The effect of coil parameters on the distribution of steep-frontedsurges in machine windings

The authors identify the coil parameters that are of importance, when assessing interturn voltages produced by steep-fronted transients. The studies are based on a multiconductor transmission line computer model of a machine winding energized by a simple ramp function. Variations in interturn voltages produced by changes in insulation thickness, insulation permittivity, turn geometry, coil length and number of turns are examined and certain guidelines for avoiding high interturn voltages are evaluated. An application study is included to show how interturn voltages can be significantly reduced by applying these guidelines     

An improved arc model before current zero based on the combined Mayr and Cassie arc models

A computer model that describes the dynamic arc behavior in the high- and low-current regions before current zero is proposed. The model divides the current and voltage waveform in two regions. A differential equation for both regions which unifies current and voltage time derivatives is obtained by means of a generalized function method. The computer waveforms reproduced with the model show good agreement with measured results published in in the low and high current regions, but further comparison with other test measurements are required to know if the model has any feature of predictability.     

Fault analysis in TCSC-compensated lines using wavelets and a PNN

This paper describes an algorithm to detect, localize and classify fault events in overhead transmission lines compensated with a thyristor-controlled series capacitor (TCSC). During a fault event, a complex pattern of traveling wave reflections and refractions is generated at the point of fault inception. The proposed algorithm uses the discrete wavelet transform combined with a probabilistic neural network to analyze all this information and determine whether a fault condition exists in the line, the fault type and also the fault distance. In order to assess the algorithm performance, several studies were carried out under varied conditions. The obtained results demonstrate that the algorithm accuracy for calculating the fault distance is smaller than 1% of the total line length, and a 100% efficiency for determining the fault type. The algorithm is also immune to harmonic interaction due to low-frequency harmonics generated by the TCSC. A comparative advantage over previous algorithms for TCSC-compensated transmission lines is the fact that the proposed algorithm not only identifies the faulted line section but also localizes accurately the distance to the fault, using only measurements at one end of the line.

     

Fluoroalkylated silicon-containing surfaces-estimation of solid-surface energy

The design of robust omniphobic surfaces, which are not wetted by low-surface-tension liquids such as octane (γlv=21.6 mN/m) and methanol (γlv=22.7 mN/m), requires an appropriately chosen surface micro/nanotexture in addition to a low solid-surface energy (γsv). 1H,1H,2H,2H-Heptadecafluorodecyl polyhedral oligomeric silsesquioxane (fluorodecyl POSS) offers one of the lowest solid-surface energy values ever reported (γsv≈10 mN/m) and has become the molecule of choice for coating textured surfaces. In this work, we synthesize and evaluate a series of related molecules that either retain the POSS cage and differ in fluoroalkyl chain length or that retain the fluorodecyl chains surrounding a linear or cyclic molecular structure. The solid-surface energy (γsv) of these molecules was estimated using contact angle measurements on flat spin-coated silicon wafer surfaces. Zisman analysis was performed using a homologous series of n-alkanes (15.5≤γlv≤27.5 mN/m), whereas Girifalco-Good analysis was performed using a set of polar and nonpolar liquids with a wider range of liquid surface tension (15.5≤γlv≤72.1 mN/m). The hydrogen-bond-donating, hydrogen-bond-accepting, polar, and nonpolar (dispersion) contributions to the solid-surface energy of each compound were determined by probing the surfaces using a set of three liquid droplets of either acetone, chloroform, and dodecane or diiodomethane, dimethyl sulfoxide, and water.     

A computer model for calculating steep-fronted surge distributionin machine windings

A computer model for predicting the distribution of steep-fronted surges in the line-end coils of machine windings is described. The model uses certain aspects of previous models combined to achieve simplification of solution while retaining accuracy. The solution technique is based on multiconductor transmission line theory and modal analysis. Parameter evaluation is based on the relationship between capacitance, inductance and wave velocity. The theory is extended to include a number of series-connected coils. Experimental and computational results are presented to illustrate the application and accuracy of the model     

A machine winding model for switching transient studies using network synthesis

This paper describes a computer model for calculating the surge propagation in the winding of electrical machines. The model considers the winding as a combination of a multiconductor transmission line and a network of lumped parameters. The frequency dependence of the winding electrical parameters is calculated and incorporated into the analysis by means of Foster and Cauer circuits. The multiconductor transmission line provides the surge propagation characteristics for the winding model and its parameters are calculated from machine design characteristics. Finally, this hybrid model is validated by a comparison of calculated and measured results inside a high-voltage machine winding.     

Theoretical chemical characterization of phosphate-metal-humic complexes and relationships with their effects on both phosphorus soil fixation and phosphorus availability for plants

BACKGROUND: Previous studies showed that phosphate can be complexed by humic acids (HA) through stable metal (M) bridges (PMHA). We studied the thermodynamic properties of PMHA and their relationships with the ability of PMHA to both decrease soil P fixation and increase P availability for plants. With this aim, we studied the theoretical stability of PFeHA, PAlHA and PCaHA by molecular modelling methods in relation to the degree and intensity of P absorption in soils and the ability of plants to take up complexed P. RESULTS: A density functional theory (DFT) quantum chemical study enabled us to obtain stable structures for the three PMHA complexes in water solution. The theoretical stabilities (ΔG⁰) were consistent with that for apparent stability obtained by Scatchard method, PFeHA ≥ PAlHA > PCaHA, though the differences were clearer by the DFT method. Also the reduction of soil P fixation and the release of P from PMHA in the presence of an anionic resin confirmed the stability order of the different PMHA. Plant studies confirmed the ability of diverse plant species to take up both P and metal complexed in PMHA. CONCLUSION: The results indicated the potential efficiency of PMHA‐based fertilizers to optimize P fertilization for crops cultivated in soils with high P fixation ability. Copyright © 2012 Society of Chemical Industry     

A three-phase model for surge distribution studies in electricalmachines

This paper describes a computer model for surge distribution studies in the windings of electrical machines. The computer model takes the coil as the basis for the analysis and uses multiconductor transmission line theory to obtain the transference matrix for the winding. Several practical formulations based on machine design characteristics are used for calculating electrical parameters. Flux penetration into the iron core and mutual coupling between coils in different phase windings are incorporated into the analysis. The model was validated by a comparison of predicted and calculated results in a high voltage motor     

Calculation of machine winding electrical parameters at highfrequencies for switching transient studies

This paper describes a multiconductor transmission line approach for calculating the machine winding electrical parameters for switching transient studies. The technique is based upon the solution of the one dimension diffusion equation in the slot of electrical machines. The coil electrical parameters are calculated considering both the magnetic flux in the iron and in the air. Several practical formulations for calculating the winding electrical parameter are proposed which take into account the machine winding design characteristics. The computer models are validated by a comparison of measured and calculated results in two high voltage induction motors     

Calculation of interturn voltages in machine windings duringswitching transients measured on terminals

This paper describes a technique for calculating interturn voltages in machine windings during transient conditions. The technique is based on the measurement of switching transients at the machine terminals and computer simulation of the surge travelling through the winding. The machine winding is treated as a multiconductor transmission line and the discrete Fourier transform and convolution techniques are used for calculating the switching transient distribution along the winding. Switching transients results obtained on two electrical motors in the Manzanillo II power plant are used in the analysis