2. The one-line diagram of a power system is shown in the figure. The three-phase power and line-line ratings are given below: Generator 1: 50 MVA, 22 kV, X = 24% Generator 2: 50 MVA, 22 kV, X = 24% Synchronous Motor: 15 MVA, 4.4 kV, X = 22.5% Transformer 1: 40 MVA, 110Y/22A kV, X = 6.4% Transformer 2: 40 MVA, 110Y/22A kV, X =6.4% 3-ph load: Delta connected, 18+ j24 0 per phase www ww The three-phase ratings of the three-winding transformer T3 are: Primary: Secondary: Y-connected Tertiary: 80 MVA, 110 kV 60 MVA, 22 kV 20 MVA, 4.4 kV Y-connected Y-connected Neglecting resistance, the leakage impedances are: Zp, = 9.6% on 80 MVA, 110 kV Zpi = 7.2% on 80 MVA, 110 kV Zu = 10% on 60 MVA, 22 kV Choose as base 100 MVA, 20 kV in the generator 1 circuit. Draw the complete per- unit impedance/reactance diagram.

2. The one-line diagram of a power system is shown in the figure. The three-phase power and line-line ratings are given below: Generator 1: 50 MVA, 22 kV, X = 24% Generator 2: 50 MVA, 22 kV, X = 24% Synchronous Motor: 15 MVA, 4.4 kV, X = 22.5% Transformer 1: 40 MVA, 110Y/22A kV, X = 6.4% Transformer 2: 40 MVA, 110Y/22A kV, X =6.4% 3-ph load: Delta connected, 18+ j24 0 per phase www ww The three-phase ratings of the three-winding transformer T3 are: Primary: Secondary: Y-connected Tertiary: 80 MVA, 110 kV 60 MVA, 22 kV 20 MVA, 4.4 kV Y-connected Y-connected Neglecting resistance, the leakage impedances are: Zp, = 9.6% on 80 MVA, 110 kV Zpi = 7.2% on 80 MVA, 110 kV Zu = 10% on 60 MVA, 22 kV Choose as base 100 MVA, 20 kV in the generator 1 circuit. Draw the complete per- unit impedance/reactance diagram.

Power System Analysis and Design (MindTap Course List)

6th Edition

ISBN:9781305632134

Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Chapter3: Power Transformers

Section: Chapter Questions

Problem 3.41P: Consider the single-line diagram of the power system shown in Figure 3.38. Equipment ratings are...

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Three single-phase two-winding transformers, each rated 3kVA,220/110volts,60Hz, with a 0.10 per-unit leakage reactance, are connected as a three-phase extended autotransformer bank, as shown in Figure 3.36(c). The low-voltage winding has a 110 volt rating. (a) Draw the positive-sequence phasor diagram and show that the high-voltage winding has a 479.5 volt rating. (b) A three-phase load connected to the low-voltage terminals absorbs 6 kW at 110 volts and at 0.8 power factor lagging. Draw the per-unit impedance diagram and calculate the voltage and current at the high-voltage terminals. Assume positive-sequence operation.
Consider a single-phase electric system shown in Figure 3.33. Transformers are rated as follows: XY15MVA,13.8/138kV, leakage reactance 10 YZ15MVA,138/69kV, leakage reactance 8 With the base in circuit Y chosen as 15MVA,138kV determine the per-unit impedance of the 500 resistive load in circuit Z, referred to circuits Z, Y, and X. Neglecting magnetizing currents, transformer resistances, and line impedances, draw the impedance diagram in per unit.
Consider the single-Line diagram of a power system shown in Figure 3.42 with equipment ratings given: Generator G1: 50MVA,13.2kV,x=0.15p.u. Generator G2: 20MVA,13.8kV,x=0.15p.u. Three-phase -Y transformer T1: 80MVA,13.2/165YkV,X=0.1p.u. Three-phase Y- transformer T2: 40MVA,165Y/13.8kV,X=0.1p.u. Load: 40MVA,0.8PFlagging,operatingat150kV Choose a base of 100 MVA for the system and 132-kV base in the transmission-line circuit. Let the load be modeled as a parallel combination of resistance and inductance. Neglect transformer phase shifts. Draw a per-phase equivalent circuit of the system showing all impedances in per unit.
Determine the positive- and negative-sequence phase shifts for the three- phase transformers shown in Figure 3.36.
Consider the oneline diagram shown in Figure 3.40. The three-phase transformer bank is made up of three identical single-phase transformers, each specified by X1=0.24 (on the low-voltage side), negligible resistance and magnetizing current, and turns ratio =N2/N1=10. The transformer bank is delivering 100 MW at 0.8 p.f. lagging to a substation bus whose voltage is 230 kV. (a) Determine the primary current magnitude, primary voltage (line-to-line) magnitude, and the three-phase complex power supplied by the generator. Choose the line-to-neutral voltage at the bus, Va as the reference Account for the phase shift, and assume positive-sequence operation. (b) Find the phase shift between the primary and secondary voltages.
Consider the three single-phase two-winding transformers shown in Figure 3.37. The high-voltage windings are connected in Y. (a) For the low-voltage side, connect the windings in , place the polarity marks, and label the terminals a, b, and c in accordance with the American standard. (b) Relabel the terminals a, b, and c such that VAN is 90 out of phase with Va for positive sequence.
How many transformers are needed to make an open-delta connection?
Figure 3.39 shows a oneline diagram of a system in which the three-phase generator is rated 300 MVA, 20 kV with a subtransient reactance of 0.2 per unit and with its neutral grounded through a 0.4- reactor. The transmission line is 64km long with a cries reactance of 0.5-/km. The three-phase transformer T1 is rated 350MVA.230/20kV with a leakage reactance of 0.1 per unit. Transformer T2 is composed of three single-phase transformers, each rated 100 MVA, 127/13.2kV with a leakage reactance of 0.1 per unit. Two 13.2kV motors M1 and M2 with a subtransient reactance of 0.2 per unit for each motor represent the load. M1 has a rated input of 200 MVA with its neutral grounded through a 0.4- current-limiting reactor, M2 has a rated input of 100 MVA with its neutral not connected to ground. Neglect phase shifts associated with the transformers. Choose the generator rating as base in the generator circuit and draw the positive-sequence reactance diagram showing all reactances in per unit.
An infinite bus, which is a constant voltage source, is connected to the primary of the three-winding transformer of Problem 3.53. A 7.5-MVA,13.2-kV synchronous motor with a sub transient reactance of 0.2 per unit is connected to the transformer secondary. A5-MW,2.3-kV three-phase resistive load is connected to the tertiary Choosing a base of 66 kV and 15 MVA in the primary, draw the impedance diagram of the system showing per-unit impedances. Neglect transformer exciting current, phase shifts, and all resistances except the resistive load.
Rework Example 3.12 for a+10 tap, providing a 10 increase for the high-voltage winding.
Three single-phase two-winding transformers, each rated 3 kVA, 220/110volts, 60 Hz, with a 0.10 per-unit leakage reactance, are connected as athree-phase extended D autotransformer bank, as shown in Figure 3.36 (c).The low-voltage D winding has a 110-volt rating. (a) Draw the positive sequencephasor diagram and show that the high-voltage winding has a479.5-volt rating. (b) A three-phase load connected to the low-voltageterminals absorbs 6 kW at 110 volts and at 0.8 power factor lagging. Drawthe per-unit impedance diagram and calculate the voltage and current atthe high-voltage terminals. Assume positive-sequence operation.
How many transformers are needed to make an open-delta connection? 2. Two transformers rated at 100 kVA each are connected in an open-delta connection. What is the total output power that can be supplied by this bank? 3. How does the NEC specify that the high leg of a four-wire delta connection be marked? 4. An open-delta three-phase transformer system has one transformer center-tapped to provide a neutral for single-phase voltages. If the voltage from line to center tap is 277 V, what is the high-leg voltage? 5. If a single-phase load is connected across the two line conductors and neutral of the transformer in Question 4 and one line has a current of 80 A and the other line has a current of 68 A, how much current is flowing in the neutral conductor? 6. A three-phase transformer connection has a delta-connected secondary, and one of the transformers has been center-tapped to form a neutral conductor. The phase-to-neutral value of the center-tapped secondary winding…