Assume that a 250-kVA distribution transformer is used for single-phase pole mounting. The transformer is connected phase-to-neutral 7200 V on the primary, and 2520 V phase-to- neutral on the secondary side. The leakage impedance of the transformer is 3.5%. Based on the given information, determine the following: (a) Assume that the transformer has 0.7 pu A in the high-voltage winding. Find the actual current values in the high- and low-voltage windings. What is the value of the current in the low-voltage winding in per units? (b) Find the impedance of the transformer as referred to the high- and low-voltage windings in ohms. (c) Assume that the low-voltage terminals of the transformer are short-circuited and 0.22 pu V is applied to the high-voltage winding. Find the high- and low-voltage winding currents that exist as a result of the short circuit in pu and amperes. (d) Determine the internal voltage drop of the transformer, due to its leakage impedance, if a 1.2 pu current flows in the high-voltage winding. Give the result in pu and volts.

Assume that a 250-kVA distribution transformer is used for single-phase pole mounting. The transformer is connected phase-to-neutral 7200 V on the primary, and 2520 V phase-to- neutral on the secondary side. The leakage impedance of the transformer is 3.5%. Based on the given information, determine the following: (a) Assume that the transformer has 0.7 pu A in the high-voltage winding. Find the actual current values in the high- and low-voltage windings. What is the value of the current in the low-voltage winding in per units? (b) Find the impedance of the transformer as referred to the high- and low-voltage windings in ohms. (c) Assume that the low-voltage terminals of the transformer are short-circuited and 0.22 pu V is applied to the high-voltage winding. Find the high- and low-voltage winding currents that exist as a result of the short circuit in pu and amperes. (d) Determine the internal voltage drop of the transformer, due to its leakage impedance, if a 1.2 pu current flows in the high-voltage winding. Give the result in pu and volts.

Introductory Circuit Analysis (13th Edition)

13th Edition

ISBN:9780133923605

Author:Robert L. Boylestad

Publisher:Robert L. Boylestad

Chapter1: Introduction

Section: Chapter Questions

Problem 1P: Visit your local library (at school or home) and describe the extent to which it provides literature...

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Concept explainers

Single Phase Transformer

A single-phase transformer is a type of power transformer. It is an electrical device that accepts converts the single phase alternating power into single phase alternating power. In this power conversion the voltage is stepped up or down. If the voltage is stepped up, the current will be stepped down and if the voltage is stepped down, the current will be stepped up.

Question

Assume that a 250-kVA distribution transformer is used for single-phase pole mounting.
The transformer is connected phase-to-neutral 7200 V on the primary, and 2520 V phase-to-
neutral on the secondary side. The leakage impedance of the transformer is 3.5%. Based on
the given information, determine the following:
(a) Assume that the transformer has 0.7 pu A in the high-voltage winding. Find the actual
current values in the high- and low-voltage windings. What is the value of the current in
the low-voltage winding in per units?
(b) Find the impedance of the transformer as referred to the high- and low-voltage windings
in ohms.
(c) Assume that the low-voltage terminals of the transformer are short-circuited and 0.22 pu
V is applied to the high-voltage winding. Find the high- and low-voltage winding currents
that exist as a result of the short circuit in pu and amperes.
(d) Determine the internal voltage drop of the transformer, due to its leakage impedance, if
a 1.2 pu current flows in the high-voltage winding. Give the result in pu and volts.

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13)This MCQ QUESTION FROM BASIC POWER ELECTRICAL ENGINEERING course.
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A 3.5 kV / 120V, 50 Hz, single phase transformer is to have an approximate e.m.f per turn of 33V and operate with a maximum flux density of 1.35T. Determine, (a) The number of primary and secondary turns. (b) The cross sectional area of the core.
calculate the iron loss P; and copper loss Peu of each transformer for full load condition.
In a practical transformer, Identify, which component of no load current supplies eddy current loss? a. I0 b. IC c. IM d. None of these
Choose the correct answer from the given alternative: 1. In an ideal transformer, (a) windings have no resistance (c) core has no losses (b) core has infinite permeability (d) all of the above. 2. The primary and secondary induced e.m.fs. El and E2 in a two-winding transformer are always: (a) equal in magnitude (b) in-phase with each other (c) antiphase with each other (d) determined by load on transformer secondary. 3. In relation to a transformer, the ratio 20: 1 indicates that (a) there are 20 turns on primary one turn on secondary (b) secondary voltage is 1/20th of primary voltage (c) primary current is 20 times greater than the secondary current. (d) for every 20 turns on primary, there is one turn on secondary. 4. A transformer has negative voltage regulation when its load power factor is: (a) zero (b) lagging. (d) unity (c) leading 5. During short-circuit test, the iron loss of a transformer is negligible because: (a) the entire input is just sufficient to meet Cu losses only…
When rated voltage at rated frequency is applied to a single phase transformer, the hysteresis loss is 420W and eddy current loss is 150W, respectively. Solve for the new core loss if the voltage is increased by 10% and frequency is decreased by 5%.
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