Prof. Dr. rer. nat. habil. Frank Gronwald
Wolf Lukas Hellweg
Hamburg University of Technology
3rd Problem Set “Electrical Engineering Fundamentals II”
9. Notions of power
For the following two RL-loads calculate for a given voltage v(t) the average power P , the reactive power Q,
the apparent power S, and the power factor cos θ. Explicit values are given by v(t) = 282.8Vcos(ωt + π6 ),
R = 100Ω, and ωL = 133.33Ω.
Summer 2011
R
Discussion of the problems: May 6th during the exercise course
Please prepare the problem set before attending the exercise course. Solving problems on your own is necessary
to deepen your understanding of the subject!
v(t)
L
v(t)
7. Mesh-current analysis applied to an AC circuit
For the following circuit calculate the current iL (t) in L by means of the mesh-current analysis. The values of
the circuit elements are given by vs1 (t) = 250Vcos(ωt + π2 ), vs2 (t) = 108.27Vcos(ωt), R = 10Ω, ωL = 30Ω,
1
ωC = 20Ω.
R
C
vs1(t)
vs2(t)
L
i L(t)
Figure 1: A simple AC circuit consisting of two independent loops
8. Thévenin equivalent circuit applied to an AC circuit
For the following
circuit calculate the current in the resistance R2 . The values of the circuit elements are given
√
1
= 1Ω. Hint: Combine the circuit elements L2 ,
by vs (t) = 5Vcos(ωt) and R1 = R2 = ωL1 = ωL2 = ωC
R1 , L1 , and C to an appropriate equivalent impedance to form a Thévenin equivalent circuit.
R1
vs (t)
L2
L1
R2
C
Figure 2: A simple AC circuit where the method of Thévenin equivalent circuits can be applied to calculate the
unknown current iR2 .
Figure 3: Two RL loads, subject to a voltage v(t)
R
L