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MMLU-Pro / 11921 / (i) A certain 230-volt motor has an armature-circuit resistance of 0.3 ohm and…

Problem

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question

(i) A certain 230-volt motor has an armature-circuit resistance of 0.3 ohm and runs at a speed of 1200 rpm, with normal excitation and 50-amp armature current. (a) If the load is increased until the armature current has risen to 60 amp, what will be the new value of speed ? (b) If the load is reduced until the armature current has dropped to 25 amp, what will the speed become ? (ii) (a) If an attempt is made to start the motor of part (i) without auxiliary resistance, what will be the value of the current at the instant of closing the switch ? (b) What series resistance should be inserted in order that the armature current at the moment of starting may be limited to 1.5 times the normal value of 50 amp ?

category

engineering

options

  1. S_2 = 1200 rpm, S_3 = 1200 rpm, I_a = 766 amp, R_s = 3 ohms
  2. S_2 = 1100 rpm, S_3 = 1320 rpm, I_a = 765 amp, R_s = 2.8 ohms
  3. S_2 = 1210 rpm, S_3 = 1180 rpm, I_a = 800 amp, R_s = 3.2 ohms
  4. S_2 = 1250 rpm, S_3 = 1150 rpm, I_a = 770 amp, R_s = 3.5 ohms
  5. S_2 = 1150 rpm, S_3 = 1275 rpm, I_a = 750 amp, R_s = 2.2 ohms
  6. S_2 = 1230 rpm, S_3 = 1165 rpm, I_a = 755 amp, R_s = 3.1 ohms
  7. S_2 = 1175 rpm, S_3 = 1225 rpm, I_a = 780 amp, R_s = 2.9 ohms
  8. S_2 = 1130 rpm, S_3 = 1300 rpm, I_a = 760 amp, R_s = 2.5 ohms
  9. S_2 = 1183 rpm, S_3 = 1242 rpm, I_a = 766 (2/3) amp, R_s = 2.77 ohms
  10. S_2 = 1190 rpm, S_3 = 1210 rpm, I_a = 765 amp, R_s = 2.6 ohms

src

stemez-ElectricalMachines

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Source and history

upstream_id / Original problem ID
11921
task_id
09a6a9fd-3109-5378-bf70-53d1e44447bd
task_key
default--test--11921
task_revision_id
1
config / split
default / test

Official source

initial import