Taketoshi Hasegawa

A New AC Current Testing Method for Non-Destructive Insulation Tests

A new nondestructive diagnosis method is developed mainly for stator coil insulation of high voltage rotating machines as a result of analysis and experience on the behavior of a current of a sample under ac voltage application. A newly-defined parameter Y, measured in this method, equals tan, plus y, where y closely relates to void volume ratio in a sample. A new apparatus to measure Y automatically is also developed which shows experimentally several advantages in a practical test. Y-V patterns and y-V patterns by this method are verified to correlate well to insulation condition and residual breakdown voltage of a sample.

Surface Flashover on Printed Circuit Boards in Vacuum under Electron Beam Irradiation

This paper deals with the surface flashover characteristics of dielectric material during electron beam irradiation in vacuum in order to design the conductive patterns on printed circuit boards used inside a spacecraft adequately. The dielectric material and the electrodes printed on it were irradiated with electrons of the energy of 3-10keV. DC high voltage was applied between the two electrodes during electron irradiation. The voltage was increased step-wisely until the surface flashover occurred on the dielectric. We obtained the result that the surface flashover voltage increased with the insulation distance between the electrodes. However, electron irradiation caused the flashover voltage to lower. The flashover voltage characteristics were obtained as parameters of the electrode distance and the energy of the electron beam

High‐frequency voltage oscillation in transformer windings and electrical breakdown properties of interturn insulation immersed in oil at VFT voltage

Switching operations in gas insulated switchgear (GIS) can generate very fast transient overvoltages (VFTO) which propagate in the GIS with little attenuation. When a transformer is directly connected to the GIS through a gas/oil bushing, the VFTO can enter the transformer and excite the voltage oscillation in the windings. In the paper, we firstly show a resonance phenomenon due to the superposition of the traveling waves which was found in the experiments using the coil windings of a 500 kV transformer. The fundamental resonance frequency ranged at about 2 MHz, and its voltage at the interturn (turn-to-turn) of the coil could reach 0.25 times of the applied voltage in the worst case. Secondly, the electrical breakdown properties of interturn insulation in oil were studied, applying the unipolar and bipolar voltages with 2 MHz oscillatory frequency. The breakdown voltages at the unipolar and bipolar VFT oscillatory stresses were about 1.25 and 1.40 times higher than that at the standard lighting impulse, respectively. We discuss the experimental breakdown stresses with the ones estimated from the analysis of VFTO in the transformer windings and also show the methods to cope with the VFTO.

Insulation Design of Printed Circuit Boards Under Electron Irradiation

This paper deals with the surface flashover characteristics of dielectric material during electron irradiation in vacuum in order to design the conductive patterns on printed circuit boards used inside spacecraft adequately. The dielectric material and the electrodes printed on it were irradiated with the electrons of the energy lower than 10keV. DC voltage was applied between the two electrodes during electron irradiation. The voltage was increased step-wisely until the surface flashover occurred on the dielectric. We obtained the result that the surface flashover voltage increased with the insulation distance between the electrodes. However, the flashover voltage in the case with electron irradiation was lower than that without electron irradiation. The flashover voltage characteristics were obtained as parameters of the insulation distance and the electron energy. The characteristics were explained by the currents flowing between the electrodes under electron irradiation.