Electrical Transformers and Rotating Machines
4th Edition
ISBN: 9781337264419
Author: Stephen L. Herman
Publisher: Cengage Learning US
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Textbook Question
Chapter 9, Problem 5RQ
A three-phase transformer connection has a delta-connected primary and a wye-connected secondary. The center tap of the wye is used as a neutral conductor. If the line-to-line voltage is 480 volts, what is the voltage between any one phase conductor and the neutral conductor?
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A transformer transforms
(a) frequency
(b) voltage
(c) current
(d) voltage and current.
2. Which of the following is not a basic element of
a transformer?
(a) core
(b) primary winding
(c) secondary winding
(d) mutual flux.
3. In an ideal transformer,
(a) windings have no resistance
(b) core has no losses
(c) core has infinite permeability
(d) all of the above.
4. The main purpose of using core in a transformer
is to
(a) decrease iron losses
(b) prevent eddy current loss
(c) eliminate magnetic hysteresis
(d) decrease reluctance of the common mag-
netic circuit.
1
Question 4
A 228 V/ 111 V single-phase transformer has a core loss of 110 W and the no-load current is 0.7 A. The no load power factor is
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Question 5
A 2 kV / 229 V transformer has the secondary turns of 47. The number of Primary turns of a transformer is given by,
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63.83
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Question 6
For the given power transfer, a delta system is associated with larger line currents and a star system is associated with a larger line voltage.
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In a three phase-four wire star connected system, the three outer wires are called as lines and the
common wire in centre is called as
Chapter 9 Solutions
Electrical Transformers and Rotating Machines
Ch. 9 - How does the National Electrical Code specify that...Ch. 9 - An open-delta three-phase transformer system has...Ch. 9 - If a single-phase load is connected across the two...Ch. 9 - Prob. 4RQCh. 9 - A three-phase transformer connection has a...Ch. 9 - A three-phase transformer bank has the secondary...Ch. 9 - A three-phase transformer bank has the primary and...Ch. 9 - Prob. 8RQ
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- 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 volts, what is the high-leg voltage?arrow_forwardTwo transformers rated at 100 kVA each are connected in an open-delta connection. What is the total output power that can be supplied by this bank?arrow_forwardAssume that a line voltage of 2400 volts is connected to the primary of the three-phase transformer and the line voltage of the secondary is 240 volts. What is the turns ratio of the transformer?arrow_forward
- A load impedance of 52 Ω is connected to the secondary winding of the transformer in question 3. How much current will flow in the secondary?arrow_forwardA transformer has a primary voltage of 240 volts and a secondary voltage of 48 volts. What is the turns ratio of this transformer?arrow_forwardA transformer has an output of 750 VA. The primary voltage is 120 V. What is the primary current?arrow_forward
- A three-phase transformer bank has the secondary connected in a wye configuration. The center tap is used as a neutral conductor. If the voltage across any phase conductor and neutral is 120 volts, how much voltage would be applied to a three-phase load connected to the secondary of this transformer bank?arrow_forwardA 10 kVA transformer has a primary voltage rating of 240 volts and a secondary voltage rating of 480 volts. The transformer is connected to a circuit protected by a 100 ampere circuit breaker. The secondary is protected by a 25-ampere fuse. Does the primary require separate overcurrent protection?arrow_forwardIf a single-phase load is connected across the two line conductors and neutral of the transformer in question #2, and one line has a current of 80 amps and the other line has a current of 68 amps, how much current is flowing in the neutral conductor?arrow_forward
- Refer to the transformer shown in Figure 5-13 to answer the following questions. What is the turns ratio of the winding between points B and E as compared to the winding between points D and E? Figure 5-13 Autotransformer practice problems.arrow_forwardAn AC power source is connected across 325 turns of an autotransformer, and the load is connected across 260 turns. What is the turns ratio of this transformer?arrow_forwardEx: A single phase 50 KVA transformer has primary voltage of 6600 v and secondary voltage of 254 v and has 32 secondary turns. Calculate the number of primary turns and primary and secondary currents.arrow_forward
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