14 Electric Motors b) Motor principle In motors, the induction principle is utilised in the reverse order: a current-carrying conductor located in a magnetic fi eld is infl uenced by a force (F) which results in a movement. a) Generator principle b) Motor principle Fig. 1.3 Principle for electromagnetic induction In both cases a magnetic fi eld is required. In Fig. 1.3 Principle for electromagnetic induction the magnetic fi eld originates from a permanent magnet, but in a motor the magnetic fi eld is generated in the stator. Typically, this is achieved by applying voltage to the stator windings. The conductors aff ected by the electromagnetic force are located in the rotor.
1.2.5 Poles, Synchronous Speed and Asynchronous Speed The synchronous speed of a motor can be calculated when the supply frequency and number of pole pairs are known. n0 = f 60 p f = frequency [Hz] n0 = synchronous speed [min -1 ] p = pole pair number While the frequency is determined by the grid or the FC, the number of poles is determined by the way the stator coils are connected.