ALTERNATE CURRENT DYNAMO-ELECTRIC MACHINES. 
245 
gradually decreased until a critical point was reached, when a further diminution of 
the motor exciting current had the effect of increasing the current between the 
machines.* It was also observed that the watts given out by the generator did not. 
vary in the proportion of the currents between the machines. 
Fig. 18. 
Table V. gives the watts given out by generator for three values of its exciting 
currents 18‘2, 18‘6, and 19 amperes, the corresponding exciting currents for the 
motor being 18, 11*5, and 8*4 amperes. The current between the machines is a 
minimum for exciting currents of 18'6 and 11’5 in the two machines, and the curves 
in fig. 17 have been taken under these conditions. 
This is a point of practical importance in transmission of power by alternate 
currents, since the size of the conductor between motor and generator is mainly 
determined by the current transmitted. The cause is readily explained from the 
curves. 
Starting with the conditions as in Experiment 2, where the motor is more highly 
excited than the generator, we see that the current (as) is accelerated in phase with 
regard to the potential difference of the machines. On increasing the exciting 
current of the generator until the machines are equally excited as in Experiment 1, 
the current (x) is still accelerated with regard to the potential difference, but not to 
such an extent. On diminishing the motor exciting current until the machines are 
excited as in Experiment 3, the current (x) is in phase with the potential difference. 
For a given power transmitted this will be the point of maximum efficiency with 
regard to the intermediate conductors. Any further diminution of the motor exciting 
* This effect has been independently observed by Mr. Mordey and Mr. Kapp (see ‘ Journal of Institute 
of Electrical Engineers,’ vol. 22, pp. 128, 173). 
