Abstract: A stator assembly includes a stator core including a plurality of slots configured to penetrate through the stator core in a circumferential direction, each of the slots including a plurality of layers in a radial direction; and a plurality of hairpin coils configured to fasten and interconnect to the slots, respectively, to form a coil winding. The hairpin coils include a main coil having a first slot pitch, an anomalous coil having a second slot pitch different from the first slot pitch, and a leader coil. In each of the slots, the main coil is disposed in each of a radially innermost layer of the layers, a radially outermost layer of the layers, and an intermediate layer of the layers between the innermost layer and the outermost layer. The leader coil is disposed in each of the innermost layer and the outermost layer.