Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-05-30
2001-01-30
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S260000, C310S270000, C310S271000, C310S196000, C310S045000, C029S596000
Reexamination Certificate
active
06181042
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to high voltage air-cooled motors and generators. More particularly, this invention is directed to a method and materials for preventing surface deterioration by corona activity of end windings and end winding support structures of such motors and generators.
BACKGROUND OF THE INVENTION
Corona is a luminous discharge surrounding high voltage conductors caused by ionization of the surrounding air. Corona occurs when the electrical fields generated by the high voltage conductors are sufficiently high to break down or ionize the air, and is always present to some degree in high voltage air-cooled ac motors and generators. Generally speaking, it is not practical to manufacture large air-cooled high voltage ac motors and generators to operate free of corona activity since doing so would adversely affect the size and efficiency of these machines.
Corona often causes oxidation of organic materials, resulting in discoloration and dusting. In air-cooled machines, the end winding surfaces on the coils and the structures that serve to separate and support the coils, including coil-to-coil space blocks, binding bands, radial rings and bar ties, are formed of organic insulating materials, and are therefore susceptible to deterioration by corona activity. The entire end winding assembly is usually coated with an organic finish paint that is also susceptible to deterioration by corona activity. The paint is usually applied by spraying to cover the end winding assembly and its connection rings and stator core to protect the winding and provide uniform surface coloring for ease of inspection. Paints currently in use on high voltage air-cooled generators and motors include water-reducible phenolic alkyd paints, acrylic waterborne paints, alkyd waterborne paints, acrylic-epoxy waterborne paints, two-component epoxy waterborne paints, and two-component epoxy solvent-borne paints that usually contain a solution of a high molecular weight bisphenol A—diglycidyl ether epoxy resin in a solvent, which is mixed with an amine-type curing agent immediately prior to being sprayed on the end winding assembly. While these coatings have performed well over the years, they are prone to discolor and form powdery deposits that cover the surfaces of stator bars and the support components of end windings.
Various factors affect corona levels and the associated surface discoloration and dusting of polymeric organic materials of end windings. Corona activity between adjacent coils in end windings is affected by coil-to-coil clearances, coil-to-coil voltages, contamination in the cooling gas (e.g., air), and the velocity of the cooling gas through the spaces in the end winding. Furthermore, coil-to-coil blocking and other support components in end windings can affect the surface voltage gradients along a coil, and therefore will also influence corona activity. Corona activity is usually the most severe at locations near coil-to-coil space blocks between phases, and at the connection ring assembly and support structure.
While discoloration and dusting can occur in the end windings of most air-cooled machines after long-term operation, deterioration of this type generally does not affect the service life of the motor or generator. Usually only the paint protecting the end winding is affected. In more severe circumstances, prolonged corona activity can penetrate the paint and begin to attack the ground insulation, but generally will not penetrate through the outermost layer of mica of the multiple layers of mica tape used as ground insulation. However, the effect of the corona activity is easily visible in many machines, and creates maintenance concerns that must be addressed.
SUMMARY OF THE INVENTION
It is an object of this invention to provide an improved coating material for end windings of high voltage air-cooled generators and motors.
It is another object of this invention to provide a method for protecting an end winding with such a coating material that resists deterioration by corona activity.
It is a further object of this invention that such a coating material is in the form of a paint containing a binder, of which at least 20% by weight is silicone.
According to this invention, the end windings of a high voltage air-cooled ac generator or motor are made more resistant to deterioration by corona activity by using a coating, referred to herein as a paint, whose binder contains at least 20% by weight silicone. In particular, the invention entails coating an end winding, including its insulated conductors and separator and support structures, with a paint containing a binder, solvent or thinner, and optional pigments, with at least 20% by weight of the binder being silicone. More preferably, at least 30% by weight of the binder is silicone, with the balance (if any) of the binder being, for example, an alkyd or acrylic resin. According to the invention, deterioration of an end winding is inhibited by applying the paint of this invention to the surfaces of the end winding, including its insulated conductors and separator and support structures. Advantageously, curing or hardening of the paint can be performed without heating.
According to the invention, paints containing at least 20 weight percent silicone exhibit markedly better resistance to corona activity as compared to prior art paints used to protect end windings. The paint of this invention exhibits no deterioration, e.g., discoloration or dusting, under identical test conditions that cause deterioration of prior art paints. The resistance to deterioration appears to be unaffected by the presence of most coloring pigments and other binder materials in the paint. In addition, the paints of this invention have been shown to successfully repair end winding assemblies with prior art paints that have deteriorated from corona activity. With this invention, the end windings in high voltage air-cooled motors and generators are expected to withstand extended service lives without deterioration.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
REFERENCES:
patent: 3824683 (1974-07-01), Rhudy
patent: 4020017 (1977-04-01), Smith et al.
patent: 4273674 (1981-06-01), Ligon, Jr. et al.
patent: 4298656 (1981-11-01), Mendelsohn
patent: 4344006 (1982-08-01), Mendelsohn
patent: 4367425 (1983-01-01), Mendelsohn et al.
patent: 4427740 (1984-01-01), Stackhouse et al.
patent: 5753729 (1998-05-01), Valet et al.
patent: 5817821 (1999-10-01), Valet et al.
patent: 992219 (1965-05-01), None
patent: 1342426 (1970-01-01), None
patent: 1240701 (1971-07-01), None
patent: 1306061 (1973-02-01), None
Grant James Jonathan
Markovitz Mark
Dougherty Thomas M.
General Electric Co.
Hartman & Hartman
Lam Thanh
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