Takayoshi Misaki

Computation of Three-Dimensional Electric Field Problems by a Surface Charge Method and its Application to Optimum Insulator Design

This paper describes an improved surface charge method for computation of three-dimensional electric field distribution and its application to optimum insulator design. In this method, each curved surface on which the charge is distributed is divided into many curved surface elements instead of planar elements. After computing numerically the charge distribution, the distributions of both potential and electric field are obtained. Because the use of many curved surface elements provides a good approximation of the insulator contour, the correction of insulator contour to achieve optimum insulator design can be performed smoothly.

Improved Structure Avoiding Local Field Intensification on Spacers in SF 6 Gas

Problems concerning local electric field intensification on a cone-type spacer which is fitted between flanges in SF6-gas-insulated apparatuses were investigated. Conventional structures, in which flat surfaces of the spacer come in contact with rounded corners of the flange, sometimes cause flashovers at considerably low voltages because of local field intensification. In the improved structure proposed by the authors, surface shape of the spacer and contact position are slightly changed in order to avoid local field intensification. Field calculations and experiments verified that the improved structure is effective for actual use.Problems concerning local electric field intensification on a cone-type spacer which is fitted between flanges in SF6-gas-insulated apparatuses were investigated. Conventional structures, in which flat surfaces of the spacer come in contact with rounded corners of the flange, sometimes cause flashovers at considerably low voltages because of local field intensification. In the improved structure proposed by the authors, surface shape of the spacer and contact position are slightly changed in order to avoid local field intensification. Field calculations and experiments verified that the improved structure is effective for actual use.

Techniques for boundary element analysis of three-dimensional eddy current distribution

An analysis of three-dimensional eddy-current distribution by a boundary-element method using field vector variables is described. A triangular element is used as a boundary element. The electric field vector and magnetic flux density vector are defined as the unknown vectors and are assumed to be constant on each triangular element. For forming simultaneous equations, the computation point on the triangular element is set at the null point, where the triangular element itself does not induce tangential components of the electric field and the magnetic flux density. >

Computation accuracies of boundary element method and finite element method in transient eddy current analysis

The computation accuracies of the boundary-element method (BEM) and finite-element method (FEM) in transient eddy-current problems are compared by using a slot-embedded conductor model and a diffusion model that can be solved theoretically. For computing the vector potential or magnetic flux density it is shown that larger time-step width can be chosen in the BEM than in the FEM method for the same accuracy. >

Computation of three-dimensional electromagnetic field in the eddy-current testing of steel pipes

The computation of three-dimensional electromagnetic field distributions in the eddy-current testing for holes in steel pipes is described. A boundary element method with vector variables was used to compute the eddy-current and magnetic-flux-density distributions. Computed and experimental results for the magnetic flux density on the inner surface are compared, and the mechanism of defect detection in steel pipes is clarified. >