2 ALTERNATING GENERATORS AND SYNCHRONOUS MOTORS. 
cases is an exciter directly coupled to the generator or 
driven by an external source. The excitation voltage 
seldom exceeds 250 volts. 
Fig. 1 indicates the connection diagram of a separately 
excited alternator. 
3. Separately Excited Alternators.—The main field cir- 
cuit is connected in the following manner. The two ends 
of the magnet coils B of the alternator A, Fig. 1, are con- 
nected to slip rings C, which receive the magnetizing 
eurrent through brushes connected to the terminals of 
the exciter D. Generally, the alternator field cireuit 
contains a regulating resistance R,, in order that the ex- 
Fie. 1.—CoNNECTION DIAGRAM OF SEPARATELY 
EXcITED ALTERNATOR. 
citation current may be varied, so as to obtain a constant 
pressure under varying loads at the generator terminals. 
For fine adjustment of the excitation, a second regulating 
resistance #, is placed in the exciter field circuit E. 
4. Self Excited Alternators.—The self excited generator 
requires no exciter, the current being taken directly 
from the alternator terminals, after passing through a 
suitable number of brushes, to a commutator C, Fig. 2. 
This commutator, of special design, takes the place of the 
slip rings, and its segments are connected to the circuits 
of the magnet winding B. 
