When the stator winding of a three phase synchronous motor is supplied by a balanced three phase power supply of frequency f, the balanced three phase currents in the winding will generate a rotating magnetic field of speed nf = 120f/P. This rotating magnetic field will drag the magnetized rotor, which is essential a magnet, to rotate at the same speed n=nf. On the other hand, this rotating rotor will also generate balanced three phase emf's of frequency f in the stator winding, which would balance with the applied terminal voltage.