The life of a transformer is limited by the degradation of its solid insulation. Winding conductors and other solid insulation materials in oil-immersed transformers have been insulated using cellulose products. For many years, manufacturers have met the needs of special applications by designing transformers using thermally upgraded materials to achieve lighter weight, higher power density and increased life. Recently, the effects of thermally upgraded insulation on diagnostic techniques such as gas-in-oil analysis, and indicators of their insulation degradation, have been reviewed. This paper describes evaluations of amine-impregnated thermally upgraded paper insulation's thermal degradation characteristics and decomposition reactions in mineral transformer oil. The thermal resistance of the thermally upgraded paper is evaluated by comparison with Kraft paper insulation. Further, aging degradation mechanisms of decompositional degradation of the thermally upgraded paper due to aging in mineral transformer oil are proposed.
In the present work, prebreakdown phenomena in dielectric liquids which have various molecular structure, especially those with chlorine or fluorine atoms and some double bonds included in their molecular formula, are observed in detail for positive and negative point polarities, under the application of an impulse voltage (1.1/225 µs) to the point electrode. As test liquids, cyclic hydrocarbon liquids such as cyclohexane, benzene, chlorocyclohexane, monochlorobenzene, hexafluorobenzene, and cyclohexene are used. Results obtained in these liquids are compared with those obtained in straight‐chain hydrocarbon liquids.As a result, the propagation of negative streamers, especially in dielectric liquids with chlorine or fluorine atoms in their molecular formula, is promoted, whereas the propagation of positive streamers in dielectric liquids with some double bonds is promoted. The former is related to a large electron affinity, the latter is due to π electrons, for both cyclic and straight‐chain hydrocarbon liquids. © 2002 Scripta Technica, Electr Eng Jpn, 139(1): 1–8, 2002; DOI 10.1002/eej.1140
This experimental study was carried out on the ignition and combustion behavior of insulation fluids, such as mineral oil, 20cSt and 50cSt silicone liquids, and synthetic ester oil, for transformers using a cone calorimeter. We focused on the fire safety performance of the silicone liquids that showed significant environmental advantages compared to other fluids, because silicone liquid is substantial environmental safety as it changes into natural materials such as SiO 2 , H 2 O and CO 2 by hydrolysis.It is important and necessary to evaluate the fire safety performance of silicone liquid as well as other insulation liquids. At least two kinds of physical information, ignitability and combustibility (or combustion behavior), are needed to achieve the fire safety evaluation expected for these insulation liquids. The ignitabilty test was carried out as the first specification on the correlation between ignition time (t ig ) and radiant heat flux on the surface of each liquid for an evaluation of ignitability. The IEC 60695-8-3 (draft) was applied partly to carry out the tests, and recommends the use of a square pan. However, in our tests, two types of pans, circular and square, were used to clear the thermal influence given by the four corners of a square pan. Figure 1 shows the correlation between the inverse square root of ignition time (t ig ) and radiant heat fluxes. Figure 1 shows that these insulation liquids behaved as thermally-thick material as they were exposed to radiant heat flux. Almost the same Fig. 1. Simulated correlation between inverse square root of ignition time (t ig ) and radiant heat flux to the samples trends were observed in thermal inertia and in ignition time at critical radiant heat flux for the silicone liquids and the synthetic ester oil, and 20cSt and 50cSt silicone liquids indicated almost the same burning behavior. The critical time to ignition of the mineral oil was shortest within these insulation liquids. Based on heat transfer mechanism, we established a simulation of the ignition time using Eq. (1), taking the thermal parameters of conductivity, density, and specific heat for each insulation fluid.Eqn.(1) provided good agreement for those cooling-insulation fluids in the correlation vs radiant heat flux as are shown by lines in Fig. 1. Figure 2 shows the time histories for the heat release rates during a test period of 1800 seconds. Mineral oil and the synthetic ester oil showed high peak heat release rates; otherwise 20cSt silicone liquid showed a lower and reducing the heat release rate with selfextinguishing properties.Based on the experimental results using the cone calorimeter, the silicone liquids showed the most excellent performance in fire safety among these insulation liquids. Kyoko Kamiya * * * Non-memberSilicone liquid has the high performance in fire safety showing fire resistance by self-extinguishing, and that is less environmentally pollutant compared with mineral oil. Applicability of silicone liquid of 20cSt to transformers was investigated from the view poi...
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