19.a. A transformer assembly that is completely equipped for 3900 kva service is commonly referred to as a A. dry transformer. B. CSP transformer. C. unit substation. D. rural-line transformer. 19.b. Comparing the transformer cores of core-form and shell-form transformers shows that the A. core form makes possible wider coils and better oil circulation. B. core form allows more flexible coil grouping. C. shell form is used exclusively in small low-voltage transformers. D. shell form provides lower reactance without increasing the transformer size.

19.a. A transformer assembly that is completely equipped for 3900 kva service is commonly referred to as a A. dry transformer. B. CSP transformer. C. unit substation. D. rural-line transformer. 19.b. Comparing the transformer cores of core-form and shell-form transformers shows that the A. core form makes possible wider coils and better oil circulation. B. core form allows more flexible coil grouping. C. shell form is used exclusively in small low-voltage transformers. D. shell form provides lower reactance without increasing the transformer size.

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 3.35P: Consider a bank of this single-phase two-winding transformers whose high-voltage terminals are...

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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.
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
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
Why is it important to reduce the moisture within a transformer to acceptable levels during transformer installation?
An ideal transformer has no real or reactive power loss. (a) True (b) False
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) -.
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.
Consider Figure 3.4. For an ideal phase-shifting transformer, the imda nce is unchanged when it is referred from one side to the other. (a) True (b) False
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.
12.a. Comparing the transformer cores of core-form and shell-form transformers shows that thea. shell form provides lower reactance without increasing the transformer size.b. core form makes possible wider coils and better oil circulation.c. shell form is used exclusively in small low-voltage transformers.12.b. Distribution transformers are generally protected from damage due to excessive internal temperatures,by the operation of aA. lightning arrester.B. circuit breaker.C. surge diverter.
B/ Fill in the blanks: 1. The purpose of providing the iron core in the transformer is to 2. A transformer transforms... 3. Power transformers are designed to have maximum efficiency at 4. The transformer ratings are usually expressed in terms of menm