Patent Application
20080029291
As shown in
In the exemplary embodiment, stator bars 104 are formed of a plurality of strands 120 of a conducting material that are bundled together prior to form to a pre-determined winding path through stator bar 104. Although strands 120 may be fabricated from several conductive materials, in some embodiments strands 120 are fabricated from copper, copper alloys, or stainless steel. In some embodiments, strands 120 may be cooled. Strands 120 may be cooled in any suitable manner, fashion, and/or by any suitable means. For example, in some embodiments strands 120 are cooled by passing a fluid, such as, but not limited to, air and/or hydrogen gas, over strands 120. Moreover, and for example, in some embodiments some or all of strands 120 are hollow cooling strands 120 that channel a fluid, such as, but not limited to, water, an oil, air, and/or hydrogen gas, for cooling strands 120. In the exemplary embodiment shown in
Adjacent strands 120 are electrically-insulated from each other by an insulating material 124. Although strands 120 may have any shape, in the exemplary embodiment strands 120 are generally rectangular in cross section. Transposition putty material 126 may surround radially inward portions 125 and/or radially outward portions 127 of strands 120 for each stator bar 104 within slots 106. Each stator bar 104 may be surrounded by multiple layers of an electrical insulation 128. The number of layers of insulation 128 and their particular arrangement are variably selectable based upon a design specification for generator 100. Although insulation 128 may include other insulation (e.g., extruded insulation), in one embodiment insulation 128 is fabricated from mica-based materials which include a binder. In one embodiment, insulation 128 is an epoxy-mica system, such as Micapal II™ (a trademark of General Electric Company). In some embodiments, insulation 128 may initially be flexible enough to be wound or wrapped around strands 120, but after curing, may be relatively hard. Although strands 120 may have any shape, in the exemplary embodiment strands 120 are generally rectangular in cross section.
As shown in
Conductive tape 130 includes cloth and a conductive or semiconductive substance. The cloth may be organic or inorganic, and the substance is an organic resin. In one embodiment, the cloth is inorganic. In one embodiment, conductive tape 130 is a woven glass cloth uniformly impregnated with a conducting epoxy resin.
Prior to curing conductive tape 130 and insulation 128 (discussed below), conductive tape 130 has an average resistivity from about 20,000 to about 200,000 ohms/sq. This average resistivity is calculated with two or four stacked thicknesses of conductive tape 130 (discussed below) on one side of stator bar 104. In one embodiment, conductive tape 130 has about 36% to about 49% binder/organic conductive filler content. In one embodiment, conductive tape 130 has a breaking strength of approximately 140 lbs./in., min., and a roll winding tension of approximately 8 lbs. min. In an exemplary embodiment of conductive tape 130, the thickness, breaking strength, and construction of conductive tape 130 must satisfy the standards in ASTM D579 (Specification for Greige Woven Glass Fabrics).
Conductive tape 130, as applied to insulation 128 of stator bar 104, must have a substantial thickness so as to allow an operator or machine to manipulate the size dimensions of the final stator bar product by removing a portion of conductive tape 130. For example, an operator can remove a few mils of the conductive tape from a length of a side of the stator bar (e.g., by sanding the bar) so that the stator bar will fit into the respective slot of the generator. Because only a small amount or portion of conductive tape 130 is removed, conductive properties of tape 130 are not significantly altered and insulation 128 (and consequently stator bar 104) is still protected.
Unlike previous known methods, conductive tape 130 is applied to insulation 128 on stator bar 104 before insulation 128 is cured. A tape machine (not shown) applies one or more layers of conductive tape 130 to stator bars 104. As shown in
In one embodiment, one half-lapped layer of conductive tape 130, which has two thicknesses of conductive tape 130, has a total thickness from about 0.008 inch to about 0.011 inch. In this embodiment, the thickness of conductive tape 130 is from about 0.004 inch to about 0.006 inch.
The total thickness of the layer(s) of conductive tape 130 is substantial enough so as to allow an operator or machine to manipulate the size dimensions of the final stator bar product by removing a portion of conductive tape 130. In one embodiment, the total thickness of the layer(s) of conductive tape 130 is about 0.035 to about 0.045 inch. More specifically, in one embodiment, the total thickness of the layer(s) of conductive tape 130 is about 0.040 to about 0.045 inch.
In one embodiment two half-lapped layers on one side of stator bar 104 have a total thickness from about 0.016 inch to about 0.022 inch. The total build (i.e., the total thickness of conductive tape 130 used on both sides) has a total thickness from about 0.035 inch to about 0.045 inch.
The width of conductive tape 130 is amenable for applying conductive tape 130 to insulation 128. In one embodiment, the width of conductive tape 130 is amenable for applying conductive tape 130 half-lapped onto insulation 128. In one embodiment, the width of conductive tape 130 is approximately one inch.
Stator bar 104 with insulation 128 and conductive tape 130 is then cured in an autoclave by known processes. In one embodiment, the duration of curing is approximately 20 hours. After curing, stator bar 104 is stripped of sacrifice material.
The curing process alters the resistivity range of conductive tape 130 and, consequently, stator bar 104. Those skilled in the art and guided the teachings herein provided know that the composition of conductive tape 130 and the curing process can be altered to reach a final desired resistivity. The desired resistivity range of the outer surface of stator bar 104 must not be too low so that a current and voltage is induced in the armor by the magnetic field. But the desired resistivity range must not be so high that it prevents discharge of the gas at the surface of stator bar 104. The acceptable resistance range is a function of the distance between a grounding point of conductive tape 130 and the core laminations.
In one embodiment, the desired surface resistivity range is from about 500 to about 100,000 ohms/square. In another embodiment, the desired resistivity range is from about 1,500 to about 100,000 ohms/square.
However, if portions of the cured conductive tape 130 or if all of the cured conductive tape 130 do not meet the desired resistance range, those skilled in the art can alter the resistance through known methods. For example, if the resistance is too high, then coating the bar with a special paint can reduce the resistance. Also, if the resistance is too low, conductive tape 130 can be removed and known glass tape processes discussed above can be used.
After curing, stator bar 104 is inspected for proper size dimensions, the existence of any flaws, and the armor resistivity is tested.
By curing insulation 128 with conductive tape 130, unlike previously known processes, a significant amount of time can be saved and costs reduced.
Several tests known by those skilled in the art, including high potential, dissipation factor and tip-up, voltage endurance, thermal aging, impact damage test, comparative wear, compressive creep tests, and winding assembly simulations, were conducted to ensure that embodiments of the present invention would perform successfully in high-voltage generators.
Exemplary embodiments of methods and stator bars are described and/or illustrated herein in detail. The methods and stator bars are not limited to the specific embodiments described herein, but rather, components of each stator bar and steps of each method may be utilized independently and separately from other components and steps described herein. Each stator bar component and method step can also be used in combination with other stator bar components and/or method steps.
When introducing elements/components/etc. of the methods and assemblies described and/or illustrated herein, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the element(s)/component(s)/etc. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional element(s)/component(s)/etc. other than the listed element(s)/component(s)/etc.
While the methods and assemblies described herein have been described and/or illustrated in terms of various specific embodiments, those skilled in the art will recognize that the methods and assemblies described and/or illustrated herein can be practiced with modification within the spirit and scope of the claims.
