ROTARY CONVERTERS. 179 



HEATING OF ARMATURE OF ROTARY CONVERTERS. f 



122. The current flowing in the armature conductors of a 

 rotary converter is the difference between the currents on the 

 alternating and direct current sides. 



Mr. C. P. Steinmetz has shown in the paper referred to above 

 that the ratio of the total energy lost in the armature of an ?i-phase 

 converter with unit power-factor to that lost in the same machine 

 as a direct-current generator at the same output is 



(7) 



On giving numerical values to n, we see that, taking the heat- 

 ing of the direct-current armature as unity, that of the machines 

 used as a converter is: (1) single phase, T37; (2) three phase, 

 0-555 ; (3) four phase, 0-37. 



When, however, the power factor is not unity, but equals cos </>, 

 the ratio of the total energy lost in the armature of an ?i-phase 

 converter to that lost in the armature when running as a direct- 

 current generator at the same output is 



8(1 + tan 2 ft) 16 , g . 



4> 11 7T 7T" 1 



T? sin 2 - 

 n 



The proof of these formulae is given in the Appendix. 



We see, therefore, that, excepting the case of the single-phase 

 converter, a greater output can be obtained from a converter than 

 from a generator of the same size for the same permissible rise of 

 temperature. 



PROBLEMS ON CHAPTER XV. 



1. What is the amount of energy wasted per second in the armature of a 

 tri-phase rotary converter, the power factor being unity, whose armature resist- 

 ance is O01 ohm, and which gives 100 amperes on the direct-current side ? 



Answer. 56 '4 x 10 7 ergs per second. 



2. What is the energy lost per second in the converter in Question 1, if the 



/tj 



power factor is ^- t and what if the power factor is \ ? 



Answers. (1) 95'9 x 10 7 ergs per second; (2) 412 x 10 7 ergs per second. 



