8-17. A 300-hp 440-V 560-A, 863 r/min shunt dc motor has been tested, and the following data were taken: Blocked-rotor test:
VA = 16.3 V | exclusive of brushes | VF = 440 V |
IA = 500 A | IF = 8.86 A |
No-load operation:
VA = 16.3 V | including brushes | IF = 8.76 A |
IA = 23.1 A | n = 863 r/min |
What is this motor’s efficiency at the rated conditions? [Note: Assume that (1) the brush voltage drop is 2 V; (2) the core loss is to be determined at an armature voltage equal to the armature voltage under full load; and (3) stray load losses are 1 percent of full load.]
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