A3-Phase,3 Wire secondary distribution system with balanced per phase loads at a,b and e feeding from a 11kV/415 V transformer as shown in fig.2. Determine the following: a. the total voltage drop of the feeder in p.u.; b. the total per phase real power (P); c. the total per phase reactive power(Q); d. the total (3-phase) kVA output of transformer and its load power factor. 415 V 11kV 0.04 + j0.012 0,08 + j0.04£2 0.08 + j0.042 30 A 0.707 lag 40 A UPF 50 A 0.8 lag Fig. 2 (a) 26.56 V (b) 34.3 kW (c) 22.3 KVAR (d) 71.72 kVA, 0.98 lagging None of these (a) 36.56 V (b) 54.3 kW (c) 72.3 KVAR (d) 101.72 kVA, 0.80 lagging (a) 16.56 V (b) 24.3 kW (c) 12.3 KVAR (d) 81.72 kVA, 0.89 lagging

A3-Phase,3 Wire secondary distribution system with balanced per phase loads at a,b and e feeding from a 11kV/415 V transformer as shown in fig.2. Determine the following: a. the total voltage drop of the feeder in p.u.; b. the total per phase real power (P); c. the total per phase reactive power(Q); d. the total (3-phase) kVA output of transformer and its load power factor. 415 V 11kV 0.04 + j0.012 0,08 + j0.04£2 0.08 + j0.042 30 A 0.707 lag 40 A UPF 50 A 0.8 lag Fig. 2 (a) 26.56 V (b) 34.3 kW (c) 22.3 KVAR (d) 71.72 kVA, 0.98 lagging None of these (a) 36.56 V (b) 54.3 kW (c) 72.3 KVAR (d) 101.72 kVA, 0.80 lagging (a) 16.56 V (b) 24.3 kW (c) 12.3 KVAR (d) 81.72 kVA, 0.89 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 3.65P: Reconsider Problem 3.64 with the change that now Tb includes both a transformer of the same turns...

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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.
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.
Reconsider Problem 3.64 with the change that now Tb includes both a transformer of the same turns ratio as Ta and a regulating transformer with a 4 phase shift. On the base of Ta, the impedance of the two comp onents of Tb is jO.1 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 pors.
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.
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.
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 ratings of a three-phase three-winding transformer are Primary(1): Y connected 66kV,15MVA Secondary (2): Y connected, 13.2kV,10MVA Tertiary (3): A connected, 2.3kV,5MVA Neglecting winding resistances and exciting current, the per-unit leakage reactances are X12=0.08 on a 15-MVA,66-kV base X13=0.10 on a 15-MVA,66-kV base X23=0.09 on a 10-MVA,13.2-kV base (a) Determine the per-unit reactances X1,X2,X3 of the equivalent circuit on a 15-MVA,66-kV base at the primary terminals. (b) Purely resistive loads of 7.5 MW at 13.2 kV and 5 MW at 2.3kV are connected to the secondary and tertiary sides of the transformer, respectively. Draw the per- unit impedance diagram, showing the per-unit impedances on a 15-MVA,66-kV base at the primary terminals.
An ideal transformer has no real or reactive power loss. (a) True (b) False
In a 25kVA single phase transformer the core loss and full load copper losses are respectively 320 and 380 Watts. A) What is the efficiency at half load and 0.866 power factor lagging? B) Determine the load in kVA in which the efficiency is maximum.
Single phase 10 kVA, 480 V / 120 V to feed a 120 V load from a 600 V source conventional transformer will be used. a. Draw the transformer connection that can do this job. b. In the connection you have drawn, the apparent power of the transformer (in rated operation state, the load power to be transferred) what happened. c. Calculate the maximum primary and secondary winding currents for the connection situation you have drawn.
30-kVA, 2200/220-V, 50-Hz distribution transformer is tested for efficiencyand regulation as follows :O.C. test( Low voltage side ) : 220 V 4.2 A, 148 W S.C. test ( Low voltage side ) : 86 V 10.5 A, 360 W 1-The working current and resistance component of no-load are.........amper , .........ohm * 2-Efficiency at full-load and half the full-load at 0.8 p.f. lagging current. * 3-Equivalent resistance referred to primary & referred to secondary..........ohm , ..........ohm * 4-Regulation of transformer at 0.5 p.f. lagging current * 5-Equivalent reactance referred to primary & referred to secondary..........ohm , ..........ohm * 6-The magnetizing current and reactance component of no-load are.........amper , .........ohm *