152 



ALTERNATING CURRENTS 



characteristics. Therefore, only the single-phase calculations 

 already described are necessary. Two conditions arise, one when 

 the machine is considered as being Y-connected and the other 

 when it is considered as being delta-connected. In each case 

 only coil values of current and voltage are used. 



68. Regulation of a Y-connected Generator. If the machine 

 is considered as being Y-connected, the coil voltage is equal to the 



40 80 120 ICO 200 2W 210 320 360 400 410 *bO 

 Field Current 



FIG. 154. Open- and short-circuit characteristics of a 1500 kv-a. alternator. 



line voltage divided by \/3- The coil current and the line 

 current are the same. The method of dealing with such a prob- 

 lem is illustrated by the following example: 



Example. Figure 154 shows the open- and short-circuit characteristics 

 of a 1,500-kv-a., 2,300-volt, 60-cycle alternator. Terminal volts and line 

 current are plotted as ordinates with values of field current as abscissas. 

 Assume that the machine is Y-connected. The resistance between each pair 

 of terminals as measured with direct current is 0.12 ohm. Assume that the 

 effective resistance is 1.5 times the ohmic resistance. Determine the 



