192 ELEMENTS OF ELECTRICAL ENGINEERING. 



times as much heat generated in it as would be generated in it by the direct current 

 alone. 



The conductors midway between the points of attachment of the collector rings 

 (a = o) are heated least, and the conductors near the points of attachment of the 

 collector rings (oc= TT/H} are heated most. For example, in a two-ring converter 

 ( ^2) the conductors midway between the points of attachment of the collector rings 

 (a = o) have only 0.453 as much heat generated in them as would be generated in 

 them by the direct current alone, and the conductors near the points of attachment of 

 the collector rings (a= 90) have three times as much heat generated in them as 

 would be generated in them by the direct current alone. 



95. The average heating of the entire armature of a rotary converter. The 



average heating over the entire armature is found by integrating the equation (ii) 

 Art. 94, with respect to a from a= TT/W to a = -f- TT/W, and dividing the result 

 by 27T/w. This gives : 



Average heating of armature of f n 2 / r ^ ^ \ f --\ 



w-ring converter is proportional to : 4 \ TT* n 2 sin 2 TT/W/ 



The average heating is therefore ( I -I s ; | * times as great as the 



\ 7T 2 ' 2 Sin 2 .TT/tt/ 



heating of the armature by the direct current alone. Therefore an w-ring converter 

 can put out 





times as much direct current as the same machine can when used as a simple direct- 

 current generator, for the same total armature heating. The table of ratings given in 

 Art. 92 is calculated in this way. 



96. The use of the double-current machine as a direct-current 

 three-wire generator. When the synchronous converter is driven 

 by an. engine and used to deliver both alternating current and 

 direct current, it is called a double-current generator. Such a 

 machine can be used to deliver direct current to an Edison three- 

 wire distributing system as mentioned on page 273 of the first 

 volume of this treatise. This use of the double-current gener- 

 ator is due to Dobrowolsky. The essential features of this 

 arrangement are shown in Fig. 160 for a two-ring machine. The 

 voltage between the direct-current brushes a and b is, say 220 

 volts, and it is desired to supply direct current to an Edison three- 



* Generally less than unity. 



