CHAPTER IX 



ARMATURE-CIRCUIT CALCULATIONS, RESISTANCES, CURRENT 

 CAPACITY, ETC. 



1. In a certain dynamo the armature resistance is 0.1 ohm; 

 when giving 50 amperes it actually generates 105 volts; what is 

 the e.m.f. at the terminals? (J min.) 



2. A bipolar machine having an armature with 48 segments 

 generates at full load an actual e.m.f. of 115 volts; the resistance 

 (brush to brush) is 0.037; with 93 amperes delivered by the arma- 

 ture, what will be the average difference of potential per segment? 

 (1 min.) 



3. In the above problem what is the actual resistance between 

 two adjacent commutator bars? (J min.) 



4. A 2-pole armature is wound with 550 turns, each including 

 three feet of No. 10 wire. Required the resistance from brush to 

 brush at 70 C. (for resistivity see table on page 104). Also find 

 the current output of the armature at 600 circular mils per ampere. 

 Also tjfe armature drop with this current. (2 min.) 



5. Required the resistance and the current output, if the above 

 armature be connected for a 4-pole, 4-path (parallel-wound) 

 machine. Also for a 6-pole, 2-path (series wound). Also for a 

 10-pole, 10-path machine. (4 min.) 



6. A 2-path armature is wound duplex for 250 volts. Each 

 winding is made up of 199 turns of 4 feet each of No. 12 wire. 

 For 500 volts the coils of the two windings are simply put in series 

 by changing the connections at the commutator segments. Re- 

 quired the resistances in both cases for 40 C. For the same 

 current density how does the power lost in the armature winding 

 in the two cases compare? (3 min.) 



7. If there is a difference of 3 volts in the e.m.f.'s set up under 

 the poles in a 2-pole generator, the armature resistance being 

 0.2 ohm and the total current through the two sides being 27 

 amperes, what current will flow under each pole? What current 

 will flow when the outside circuit is open? (2 min.) 



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