Q1: 220V, 7 Hp DC series motor coupled to a fan. The motor draws 25 A and runs at 300 rpm at a terminal voltage of 220V with no external resistance. The torque of the fan is proportional to the square of the speed. If Ra = 0.6 Ω and Rf = 0.4 Ω (Neglect rotational losses): a) Determine the power supplied to the fan and the torque developed by the motor. b) The speed is to be reduced to 200 rpm by inserting external resistance. Determine the value of this resistance and the power delivered to the fan.
Added by Judith B.
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The total resistance (R_total) in the circuit is the sum of the armature resistance (Ra) and the field resistance (Rf). \[ R_{\text{total}} = R_a + R_f = 0.6 \, \Omega + 0.4 \, \Omega = 1.0 \, \Omega \] Show more…
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