Twentieth century hand-book for steam engineers and electricians, with questions and answers .. . IGURE 56. to posts P2 and P, thence to posts P2 and P on the con-troller magnet, through the controller magnet to current passes in the direction indicated by thearrows When an arc machine is to be run frequently at asmall fraction of its normal capacity, the use of a lightload device is advisable to secure the best results inregulation. The rheostat for this purpose (see Fig. 57) is con-nected in shunt with the right field of the generator. ELECTRICITY FOR ENGINEERS 97 Facing the rheostat
Twentieth century hand-book for steam engineers and electricians, with questions and answers .. . IGURE 56. to posts P2 and P, thence to posts P2 and P on the con-troller magnet, through the controller magnet to current passes in the direction indicated by thearrows When an arc machine is to be run frequently at asmall fraction of its normal capacity, the use of a lightload device is advisable to secure the best results inregulation. The rheostat for this purpose (see Fig. 57) is con-nected in shunt with the right field of the generator. ELECTRICITY FOR ENGINEERS 97 Facing the rheostat with the right binding posts at thebottom, the contact on the right side or No. I givesopen circuit and throws the rheostat out of use. PointNo. 2 gives a resistance of 44 to 46 ohms and PointNo. 3 gives a resistance of 20 to 22 ohms. This rheostat with a 75-light machine allows the fol-lowing variations: Point 1, 75 to 48 lights; Point 2,48 to 25 lights; Point 3, 25 lights or less. For use with. FIGURE 57. other sizes of generators, the adjustment of the rheo-stat must be made to suit the conditions. When the rheostat is in use, the sparks at the com-mutator will be somewhat larger than normal, but willnot be detrimental. The controller magnet (see Fig. 58) is to be fastenedsecurely by screws to the wall or some rigid uprightsupport, taking care to have it perfectly plumb. It isconnected to the machine in the manner shown in , , the binding post P2 on the controller magnet is 98 ELECTRICITY FOR ENGINEERS connected to the binding post P2 (see Fig. 55) on theend of the machine, and likewise the post P on thecontroller to the post P on the leg of the machine;the post P1 forms the positive terminal from which thecircuit is run to the lamps and back to N. Great care should be taken to see that the wires P P
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