why do dc machines always have double layer winding?is it possible to create a single layered winding dc machine?
More generic Question: Can anyone explain the logical evolution of dc machine from the prototype (single coil) to the actual double layer-distributed winding case?
Usually in text books they use single coil to explain the principle of operation and suddenly jump to parallel paths-multiple commutator segments-double layer closed winding case .Single coil doesn't have any parallel paths and i doubt whether it is closed too.What is the logic behind the actual implementation of a dc machine and how can it be explained as progressive evolution of the simple case?
Please note I understand the reason for use of distributed winding(more no:of windings in series and hence less ripple) and to a fair extent the working of actual implementation as well.What bothers me is "can i have a dc machine with single layer, with any no: of parallel path(can it be one?),closed or un-closed winding for achieving the same emf?".
Also i'm concerned about the conceptual understanding.I tried theoretically to extend the single coil case to 2 coils in perpendicular connected in series.But i couldn't find a suitable commutator connection which will give me the required o/p(sum of their emfs).The only possible way was to go for double layer-closed form winding(which makes it 4 coils).I was not sure of this and wanted to confirm this.
Best Answer
The double layer windings are the most widely used class of windings. Though both lap and wave types are possible, because of inherent problems of a wave windings, it is now an accepted practice to use the lap type for double layer ac windings. Double layer windings fall into two main classes depending upon the value of SSP-integral slot winding when SPP is an integer and fractional slot winding when SPP is a fractional number. To meet the requirement of symmetry among phases, the number of slots phase (S/3) must be a whole number.
Double layer windings in open slots have the following advantages over single layer windings in semi-closed slots.