Basic DC Generator

Separately Excited Shunt Generator

ff

p

ff G

a p G

bat

f

f rheo

N I

nN I kE n k

EIR R

R

R

If the Rheostat resistance is reduced, If increases, Φp increases, Ea increases, as shown in the “Magnetization” Curve

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 “counter-torque” 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

0a p G

a

p

p G

E n kEnk

T a a a

T a

a

a

V I R EV EIR