Magnetic winding wire, also referred to as magnet wire, is used in a multitude of electrical devices that require the development of electrical and/or magnetic fields to perform electromechanical work. Examples of such devices include electric motors, generators, transformers, actuator coils, and so on. Typically, magnet wire is constructed by applying electrical insulation to a metallic conductor, such as a copper, aluminum, or alloy conductor. The conductor typically is drawn or formed to have a rectangular or round cross-section. The electrical insulation is typically formed as a coating that provides for electrical integrity and prevents shorts in the magnet wire. Conventional insulations include polymeric enamel films, polymeric tapes, paper insulation, and certain combinations thereof.
In certain applications, it is desirable to have magnet wire that includes relatively higher electrical properties, such as a higher dielectric strength and/or a higher partial discharge inception voltage (“PDIV”). The dielectric strength of a material generally refers to the maximum applied electric field that the material can withstand without breaking down. The PDIV generally refers to a voltage at which localized insulation breakdowns can occur. Partial discharge typically begins within voids, cracks, or inclusions within a solid dielectric; however, it can also occur along surfaces of an insulation material. Once begun, partial discharge progressively deteriorates an insulation material and ultimately leads to electrical breakdown.
Additionally, in certain applications, it is desirable to limit or minimize insulation thickness in order to permit a higher amount of magnet wire to be packed or formed into an electrical device coil. For example, with many devices intended to be utilized in vehicles, it is desirable to reduce the size of magnet wire in order to more tightly pack wire into an available housing. The performance of an electrical device is strongly correlated to an amount of magnet wire that can be placed into an available core slot area. Accordingly, reducing the thickness of magnet wire insulation may permit higher power output and/or increased performance.
For certain applications, such as vehicle applications, it may also be desirable for magnet wire to be resistant to hydrocarbon oil and/or moisture. For example, in some motor applications, magnet wire is at least partially submerged in transmission fluid. This transmission fluid can break down traditional magnet wire insulation materials, such as enamel insulations.
As set forth above, traditional magnet wire is formed with polymeric enamel insulation that is applied in successive layers and baked in a furnace. In order to achieve higher dielectric and partial discharge performance, it is typically necessary to apply a greater number of layers and, therefore, thicken the enamel. However, each successive pass through the baking furnace lowers the adhesive force between the enamel and the conductor, and it is difficult to build the thickness of the enamel beyond a certain point. Additionally, increased enamel layering may lead to solvent blisters or beading and/or reduced flexibility.
Recently, as described in U.S. Pat. No. 8,586,869, attempts have been made to improve insulation performance by extruding a polyphenylene sulfide (“PPS”) resin over an enamel layer. However, an adhesive layer is required between the enamel and the polyphenylene sulfide. Additionally, although the use or PPS may lead to a wire that is resistant to oil and moisture, ultraviolet light can be detrimental to PPS and lead to significant corona discharges that break down the insulation. Thus, PPS is not a good choice for applications that are subject to a higher frequency of PDIV events. Accordingly, there is an opportunity for improved insulated magnet wire, and more particularly, improved insulated magnet wire having a partial discharge inception voltage greater than 1,000 volts and a dielectric strength greater than 10,000 volts.
USPTO Backgrounds
USPTO Backgrounds