Question

Problem 3 (25 p) A 120-V, 60-Hz, three-phase, Y-connected, 6 poles, wound-rotor, synchronous motor has a synchronous reactance of 3 ohms. The motor takes a current of 10 A at 0.8 pf leading when operating at a certain field current. The load is gradually increased until the motor develops its maximum torque while the field current is held constant. Determine: a) The new line current b) The power factor c) Torque developed by the motor

Answer 1

solution. fole, pro frequency, fason? I > NS 120€ 120 x 60 صدا و EES I.NE? dzworom by synchronous speed, line voltage, Y 2 120v (oms Cline Cline to t-c 120 69.28 vi Voni Tuce) (phase vollege, 2 En Synchronous reactance, X = 31 vol - I Cosy z o.f freeing ca Estons) = 36.86² fe : رات Ega - TZ » Era 69.246002 10236.86* 34.90 7) 69.28 - 302126.86 ELE :. Ex. 90.52. C-15.38. Tv ho प V [ 15:38 Taxi Phasor diagram EE

motor - As wad is gradullay increased, the develops in manimum torque, while the current is hold constant El Constant (because field 1 i's constant) TEN/ = 90.52 v is brained at Manimum torque power angle (16 8) is equal to go. '. 90.522-93 69.2800 Iaz 90.52 L-901 ū_Ej X 3 Las Ta = 37.99 %-37.43° (a) New line current Is a 37499 (-37.430 (6) The power factor, PF: cospa wis (637.43) PE=0.79 (logging

Torque developed by the motor 2 1. Р VEJ 64, 2px 90.32 84% x Simque Т. ус Зх. 2. ва Х 2 x ) 2 10 1 : 2 Т. Ч. 2o -