The inverter surge-resistant insulated electric wire having a baked enamel layer, an adhesive layer, and an extrusion-coated resin layer at an outer periphery of the conductor, wherein the thickness of the layer of the baked enamel, the extrusion-coated resin layer, and the adhesive has a thickness of the sum of the thicknesses of the layer of the baked enamel, the extrusion-coated resin layer and the adhesive has a thickness of 60 μm or more, wherein the baked enamel layer has a thickness of 50 μm or less, and wherein the extrusion-coated resin layer is formed by a polyphenylene sulfide resin composition comprising a polyphenylene sulfide having a melted viscosity at 300° Celsius polymer C of 100 Pa-s or more, a thermoplastic elastomer and an antioxidant of 2 to 8 mass%, a tensile elastic modulus of 2500 MPa or more at 25° C., and a tensile elastic modulus of 10 MPa or more at 250° C.


We developed polyesterimide (PEI) nanocomposite enameled wires using surface-modified silica nanoparticles with binary surface chemistry. Modification using ultrasound-assisted silane facilitated high-density modification. Two different trimethoxysilanes were selected for modification based on the similarity of silica surface chemistry to PEI varnish. Optical observations and viscosity measurements confirmed that the surface-modified silica was well dispersed in the PEI varnish. The glass transition temperature of the silica-PEI nanocomposites increased with increasing silica content. The PEI varnish dispersed in silica was then used to fabricate enameled wires. Under partial discharge conditions, the silica-PEI nanocomposite enameled wires exhibited a longer service life than the pure PEI enameled wires.

Enameled wires consist of a copper or aluminum conductive core surrounded by an insulating layer made of polymer. The service life of the motor depends greatly on the thermal and electrical properties of the insulation. In high-speed switching inverter-driven motors, especially when the transient superimposed voltage called surge voltage is higher than the partial discharge initiation voltage (PDIV), the insulation layer deteriorates as a result of partial discharges (PD), which can lead to insulation breakdown. Therefore, surge-resistant enameled wires have attracted attention in order to extend the life of various electrical devices installed in inverter-driven motors such as electric vehicles.

To prevent degradation, nano-sized inorganic fillers are doped into the insulation layer, and the corona generated by the partial discharge can be trapped or reflected on the surface of the inorganic fillers to retard degradation.