Problem 4- Per unit computations Consider the one-line diagram of a three phase, 60 Hz power system shown in the figure below. The transformer nameplate values are 100 MVA, 23/115 kV and a reactance of 20%. The load at Bus 3 is very sensitive to voltage variations, and it is required to keep the voltage at 115 V. Using Bus three as the reference bus (angle is zero) find the voltages at Buses 1 and 2. S₂ Gen.) = 184.8 MW + j20 MVar V₁ Hot V₂ ZL=j66.1250 V3 = 115/0° S3 = j20MVar

Problem 4- Per unit computations Consider the one-line diagram of a three phase, 60 Hz power system shown in the figure below. The transformer nameplate values are 100 MVA, 23/115 kV and a reactance of 20%. The load at Bus 3 is very sensitive to voltage variations, and it is required to keep the voltage at 115 V. Using Bus three as the reference bus (angle is zero) find the voltages at Buses 1 and 2. S₂ Gen.) = 184.8 MW + j20 MVar V₁ Hot V₂ ZL=j66.1250 V3 = 115/0° S3 = j20MVar

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 3.48P: With the same transformer banks as in Problem 3.47, Figure 3.41 shows the oneline diagram of a...

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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.
The per-unit equivalent circuit of two transformers Ta and Tb connected in parallel, with the same nominal voltage ratio and the same reactan of 0.1 per unit on the same base, is shown in Figure 3.43. Transformer Tb has a voltage-magnitude step-up toward the load of 1.05 times that of Ta (that is, the tap on the secondary winding of Tb is set to 1.05). The load is represented by 0.8+j0.6 per unit at a voltage V2=1.0/0 per unit. Determine the complex power in per unit transmitted to the load through each transformer, comment on how the transformers share the real and reactive powers.
In developing per-unit circuits of systems such as the one shown in Figure 3.10. when moving across a transformer, the voltage base is changed in proportion to the transformer voltage ratings. (a) True (b) False
Three single-phase two-winding transformers, each rated 25MVA,54.2/5.42kV, are connected to form a three-phase Y- bank with a balanced Y-connected resistive load of 0.6 per phase on the low-voltage side. By choosing a base of 75 MVA (three phase) and 94 kV (line-to-line) for the high-voltage side of the transformer bank, specify the base quantities for the low-voltage side. Determine the per-unit resistance of the load on the base for the low-voltage side. Then determine the load resistance RL in ohms referred to the high-voltage side and the per-unit value of this load resistance on the chosen base.
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How many types of winding in distribution transformers? What is the impact of each type on calculations zero sequence impedance ?
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4. What do you mean by transformer connection Ydl and Dy11?