Chapter 5, Problem 5.3P

Figure shows the one-line diagram of a simple three-bus power system with generation at buses 1 and 3. The voltage at bus 1 is V1 is 1.025 at an angle of 0◦ per unit. Voltage magnitude at bus 3 is fixed at 1.03 pu with a real power generation of 300 MW. A load consisting of 400 MW and 200 MVAr is taken from bus 2. Line impedances are marked in per unit on a 100 MVA base. (a) Construct Ybus matrix for the system in Figure (b) Using Gauss-Seidel method and initial estimate of V2(0) = 1.0 + j0 and V3(0) = 1.03 + j0 and keeping |V3| = 1.03 pu, determine the phasor values of V2 and V3. Perform two iterations.

The 6-bus power system network of an electric utility company is shown in the Figure below. The line and transformer data containing the subtransient series resistance and reactance in per unit, and one-half of the total capacitance in per unit susceptance on a 100-MVA base, is tabulated below. The prefault voltage profile of the power system as obtained from four iterations of the newton Raphson power flow method are provided below as well.

Transmission line conductance is usually neglected in power system studies. True False

Considering two parallel three-phase circuits that are close together, when calculating the equivalent series-impedance and shunt-admittance matrices, mutual inductive and capacitive couplings between the two circuits can be neglected. True False

Q2. Figure Q2 shows the single-line diagram. The scheduled loads at buses 2 and 3 are as marked on the diagram. Line impedances are marked in per unit on 100 MVA base and the line charging susceptances are neglected. a) Using Gauss-Seidel Method, determine the phasor values of the voltage at load bus 2 and 3 according to second iteration results. b) Find slack bus real and reactive power according to second iteration results. c) Determine line flows and line losses according to second iteration results. d) Construct a power flow according to second iteration results. Slack Bus = 1.04.20° 0.025+j0.045 0.015+j0.035 0.012+j0,03 3 |2 134.8 MW 251.9 MW 42.5 MVAR 108.6 MVAR

A single line diagram of a small power system is shown below. The corresponding reactances specified in per unit. The generator no. 1, 2, and 3 with emf equal to 1.25 with angle 0° pu are connected to bus A, B, and C, respectively. (a) Calculate and write all admittances corresponding to all subscripts in per-unit admittance diagram with current sources replacing voltage sources. All nodes and branches are unchanged. (b) Calculate [Ybus] of this system

iv. For a long high voltage transmission line with light loading : (a) The voltage is generally high due to reactive power generated by the line. (b) The voltage is generally high due to the light loading. (c) The voltage is generally high due to high reactive power generated and the low reactive power consumed by the line.

i. Some reasons for adopting per unit system in tackling power system problems are ------and ii. The surge impedance loading of a transmission line is defined as

Three zones of a single-phase circuit are identified shown in Figure below. The zones are connected by transformers T1 and T2, whose ratings are also shown. Using base values of 33 kVA and 232 volts in zone 1, Find: 1- Draw the per-unit circuit including the per-unit impedances and the per-unit source voltage. 2- Calculate the load current both in per-unit and in amperes (actual or original value). Vs Zone 1 232.940° Vs G. 38 T₁ 30 KVA 240/480 volts Xeq = 0.10 p.u. Zone 2 Xiine = 4 Ω T₂ 20 KVA 460/115 volts Zload = Xea = 0.10 p.u. Zone 3 u 1+j2.2 Ω 2