Patent Application
20050026763
This invention relates generally to turbine generator construction and specifically, to a bag construction used to encapsulate a stator bar for collection of stray helium gas in a test for leaks.
Current gas bags used during helium tests are time consuming to manufacture, and difficulties are experienced subsequently during both installation and removal. The bags require multiple materials, thus increasing the chances for false positive leaks and poorly sealed bags.
More specifically, the current practice is to manually fabricate the bags on-site from various plastics or polymers.
The bags are then hand cut, and strips of duct tape applied along marginal edges for securing the side panels.
The disadvantages include the tape sticking to itself, disallowing the bag to be used and often creating a poor seal to the stator bars. In addition, residue may remain on the stator bar from the adhesive. The current practice is also labor intensive, utilizing manpower that could be better employed, for example, for wrapping the stator bars.
The present invention provides a pre-cut and pre-measured tracer gas bag that will comply with all generator stator bar designs, and that allows for quick attachment. The tracer gas bags in accordance with this invention will improve the reliability of the helium leak test, decrease the chances for helium leaks escaping and giving false positives, and will reduce installation time and cost.
In the exemplary embodiment of the invention, a two-sided adhesive tape is laminated to the outer edges of a single poly sheet, preferably along all four marginal edges of the sheet. The bag is formed simply by folding the sheet over on itself and sealing the marginal edges via the double-sided adhesive. When applied over the ends of one or more stator bar ends, some edge portions of the sheet will seal directly to the stator bar ends while other edge portions will seal directly to each other, depending on the stator bar end configuration. The result is a sealed enclosure about the one or more stator bar ends that is suitable for gas leakage tests.
In another embodiment, wider strips of single-sided adhesive are applied to the opposite short ends of the sheet. In one example, four inch wide tape is applied to the ends, with a one inch overlap. The adhesive side is covered with a conventional peel strip and, when removed, the sheet may be folded over itself and the stator bar end(s) as described above. The use of wider tape on opposite ends of the bag effectively lengthens the bag.
In use, the bag is sealed about one or more stator bar ends and, after a predetermined period of time, a gas detector probe is inserted through the bag to detect any leakage of gas from the stator ends. After the test is completed, the probe is withdrawn and the hole sealed by another strip of tape. The bag may be re-used and the taped hole can be uncovered for later re-insertion of the probe.
Thus, in one aspect, the present invention relates to a tracer gas bag for stator bar testing comprising a polymer sheet folded over itself and joined about at least the peripheral edges by a two-sided adhesive tape.
In another aspect, the invention relates to method of constructing a tracer gas bag for a stator bar leak test comprising a) providing a thin sheet for forming first and second faces of the gas bag; b) applying a double sided adhesive tape along marginal edges of at least three sides of the sheet; and c) folding the sheet about a stator bar end and sealing the marginal edges utilizing the strips of adhesive tape.
The invention will now be described in connection with the drawings described below.
With reference to
In still another embodiment, best seen in
In the exemplary embodiments, the poly film layers or sheets may be comprised of polyvinyl chloride film, but it will be appreciated that other suitable materials may be used. The double-sided adhesive may be of any suitable kind, for example, an acrylic adhesive on a polypropylene substrate, synthetic rubber and resin type adhesives on a low density polyethylene substrate, or other suitable adhesive tape. The film or sheet thickness may be about 8 mil, but may vary as required for different applications. It will also be appreciated that the overall dimensions of the bag may vary as well. One suitable size for the sheet 12 is about 24 to about 36 inches in length and 12-18 inches in width. In one example, the bag is 30 inches in length by 18 inches in width.
Turning now to
While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.
