Page 645 - Basic Electrical Engineering

I ao 2 R from the no-load input to the motor. By knowing the constant losses,
a
efficiency of the machine can be calculated at any load current. For the sake

of actual calculation of efficiency, let us take up one example.

Figure 7.25 Swineberne’s test for determining efficiency

Example 7.1 A 220 V, 50 kW dc shunt generator was run as a motor on no
load at rated speed. The current drawn from the line was 8 A and the shunt

field current was 2 A. The armature resistance of the machine is 0.1 Ω.
Calculate the efficiency of the generator at full load.

Solution:

Input power at no load = VI
= 220 × 8

= 1760 W

Figure 7.26