When on normal full-load, a 500 V, d.c. shunt motor runs at 800 rp.m. and takes an armature curent 42 A. The flux per pole is reduced to 75% of its normal value by suitably increasing the field circuit resistance. Calculate the speed of the motor if the total torque exerted on the armature is (a) unchanged (b) reduced by 20%. The armature resistance is 0.6 2 and the total voltage loss at the brushes is 2 V.

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Problem 1
When on normal full-load, a 500 V, d.c. shunt motor runs at 800 r.p.m. and takes an armature current
42 A. The flux per pole is reduced to 75% of its normal value by suitably increasing the field circuit
resistance. Calculate the speed of the motor if the total torque exerted on the armature is (a) unchanged
(b) reduced by 20%.
The armature resistance is 0.6 2 and the total voltage loss at the brushes is 2 V.
Transcribed Image Text:Problem 1 When on normal full-load, a 500 V, d.c. shunt motor runs at 800 r.p.m. and takes an armature current 42 A. The flux per pole is reduced to 75% of its normal value by suitably increasing the field circuit resistance. Calculate the speed of the motor if the total torque exerted on the armature is (a) unchanged (b) reduced by 20%. The armature resistance is 0.6 2 and the total voltage loss at the brushes is 2 V.
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