. Practical wireless telegraphy; a complete text book for students of radio communication . ircuit at R permits an increase or decrease of the strength of the current flowing. Thefield winding of the shunt dynamo is composed of a large number of turns of com-paratively fine insulated wire, the actualnumber of turns being governed by theflux required, whereas the arm::ture coilshave comparatively coarse wire. Twopaths are presented to the current as itflows from the armature of this machine,one being the field circuit and the other,the external circuit. In well designed shunt dynamos, the re-si
. Practical wireless telegraphy; a complete text book for students of radio communication . ircuit at R permits an increase or decrease of the strength of the current flowing. Thefield winding of the shunt dynamo is composed of a large number of turns of com-paratively fine insulated wire, the actualnumber of turns being governed by theflux required, whereas the arm::ture coilshave comparatively coarse wire. Twopaths are presented to the current as itflows from the armature of this machine,one being the field circuit and the other,the external circuit. In well designed shunt dynamos, the re-sistance of the shunt circuit is alwaysgreater than the resistance of the armatureand external circuit, but the strength of thecurrent flowing in the shunt coil is in factcomparatively small even in the larger typesof generators. The student may question how currentis set-up in a machine of this type when itis first put into motion. The fact is that theinitial building of the current is due to residual magnetism in the field cores. When . pig. 25—Circuit of Sliunt Wound D. C. 28 PRACTICAL WIRELESS TELEGRAPHY. ^OLES a piece of soft iron has been magnetized, no matter how soft the iron may be, a certain num-ber of magnetic lines of force are retained when the magnetizing current has been turnedoff. These lines are known as the residual lines of force and the cores of the field windingare said to possess residual magnetism. When the dynamo armature is first set into rotation, the residual lines of force pass inand out of the armature conductors through the core, generating therein a feeble currentwhich flows to the field winding and increases the number of lines of force threading throughthe armature coils. This induces a stronger current in the armature conductors which con •tinually adds to the strength of field until the normal voltage of the dynamo is complete process usually requires from 10 to SO seconds. After the generator armatureattains its
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Keywords: ., bookcentury1900, bookdecade1910, booksubjecttelegra, bookyear1917
