Hydrophobicity and insulated resistance of composite insulators with biological contamination
Biological growth has been observed on insulators installed all over the world. However its impact on the electrical performance is not well known. This paper described the investigations on the performance of post insulators with biological growth at a converter station. Both the ceramic and composite insulators were investigated. Two kinds of biological agents, lichen and mold were found on the composite insulator surface, but interestingly, no biological agent was found on the surface of ceramic insulators in the same environment condition. Lichen concentrated on the upper surface and mold on the lower surface. It seemed that the impact of lichen growth on the hydrophobicity is low, but hardly no hydrophobicity when mold growth. In addition, the insulated resistance test was carried out on the biologically contaminated insulators with and without salt water. Results show that whatever the surface was dry or not, high resistance were obtained with only less biological agent growth at the edge of insulators, but declined sharply when most of the surface was covered with lichen and mold. Therefore, it is strongly recommended to remove the mold, with which most the insulator surface is covered.
Performance of ceramic and polymeric distribution insulators with mold growth on its surface
There are several studies presented on insulator contamination by biological agents and its impact on the electrical performance is not well known. This paper describes a study developed in Bogotá, Colombia on electric performance of insulators contaminated with a common mold (i.e. Asperguillus Nigger). Ceramic and polymeric (non-ceramic) insulators used in Colombian distribution systems were selected. Biological contamination was made under controlled conditions using an isolated chamber that adjusts temperature, humidity and solar (ultraviolet) radiation. Electrical tests performed include flashover voltage and leakage currents measurements to determine how insulators are affected by bio-contamination. After laboratory tests, a significant impact on electrical performance of both types of insulators due to the biological contamination was noted.
VLA stereoscopy of solar active regions. 2: Altitude, relative motion, and center-to-limb darkening of 20 centimeter emission
A newly developed method of stereoscopic correlation is applied to solar radio maps at a wavelength of 20 cm. On the basis of stereoscopic correlations between radio maps obtained on 6 different days we establish the presence of 66 radio source components associated with 22 active regions. We find the following statistical results for active region source structures at 20 cm: 1. The observed lifetime is consistent with an exponential distribution having an e-folding time scale of greater than 18 days. 2. The average altitude of 20 cm sources is 25 +/- 15 Mm; 90% of the sources are found in heights less than 40 Mm. 3. The average diameter of discrete source structures is 48 +/- 15 Mm, implying a vertical/horizontal aspect ratio of q(sub A) approx. = 0.5. 4. No significant source motion has been found with respect to the standard differential rotation rate of Omega = 13.45 deg - ((3 deg (sin(exp 2)B)). 5. We find a statistical limb darkening, which can be described by the relation (T(sub B)(alpha))/T(sub B)(0)) = 0.4 + ((0.6(cos(exp 2) alpha)) for sources with T(sub B) greater than 0.5 MK. 6. The degree of source polarization is 15% +/- 10% and is independent of source location. 7. Bright sources (greater than or approximately equal to 0.5 MK), or equivalently, long-lived sources (greater than or approximately equal to 5 days) show a systematic variation of their altitude as function of the center-limb distance.