Part b) ull Three WIFİ Call ?10:2427%thQ2.a)considered beneficial.Discuss the circumstances where parallel operation of transformers may beb)Two three-phase transformers have the following secondary equivalent circuitparameters per phase where the values have been derived from your studentnumber using the same method as in Question 1:X=2 y=8Transformer 1:R = 0.03X 0Transformer 2R2 = 0.04Y 0X, = 0.09X NX2 = 0.12Y 0For example:If your student number is c1700123, then R, = 0.032 N and R2 = 0.043 N.Calculate the current delivered by each transformer if the load draws a currentof 200 A at a power factor of 0.8X lagging when connected in parallel. Stateany assumptions which you make.For example:If your student number is c1700123, the power factor is 0.82 lagging.

Transformers are used to step up and step down voltages, it uses the principle of mutual inductance.…

Q2. a) Discuss the circumstances where parallel operation of transformers may be considered beneficial. b) Two three-phase transformers have the following secondary equivalent circuit parameters per phase where the values have been derived from your student number using the same method as in Question 1: x=2 y=8 Transformer 1: Transformer 2 R = 0.03X 0 R2 = 0.04Y 0 X, = 0.09X X2 0.12Y0 For example: If your student number is c1700123, then R, = 0.032 n and R, = 0.043 0. Calculate the current delivered by each transformer if the load draws a current of 200 A at a power factor of 0.8X lagging when connected in parallel. State any assumptions which you make. For example: If your student number is c1700123, the power factor is 0.82 lagging.

Q2. a) Discuss the circumstances where parallel operation of transformers may be considered beneficial. b) Two three-phase transformers have the following secondary equivalent circuit parameters per phase where the values have been derived from your student number using the same method as in Question 1: x=2 y=8 Transformer 1: Transformer 2 R = 0.03X 0 R2 = 0.04Y 0 X, = 0.09X X2 0.12Y0 For example: If your student number is c1700123, then R, = 0.032 n and R, = 0.043 0. Calculate the current delivered by each transformer if the load draws a current of 200 A at a power factor of 0.8X lagging when connected in parallel. State any assumptions which you make. For example: If your student number is c1700123, the power factor is 0.82 lagging.

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 3.25P: Consider a single-phase electric system shown in Figure 3.33. Transformers are rated as follows:...

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Three single-phase, two-winding transformers, each rated 450MVA,20kV/288.7kV, with leakage reactance Xeq=0.10perunit, are connected to form a three-phase bank. The high-voltage windings are connected in Y with a solidly grounded neutral. Draw the per-unit equivalent circuit if the low-voltage windings are connected (a) in with American standard phase shift or (b) in Y with an open neutral. Use the transformer ratings as base quantities. Winding resistances and exciting current are neglected.
A bank of three single-phase transformers, each rated 30MVA,38.1/3.81kV, are connected in Y- with a balanced load of three 1, Y-connected resistors. Choosing a base of 90MVA,66kV for the high-voltage side of the three-phase transformer. spify the base for the low-voltage side. Compute the per-unit resistance of the load on the base for the low-voltage side. Also, determine the load resistance in ohms referred to the high-voltage side and the per-unit value on the chosen base.
In developing per-unit equivalent circuits for three-phase transformers. under balanced three-phase operation. (i) A common Sbase is selected for both the H and X terminals. (ii) The ratio of the voltage bases Vbase/VbaseX is selected to be equal to the ratio of the rated line-to-line voltages VratedHLL/VratedXLL. (a) Only one of the above is true. (b) Neither is true. (C) Both statements are true.
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
The direct electrical connection of the windings allows transient over voltages to pass through the auto transfonner more easily, and that is an important disadvantage of the autotransformer. (a) True (b) False
In per-unit equivalent circuits of practical three-phase transformers, under balanced thr-phase operation, in which of the following connect ions would a phase-shifting transformer come up? (a) Y-Y (b) Y- (c) -
Consider three ideal single-phase transformers (with a voltage gain of ) put together as three-phase bank as shown in Figure 3.35. Assuming positive-sequence voltages for Va,Vb, and Vc find Va,Vb, and VC. in terms of Va,Vb, and Vc, respectively. (a) Would such relationships hold for the line voltages as well? (b) Looking into the current relationships, express IaIb and Ic in terms of IaIb and Ic respectively. (C) Let S and S be the per-phase complex power output and input. respectively. Find S in terms of S.
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.
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.
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.
For developing per-unit equivalent circuits of single-phase three-winding transformer, a common Sbase is selected for all three windings and voltage bases are selected in proportion to the rated voltage of the windings (a) True (b) False
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.