A rotor assembly includes: coil turns each of which has a plurality of conductors stacked in a multilayer structure and includes a linear part interposed between teeth of a rotor body and formed in a longitudinal direction with ducts through which cooling fluid moves, and a curved part extending from the linear part and disposed in an arc shape on an outer circumferential surface of a spindle; and a turn insulator interposed between the conductors, and insulating the conductors from each other. The curved part may include a wave-shaped cooling path, which is formed in a longitudinal direction in a planar surface thereof, communicates with the ducts, and guides the cooling fluid to the ducts. Furthermore, through holes each of which is shorter than the duct are formed in the turn insulator at a position corresponding to the duct.