5. A 50-kVA 20,000/480-V 60-Hz single-phase distribution transformer is tested with the following results: Open-circuit test (measured from secondary side) Voc 480 V Ioc = 4.1 A Poc 620 W Short-circuit test (measured from primary side) Vsc=1130 V Isc = 1.30 A Psc=550 W a) Find the per-unit equivalent circuit for this transformer at 60 Hz. b) What is the efficiency of the transformer at rated conditions and unity power factor? What is the voltage regulation at those conditions? c) What would the ratings of this transformer be if it were operated on a 50-Hz power system? d) Sketch the equivalent circuit of this transformer referred to the primary side if it is operating at 50 Hz. e) What is the efficiency of the transformer at rated conditions on a 50 Hz power system, with unity power factor? What is the voltage regulation at those conditions? f) How does the efficiency of a transformer at rated conditions and 60 Hz compare to the same physical device running a 50 Hz?

5. A 50-kVA 20,000/480-V 60-Hz single-phase distribution transformer is tested with the following results: Open-circuit test (measured from secondary side) Voc 480 V Ioc = 4.1 A Poc 620 W Short-circuit test (measured from primary side) Vsc=1130 V Isc = 1.30 A Psc=550 W a) Find the per-unit equivalent circuit for this transformer at 60 Hz. b) What is the efficiency of the transformer at rated conditions and unity power factor? What is the voltage regulation at those conditions? c) What would the ratings of this transformer be if it were operated on a 50-Hz power system? d) Sketch the equivalent circuit of this transformer referred to the primary side if it is operating at 50 Hz. e) What is the efficiency of the transformer at rated conditions on a 50 Hz power system, with unity power factor? What is the voltage regulation at those conditions? f) How does the efficiency of a transformer at rated conditions and 60 Hz compare to the same physical device running a 50 Hz?

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 3.16P: A single-phase, 50-kVA,2400/240-V,60-Hz distribution transformer has the following parameters:...

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Similar questions

For a short-circuit test on a 2-winding transformer, with one winding shorted, can you apply the rated voltage on the other winding? (a) Yes (b) No
The ideal transformer windings are eliminated from the per-unit equivalent circuit of a transformer. (a) True (b) False
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.
An ideal transformer has no real or reactive power loss. (a) True (b) False
A single-phase l0-kVA,2300/230-volt,60-Hz two-winding distribution transformer is connected as an autotransformer to step up the voltage from 2300 to 2530 volts (a) Draw a schematic diagram of this arrangement, showing all voltages and currents when delivering full load at rated voltage. (b) Find the permissible kVA rating of the autotransformer if the winding currents and voltages are not to exceed the rated values as a two-winding transformer. How much of this kVA rating is transformed by magnetic induction? (C) The following data are obtained from tests carried out on the transformer when it is connected as a two-winding transformer: Open-circuit test with the low-voltage terminals excited: Applied voltage =230V, input current =0.45A, input power =70W. Short-circuit test with the high-voltage terminals excited: Applied voltage =120, input current =4.5A, input power =240W. Based on the data, compute the efficiency of the autotransformer corresponding to full load, rated voltage, and 0.8 power factor lagging. Comment on why the efficiency is higher as an autotransformer than as a two-winding transformer.
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
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 a bank of this single-phase two-winding transformers whose high-voltage terminals are connected to a three-phase, 13.8-kV feeder. The low-voltage terminals are connected to a three-phase substation load rated 2.0 MVA and 2.5 kV. Determine the required voltage, current, and MVA ratings of both windings of each transformer, when the high-voltage/low- voltage windings are connected (a) Y-, (b) -Y, (c) Y-Y, and (d) -.
For an ideal 2-winding transformer, the ampere-turns of the primary winding, N1I1 is equal to the ampere-turns of the secondary winding, N2I2 (a) True (b) False
A single-phase, 50-kVA,2400/240-V,60-Hz distribution transformer has the following parameters: Resistance of the 2400-V winding: R1=0.75 Resistance of the 240-V winding: R2=0.0075 Leakage reactance of the 2400-V winding: X1=1.0 Leakage reactance of the 240-V winding: X2=0.01 Exciting admittance on the 240-V side =0.003j0.02S (a) Draw the equivalent circuit referred to the high-voltage side of the transformer. (b) Draw the equivalent circuit referred to the low-voltage side of the transformer. Show the numerical values of impedances on the equivalent circuits.
Why is it important to reduce the moisture within a transformer to acceptable levels during transformer installation?
The ratings of a three-phase, three-winding transformer are Primary: Y connected, 66kV,15MVA Secondary: Y connected, 13.2kV,10MVA Tertiary: connected, 2.3kV,5MVA Neglecting resistances and exciting current, the leakage reactances are: XPS=0.09 per unit on a 15-MVA,66-kV base XPT=0.08 per unit on a 15-MVA,66-kV base XST=0.05 per unit on a 10-MVA,13.2-kV base Determine the per-unit reactances of the per-phase equivalent circuit using a base of 15 MVA and 66 kV for the primary.