Page 97 - Offshore Electrical Engineering Manual

84 CHAPTER 6 DC Generators

(A) (B)
+

ARM. RHEOSTAT ARM. RHEOSTAT
SHUNT FIELD SHUNT FIELD

–
SERIES FIELD SERIES FIELD
FIGURE 2.6.1
Compound-wound direct current generator: (A) short shunt connected and (B) long shunt
connected.

RATED VOLTAGE
VOLTAGE DUE TO SHUNT FIELD
(B)

VOLTAGE (A) VOLTAGE DUE TO SERIES FIELD

FULL LOAD

AMPERES
FIGURE 2.6.2
Characteristics of a compound-wound generator: curve A, as a series generator and curve
B, as a shunt generator.

Variations in characteristics can be obtained by altering the strength of the
series winding, such as undercompounding, flat compounding or overcompounding
(Fig. 2.6.3), although the arrangement usually adopted is flat compounding.
It can be observed that the curves in Fig. 2.6.3 are not completely linear because
of the saturation effects, and so even with flat compounding, a hump of 2%–3% is
normal, but in small generators may be as much as 6%–7%.