Reference frame theory : development and applications Reference frames are commonly used in the analysis of electric machines and power system components and include arbitrary stationary rotor and synchronous reference frames. Reference frame theory is used to move between a stationary reference frame to a rotating reference that can be either synchronized with the speed of the rotating machine or a set angular frequency (such as 60 Hz or 377 radians sec). Understanding reference frame theory is necessary to design rotating machines as well as their dynamic interactions with the electrical system to which they are connected