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The composition and treatment of electrical steel, the use of insulating coatings, and a number of practical considerations work together to influence core loss
TWO DECADES HAVE NOW PASSED SINCE everyone began to recognize the importance of effciency in integral horsepower a-c motors. From that very beginning, one of the big issues has been core loss. "Better steel" (and more of it) was a basis for more efficient motor design. And the manufacturers tried so many variants that the same product line on the same assembly floor might be using two or three different lamination steels at the same time.
Also from the beginning, the repair industry was involved in the core loss issue up to its eyebrows. Still being made today are studies of the rewind process aimed at establishing procedures that won't increase core loss. Test, calculation, and information gathering methods are being sought that will enable a shop to know if a motor coming in for repair has already been damaged, as well as whether or not a subsequent repair does any harm.
Those concerns raise such questions as: Do today's lamination steels really behave differently, and if so in what ways? What variations must be dealt with? As background, let's have a short true-false quiz. Don't worry; there are no grades (no prizes, either-just test yourself on your knowledge of magnetic steel usage in motors. You may be surprised . .
1. At a given magnetic field strength (other things being equal), the basic loss in steel depends entirely on its silicon content. T_ F_
2. Because standard lamination steels were too thick to achieve a low eddy current loss, thinner materials had to be developed before more efficient motors were possible. T_F_
3. Internal loss, in watts per pound of weight (or per cubic inch of volume), is the only fundamental lamination steel property that directly influences total motor loss. T_ F_
4. The only purpose served by insulating motor laminations is to block eddy current flow. T_ F_
5. The condition of insulation (coreplate) on laminations can be measured accurately by standard tests in use for many years. T_ F_
6. The loss-reduction value of certain coreplate coatings is determined only by their electrical resistance. T_ F_
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