Since the latter posts, I got to reading a little more last night on losses in
strip wound cores and it hit me that I had forgot yet another reason for the
losses. When those cores are wound, one must remember they are wound in a
spiral. Well, in nature, those magnetic lines of flux dont flow in a spiral but
a circular or oval pattern following the shape of the core. The thing is during
a cycle of current, lets say the line starts in the center of the core, and
begins to go out through the legs. As it gets into the legs it wants to make a
straight path downward before it gets bent again. Since the line wants to go
straight, and the core is spiral wound, as the line gets lower, it starts
moving from the middle of the lam to the skin. After it gets so far, it has to
jump over to the next lam so as to make a straight line. Now, where it jumps is
only one thing, a gap! Thus, the more tuns on the core, the more gaps there is
adding up, besides any from a cut where the core goes to
gether. This even being on a toroid that is spiral wound. Another thing, this
could cause more than one gap between each lam or the flux may have to jump
over more than once per layer to keep in a straight line ( I would think maybe
twice). That is according to the design of the core and its shape.
If one wanted to make one with the very least amount of losses, one would need
to make rings out of the strip and butt weld each together. Each ring then
would progress in size. Then each stacked over the other until the proper
thickness was made. That way, the flux would have a straight path with no
breaks around the core, and not have to hop over any gaps.
This kind of throws a wrench in my earlier post about strip wound toroids being
the best. However they probably are over the other types now available, but
maybe not over an EI lam as it would be according to all the gaps adding up,
and which had less.
One other thing, which is just a theory, is about the flux moving in a CRGO
sheet used in an EI section. A perfect 100% grain could hurt more than help in
this case I would think. The reason being, in a core using CRNO steel, the flux
can move easily in any direction. In CRGO, it moves easily in only one
direction. The problem is that the flux has to bend around at the top and
bottom of the core into the legs. Using 100% oriented, it would cause a greater
reluctance in these areas than using say an orientation of maybe 75%. This is
just a theory of mine of course. The thing is, the steel manufacturers tests
are done on a straight piece of steel for the losses. They show 100% with less
losses than something of 75%. Any thoughts on this would be welcome.
Best,
Will
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|