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In order to study the effect of glaze erosion on the performance of porcelain post insulator, an inclined plane (IP) test similar to IEC 60587 standard was conducted on a cylindrical insulator sample under laboratory conditions for ac voltage, and a new test method, called graphite-layer-based glaze erosion test was proposed in this paper and performed on the sheds of a 40.5 kV post insulator. The experimental details of the graphite-layerbased glaze erosion test was introduced, the technical points of which are coating a graphite layer on the surface of the shed using a brush mold which contains multiple hollowed-out rhombic grids, and arranging high voltage electrode at shed root and grounded electrode at shed edge respectively at both ends of the graphite layer, so as to form continuous and stable surface arcing under ac voltage and therefore achieve desired glaze electrical erosion effect. The graphite layer is a uniform viscous mixture made up with flake graphite and liquid glue according to a quality ratio of 1:1.2. The arcing process, arc current characteristics, surface temperature, and glaze erosion appearance were analyzed. Leakage current under power frequency voltage and flashover voltage of the eroded cylindrical insulator by IP test were measured, while porosity test and scanning electron microscopy (SEM) tests were conducted on samples taken from the sheds after graphite-layer-based glaze erosion test. The results indicate that glaze erosion will decrease both electrical and mechanical performance of the porcelain post insulator. The new test method proposed in this paper has been proved to be effective for glaze erosion test and consumes much less time compared with IP test, which provides a new idea for accelerated tracking and erosion test of glaze and porcelain materials so as to study the aging characteristics of porcelain insulators. [ABSTRACT FROM AUTHOR]

There has been a significant interest in many technical applications and natural phenomena concerning two-phase mixture discharges (TPMDs). Few studies have focused on the influences of different macroparticles on TPMDs. The dielectric constant is usually considered to be the only factor affecting the discharges, but in this paper, 21 kinds of different dielectric materials were used to investigate the effects on TPMDs. By the experimental results, this paper reveals the effects of macroparticle sizes, and the dielectric constant has little influence. When the diameter of TPMs is less than about 0.01 mm, the percentage of the selection of TPMs is always smaller than 50%, the discharge path selects the air but TPM, and the breakdown voltage is higher than that in air. However, when the diameter is greater than about 0.1 mm, the conclusion is opposite. When the diameter is in the range of 0.01–0.1 mm, the TPMDs have a polarity effect. The dipole-enhanced approximation model is applied to explain the experimental phenomena. It is very important in TPMDs that the macroparticle dielectric constant, the saturation charge, and the adsorption/desorption process on the material, except the effects of TPMDs, are highly correlated with the macroparticle sizes. [ABSTRACT FROM AUTHOR]

The effects of corona-generated space charge on the resultant electric field near a conductor were determined both for a simulated test line and a corona cage, since both are used in predicting the corona behavior of EHV and UHV transmission lines. Programs were developed for the calculation of the potential, the electric field and the space charge distributions for a simulated test line and a corona cage. Algorithms based on the charge simulation and the finite-element methods were used to solve Poisson?s equation; and the method of characteristics to solve the current continuity equation. The resultant electric field on the ground plane of the two configurations was measured with a rotating field-mill, and the results fitted well with the calculated data. It was found the electric field at the surface of the conductor increased linearly, for both experimental configurations, before the voltage reached the corona inception value; but was reduced once corona-generated space charge was produced. The space charge and density distribution in the corona cage differed greatly from that around the test line: the electric field at the surface of the conductor in the test line decreased faster with voltage than that in the corona cage, the relative difference increasing as V/usb>app/Von was raised. The difference reached an asymptote of about 16% when the applied voltage was about 25% above the corona inception level. [ABSTRACT FROM AUTHOR]