Kenji Sakanishi

Investigation of Contamination Flashover Voltage of A Porcelain Long Rod Insulator with Silicone Rubber Coating on The Trunks

Higher flashover voltages of transmission line polymer insulators were found to be due to large ratio of shed to trunk diameter. This causes current density at the trunks to be very high and all the trunks get dried causing the applied voltage to the whole insulator divided and allotted to individual trunks. Similar effect was aimed by applying hydrophobic silicone rubber coating to the trunks of a porcelain long rod insulator. In this paper, investigation results of the contamination flashover voltages of porcelain long rod insulators coated with RTV silicone rubber coating on the trunks are presented

Improvement of Contamination Flashover Voltage Performance of Cylindrical Porcelain Insulators

Superior contamination flashover voltage performance of polymer insulators for transmission or distribution line is attributable not only to the hydrophobicity of silicone rubber housing material but also to their configurations. In the case of transmission or distribution line polymer insulators, core diameters are small and so the ratio of shed to core diameters is very large enough to improve the voltage distribution along the insulator owing to the divided and allotted voltages to its individual core portions having much higher surface resistances compared with shed portions due to the heavier leakage current density. We tried to improve the contamination flashover voltage performance of a porcelain long-rod insulator by applying hydrophobic silicone rubber coating only to all its core surfaces without coating shed surfaces and successful results have been confirmed. In this paper, contamination flashover voltage performances were evaluated among four kinds of specimens with different silicone rubber coatings by the salt fog test method. The detailed investigation results are presented.

Effect of Non-soluble Contaminants on The Flashover Voltages of Hydrophobic Polymer Insulators

Different non-soluble materials are used as non-soluble contaminants in the contamination flashover voltage tests of insulators. Flashover voltage of a porcelain insulator is influenced by the kind of non-soluble contaminants. Kind of non-soluble contaminants may have a significant effect on the flashover voltage performance of polymer insulators. In this paper we present comparative investigation results of the flashover voltage and hydrophobicity recovery characteristics among three most common non soluble contaminants like Tonoko, Kieselguhr and Kaolin

Consideration into CIGRE round robin contamination test of polymer insulators

Hydrophobic polymer insulators show higher contamination flashover voltages compared with ceramic insulators, but standard artificial contamination test methods have not yet been established. Test methods used for ceramic insulators are now usually used also for polymer insulators, but due to different surface properties and configurations between ceramic and polymer insulators, test procedures and conditions for ceramic insulators may not be pertinent for assessing polymer insulators. Under such circumstances, CIGRE WG C4.303 started round robin tests and results from four laboratories were presented but some differences were obtained. In order to clarify the factors for such differences, effects of ambient temperature, artificial fog injection rate into test chamber and kind of non-soluble contaminants were investigated. Any significant effect of ambient temperature on contamination flashover voltage was not found, but discernible effect of fog injection rate was found on the flashover voltage of longer time rested insulators. In addition, about 10% difference in flashover voltage was found between Kaolin and Tonoko both under the no rest time and the longer rest time conditions.

Evaluation Methods of Contamination Flashover Voltage Performance of Semi-conducting Glaze Insulators

Superior insulation performance of semi-conducting glaze porcelain insulators under contaminated and wet conditions is attributable mainly to its drying effect by the leakage current flowing in the glaze. Contamination flashover voltages of semi-conducting glaze insulators have been evaluated by the same test methods for normal porcelain and glass insulators. In the case of the clean fog test, 3 to 5 g/m3 of fog density has been used also for semi-conducting glaze insulators. Now in view of the importance of drying effect on the contamination flashover voltages of semi-conducting glaze insulators, we considered that heavier fog density might give lower flashover voltages. In this paper, firstly, contamination flashover voltage test results under the heavier fog density of 13 g/m3, compared with the results under the conventional fog density of 3 to 5 g/m3, shall be presented. Conventional contamination design criterion of this type insulator under cold-wet switch-on conditions is based on the results by the test procedure where a contaminated and dried specimen insulator is wetted in artificial fog before applying a test voltage. However, in most cases of the cold-wet switch-on conditions, time durations without energization are very short as is the case of lightning, and so drying effect by the energization before de-energization may be remaining to some extent at the time of re-energization. We had made tests simulating such conditions. Of course, enhanced surface resistances at the time of re-enegization could be confirmed, but, unexpectedly, lower flashover voltages were obtained compared with the values estimated from the conventional relationship between the surface resistance and the minimum flashover voltage. Such results may be explained as follows; By the pre-energization, dry bands are formed and voltage distribution along the insulator surface becomes very non-uniform, resulting in lower flashover voltages. In this paper, secondly, additional investigation results of the effect of de-erergized time duration on the flashover voltage of a contaminated semi-conducting glaze insulator by both the clean fog and the salt fog tests shall be presented.

Cold-wet-switch-on characteristics of semi-conducting glaze insulators

Semi-conducting glaze insulators show higher flashover voltages under contaminated conditions when they are continuously energized with the operating voltage. Such a superior performance is owing mainly to the drying effect by the Joules heating caused by the leakage current flowing in the semi-conducting glaze layer. So, under cold-wet-switch-on conditions, in which drying effect does not exist, such a superior performance cannot be expected. Based on the test data obtained under heavily wet conditions simulating the worst wet conditions in fields, present design withstand voltage is proposed. However, considering shorter interruption duration in most of the outages in electric power systems, the present design criterion may not be adequate for rationalized actual applications. Now we are investigating the time variation of surface resistance after interrupting the operating voltage on artificially contaminated insulators under natural wet conditions. Based on the analysis of the data obtained so far, a higher design withstand voltage can be practically proposed even for cold-wet-switch-on conditions.

An investigation of DC contamination flashover phenomena of suspension insulators

A description is given of the basic results of an investigation into DC contamination flashover phenomena of suspension insulators. A novel real-time system was developed that was capable of observing the partial discharge arcs visually and the leakage current quantitatively. Insulators were tested and the leakage current was analyzed, with the result that the effectiveness of the system was confirmed.<<ETX>>