Akira Yamagishi

Investigation of charge behavior in low viscosity silicone liquid by kerr electro-optic field measurement

From the viewpoints of less flammability and environment protection, a new type of electrical insulating liquid for power transformers is strongly required. Low viscosity silicone liquid (20 cSt) is suitable for the requirements owing to the following excellent features; high flash point, low environmental impact concerning pollution and high chemical stability. In this paper, we investigated the charge behavior under dc voltage application by direct measurement of the electric field using Kerr electro-optic method. At first, Kerr constant of 20 cSt silicone liquid was investigated. Then, the time dependence of electric field strength in silicone liquid / pressboard (PB) composite systems was measured. The time constant of the decay was much larger in silicone liquid than in mineral oil. We discussed the charge behavior based on the physical properties of silicone liquid and we suggested that the influence of negative charge injection from a negative electrode¿s surface in silicone liquid played a significant role because of the high volume resistivity.

Analysis of gasses generated by electrical discharges in low viscosity silicone oil

Silicone oil has merits of less flammability and excellent environment-friendliness. High-viscosity silicone oil of 50 cSt has been widely applied to power and distribution transformers. Recently, application of low-viscosity silicone oil of 20 cSt to transformers has been considered for its excellent cooling performance. Detection of incipient fault conditions in low-viscosity silicone oil immersed transformers becomes more important when they are operated in electric power systems. Detection of certain gases generated in a transformer is usually the useful indication of an abnormal condition. To clarify its applicability to a low-viscosity silicone oil immersed transformer, this paper described gas characteristics generated by electrical discharges in detail. It was clarified that the identification of abnormal conditions are possible by considering the amounts and types of generated gases. Finally, gas characteristics were compared with those in 50 cSt silicone oil and mineral oil.

A system to detect small amounts of oil leakage with oil visualization for transformers using fluorescence recognition

A system has been developed for detecting and visualizing small amounts of oil leakage from a transformer. The system uses a method of detecting fluorescence emitted from oil when it is irradiated by black light. Image processing using the relationship between saturation and intensity in a hue-saturation-intensity color space is used to recognize the leaked oil. According to the saturation-intensity relationship, the intensity of a surface without oil adhesion linearly increases as saturation increases. The oil-adhered area on the surface showed higher intensity. An algorithm was constructed for automatically setting a threshold value line to recognize the oil. On the other hand, in order to recognize the specular reflection light noise, images obtained after black light irradiation from two directions were compared. The developed system using the algorithm can detect and visualize oil leakage from a transformer at an amount of less than 1 mL.

Recent trends of low-viscosity silicone liquid immersed transformers

In this paper we report on “verification of arcing in insulation fluid” and “fire resistance evaluation of insulation fluid” for accident spread prevention measures, as recent trends in low-viscosity (kinematic viscosity 20 mm/s2, (20cSt) at 25°C) silicone liquid immersed transformers. The “verification of arcing in insulation fluid”, which simulated transformer internal short-circuit accidents, indicated that protection coordination similar to that for oil-immersed transformers can probably be applied in silicone liquid immersed transformers as well, and also clarified the produced gas patterns. The “fire resistance evaluation of insulation fluid”, which simulated transformer disaster accidents, quantitatively evaluated the fire resistance and self-extinguishing performance of 20cSt silicone liquid.