246 ALTERNATORS. 



Thus, in Fig. 1 1 6 it is seen that the voltage b c is nearly 

 J period in advance of the current in phase. If the external 

 circuit is non-inductive, the terminal voltage of the alter- 

 nator will be in phase with the current and nearly J period 

 behind the voltage b c. In this case the armature impedance 

 will only diminish the terminal voltage to a slight extent. 

 If the external circuit is so highly inductive that the terminal 

 voltage makes the same angle with the current as the arma- 

 ture loss voltage b c, the full value of this voltage will be sub- 

 tracted from the total voltage generated to produce the 

 terminal voltage. This action has already been discussed at 

 some length on page 233. 



The following is a simple approximate construction for 

 determining the loss of voltage for any value of the power 



SCALE OF VOLTS 



i i r i i i i i i i i i I 



20 40 60 80 100 120 140 160 .180 200 

 FIG. 117. CONSTRUCTION FOR FINDING Loss OF VOLTAGE AT ANY POWER-FACTOR. 



factor of the circuit from the results of the experiment just 

 given. The principles upon which it depends are exactly 

 similar to those given for a similar purpose in connection with 

 a transformer, p. 162 .and seq. 



Let it be desired to determine the voltage drop of an 

 alternator when working with its full load on a circuit of 

 varying power-factor. 



Draw a semi-circle A E B with centre and radius equal 

 to the open circuit voltage of the machine. (See Fig. 117.) 



Construct the triangle a b c obtained from the experiment 

 in the manner j ust described, choosing the values correspond- 



