An elementary book on electricity and magnetism and their applications . FlG. Stf. — Stationary armature of figure 23b for high-speed alternator. ALTERNATING-CURRENT GENERATORS 351 revolves) or the magnetic flux moves across stationary con-ductors (that is, the field revolves, as shown in figure 235).As a matter of fact, the revolving-armature type is rarely usedeven in very small sizes, so that practically all alternators arebuilt with a rotating field and stationary armature. Thereasons for this construction are that it offers better oppor-tunity for insulation of the armature windings and i
An elementary book on electricity and magnetism and their applications . FlG. Stf. — Stationary armature of figure 23b for high-speed alternator. ALTERNATING-CURRENT GENERATORS 351 revolves) or the magnetic flux moves across stationary con-ductors (that is, the field revolves, as shown in figure 235).As a matter of fact, the revolving-armature type is rarely usedeven in very small sizes, so that practically all alternators arebuilt with a rotating field and stationary armature. Thereasons for this construction are that it offers better oppor-tunity for insulation of the armature windings and it is notnecessary to have such a high voltage on the collecting Fig. 235. — Diagram of revolving field and stationary armature. Figure 236 shows the cylindrical type of revolving field,which is merely a steel drum with slots cut in its peripheryand with heavily insulated copper conductors set in so as toform two or four magnetic poles. This rotates at very highspeed within a shell made up of laminated steel with slots cutin its inner surface for the armature windings, as shown infigure 237. The whole machine is inclosed so that it can becooled by a forced draft of air. Such machines are built insizes ranging from about 500 kv-a. up to the giant 45,, and run at speeds of 750, 1500, 1800, and3600 , depending upon whether the field has two or fourpoles, and whether the machine is intended to operate at25 cycles or 60 cycles. 352 ELECTRICITY AND MAGNETISM Governor Figure 238 shows a salient-pole type of revolving field whichlooks and acts very much like a great flywheel. The polesare alternately north and south and are
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmagnetism, bookyear19
