Basic DC Generator
Separately Excited Shunt Generator
NI
 
R
f
f
p
nN I k
E  n k 
R
E
I 
R R
f
a
p
G
bat
f
f
rheo
If the Rheostat resistance is reduced, If increases, Φp increases,
Ea increases, as shown in the “Magnetization” Curve
f
G
Operating Point
Ebat = If(Rf +Rrheo)
looks like y=mx + b
Superimpose on the
Magnetization curve
Operating Point (continued)
Intersection with the
Magnetization curve yields
the operating point
Generator-to-Motor Transition
• Permanent-magnet
field
• One-turn armature
• Drive so that Ea>Ebat
• Current Ia flows to
charge Ebat
From a Circuit Point-of-View
• “Generate” voltage Ea
• When supplying
current, the machine
develops a “countertorque” in opposition
to the driving torque
Motor-to-Generator Transition
• “Uncouple” the Prime
Mover
• Eventually, Ea will
decrease so that
Ea<Ebat
• Ia flows as shown
• Armature turns in the
same direction
From a Circuit Point-Of-View
• Counter-emf, Ea, is
induced, opposing the
driving voltage Ebat
• Machine develops a
driving torque
Reversing Direction Method 1
Reverse the Armature Current
Reversing Direction – Method 2
Reverse the Direction of the Field
Basic DC Motor – Shunt Motor
Characteristics of a Shunt Motor
• Shunt field provides
the pole flux
• Power in the field is
independent of the
LOADing
• Generate counter-emf
in the armature
E  n k
a
p
V I R E
T
E
n 
 0
k
a
p
p
G
a
a
G
V E
I 
R
T
a
a
a
a