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1. flex life,
2. ease in terminating,
3. Power capacity edge over solid,
4. Length of conductor less sensitive to temperature,
flexure and other environmental conditions.
Whether this difference is significant in VFD applications, I don't know.Special winding construction, using litz wire or foil, is often necessary to control eddy-current losses in high-frequency transformer and inductor windings. The high cost of these techniques is a major limitation in developing high-powerdensity, high-efficiency components for power electronics. A much lower-cost alternative is simple stranded copper wire with uninsulated, bare strands. In addition to the wire cost advantage arising from avoiding the insulation process, there is a component-manufacturing cost advantage arising from the easier termination of bare strands. The loss with uninsulated strands will certainly be higher than in true litz wire with individually insulated strands. However, the high-frequency loss can be substantially lower than in solid wire—the separation into strands impedes eddy currents, even if it does not completely stop them. Anecdotal evidence has supported the idea that this can work well in some applications. However, until now, there has not been a model available to predict the eddy-current losses in stranded wire with uninsulated strands, which we will refer to simply as stranded wire for the remainder of this paper. Thus, it has not been possible for a designer to evaluate this lowcost alternative and determine whether it is a good choice for a particular application, and it is almost never used.
SHEE said:Increase in Resistance Due to Stranding. If it were true that no current flows from wire to wire through their lineal contacts, the proportional increase in the total resistance would be the same as the proportional increase in total weight. If all the wires were in perfect and complete contact with each other, the total resistance would decrease in the same proportion that the total weight increases, owing to the slightly increased normal cross section of the cable as a whole. The contact resistances are normally sufficient to make the actual increase in total resistance nearly as much, proportionately, as the increase in total weight, and for practical purposes they are usually assumed to be the same.