity coefficient for Brunei Darussalam using measured data on solar radiation for a period of 5 years (1990–1994). The data were collected from the Meteorological Department of Civil Aviation, Ministry of Communication, Brunei Darussalam. A comparison of the modified model is made with those by Pinazo and Iqbal. The preliminary calculations reveal that the modified model is capable of computing Ångström turbidity coefficient more accurately than that developed by Pinazo and it can be used to compute Ångström turbidity coefficient for any location irrespective of the climatological zones.     

Response of ductile metal sheet parameters to the cone angle of indenting conical tool and fracture toughness evaluation

The indentation and perforation of ductile metal sheet with a conical tool is accompanied by elastoplastic bending, stretching, plastic flow, and crack initiation and propagation. This ultimately results in material fracture in the form of petals. It has been observed that the perforation process is dependent upon the angle of the conical tool. Fracture toughness, crack initiation, work input before and after crack initiation, number of petals, and sheet and petal bending angles all depend on the tool angle. Crack initiation has resulted at minimum tool displacement for a tool angle α=45°, while minimum work input before and after the crack initiation is observed when the tool has an angle α=35°. The optimum range of tool angles for the indentation process is α=22.5 to 50°. In this range, the aluminum sheets showed minimum fracture toughness as well as minimum work input to overcome the offered resistance.     

Room Temperature Impedance and ac Conductivity Studies on Na-, K-Doped Tc-Enhanced High Tc Superconductors

Impedance and ac conductivity studies on parent Y–Ba–Cu–O and Na-, K-doped Tc-enhanced and other superconductors indicate that either the mechanism of ac conductivity or nature of charge carriers or both in the Na-, K-doped Y–Ba–Cu–O differ from the parent Y–Ba–Cu–O and other superconductors. This is indicated by the random walk type (RWT) model curve fittings.     

Blood lead levels in preschool children in Rawalpindi

Blood lead levels were determined in preschool children residing in Urban areas of Rawalpindi city. Of 92 (50 males and 42 females) children aged one to 5 years were included in the study. Blood lead levels ranged from 7 micrograms/dl to 34 micrograms/dl (mean 18.8 micrograms/dl). The mean lead levels were slightly higher in males (20.3 micrograms/dl) than in females (17.2 micrograms/dl) and over 90% children had lead levels above the acceptable limit of 10 micrograms/dl. Use of leaded petrol, contaminated surma, leaded paints and pica in children are common in our country and may lead to increased lead levels and appropriate measures should be taken to control this trend.     

Countercation intercalation and kinetics of charge transport during redox reactions of nickel hexacyanoferrate

The dynamics of charge propagation in nickel hexacyanoferrate, a model metal-substituted analogue of Prussian Blue-type cyanide-bridged systems, was considered in electrolytes containing potassium and other alkali metal cations. The apparent (effective) diffusion coefficients for charge transport were determined using a large-amplitude potential-step chronocoulometry and small-amplitude potential-step chronocoulometric potentiostatic intermittent titration. The dependence of diffusion coefficient on the potential applied is consistent with the intercalation like model of the counter-cation sorption/desorption during redox processes of nickel hexacyanoferrate. Some differences in diffusion coefficients may originate from distinct charge densities (membrane properties) of the oxidized and reduced metal hexacyanoferrate structures. The existence of strong attractive interactions between an alkali metal cation and the cyanometallate matrix is also expected. The overall dynamics of charge propagation seems to be controlled by transport of electrolyte cations within the film rather than by electron self-exchange (hopping) between the mixed-valence hexacyanoferrate(III,II) ionic sites.     

Thermally controlled molecular disassembly of a crosslinked polymer network by the incorporation of sterically hindered urea linkages

Crosslinked polymer networks are excellent materials for multiple applications. However, although their crosslinked structure gives them many positive attributes, it also makes them intractable. Therefore, it is exceedingly difficult to reprocess crosslinked networks without exposure to extreme degradation conditions. In this work, we were able to create a crosslinked network that showed controlled disassembly upon stimulus. It was found that a controlled network disassembly process could be invoked by the incorporation of sterically hindered urea linkages into the polymer network. The network was shown to disassemble upon exposure to heat, whereas in the absence of heat, the network was found to maintain its crosslinked structure. The disassembly temperature could be varied by careful selection of the cleaving agent. This work focuses on showing the controlled network disassembly of a crosslinked polymer matrix as a function of temperature. Herein, we describe the factors that control the disassembly temperature and conclude with a possible mechanism for the disassembly process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 856–864, 2002     

Experimental results of a supplementary technique for auto-reclosing EHV/UHV transmission lines

A technique to discriminate between the line charging inrush current and the current resulting on closing or auto-reclosing a faulted EHV/UHV transmission line has been implemented on a 32-b digital signal processor (DSP) board. The technique is based on the voltage signals before switching and the current signals. This technique is proposed to be a supplement to the main protection schemes for both single-circuit and double-circuit lines. The scheme is tested on a physical model of a transmission system with a source at each end. Laboratory tests show that the proposed technique is effective for three-pole and single-pole reclosing on a faulted or healthy line.