Research on Differential Protection of Generator Based on New Braking Mode

In view of the difficulties in coordination between reliability and sensitivity of conventional generator differential protection, this paper presents a novel generator differential protection scheme based on a new braking method. On the basis of the mathematical model of the field-circuit coupling method and the electrical network cascade characteristics, the stator windings were combined and decoupled by the improved six-sequence component method to eliminate electromagnetic coupling between winding coils. In accordance with the basic characteristics of longitudinal impedance, the function of sub-item discrimination was realized. Numerous simulations and the up-to-date dynamic experiments showed that the proposed method has good state discrimination ability and can effectively resist the influence of current transformer saturation. Thus, it has an excellent prospect for engineering promotion.

Association Between Resistance to Cerebrospinal Fluid Flow Near the Foramen Magnum and Cough-Associated Headache in Adult Chiari Malformation Type I

Background and Purpose: Cough-associated headaches (CAH) are thought to be distinctive for Chiari malformation type I (CMI) patients and have been shown to be related to the motion of cerebrospinal fluid (CSF) near the foramen magnum. We used computational fluid dynamics (CFD) to compute patient-specific resistance to CSF motion in the spinal canal for CMI patients to determine its accuracy in predicting CAH. Methods: 51 symptomatic CMI patients with cerebellar tonsillar position (CTP) = 5 mm were included in this study. The patients were divided into two groups based on their symptoms (CAH and non-CAH) by review of the neurosurgical records. CFD was utilized to simulate CSF motion and the integrated longitudinal impedance (ILI) was calculated for all patients. A receiver operating characteristic (ROC) curve was evaluated for its accuracy in predicting CAH. Results: The ILI for CMI patients with CAH (776 dyn/cm5, 288-1444 dyn/cm5; median, inter-quartile range) was significantly larger compared to non-CAH (285 dyn/cm5, 187-450 dyn/cm5; p = .001). The ILI was more accurate in predicting CAH in CMI patients than the CTP when the comparison was made using the area under the ROC curve (0.77 and 0.70, for ILI and CTP, respectively). ILI = 750 dyn/cm5 had a sensitivity of 50% and a specificity of 95% in predicting CAH. Conclusions: ILI is a parameter, used to assess CSF blockage in the spinal canal and can predict patients with and without CAH with greater accuracy than CTP.

The influence of ground wires on the resistance and reactance of high voltage overhead power lines

In this paper, the influence of ground wires on the resistance and reactance (longitudinal impedance) of high voltage overhead power lines (OPLs) is considered and the method for its calculation is described in detail. This is important considering the power flow calculation and the design of the protection system of OPLs, especially those which use distance relays. In addition to symmetric, asymmetric operating conditions of OPLs are also studied, for the analysis of which symmetric components are used. Specifically, this meant the calculation of longitudinal impedances of OPL for positive, negative and zero sequences in each considered case. Special attention is paid to the symmetric system with zero sequences, because the influence of ground wires on the change of longitudinal impedance of OPLs is the greatest in that case. The cases of OPLs with one (110 kV OPL) and two (400 kV OPL) ground wires are considered, using the values o f their parameters that can be found in real systems. Values of longitudinal impedances, obtained with and without ground wires influence or the influence of some of their parameters, are compared, based on which appropriate conclusion is made.

An Analytical Solution for Longitudinal Impedance of a Large-Diameter Floating Pile in Soil with Radial Heterogeneity and Viscous-Type Damping

An analytical model is presented for solving the longitudinal complex impedance of a large-diameter floating pile in viscoelastic surrounding soil with radial heterogeneity and viscous-type damping, taking the effect of three-dimensional wave propagation of soil and lateral inertia of the pile shaft into account. The corresponding analytical solution for longitudinal impedance is also derived and validated via comparisons with existing solutions. The influences of the pile length, Poisson’s ratio of the pile shaft and the viscous damping coefficient, as well as the degree and radius of disturbed surrounding soil, on the longitudinal impedance of the pile shaft are examined by performing parametric analyses. It is demonstrated that the proposed analytical model and solution are suitable for the longitudinal vibration problem of a large-diameter pile and radially inhomogeneous surrounding soil, especially when the pile slenderness is low. In addition, the present solution can be easily degenerated to describe the longitudinal vibration problem relating to a large-diameter floating pile in radially homogenous soil or a pile with fixed-end supports.

Perturbation analysis for pulsatile flow of Carreau fluid through tapered stenotic arteries

The pulsatile flow of blood in a tapered narrow artery with overlapping time-dependent stenosis is mathematically analyzed, modeling blood as Carreau fluid. Perturbation method is employed for solving the resulting nonlinear system of equations along with the appropriate boundary conditions. The analytic solutions to the pressure gradient, velocity distribution, flow rate, wall shear stress and longitudinal impedance to flow are obtained in the asymptotic form. The variation of the aforesaid flow quantities with respect to various physical parameters such as maximum depth of the stenosis, angle of tapering of the artery, power law index, Reynolds number, pulsatile amplitude of the flow and Weissenberg number is investigated. It is found that the wall shear stress and longitudinal impedance to flow increase with the increase of the angle of tapering of the artery, the maximum depth of the stenosis and pulsatile Reynolds number and these decrease with the increase of the amplitude of the flow, power law index and Weissenberg number. The mean velocity of blood decreases significantly with the increase of the artery radius, maximum depth of the stenosis, angle of tapering of the artery.