• Given the one-line diagram of an unloaded power system, Draw the reactance diagram with all reactances in per unit. Choose a base of 30MVA, 6.9 kV in the circuit of gen 1. 1000 SONY 472 B 100 C 800 10100 • Generator 1: 20 MVA, 6.9 kV, X" = 0.15 pu • Generator 3: 30 MVA, 13.8 kV, X" = 0.15 pu Generator 2: 10 MVA, 6.9 kV, X" = 0.15 pu Transformer T1: 25 MVA, 6.9A/115Y KV, X = 10% • Transformer T2: 12 MVA, 6.9A/115Y kV, X = 10% • Transformer T3: 3-single-phase units each rater 10MVA, 7.5/75 kV, X = 10%

X₂=0.1 1 XL +03 Soto X₁ = 0.2 X = 0.1 X = 0.1 Above is the one-line diagram of a simple power system. Each generator is represented by an emf behind the subtransient reactance. All impedances are expressed in per unit on a common base. All resistances and shunt capacitance are neglected. The generators are operating on no load at their rated voltage with their emfs in phase. A symmetrical fault occurs at bus 1 through a fault impedance Z, =j0.08 per unit. a) Using Thevenin's Theorem, determine the impedance to the point of fault and the fault current in per unit. b) Find the bus voltages and line currents during the fault. 2 O oto

A 30 MVA, 11 kV generator has a reactance of 0.10p.u.on its own base. Determine the per-unit reactance when referred to base kVA of 50,000 kVA and base kV of 33 kV.

The reactance of a generator is given as 0.1 pu based on the generator of 17 KV, 300 MVA. Determine the pu reactance on a base of 17 KV, 250 MVA. New pu reactance is.......

The reactance of a generator is given as 0.4 per unit based on the generator's nameplate rating of 100 kV, 200 MVA. The reactance in per unit for a base of 50 kV, 100 MVA is O 0.4 pu O 0.2 pu O 0.8 pu O 1.6 pu

In the system shown in Figure 1, the transformers are connected star-star with both star points grounded and the generators are connected in star with thier star points grounded. The system base is 15 MVA. The transformers all have reactances of 0.04 p.u. on this 15 MVA base. The reactances of all other elements are given in Table 1 (in 2) and the voltage levels are given in Table 2. p.u. G1 p.u. T1 jö Per-Unit Convert all values to p.u. on a 15 MVA base. Xa= p.u. Xc₂= XL = V BABE G1 2 X 9 T3 Figure 1: A section of the distribution system T1 L Table 1: Sequence reactances (2) 3 G1 L G2 0.3 0.59 0.01 4 L 9/10 10 Fault Voltage What is the voltage at bus 3 (in Volts) after the fault has occurred? Vp= V T2 5 T2 34 10/4 Table 2: Voltage bases (kV) G2 4 T3 10/9 | G2 Fault Current A three-phase fault with a fault reactance of 0.01 p.u. occurs at bus 3. Calculate the fault current flowing at the fault point in KA. Ip=-j KA So

Problem 1 - Series en Parallel AC networks [19] Look at the circuit in Figure 1 and determine the following: (a) Total Admittance. (b) Total Impedance. (c) Total Current (l:). (d) Current (I1) through impedance Z2. (e) Current (12) through impedance Z3. (f) Current (I3) through impedance Z4. (g) Is this an inductive or capacitive circuit? A. B Zs 220V;50HZ Figure 1 (h) Voltage across Z1. (i) Voltage across A and B. G) Voltage across Zs. Z1 = 3 + j5 ohm Z2 = 10 + jo ohm Z3 = 5 + j15 ohm Z4 = 10 – j30 ohm Zs = 20 – j30 ohm Admittance and Impedance in rectangular notation. All currents and voltage in polar notation. Take voltage as reference.

The reactance of a generator is given as 0.25 per-unit based on the generator’s of 18 kV, 500 MVA. Find its per-unit reactance on a base of 20 kV, 100 MVA. a. 0.0505 b. 0.0605 c. 0.0405 d. 0.0606

A power station consists of two synchronous generators A & B of ratings 250 MVA and 500MVA with inertia 1.6 pu and 1.0 pu respectively on their own base MVA ratings. The equivalent pu inertia constant for the system on 100 MVA common base is:- (a) 2.6 (b) 0.615 (c) 1.625 (d) 9.0

Connect three single-phase transformers in Y-Y, with subtractive polarity, so that the line-to-line voltages on the primary are 30 degrees delayed to their respective line-to-line voltages on the secondary. It should show each step that is needed to make this connection (example: the phasor diagram) and should show the final connection of the three transformers including the polarity markings. Assume phase A on the primary is terminal "H1".