For the analysis of the AC electrical machines, it is common to introduce rotational reference frames for the simplified analysis of AC electrical machines. Traditionally, the deduction of the governing equation under the rotational reference frames involve two steps. Step1 is constructing the voltage governing equation based on Faraday’s law under the “windingfixed reference frame”. Step2 is using the coordinate transformation to deduce of the governing equations under the rotational reference frame. The deduction processes are mathematically rigorous. However, it is difficult to understand and remember the physical meanings behind these mathematical equations. Inspired by the “inertial frame of reference” in the mechanical system, depending on whether Faraday’s law of electromagnetic induction applies, a kind of socalled “Faraday reference frame” is introduced. It is specially used to distinguish the governing equations under the windingfixed coordinate frame from the rotational reference frame. In this way, an additional “entrainment electromotive force” should be introduced for “nonFaraday reference frames” to characterize the effect of entrainment motion, motivated by the “inertia force” in the noninertial frame of reference.