Permanent magnet excited D.C. machine - has field pole of 180 degrees electrical arc with armature winding step reduction

摘要

The D.C machine consists of an armature coil (1), armature core (2), and field poles (N,S) the pole pitch spanning the spatial angle of 180 deg./P where P is the number of pole pairs. The electrical angle amounts to 180 degrees and the pole arc (b) of the poles, differs from the pole pitch by a given step reduction (Vz). The coil width (w) of the armature winding is augmented by a step reduction (V1) of the armature winding (1). Commutation in normal D.C machines takes place in the field-free space between poles, therefore a machine whose pole arc is exactly 180 electrical degrees, cannot commutate within this space. Neglecting self inductance, the change in flux must be kept to a min. and with a rectangular shape of the magnetic field, this will be the case as long as the armature coil (1) is revolving into the angle formed by the step reductions (V1 + V2). Commutation takes place inside this angle, and due to the shift of the neutral zone width in the armature, field poles with extreme pole arc can be used without the disadvantages of noise, thermal stress, inherent in conventional machines.