Electric machinery fundamentals
5th Edition
ISBN: 9780073529547
Author: Chapman, Stephen J.
Publisher: MCGRAW-HILL HIGHER EDUCATION
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Textbook Question
Chapter 2, Problem 2.20Q
A distribution transformer is rated at 18 kVA, 20,000/480 V, and 60 Hz. Can this transformer safely supply 15 kVA to a 415-V load at 50 Hz? Why or why not?
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A Single-phase transformer has a turns ratio 1: 2,
and is connected to a purely resistive load as
shown in the figure. The magnetizing current
drawn is 1 A, and the secondary current is 1 A. If
core losses and leakage reactances are
neglected, the primary current is
1:2
llllllll
A
The circuit for a 20-kVA, 220/3960 V, 50-Hz transformer is shown in Figure (1). The open-
circuit test and the short-circuit test was performed on this transformer and the following
data were taken:
Open-Circuit test: Voc=240 V, Ioc=2.8 A, Poc=260 W
Short-Circuit test: Vsc = 350 V, Isc=7.6 A, Psc = 420 W
1) Find the values of Rc, XM, Rp and Xs for this transformer.
2) Find the equivalent circuit of this transformer referred to the high-voltage side and draw
the circuit.
j 0.163 Q
jXM
0.02 02
jXs
1. Explain why transformer saturation occurs at a lower voltage value when the
frequency of the ac power source is decreased?
Chapter 2 Solutions
Electric machinery fundamentals
Ch. 2 - Is the turns ratio of a transformer the same as...Ch. 2 - Why does the magnetization current impose an upper...Ch. 2 - What components compose the excitation current of...Ch. 2 - What is the leakage flux in a transformer? Why is...Ch. 2 - List and describe the types of losses that occur...Ch. 2 - Why does the power factor of a load affect the...Ch. 2 - Why does the short-circuit test essentially show...Ch. 2 - Why does the open-circuit test essentially show...Ch. 2 - How does the per-unit system of measurement...Ch. 2 - Why can autotransformers handle more power than...
Ch. 2 - What are transformer taps? Why are they used?Ch. 2 - What are the problems associated with the Y—Y...Ch. 2 - What is a TCUL transformer?Ch. 2 - How can three-phase transformation be accomplished...Ch. 2 - Prob. 2.15QCh. 2 - Can a 60-Hz transformer be operated on a 50-Hz...Ch. 2 - What happens to a transformer when it is first...Ch. 2 - What is a potential transform? How is it used?Ch. 2 - What is a current transformer? How is it used?Ch. 2 - A distribution transformer is rated at 18 kVA,...Ch. 2 - Why does one hear a hum when standing near a large...Ch. 2 - A 100-kVA, 8000/277-V distribution transformer has...Ch. 2 - A single-phase power system is shown in Figure...Ch. 2 - Consider a simple power system consisting of an...Ch. 2 - The secondary winding of a real transformer has a...Ch. 2 - When travelers from the USA and Canada visit...Ch. 2 - A 1000-VA, 230/115-V transformer has been tested...Ch. 2 - A 30-kVA, 8000/230-V distribution transformer has...Ch. 2 - A 150-MVA, 15/200-kV, single-phase power...Ch. 2 - A 5000-kVA, 230/13.8-kV, single-phase power...Ch. 2 - A three-phase transformer bank is to handle 500...Ch. 2 - A 100-MVA, 230/115-kV, Y three-phase power...Ch. 2 - Three 20-kVA, 24,000/277-V distribution...Ch. 2 - A 14,000/480-V, three-phase, Y-connected...Ch. 2 - A 13.8-kV, single-phase generator supplies power...Ch. 2 - An autotransformer is used to connect a 12.6-kV...Ch. 2 - Prove the following statement: If a transformer...Ch. 2 - A 10-kVA, 480/120-V conventional transformer is to...Ch. 2 - A 10-kVA, 480/120-V conventional transformer is to...Ch. 2 - Two phases of a 14.4-kV, three-phase distribution...Ch. 2 - A 50-kVA, 20,000/480-V, 60-Hz, single-phase...Ch. 2 - Prove that the three-phase system of voltages on...Ch. 2 - Prove that the three-phase system of voltages on...Ch. 2 - A single-phase, 10-kVA, 480/120-V transformer is...Ch. 2 - Figure P2-4 shows a one-line diagram of a power...
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Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, electrical-engineering and related others by exploring similar questions and additional content below.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) Noarrow_forwardWhy is it important to reduce the moisture within a transformer to acceptable levels during transformer installation?arrow_forwardWhat is the purpose of a transformer? Draw the symbols for a transformer.arrow_forward
- What are the advantages of correctly specifying a transformer most Suita ble for its application?arrow_forwardAn ideal transformer has no real or reactive power loss. (a) True (b) Falsearrow_forwardA 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.arrow_forward
- For an ideal transformer, the efficiency is (a) 0 (b) 100 (c) 50arrow_forwardThe symbol shown is a(n) a. iron core transformer. b. auto transformer. c. current transformer. d. air core transformer.arrow_forwardFor the transformer in Problem 3.10. The open-circuit test with 11.5 kV applied results in a power input of 65 kW and a current of 30 A. Compute the values for GcandBm in siemens referred to the high-voltage winding. Compute the efficiency of the transformer for a load of 10 MW at 0.8 p.f. lagging at rated voltage.arrow_forward
- An open-delta three-phase transformer system has one transformer center-tapped to provide a neutral for single-phase voltages. If the voltage from line to center tap is 277 V, what is the high-leg voltage?arrow_forwardThe equivalent circuit impedances of a 20-kVA, 8000/240-V, 60-Hz transformer are to be determined. The open-circuit test and the short- circuit test were performed on the primary side of the transformer, and the following data were taken: Open-circuit test (on primary) Short-circuit test (on primary) 8000 V V= 489 V I0.214 A 2.5 A P= 400 W P= 240 W Find the impedances of the approximate equivalent circuit referred to the primary side, and sketch the circuit.arrow_forwardFor the 13-kVA, 1540/220-V transformer shown in Figure (2): a) Calculate the full-load voltage regulation at 0.75 lagging power factor, 1.0 power factor, and 0.75 leading power factor using the exact equation for Vp. b) What is the efficiency of the transformer at full load with a power factor of 0.75 leading? 0.042 2 j 0.048 2. Is Vp 4.49 www j 6.5 Q 95 ΚΩ [j8 ΚΩ Figure (2) Vsarrow_forward
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