Compositions – Fluent dielectric – O-containing
Reexamination Certificate
1997-02-28
2001-08-28
Gupta, Yogendra N. (Department: 1751)
Compositions
Fluent dielectric
O-containing
C252S579000, C252S570000, C174S0170LF
Reexamination Certificate
active
06280659
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
N/A
BACKGROUND OF THE INVENTION
Internal parts of electrical power transformers and switchgear are normally immersed in an electrical insulating fluid. The electrical insulating fluid performs several functions and has specific requirements. It acts as an insulating medium between energized parts of the electrical equipment. It cools equipment by transferring heat from the windings and core of a transformer to a cooling surface. It quenches an arc created in the operation of switchgear or a fuse.
In case of accidental spills, the fluid should not be hazardous to animal or plant life. It should be biodegradable, meaning that microbes present in soil and water should be able to break down the chemical compounds of the fluid over time to substances that are less toxic, non-toxic, or inert. The fluid should be chemically stable during the useful life of the electrical equipment. It should exhibit low flammability, in case of a fire involving the electrical equipment.
Liquid insulating or dielectric fluids in electrical transformers and switchgear are well known in the art. See for example, U.S. Pat. Nos. 3,000,807; 3,095,366; 3,587,168; and 3,753,188. These patents describe the use of insulating fluids in equipment and the types of fluids so used. The most commonly used fluids have been petroleum oils, silicone fluids, or synthetic, hydrocarbon fluids. However, each of these materials has certain drawbacks, particularly with respect to environmental impact and biodegradability.
Silicone fluid, for example has been used widely as a fire-resistant insulating oil, but has been shown not to biodegrade to any appreciable extent. In addition, silicone fluid polymerizes when exposed to an electric arc, forming silicone gel particles that later interfere with the dielectric or insulating function of the fluid.
Petroleum fluids work well in most applications, but, depending on their chemistry, biodegrade very slowly. Spills of petroleum fluids have damaged soil and water ecosystems and can persist in the environment for years.
Petroleum, silicone, and synthetic hydrocarbon fluids thus perform well as insulating oils, but do not address the ever-increasing demands that fluids be more easily biodegraded and less harmful to the environment when spilled onto soil or water.
Due to lack of standardization of test methods and agreement on desired characteristics by industry, many levels of biodegradation exist. Petroleum products, for example, have been shown to biodegrade to a certain extent, if the proper conditions and species of bacteria are available in soil or water.
Because of their molecular structure, vegetable seed oils can be shown to biodegrade much more rapidly and completely than the above described electrical insulating fluids.
Vegetable seed oils have been tried as insulating oils in the past, but their use has been hindered by their poor stability. Vegetable seed oils age and become unstable at a much faster rate than petroleum or silicone products, especially at the elevated temperatures and in the presence of metal, typically found in electrical transformers.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to an improved vegetable seed oil based electrical insulating fluid that is stable in use, relatively nonflammable, rapidly and highly biodegradable, environmentally safe, and competitively inexpensive.
The present invention also relates to improved methods for manufacturing electrical insulation fluids of this type.
The fluid of the present invention preferably comprises highly saturated vegetable seed oils obtained from various sources including genetically improved species of plants. Vegetable seed oils can be used “as is” if they are naturally highly saturated. On the other hand, if the oil is highly unsaturated, it may still be used as an insulating oil if it is first processed by hydrogenation or other means to increase the degree of saturation and thus the degree of oleic acid concentration to improve stability. Such oils may be used either alone or as blends of oils, and may advantageously further include appropriate chemical additives that enhance the oxidation and chemical stability of the seed oils, improve low temperature viscosity and flow characteristics, and act as metal scavengers.
More specifically, the improved electrical insulating fluid of the present invention may preferably comprise vegetable seed oils or blends of vegetable seed oils found to have greater stability than previously used oils or combinations of oils. Such oils and/or blends, when processed in accordance with the methods of the present invention and fortified with additives described herein, form an electrical insulating fluid that meets all functional standards set forth in ASTM D3487 for conventional transformer oil.
The present invention also relates to the use of the improved insulating fluids in equipment, and to equipment containing such fluids.
Various other features, objects, and advantages of the invention will be made apparent from the following detailed. description and the drawings.
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K.M. Kamath et al, “Variation of Dielectric Properties of Some Vegetable Oils in the Liquid-Solid Transition Phase”, Indian Journal Technology, vol. 9, Aug. 1971, pp. 312-313.
H.C. Keshavamurthy et al, “Rape Seed Oil as a New Capacitor Impregnant”, Central Power Research Institute, Bangalore, India, Presented at IEEE International Sympsium on Electrical Insulation, Pittsburgh, Jun. 1994, pp. 418-421.
H.C. Keshavamurthy et al, “Rape Seed Oil Derivative as a New Capacitor Impregnant,” Central Power Research Institute, Bangalore, India, presented at IEEE International Symposium or Electrical Insulation, Pittsburgh, Jun. 1994.
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Andrus Sceales Starke & Sawall LLP
Gupta Yogendra N.
Hamlin Derrick G.
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