CORONA-RESISTANT WIRE ENAMEL COMPOSITIONS AND CONDUCTORS INSULATED THEREWITH
Why Choose Corona Resistant Paint?
When conductors and dielectrics are subjected to voltages above the corona initiation voltage, the dielectric material that acts as the conductor insulator may fail due to corona. This type of failure can occur in certain motor applications. Corona-induced failures are particularly likely to occur when the insulator material is a solid organic polymer. Therefore, an improved dielectric material with resistance to corona discharge-induced degradation would be highly desirable. In some applications, mica-based insulation systems have been used as a solution to this problem, i.e., the mica provides resistance to corona. However, due to the inherent poor physical properties of mica, this solution is not ideal because of the relatively large amount of space required for mica-based assemblies.
How to use anti-corona enamel on enameled wire?
A corona-resistant wire enamel composition comprising a polyimide, polyamide, polyester, polyamideimide, polyesterimide or polyetherimide resin and from about 1% to about 35% by weight of submicron alumina particles. The aluminum in the alumina is bound only to oxygen atoms.
Preferably, fumed alumina is used. The alumina is dispersed in the composition of the enameled wire under high shear stirring, preferably at a concentration of about 1 to about 20 parts by weight per hundred parts of resin. The size of the alumina particles is preferably less than about 0.1 micron. Alternatively, a method of providing anti-corona insulation for electrical conductors employs the above compositions. The method includes applying the composition to a conductor, such as a wire, by using multiple coats and wiping molds and curing at various rates between about 330°C and 370°C.
It has been noted that it is impossible to obtain a smooth continuous coating without completing the dispersion by high shear mixing, which is required to produce any insulating film of the minimum thickness required for commercial electrical insulated conductors.
Thus, in its broad aspect, the present invention includes a corona-resistant enameled wire composition comprising a polyimide, polyamide, polyester, polyamideimide, polyesterimide or polyetherimide resin and from about 1% to about 35% by weight of submicron-sized alumina particles dispersed therein by high shear mixing, and for preparing such a composition by high shear mixing of alumina particles in said resin method of preparing such compositions by high shear mixing of alumina particles in said resin. The improvements provided by the present invention are not only observed in high temperature resistant resins such as polyimide, but also provide significant corona resistance for resins that are typically considered low temperature capable materials, such as polyamides (nylon) and polyesters. Corona-resistant enameled wire compositions are used to coat conductors.
