For a 7.46 kW, 200 V dc shunt motor with full load efficiency of 85% has armature resistance of 0.25 ohms. Calculate the value of starting resistance in ohms for a current 1.5 times of the full load current.(a) 2.788(b) 3.038(c) 2.688(d) 2.588I got this question in an interview for job.This key question is from DC Motor Starting topic in section DC Motors of Electrical Machines

For a 7.46 kW, 200 V dc shunt motor with full load efficiency of 85% h

1.	For a 7.46 kW, 200 V dc shunt motor with full load efficiency of 85% has armature resistance of 0.25 ohms. Calculate the value of starting resistance in ohms for a current 1.5 times of the full load current.(a) 2.788(b) 3.038(c) 2.688(d) 2.588I got this question in an interview for job.This key question is from DC Motor Starting topic in section DC Motors of Electrical Machines
Answer» Right OPTION is (a) 2.788 Explanation: FULL load CURRENT = 7460/(2000.85) = 43.88 A Starting current = 1.543.88 = 65.883 A R = V/I = 200/65.883 = 3.038 OHMS Starting resistance = 3.038 – 0.25 = 2.788 ohms.

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