8-15. A 300-hp 440-V 560-A, 863 r/min shunt dc motor has been tested, and the following da...

8-15. 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:

No-load operation:

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.]