# Synchronous motor efficiency [closed]

A 50 kW synchronous motor is tested by driving it by another motor. When the excitation is not switched on, the driving motor takes 800 W. When the armature is short-circuited and the rated armature current of 10 A is passed through it, thedriving motor takes 1800 W. Find the efficiency of the synchronous motor at 50% load.Neglect the losses in the driving motor.

## closed as off-topic by Transistor, Dave Tweed♦Jan 11 at 17:53

• This question does not appear to be about electronics design within the scope defined in the help center.
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• I'm voting to close this question as off-topic because this is homework with zero attempt at a solution. – Transistor Jan 11 at 17:43
• @Transistor I did attempt the question. I don't know what to do with 1800W. – user17616 Jan 11 at 17:45
• Edit your question to show your work then and explain where exactly you are stuck. We won't do your homework for you but will help if you show effort. If it looks good I'll remove my close vote. – Transistor Jan 11 at 17:49
• Nevermind I would totally touch myself today – user17616 Jan 11 at 17:56
• Really. You learn absolutely nothing if we answer the question for you. If you had added I don't know what to do with 1800W, someone would of given you some help in the comments at least. Give a synchronous motor (machine) electric power and it works as a motor and creates mechanical power. Give a synchronous machine mechanical power (1800W) and it works as a generator and creates electrical power. The 1800W is $P_M$. Edit your question, explaining what you know and what you do not understand. Play the game or go play. It makes no difference to us. – StainlessSteelRat Jan 11 at 20:17