Insulated winding wire

An insulated winding wire comprising:

• a conductor;
• and
• insulation formed around the conductor, the insulation providing a partial discharge inception voltage greater than approximately 1,400 volts, the insulation comprising:
• at least one layer of enamel formed around an outer periphery of the conductor;
• and
• an extruded thermoplastic layer formed around the enamel, the thermoplastic layer comprising (i) at least one polymer comprising a ketone group and (ii) at least one fluoropolymer,
• wherein the ratio of the dielectric constant of the thermoplastic layer to the dielectric constant of the at least one layer of enamel is less than or equal to approximately 1.0 at 250° C.

A method for forming an insulated winding wire, the method comprising:

• providing a conductor;
• forming at least one base layer of insulating material around an outer periphery of the conductor;
• and
• extruding a thermoplastic layer around the base layer, the thermoplastic layer comprising (i) at least one polymer comprising a ketone group and (ii) at least one fluoropolymer,
• wherein the ratio of the dielectric constant of the thermoplastic layer to the dielectric constant of the at least one base layer is less than or equal to approximately 1.0 at 250° C.

An electric machine comprising:

• at least one winding of insulated wire, the insulated wire comprising:
• a conductor;
• and
• insulation formed around the conductor, the insulation comprising:
• a base insulation layer formed around the conductor, the base insulation layer having a first dielectric constant (ε1);
• and
• an extruded thermoplastic layer formed around the base insulation layer and having a second dielectric constant (ε2), the extruded thermoplastic layer comprising (i) at least one polymer comprising a ketone group and (ii) at least one fluoropolymer,
• wherein the ratio of the dielectric constant (ε2) of the extruded thermoplastic layer to the dielectric constant (ε1) of the base layer at 250° C. is less than approximately 1.0.