# Chapter 7: D.C. Machines¶

## Example 7.1, Page 243¶

In :
#Variable declaration
Rf = 200;    # The resistance of field winding of a shunt generator, ohm
Po = 80e+03;     # Power delivered by the machine, watt
V = 450;    # The terminal voltage, volt
E = 475;    # The generated emf, volt

#Calculations
# Part (a)
# Po = V*I_L, solving for I_L
I_L = Po/V;     # Load current, A
I_f = V/Rf;     # Current through field resistor, A
I_a = I_L + I_f;    # Current through armature resistance, A
# As I_a*Ra = E - V, solving for Ra
Ra = 25/I_a;    # Armature resistance, ohm

# Part (b)
Po = 50e+03;    # Output power delivered by the machine, watt
V = 460;    # The terminal voltage, volt
I_L = Po/V;     # Load current, A
I_f = V/Rf;     # Current through field resistor, A
I_a = I_L + I_f;    # Current through armature resistance, A
# As I_a*Ra = E - V, solving for E
E = V + I_a*Ra;     # The generated voltage, volt

#Results
print "The armature resistance = %5.3f ohm"%Ra
print "The value of generated emf = %5.1f V"%E

The armature resistance = 0.139 ohm
The value of generated emf = 475.4 V