Electricity: conductors and insulators – With fluids or vacuum – Boxes and housings
Reexamination Certificate
1999-06-08
2001-08-07
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
With fluids or vacuum
Boxes and housings
C174S017070, C174S1100PM, C336S055000
Reexamination Certificate
active
06271463
ABSTRACT:
The present invention relates to improved barrier components for use in high voltage liquid-filled transformers. The barrier components are prepared from expandable epoxy systems or laminated structures of alternating layers of expandable epoxy resin matrix and substrate material. The present invention further relates to methods for preparing said barrier materials and the use thereof in high voltage liquid-filled transformers.
BACKGROUND
Liquid-filled transformers have historically used cellulose paper as a primary solid electrical sheet insulation. Cellulose paper has several shortcomings, such as moisture absorption, water generation, and limited thermal capabilities. Cellulose paper must be thoroughly dried prior to impregnation under vacuum with a transformer or dielectric liquid. Accordingly, the manufacturing process for high voltage transformers with liquid impregnated cellulose paper is lengthy and labor intensive. Following the heat and vacuum process, the cellulose is typically impregnated with mineral oil to slow the re-absorption of moisture. Water generation occurs as the cellulose ages due to heat. Water generation results in reduced dielectric strength of the oil, and may eventually cause a transformer to fail.
High voltage transformers must be manufactured to very precise dimensional tolerances. Dimensional instability can produce significant electrical losses. Cellulose materials also exhibit a high degree of mechanical creep and measurable deformation from long term static loads and dynamic loads. Additionally, natural cellulose can react with transformer oils to form acid by-products which in turn can cause accelerated degradation of electrical insulation.
In view of these shortcomings of cellulose paper, there is a need in the field for improved barrier materials for use in high voltage liquid-filled transformers.
SUMMARY OF THE INVENTION
The present invention relates to a high voltage liquid-filled transformer including a housing and a dielectric liquid impregnated barrier material within the housing. The barrier material is prepared from an expandable epoxy resin formulation comprising: (i) at least one polyglycidyl compound; (ii) at least one curing agent for the polyglycidyl compound; and (iii) at least one blowing agent. Preferably, the dielectric liquid impregnated barrier material is a laminated structure of alternating layers of cured expandable epoxy resin formulation and a substrate material.
An additional aspect of the present invention is a barrier component for a liquid-filled transformer that is a dielectric liquid impregnated barrier material prepared from an expandable epoxy resin formulation. The expandable epoxy resin formulation contains (i) at least one polyglycidyl compound, (ii) at least one curing agent for the polyglycidyl compound, and (iii) at least one blowing agent. Preferably, the barrier component further comprises at least one layer of a substrate material, more particularly, the substrate material is at least one ply of a non-woven polyester material.
The present invention further relates to a method of manufacturing the barrier component by reacting (i) at least one polyglycidyl compound and (ii) at least one curing agent for the polyglycidyl compound in the presence of at least one blowing agent to produce a porous solid article.
The present invention also relates to a method for manufacturing the barrier component having multiple laminated layers by blending (i) at least one polyglycidyl compound and (ii) at least one curing agent for the polyglycidyl compound in the presence of at least one blowing agent to produce a foamable resin system. A first layer and a second layer of the foamable resin system are then applied onto each major surface of a first substrate layer to produce a laminated structure. The laminated structure is then subjected to heat and pressure as the first and second layer of the foamable resin system react.
The present invention also relates to a method of manufacturing the transformer by reacting (i) at least one polyglycidyl compound and (ii) at least one curing agent for the polyglycidyl compound in the presence of at least one blowing agent to produce a porous solid article. The porous solid article is then fitted for and placed within a housing on the transformer and subsequently impregnated with a dielectric liquid.
In an alternative embodiment, the present invention relates to a method for manufacturing the transformer by blending (i) at least one polyglycidyl compound and (ii) at least one curing agent for the polyglycidyl compound in the presence of at least one blowing agent to produce a foamable resin system. A first layer and a second layer of the foamable resin system are then applied onto each major surface of a first substrate layer to produce a laminated structure. The laminated structure is then subjected to heat and pressure as the first and second layer of the foamable resin system react. The resulting laminated structure is fitted for and placed within a transformer housing and subsequently impregnated with a dielectric liquid.
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Ferng William Bin
Kultzow Robert John
Pilato Luciano
Rajadhyaksha Mangesh Yeshwant
Estrada Angel R.
Lyon & Lyon LLP
Neuman Kristin H.
Reichard Dean A.
Shalek James H.
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