Page 655 - Basic Electrical Engineering

Thus, power output = 19.4 × 0.735 = 14.26 hp.

Example 7.8 A 220 V dc shunt motor takes 5 A at no load. The armature
resistance is 0.2 Ω and field resistance is 110 Ω. Calculate the efficiency of

the motor when it takes 40 A on full load.

Solution:

Figure 7.32

At no-load, I = 5 A
L
therefore, I = 5 − 2 = 3 A
a

At no-load, when the motor output is zero, the input = V I (No-load) = 220 ×
L
5 = 1100 W.

2
2
The whole of input is lost as I R loss + I R loss + Iron loss + Friction and
f
f
a
a
Windage loss.

2
2
I R = 5 × 0.2 = 5 W
a
a
2
2
I R = 2 × 110 = 440 W
f
f