Method of making partial-discharge-resistant insulated wire

1. A method of making a partial-discharge-resistant insulating varnish, comprising:

mixing a polyamide-imide enamel varnish with an organo-silica sol,

wherein the polyamide-imide enamel varnish comprises a polyamide-imide resin and a mixed solvent used for a synthesis reaction of the polyamide-imide enamel varnish, the mixed solvent comprising 67 to 87% by weight of γ-butyrolactone and a balance consisting of 1) at least one of N-methyl-2-pyrrolidone and N,N-dimethylformamide, or 2) cyclohexanone and N,N-dimethylformamide,

wherein the organo-silica sol comprises silica and a dispersion solvent comprising γ-butyrolactone, and

wherein a total amount of γ-butyrolactone comprised in the mixed solvent and the dispersion solvent is 50% or more and less than 100% by weight relative to a total amount of the mixed solvent and the dispersion solvent.

2. The method according to claim 1 , wherein:

the organo-silica sol comprises 80 to 100% by weight of γ-butyrolactone to a total amount of the dispersion solvent.

3. The method according to claim 1 , wherein:

a total amount of γ-butyrolactone comprised in the mixed solvent and the dispersion solvent is 50 to 89.7% by weight relative to a total amount of the mixed solvent and the dispersion solvent.

4. A method of making an insulated wire, comprising:

preparing a partial-discharge-resistant insulating varnish by mixing a polyamide-imide enamel varnish with an organo-silica sol; and

coating the partial-discharge-resistant insulating varnish on the surface of a conductor and then baking the varnish to form a coating film on the conductor,

wherein the polyamide-imide enamel varnish comprises a polyamide-imide resin and a mixed solvent used for a synthesis reaction of the polyamide-imide enamel varnish, the mixed solvent comprising 67 to 87% by weight of γ-butyrolactone and a balance consisting of 1) at least one of N-methyl-2-pyrrolidone and N,N-dimethylformamide, or 2) cyclohexanone and N,N-dimethylformamide,

wherein the organo-silica sol comprises silica and a dispersion solvent comprising γ-butyrolactone, and

wherein a total amount of γ-butyrolactone comprised in the mixed solvent and the dispersion solvent is 50% or more and less than 100% by weight relative to a total amount of the mixed solvent and the dispersion solvent.

5. The method according to claim 4 , further comprising:

forming an organic insulation coating film on the surface of the conductor,

wherein the partial-discharge-resistant insulation coating film is formed on the surface of the organic insulation coating film.

6. The method according to claim 4 , wherein:

a total amount of γ-butyrolactone comprised in the mixed solvent and the dispersion solvent is 50 to 89.7% by weight relative to a total amount of the mixed solvent and the dispersion solvent.