CHAPTER III 

 THE DESIGN OF ELECTROMAGNETS 



13. Introductory. The object of this chapter is partly to 

 summarize and coordinate what has already been discussed; 

 but mainly to familiarize the reader with the laws of the magnetic 

 circuit and the simple computations which will enable him to 

 proportion the iron cores and calculate the field windings of 

 electric generators. A little practice in the design of the simple 

 forms of lifting magnet, or magnetic brake, will be of the greatest 

 value in illustrating the practical application of the fundamental 

 principles underlying the design of all electromagnetic machinery. 

 The designer who wishes to specialize in lifting magnets, magnetic 

 clutches, and electromagnetic mechanisms generally, must pursue 

 his studies elsewhere : he is referred to other sources of information 

 such as MR. C. R. UNDERBILL'S book on electromagnets. 1 

 There are many matters of interest, such as the means of ob- 

 taining quick, or slow, action in magnets; equalizing the pull 

 over long distances; special features of alternating-current electro- 

 magnets; and the mechanical devices introduced to attain specific 

 ends, but none of these can receive adequate attention here. 



In the design of electromagnets with movable armatures or 

 plungers, the work to be done is usually reckoned as the initial 

 or starting pull, in pounds, multiplied by the travel, in inches. 

 Many designs, of varying sizes and costs, can be made to comply 

 with the terms of a given specification, and the main object 

 of the designer should be to put forward the design of lowest 

 cost which will fulfil the conditions satisfactorily. It is not 

 proposed to devote much space, either here or elsewhere, to the 

 detailed discussion of the commercial aspects of design; but it 

 is well to emphasize the fact that a designer who does not con- 

 stantly bear in mind the factors of first cost and cost of upkeep, 

 is of little or no value to the manufacturer. In the design of 

 electromagnets, especially of the larger sizes, the material 



1 "Solenoids, Electromagnets and Electromagnetic Windings:" D. VAN 

 NOSTRAND Co. 



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