ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 79 
In order to obtain the terminal pressure on the armature 
carrying a current of 26 amperes at cos g = 1, the follow- 
ing operation has to be performed. 
Supposing that the field excitation is 30 amperes, the reactive 
ampere turns A B" are first determined as in Par. 732; 
then a semicircle with O A as diameter is described on 
OA. This semicircle when intersected by A B* from 
center A, gives O T as the excitation corresponding to the 
load voltage. It is obvious from the figure that O T and 
AT form an angle of 90 degrees, corresponding to cos P 
= 1. In the above case O T is equal to 28 amperes and 
the load pressure, 6,300 volts. 
135. Actual Load Characteristic.—The actual load char- 
acteristic of the 235 KVA. alternator, Fig. 34, indicates 
that with the above described method, the inherent regula- 
tion from the no-load and short circuit characteristics can 
be satisfactorily determined. 
The design of an alternator with a specified pemalation is 
therefore reduced to the proper predetermination of the 
open circuit and short cireuit characteristics. 
136. Elements which Affect Regulation.—tThe principal 
elements which affect the regulation of an alternator are 
as follows: 
1. Voltage drop due to the ohmic resistance of the arma- 
ture. 
Voltage drop due to hysteresis and eddy currents. 
Leakage of exciting field. 
Leakage of armature field. 
. The demagnetizing effect of the armature ampere turns. 
In a properly designed alternator, the two items 1 and 2 are 
so small that they may be neglected; but the magnetic 
properties mentioned under 3, 4 and 5 have to be carefully 
considered. 
The action of the magnetic properties mentioned above will 
oR go by 
