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 legn12 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. 3phase wycconnected loads are in parallel across a 3phase.
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 ayeconnected 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 wyeconnected. balanced. threephase 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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 Spring '09
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