Patent Application
20090174279
The present application relates generally to insulation for electrical machines and more particularly relates to improving the thermal conductivity of resins, varnishes, putties, and other materials used with stator bar components and insulation.
By reducing the thermal resistance of stator bar components, improved heat transfer may be obtained between the stator bar conductors and the stator core. Specifically, reducing the thermal resistance of the stator bar components may reduce the temperature differential between the respective conductors caused by non-uniform magnetic fields therein. Moreover, the current density of the copper conductor may be increased by effectively cooling the conductors.
By way of example, the thermal conductivity of ground wall insulation surrounding the stator bar components has improved in recent years from about 0.3 W/mK to about 0.5 W/mK (Watts per meter per degrees Kelvin) via the addition of high thermal conductivity fillers. The focus to date, however, has been on the insulation as opposed to improving heat transfer among the conductors themselves or between the conductor package and the ground insulation. These conductors interface with the higher thermal conductivity ground insulation products.
There is thus a desire for even further thermal conductivity improvements in stator bar components and insulation. Preferably, such an improved overall stator bar may produce more power from a smaller unit at a more economical cost or at higher efficiency from an existing unit.
The present application thus describes a stator bar or any similar type of armature coil. The stator bar may include a conductor, a layer of insulation positioned about the conductor, and a high thermal conductivity varnish to bond the layer of insulation to the conductor.
The application further describes a stator bar. The stator bar may include a number of conductors, a layer of insulation positioned about the conductors with the conductors forming a gap against the layer of insulation, and a high thermal conductivity putty within the gap.
The application further describes a stator bar. The stator bar may include two or more conductor tiers and a vertical separator positioned between the conductor tiers. The vertical separator may include a high thermal conductivity resin.
These and other features of the present application will become apparent to one of ordinary skill in the art upon review of the following detailed description when taken in conjunction with the several drawings and the following claims.
Referring now to the drawings, in which like numerals refer to like elements throughout the several views,
Generally described, each stator bar 100 may include a number of conductors 120. The conductors 120 may be made out of copper, copper alloys, aluminum, or similar materials. A layer of conductor insulation 130 may separate the individual conductors 120. In this example, the conductor insulation 130 may include a typical E-Glass, Daglass, or a similar type of glass material. The E-Glass may be a low alkali borosilicate fiberglass with good electro-mechanical properties and with good chemical resistance. E-Glass, or electrical grade glass, has excellent fiber forming capabilities and is used as the reinforcing phase in fiberglass. The E-Glass may have a thermal conductivity of about 0.99 W/mK. The Daglass may be a yarn with a mixture of polyester and glass fibers. The Daglass may have a thermal conductivity of about 0.4 W/mK. A glass cloth made from the E-Glass, the Daglass, or from similar types of materials may have any desired woven densities, weights, thicknesses, strengths, and other properties.
In the embodiment as shown, the stator bar 100 may include two or more tiers 140 of the conductors 120. Any number of tiers 140 may be used. The tiers 140 may be separated by a vertical separator 150. Typical vertical separators 150 may include paper, felt, or a glass fabric that is treated with a partially-cured resin that, when cured, flows and bonds the tiers 140 together. The separators 150 also provide additional electrical insulation.
The tiers 140 also may be surrounded by one or more layers of ground insulation 155. As described above, the ground insulation 155 commonly may be constructed of a combination of a mica paper, a glass cloth or unidirectional glass fibers, and a resin binder in multilayers to form a composite.
As is shown in
The use of the high thermal conductivity varnish 165, the putty 210, and the resin 270 thus may increase the thermal conductivity of the stator bar 100, both between the conductors 120 and between the conductors 120 and the ground insulation 155. For example, certain conductors 120 may be closer to the source of the magnetic field and hence may be subject to higher magnetic fields. Such higher magnetic fields may induce higher currents so as to set up a temperature differential between the closer and the farther conductors 120 within the stator bar 100. The improved thermal conductivity described herein may allow for improved heat flow and a lower temperature difference between the respective conductors 120.
Likewise, certain stator bars 100 may use hollow conductors to serve as passages for fluid flow therethrough so as to remove heat from the stator bar 100 as a whole. In such designs, the higher thermal conductivity should allow more efficient cooling and a higher ratio of solid to hollow conductors 120. As a result, the amount of copper and the amount of conductors 120 may increase in a stator bar 100 of the same size.
It should be apparent that the foregoing relates only to the preferred embodiments of the present application and that numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the invention as defined by the following claims and equivalents thereof.
