Twentieth century hand-book for steam engineers and electricians, with questions and answers .. . figure 69. direct current is usually obtained from another sourceaside from the current generated in the armature ofthe alternating current dynamo. A separate dynamo,called an exciter, is employed for supplying the cur-rent to the fields. There are some types of so calledcomposite wound alternating current dynamos inwhich a part of the current from the alternator arma- 124 ELECTRICITY FOR ENGINEERS ture is rectified or commutated by means of a commu-tator mounted on the same shaft with the armatur
Twentieth century hand-book for steam engineers and electricians, with questions and answers .. . figure 69. direct current is usually obtained from another sourceaside from the current generated in the armature ofthe alternating current dynamo. A separate dynamo,called an exciter, is employed for supplying the cur-rent to the fields. There are some types of so calledcomposite wound alternating current dynamos inwhich a part of the current from the alternator arma- 124 ELECTRICITY FOR ENGINEERS ture is rectified or commutated by means of a commu-tator mounted on the same shaft with the armature, Armatures are woundin two layers. .__ upper coil. lower » FIGURE and this commutated current passed around the fieldcoils in a manner similar to the direct current com- ELECTRICITY FOR ENGINEERS 125 pound wound dynamo. In Fig. 70 we have a diagramof connections of a composite wound machine made bythe General Electric Company. It will be noticed thatin connection with this dynamo we still employ a sepa-rate direct current exciting machine. The object of thiscomposite winding is the same as with the compoundwound direct current dynamo, namely, regulationunder variable loads without the necessity of changingthe strength of the field exciting current from theexciter dynamo. The winding of the alternate currentarmature consists of the same number of armature coilsas there are pole pieces in the fields of the outer end of the first armature coil is left free tobe connected to one of the collector rings, while theother end of the coil is connected to the inner end ofthe second coil; the outer end of the second coil isconnected to the outer end
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