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3100_assign2_prob - Dalhousie University Department of...

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Unformatted text preview: Dalhousie University Department of Electrical and Computer Engineering ECED 3100 Electrical Materials Assignment 2 Instructor: T. A. Little Due Sept. 23ft]? 1) Two motors have torque speed curves given by the equations as follows: Ml: r = 100 — one? a - onczs m1 M2: T = {so + 4c cos[fl.{]4?'i' a); s. (l—fl.flflflfl2?3 a?) Both motors are connected to identical fans having a torque curve given by: Fan r = access a}: The total system inertia is [3.5 leg-n12 and the coefficient of viscous friction is {1.023 N- mlradl s. a) Using cscel or MatLab plot the motor and fan characteristics on the same axis and determine the horsepower each motor needs to drive the fan and at what speed. b) Use a step by step method to solve the differential equation that governs the dynamic behavior of the drive system in order to plot the speed as a mnction of ._....._ _—--— ti__r_n_e. (Hint to; = {no + a: (dtoldt) where at is the time step and don'dt is the torque equation solved for the derivative.) c) Repeat step b with double the inertia. 2) The WEG motor data sheet shows the performance for a three phase. Slit} hp induction motor. If the motor is operated at full load. approsimately how long will it take for the internal motor temperature to reach 30“ above the ambient temperature. Assume no heat is lost by radiant cooling (ie the fan is broken). Assume also that iron and copper have the same specific heat coefficth at Ill koallkg-“C. (Hint nQ = M c AT). 3) Two balanced. 3-phase wyc-connected loads are in parallel across a 3-phase. balanced 4oo v supply. Load 1 draws a current of 20 A at 0.9 pf leading. Load 2 draws a current of 30 A at {1.3 pf lagging. For the combined load compute: a) The supply current (43A) b) The real power supplied from the source. (29.1 kW) c) If a bank of aye-connected capacitors was placed in parallel with these two loads. what value of capacitance would be required in each phase to make the source power factor unity? 4] Two wye-connected. balanced. three-phase loads are in parallel across a 203 ‘v' supply. Load 1 takes 12 kw at [1.6 pf lag and Load 2 takes lSkVA. at L18 pf lag. a. Draw the power triangle for each load and the combination b. What is the total kVA supplied? (34.66 INA) c. Compute the magnitude the current drawn by each load and from the supply ...
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