ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 71 
a weakening effect on the magnetic field which cuts the 
armature coils and, consequently, there will be a drop in 
the terminal voltage. 
If, for a certain armature current, the terminal voltages are 
- measured for different excitations and the results plotted 
in terms of the field ampere turns, the so-called load 
characteristic of the alternator is obtained. Such a curve 
is given in Fig. 34, corresponding to the normal ,current 
on an inductive load with a power factor cosp~—0O. The 
ordinate lengths between the open ecireuit characteristic 
and the load characteristic curves represent the drops in 
volts. For instance, the drop of the terminal voltage is 
6,500 — 5,300 = 1,200 volts when the exciting current 
is 30 amperes, with an armature current of 26 amperes 
lagging 90 degrees behind the E. M. F. 
123. Load Characteristics with Various Power 
_ Factors.—Load characteristies indicating the inherent 
regulation can be obtained for different current values, 
as well as for different power factors, but in the first 
instance it is interesting to know the voltage drop on the 
armature when carrying the normal current with the 
‘power factors cos p = 0 and cos Y = 1, the former being 
the inductive and the latter the non-inductive load. | 
It is important to note, that a small voltage drop on a non- 
inductive load, does not always result in good regulation 
on an inductive circuit, but if the inductive regulation is 
good, then the regulation on a non-inductive load will no 
doubt be satisfactory. 
For an all round good regulation the inductive (cos p = 0) 
voltage drop gives the only reliable guide. 
124. Necessity for Good Inductive Voltage Drop.— 
It is best to design the alternator for a commercially good 
inductive voltage drop, especially if the generator is 
intended to supply a power circuit. 
