Vector Analysis Application In Rotating Magnetic Fields

Rotating magnetic fields in three-phase electrical machines has been one of the hardest topics to convey to our students in the area of energy conversion. These fields are transformed into phasors (vectors) that rotate in space around the stator of an electrical machine. The mathematical proof of such rotation will be shown and a MATLAB simulation describing these vectors will be given. Classic textbooks approach this concept mathematically and usually the students are left to imagine the space vector rotation. This is no longer the case, now we can simulate and SEE in our desktop computers, using Matlab, rotating phasors. Polyphase Analysis Three phase induction machines are the work-horse of industry, and these machines have a “rotating magnetic field”. We will give a brief physical description; consider a sequence a-b-c and a symmetric distribution of the phases by 120 electrical degrees each in space and around the air gap. The basic three-phase machine will have three coils that we consider to have the following terminals: a a’ b b’ c c’ These coils are excited by a time dependent sinusoidal alternating current producing a sinusoidal magneto-motive force (mmf) wave at the center of the magnetic axis of particular phase. Therefore the three-space sinusoidal mmf waves are displaced 120 electrical degrees in space. Figure 1 shows how we determine the magnetic axis of a coil. Figure two indicates three magnetic-axis of three coils placed in space around the stator. A three-phase system requires three coils to create three magnetic fields that will interact among each other to obtain a resulting magnetic component. Furthermore, this resultant component will rotate in space around the air gap of the electric machine. P ge 7.294.1