. A text-book of electrical engineering;. s used up in overcoming theopposing forces due to the induced eddy currents in the copper sheet, andthe energy is converted into heat in accordance with Joules law. It isevident that eddy currents represent, under all circumstances, a loss ofenergy, and to avoid this loss the armatures of machines are always built upof sheet iron stampings or discs, as shown in the lower half of Fig. 88. Theplates are insulated from one another by means of varnish or thin paper,or sometimes by nothing more than the oxide on the surface. The ironmust evidently be lamina
. A text-book of electrical engineering;. s used up in overcoming theopposing forces due to the induced eddy currents in the copper sheet, andthe energy is converted into heat in accordance with Joules law. It isevident that eddy currents represent, under all circumstances, a loss ofenergy, and to avoid this loss the armatures of machines are always built upof sheet iron stampings or discs, as shown in the lower half of Fig. 88. Theplates are insulated from one another by means of varnish or thin paper,or sometimes by nothing more than the oxide on the surface. The ironmust evidently be laminated in a plane perpendicular to the armatureconductors, so as to break up the path along which the eddy currentswould flow. When the armature winding is placed in open slots it is often necessaryto laminate the pole-shoes, as the lines of force go mainly through the teeth,and cross to the pole-face in tufts as shown in Fig. 152. The flux-densityin the pole-shoe is greater opposite a tooth than opposite a slot, so that, V////////////////A. ///////////////MFig. 88
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