CHAP. XIII] ^TORQUE AND TRACTIVE EFFORT 259 



Art. 24 and prob. 18 in Art. 26). Take 6 to correspond to 

 two pole pitches, or 0=2?r/(ip); then *=!//, where / is the 

 frequency of the magnetic cycles. Substituting these values and 

 using the value of E from eq. (37), Art. 31, we get, after 

 reduction, 



T ave =iNp0 /n joules, ..... (196) 



where is in webers; or 



T ace = 0.0325i\Vp0 X ID' 2 kg-meters, . . (196a) 



being in mcgalines. 



This formula does not contain the speed of the machine, 

 the torque depending only upon the armature ampere-turns iN 

 and the total flux p0. Consequently, the formula can be used 

 for calculating the starting torque or the starting current of 

 a motor. Eqs. (196) and (196a) give the total electromagnetic 

 torque, part of which serves to overcome the hysteresis, eddy 

 current s, friction and windage. The remainder is available on 

 the shaft. When calculating the starting torque, it is necessary 

 to take into account the effort required for accelerating the 

 revolving masses. 



(6) The Torque in a Synchronous Machine. The equation of 

 energy is 



T ave O=miEcos<j>'.t, ..... (197) 



where m is the number of phases, i and E are the effective values 

 of the armature current and the induced voltage per phase, and 

 ^' is the internal phase angle (Fig. 37). Taking again a dis- 

 placement over two poles and using the value of E from eq. (3) 

 Art. 26, we get 



^ow- 0.0361fc 6 mitf cos tf/ptfK)- 2 kg-metere. . (198) 



(c) The Torque in an Induction Machine. The torque 

 exerted between tin- primary and the secondary members of 

 an induction machine, it may be considered from the point of 

 view of either innnlM-r. Thi- i- localise the torque of reaction 

 upon the stator is equal and opposite to the direct torque upon 

 tin rotor. For purposes of computation it is more convmi, -m 

 to consider the torque from the point of view of the primary 

 winding, in order to be able to use the primary frequency and 



