Problem 3: A Potpourri of Different Problems
(a) Consider a delta-connected balanced source for which the voltage differences between the lines are given by Vab, Vbc, Vca that satisfy Vbc = Vab - j2n/3 and Vca = Vab + j2n/3. Find an equivalent wye-connected source with voltage differences Van, Von, Ven in terms of Vab, Voe, and Vea that satisfy Vab = Van - Von, Vbc = Von - Vcn, and Vca = Vcn - Van.
(b) In this problem, we perform a sanity check on our voltage-current relationships across a transmission line. Consider a transmission line of length d1 + d2 as shown in Figure 1.
Per our analysis in class, we have
where the matrix T(d) is a 2x2 matrix for a given distance d and is given by
cosh(d) Z
sinh(d) cosh(d)
The voltage-current relationships for the (d1 + d2) length transmission line must satisfy
Prove that T(d + d) = T(d)T(d) for (6) and (8) to be consistent.
A three-phase line, which has an impedance of (1 + j2) per phase, feeds two balanced three-phase loads that are connected in parallel. One of the loads is wye-connected with an impedance of (15 + j20) per phase, and the other is delta-connected with an impedance of (60 - j45) per phase. The line is energized at the sending end from a 60-Hz, three-phase, balanced voltage source of 120/√3 V.
Compute the current, real power, and reactive power delivered by the sending-end source. Find the line-to-line voltage at the load and the current per phase in each load. Calculate the total three-phase real and reactive powers absorbed by each load and report its magnitude in volt-amperes, whether it is leading or lagging, and the power factor.