Patent ID: 7816821

Claim:
A varnish impregnation state determination method for determining a varnish impregnation state of a core assembly that is formed by disposing a coil inside a slot of a motor core and impregnating the coil and an interior of the slot with a varnish, comprising: applying an alternating current voltage between the motor core and the coil to determine tan δ that serves as a dielectric dissipation factor, the tan δ being measured after the varnish is hardened, and determining that the varnish impregnation state of the core assembly is normal when a value of the tan δ is equal to or smaller than a predetermined non-defective article reference value, wherein: a relationship between the tan δ and a varnish impregnation ratio, that is a varnish impregnation amount relative to a varnish impregnable gap inside the slot of the motor core, is determined in advance, when the value of the tan δ is equal to or smaller than the predetermined non-defective article reference value, the varnish impregnation ratio is determined to be equal to or greater than a predetermined value, the varnish is dripped onto a coil end portion projecting from each axial end surface of the motor core, and the dripped varnish is hardened by heating the coil and the motor core in order to form the core assembly, and a voltage value of the alternating current voltage is set to or above a voltage value when corona discharge is generated in the core assembly.