By Gerhard Henneberger
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Extra resources for Electrical machines
81: DC machine, basic design L Fig. 82: air gap field vs. 12) Equivalent to an armature turn of one pole pitch, the flux linkage of the armature winding reverses from +φ to -φ. 14) The number of armature conductors is z. 15) 2⋅a = 2 IA /2 IA IA IA /2 Fig.
Usual for the design of large DC machines is an arrangement of any coil being composed of more than one turn (ws > 1) and a slot filling with more than one coil each (u > 1). N S N Fig. 80b: lap winding Fig. 2 Basic equations As the general design of a DC machine is illustrated in Fig. 81, Fig. 82 shows the air gap field caused by exciter windings versus a complete circumference of the armature. B( α ) main pole (solid) B L exciter winding X F x x x α ·π yoke (solid) n i x x IA 0 IA π 2π p·α F X armature winding B Fig.
The armature needs to be laminated, because armature bars carry currents of frequency f = p ⋅ n . Since number of pole pairs and speed is not related for DC machines, frequencies higher than 50 Hz may appear. φ /6 x + x x x x x x - Large DC machine models are designed with more than 2 poles. Machines with p poles show p-times repeating electrical structure along the circumference. x x x x x - x x x + x x - + x Advantages: lower core cross sections, shorter end turns, short magnetic distances Disadvantages: more leakage, more iron losses, caused by higher armature current frequency, commutation more difficult.