A 200 hp, 2300V, three phase, 60Hz, wound rotor induction motor has a blocked ro

Question

A 200 hp, 2300V, three phase, 60Hz, wound rotor induction motor has a blocked rotor voltage of 104V. The shaftspeed and slip speed, when operating at rated load are 1775 r/min and 25 r/min, respectively. Determine (a) number of poles; (b) slip; (c) rotor voltage at slip speed.

Explanation / Answer

slip speed=Ns-Nr =>Ns=slip speed+Nr =>Ns=25+1775=1800 rpm Frequency,f=PNs/120 =>P=120*f/Ns =>P=120*60/1800=4 Slip=slip speed/Ns=25/1800=0.01388 Rotor voltage under blocked rotor condition means under standstill condition. Rotor voltage under running conditions Er=Slip*E2 Where Er is rotor voltage/phase under running conditions and E2 is rotor voltage/phase under standstill condition E2/ph=104/sq.root(3)=60.04V Hence,Er/ph=slip*E2/ph=0.01388*60.04=0.8338V

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