为有效提高变电站接地网导体故障诊断的准确性,以某35 k V变电站为依托,基于量纲相似原理设计和定制了不规则形状的接地网模型,根据接地网模型的地表电位和地表磁感应强度的计算结果,通过模拟典型故障,对采用地表电位和磁感应强度诊断...为有效提高变电站接地网导体故障诊断的准确性,以某35 k V变电站为依托,基于量纲相似原理设计和定制了不规则形状的接地网模型,根据接地网模型的地表电位和地表磁感应强度的计算结果,通过模拟典型故障,对采用地表电位和磁感应强度诊断接地网典型故障的测试结果进行了对比,总结了接地网典型故障时地表电位和磁感应强度的变化规律,据此提出了基于灰色关联理论的接地网状态评价指标。结果表明,接地网导体节点处电位较高,网孔上方地表电位略低;导体上方磁感应强度较高,且激励电流注入点处的地表磁感应强度最大;所提出的接地网导体健全度评价指标可准确判断接地网故障类型和故障位置。展开更多
two equations for the calculation of surface tension of pure liquids are derived based on statistical thermodyanics by expressing the intermolecular potential as lennard-Jones pair potential.This method is simple,accu...two equations for the calculation of surface tension of pure liquids are derived based on statistical thermodyanics by expressing the intermolecular potential as lennard-Jones pair potential.This method is simple,accurate and easy to use.The calculation results for the 22 pure liquids show that these equations are superior to the empirical forula and other theoretical equations.The average relative deviations for these two equations are within 5% and 1.5% respectively.展开更多
Analytical and numerical simulation techniques have been developed for the calculation of earth resistance/ impedance and to estimate the potential distribution in the vicinity of earth electrodes.However,very little ...Analytical and numerical simulation techniques have been developed for the calculation of earth resistance/ impedance and to estimate the potential distribution in the vicinity of earth electrodes.However,very little literature is available on experimental validation of these calculation techniques.To address this,a programme of experimental tests on various earth electrodes has been carried out at the lower water reservoir of a hydro pumped-storage power station in North Wales.In this paper,the earthing test facility at Dinorwig power station is described including the details of the experimental set up.The results from experimental tests on a 5 mX5 m earth grid,immersed in water and energized under ac,dc and impulse,are presented.The values of measured earth resistance/impedance and water surface potential distributions are compared with those obtained from analytical calculations and detailed numerical computer simulations.展开更多
DC magnetic biasing problem,caused by the DC grounding electrode, threatened the safe operation of AC power grid. In this paper, the characteristics of the soil stratification near DC grounding electrode was researche...DC magnetic biasing problem,caused by the DC grounding electrode, threatened the safe operation of AC power grid. In this paper, the characteristics of the soil stratification near DC grounding electrode was researched. The AC-DC interconnected large-scale system model under the monopole operation mode was established. The earth surface potential and DC current distribution in various stations under the different surface thickness was calculated. Some useful conclusions are drawn from the analyzed results.展开更多
The potential based low order surface panel method is used to predict the hydrodynamic performance of marine propellers. In present method the hyperboloidal quadrilateral panels are employed to avoid the gap between t...The potential based low order surface panel method is used to predict the hydrodynamic performance of marine propellers. In present method the hyperboloidal quadrilateral panels are employed to avoid the gap between the panels. The influence coefficients of panels are calculated by Morino’s analytical formulations for increasing numerically calculating speed. The pressure Kutta condition is satisfied on the trailing edge of propeller blade by Newton-Raphson iterative procedure. Therefore the pressure coefficients of the suction and pressure faces of blade are equal on trailing edge. The method developed by Yanagizawa is used to determine the velocities on propeller surface, and to avoid the singularity in the numerical differentiation. The predicted pressure distributions and open water performances of general propellers and highly skewed propellers have a good agreement with experimental dat and other calculation results.展开更多
文摘为有效提高变电站接地网导体故障诊断的准确性,以某35 k V变电站为依托,基于量纲相似原理设计和定制了不规则形状的接地网模型,根据接地网模型的地表电位和地表磁感应强度的计算结果,通过模拟典型故障,对采用地表电位和磁感应强度诊断接地网典型故障的测试结果进行了对比,总结了接地网典型故障时地表电位和磁感应强度的变化规律,据此提出了基于灰色关联理论的接地网状态评价指标。结果表明,接地网导体节点处电位较高,网孔上方地表电位略低;导体上方磁感应强度较高,且激励电流注入点处的地表磁感应强度最大;所提出的接地网导体健全度评价指标可准确判断接地网故障类型和故障位置。
文摘two equations for the calculation of surface tension of pure liquids are derived based on statistical thermodyanics by expressing the intermolecular potential as lennard-Jones pair potential.This method is simple,accurate and easy to use.The calculation results for the 22 pure liquids show that these equations are superior to the empirical forula and other theoretical equations.The average relative deviations for these two equations are within 5% and 1.5% respectively.
文摘Analytical and numerical simulation techniques have been developed for the calculation of earth resistance/ impedance and to estimate the potential distribution in the vicinity of earth electrodes.However,very little literature is available on experimental validation of these calculation techniques.To address this,a programme of experimental tests on various earth electrodes has been carried out at the lower water reservoir of a hydro pumped-storage power station in North Wales.In this paper,the earthing test facility at Dinorwig power station is described including the details of the experimental set up.The results from experimental tests on a 5 mX5 m earth grid,immersed in water and energized under ac,dc and impulse,are presented.The values of measured earth resistance/impedance and water surface potential distributions are compared with those obtained from analytical calculations and detailed numerical computer simulations.
文摘DC magnetic biasing problem,caused by the DC grounding electrode, threatened the safe operation of AC power grid. In this paper, the characteristics of the soil stratification near DC grounding electrode was researched. The AC-DC interconnected large-scale system model under the monopole operation mode was established. The earth surface potential and DC current distribution in various stations under the different surface thickness was calculated. Some useful conclusions are drawn from the analyzed results.
文摘The potential based low order surface panel method is used to predict the hydrodynamic performance of marine propellers. In present method the hyperboloidal quadrilateral panels are employed to avoid the gap between the panels. The influence coefficients of panels are calculated by Morino’s analytical formulations for increasing numerically calculating speed. The pressure Kutta condition is satisfied on the trailing edge of propeller blade by Newton-Raphson iterative procedure. Therefore the pressure coefficients of the suction and pressure faces of blade are equal on trailing edge. The method developed by Yanagizawa is used to determine the velocities on propeller surface, and to avoid the singularity in the numerical differentiation. The predicted pressure distributions and open water performances of general propellers and highly skewed propellers have a good agreement with experimental dat and other calculation results.
