A DC Motor Part A Compute the field current I Express your answer in amperes A s

Question

A DC Motor Part A Compute the field current I Express your answer in amperes A shunt-wound DC motor with the field coils and roton connected in parallel (see the figure) (Figure 1) operates from a 140 V DC power line. The resistance of the field windings, Rf, is 209 . The resistance of the rotor, R, is 4.10 ·When the motor is running, the rotor develops an emf E. The motor draws a current of 5.00 A from the line. Friction losses amount to 49.0 W Hints Submit My Answers Give Up Part B Compute the rotor current I Hints Figure 1 Submit My Answers Give Up Part C Compute the emf Hints dc Submit My Answers Give Up

Explanation / Answer

Part A -

Field current, If = V / Rf = 140 / 209 = 0.67 A

Part B -

Rotor Current, Ir = Itot - If = 5.00 - 0.67 = 4.33 A

Part C -

The emf is equal to the rotor current multiplied by the rotor resistance is the difference between the line voltage and the counter emf.

means -
emf = Vline - Irotor*Rrotor = 140 - 4.33*4.10 = 122.25 V

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