## Armature Windings:

AC Winding : Ac winding are generally of a 3-phase kind because of the inherent advantages of a 3-phase machine. The armature coils must be connected to yield balanced (equal in magnitude and successive phase difference of 2π/3 rad) 3-phase emfs. To begin with the slots around the armature periphery must be divided into phase-bands. Phase Grouping: Initially a simple case will be assumed where SPP is an integral number; such AC Winding is referred to as integral-slot winding. For illustrative purposes, let m = 2 which means 12 slots per pole pair for a 3-phase Armature Windings. Slot angle is 360°/12 = 30°. Further …

Construction and Working of DC Machine : A Construction and Working of DC Machine is a heteropolar structure with stationary poles and the rotating armature (Fig. 5.8). DC Machine Basic Structure: An alternating emf of the same wave shape as that of B-wave is induced in every coil. As the armature rotates, the emf s induced in the belt of coil-sides under a given pole is unidirectional and the pattern alternates from pole to pole as shown in Fig. 6.11 for a 4-pole DC Machine. For obtaining a constant voltage from armature coils, rectification action is required. This can be achieved by the mechanical …

Tooth Ripple : Because of lower reluctance of the magnetic path corresponding to the teeth as compared to the slots, the flux density wave in the air-gap is ripple as shown in Fig. 6.9. Unlike the space harmonics of the B-wave which move at the same peripheral speed as the fundamental, the tufts of flux embracing the teeth move back and forth as the teeth move relatively past the pole-shoes. Since there is no net movement of B-wave ripple, no space harmonic is produced by these. However, due to cyclic variation in reluctance of the magnetic path offered to the field poles by …

Types of Armature Winding : We Know that field and Armature Windings Machine are the essential features of electric machines. The field windings are simple arrangements with concentrated coils (i.e coils in which all the turns have the same magnetic axis). Types of Armature Windings Machine on the other hand comprise a set of coils (single or multiturn) embedded in the slots, uniformly spaced round the armature periphery. The emfs are induced in armature coils due to relative motion between them and the B-wave in the air-gap established by the field windings. In an ac machine (3-phase) the armature coils are symmetrically …

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