Pulsating corona discharge is considired as an important technical problem inhrent on UHV-AC overhead power transmission line.
This paper describes the characteristics of AC (50Hz) corona pulse and noise with a needle-plane system. Results obtained can be summarized as follows:
(1) The probability distribution of amplitude and repetition rate of corona pulse due to line voltage phase angle subjects to either Gaussian or Poisson's one in accordance with a certain radius curvature of needle electrode.
(2) A random pulse train model method for the analysis of corona noise was developed based on measurements of the corona pulse amplitude and repetition rate.
The measured results of QP-reading meter were qualitativerly similar to that analized by the random pulse train ones.
(3) The mean properties of corona pulses can be explained well by this an analytical method of noise.

View full abstract

The time lags of a gap in SF₆ gas has been often measured by using an impulse voltage application. However, these values of the time lags may be very long in some case. For this reason, a step impulse voltage which has no-decay of its tail was used in the present experiment and the changes in the time lags of an aluminum sphere gap with successive breakdowns in SF₆ were measured repeatedly using a digital timer and a personal computer. SF₆ was enclosed in the test chamber at atmospheric pressure. Results are summarized as follows.
(1) It is found that the mean time lag of the gap is decreased markedly with an increasing number of the breakdowns, but the change in a static breakdown voltage is only about 1%.
(2) When some desiccant such as activated alumina or synthetic zeolite is enclosed in the test chamber, any decrease in the mean time lag is never found with so many repeated breakdowns.
(3) In the present experiment, it may be considered that the cause of the decrease in the mean time lag with successive breakdowns is mainly attributable to the interaction of the electrode surface and the water vapor remaining in the chamber, neither to an increase in the roughness on the electrode surface nor to an accumulation of some decomposition products in the chamber.

View full abstract

The surface discharge phenomena on PET film with the thickhess from 0.05 to 1.05mm were investigated in the atmosphere under 1/40μs positive impulse voltage. The 50% flashover voltage V₅₀ and the 50% corona onset voltage Vc50 were measured varying the creeping distance from 0.4 to 10cm. The surface discharge phenomena were observed with an image converter camera together with an image intensifier under V₅₀.
As the results of this investigation, it has been found that the V₅₀-d characteristics are divided into two regions at a certain creeping distance d_c depended on the thickness of PET film. The V₅₀-d characteristics and the surface flashover processes in the creeping distance from 0.4cm to d_c are similar to those of acryl resin plate. However, the surface flashover characteristics and processes in the creeping distance from d_c to 10cm differ from those of acryl resin plate. In this region, the filamentary streamers decrease its length with the increase of specific capacitance of dielectric plate. These surface flashover processes are illustrated with the typical photographs, and are explained in connection with the surface flashover characteristics.

View full abstract

In order to analyze the surface current and the repulsive force in two dimensional magnetic field produced by external line currents and perfect diamagnetic bodies, the numerical methods, that is, the image method, the surface current method using Tchebycheff polynomials and the discrete surface current method (DSCM), are formalized. A configuration including infinitely long cylindri cal perfect diamagnetic bodies and an external line current is taken as an example. The surface current and the force are analyzed numerically in three ways. The first way is the DSCM using the zero Bn(Bn) boundary condition. The second is the DSCM using the constant vector potential (As) boundary condition. The last is the surface current method using Tchebycheff polynomials. Each solution is compared with the solution computed by the image method. As the result, in view of the accuracy of computation, the Bn boundary condition is found to be better than the As boundary condition. The DSCM has a sufficient accuracy in the computation of the force, and its computation time is shorter than that of other numerical methods because its algorithm is simple. When the number of contour points is increased in the DSCM, the DSCM has also the accuracy of the surface current density as the same order as that of the surface current method using Tchebycheff polynomials. As an explicit example, the magnetic field including perfect diamagnetic plates and a permanent magnet is analyzed using the DSCM. Finally, when the magnetic field including supercon ductors is analyzed using the numerical methods, the difference between the perfect diamagnetic body and the superconductor is discussed.

View full abstract