ALTERNATOR REGULATION AND OPERATION 153 



synchronous reactance of the generator and its regulation at 0.85 power- 

 factor, current lagging. 



From Fig. 154, the maximum value of the short-circuit current is 1,400 

 jimp., \\hu-h is equal to the coil current. This corresponds to 240 amp. in 

 the field, and at 240 amp. field current the open-circuit terminal voltage is 

 2,180 volts. The corresponding coil voltage is 



-'- = 1,260 volts 



V3 



1 'Mid 



Z. (per coil) = j - n = 0.90 ohm = A', nearly. 

 1,4UU 



If the resistance between terminals is 0.12 ohm, it includes two coils in 

 series, as the Y-connection is assumed, so that the ohmic resistance per coil 

 is 0.12/2 = 0.06 ohm. The effective resistance per coil is equal to 1.5 X 

 0.06 = 0.09 ohm. 



1 500 (100 



The rated current of the machine = - J pr = 376 amp. per terminal. 



2,300\/3 



2 *^00 



The rated voltage per coil = - - = 1,330 volts. 



V3 



The no-load volts per coil is found by applying equation (39), page 139. 



cos 6 = 0.850 _ 6 = 31.8 _ sin = 0.527 _ 

 E = V[(1,330X 0.850) + (376X 0.09)]'+ [(1,330 X 0.527) + (376 X 0.90)}' 

 = 1,560 volts. 



j 5g0 _ 1 330 

 The percentage regulation per coil = ^ oon'^ " 100 = 17-4 per rent. 



Ant. 



The open-circuit terminal voltage = l,560\/3 = 2, 700 volts. 



2,700 - 2,300 

 The percentage regulation using this value = - = 1 , . J 



per cent. Ans. 



69. Regulation of a Delta -connected Generator.- It is im- 



pos>ihle to determine whether a machine is Y -connected or dclta- 

 conneeted unless the winding itself he inspected. Fortunately 

 it makes no difference, so far as calculation of the regulation 

 noerned, whether the machine be Y-connected or delta- 

 conneeted. It may be assumed to be either and the result is 

 the same if the work is consistent. In the delta machine, the line 

 voltage and the coil voltage are equal, but the coil current is t In- 

 line current divided by \ :j. The ammeters connected in delta. 

 as shown in l-'iir. 153 (c), measure the coil cm-rent directly. 



Let it be assumed in the problem of the preceding paragraph 

 that the machine is delta-connected. Using 240 amp., the 



