 For
a linear magnetic circuit:
 Substituting
 We
obtain:
 Where:
 Permanent
magnet DC machine
 Separately excited DC machine
 Self excited DC machine
Shunt wound DC machine
 Series wound DC machine
 Compound wound DC machine



Cumulative compound
 Short shunt DC machine
 Long shunt DC machine
Differential compound
 Short shunt DC machine
 Long shunt DC machine
 A PM
motor does not have a field winding on the
stator frame
 The
armature and the field are fed from two
independent sources.
 From
the figure beside:
The characteristics of the shunt machine are similar to
those of the separately excited machine
 From
figure beside:
 The
speed of the DC series motor is approximately
inversely proportional to the input current.
 Therefore, on light loads dangerously high speeds
could be reached. In practical applications of the
motor, protective devices are used to guard against
this contingency.
 The torque equation:
 Calculate
the voltage induced in the armature
winding of a 4-pole, lap-wound, dc machine
having 728 active conductors and running at 1800
rpm. The flux per pole is 30 mWb.
 The
armature is lap wound, a=p
 What
is the voltage induced in the armature of the
machine of example 1, if the armature is wave
wound?
 For
a wave-wound armature, a = 2. Thus,
230-V, shunt generator has Ra=0.05 Ω
and Rf =57.5 Ω. If the generator operates at rated
voltage, calculate the induced voltage at full-load.
Neglect brush contact drop.
 A 100-kW,
 If
the generator of example 3 has a total
mechanical and core loss of 1.8 kW. Calculate:
The generator efficiency at full-load
 The horsepower output from the prime mover to drive
the generator at this load.

 From
example 3:
 The copper losses in the field and armature
winding are:
 A separately
excited dc generator has a constant
loss of Pc(W), and operates at a voltage V and
armature current Ia. The armature resistance is Ra.
At what value of Ia is the generator efficiency a
maximum?
 For
η to be a maximum, dη/dIa=0, or
 Therefore:
 the
efficiency is maximized when the armature
loss equals the constant loss, Pc.
 At
what load does the generator of examples (3)
and (4) achieve maximum efficiency? What is the
value of this maximum efficiency?
 From
problem 4, the constant losses are:
 From
example (5):
 And
 A 10-hp,
230-V shunt motor takes a full-load line
current of 40 A. The armature and field resistances
are 0.25 Ω and 230 Ω, respectively. The total
brush-contact drop is 2 V and the core and friction
losses are 380 W. Calculate the efficiency of the
motor. Assume that stray-load loss is 1% of output.