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QUESTION TWO Power transformers are used in the power system to change the voltage levels to a level suitable for generation, or transmission or distribution. They are three-phase transformers, and can either be constructed as a single-unit or a bank of three single-phase units. In a hydro power station, a number of synchronous generators are used to generate electricity at 17.5 kV. The voltage is stepped up to 330 kV for transmission by parallel connected three-phase transformers. Each three-phase transformer consists of a bank of three single-phase units with each unit rated 100 MVA, 50 Hz, 330/17.5 kV. (a) With good reasons, explain the most suitable connection of the windings on the high-voltage side and the low-voltage side of each three-phase transformer, respectively. (b) What are the advantages of using a bank of single-phase transformers for each three-phase unit? (c) What are the disadvantages of using a bank of single-phase transformers for each three-phase unit? (d) At a certain time, the load on one transformer (three-phase) was measured to be 200 MW at a power factor of 0.8 lagging. (1) Calculate the line current, and the phase current on the high-voltage side of the transformer. (ii) Calculate the line current, and the phase current on the low-voltage side of the transformer. (e) Due to failure of one single-phase transformer, the two remaining single-phase transformers are connected in open-delta (V-V). What is the maximum load that the V-V connected transformer can supply without being over-loaded?

QUESTION TWO Power transformers are used in the power system to change the voltage levels to a level suitable for generation, or transmission or distribution. They are three-phase transformers, and can either be constructed as a single-unit or a bank of three single-phase units. In a hydro power station, a number of synchronous generators are used to generate electricity at 17.5 kV. The voltage is stepped up to 330 kV for transmission by parallel connected three-phase transformers. Each three-phase transformer consists of a bank of three single-phase units with each unit rated 100 MVA, 50 Hz, 330/17.5 kV. (a) With good reasons, explain the most suitable connection of the windings on the high-voltage side and the low-voltage side of each three-phase transformer, respectively. (b) What are the advantages of using a bank of single-phase transformers for each three-phase unit? (c) What are the disadvantages of using a bank of single-phase transformers for each three-phase unit? (d) At a certain time, the load on one transformer (three-phase) was measured to be 200 MW at a power factor of 0.8 lagging. (1) Calculate the line current, and the phase current on the high-voltage side of the transformer. (ii) Calculate the line current, and the phase current on the low-voltage side of the transformer. (e) Due to failure of one single-phase transformer, the two remaining single-phase transformers are connected in open-delta (V-V). What is the maximum load that the V-V connected transformer can supply without being over-loaded?

Introductory Circuit Analysis (13th Edition)
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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Answer (d) and (e)
QUESTION TWO Power transformers are used in the power system to change the voltage levels to a level suitable for generation, or transmission or distribution. They are three-phase transformers, and can either be constructed as a single-unit or a bank of three single-phase units. In a hydro power station, a number of synchronous generators are used to generate electricity at 17.5 kV. The voltage is stepped up to 330 kV for transmission by parallel connected three-phase transformers. Each three-phase transformer consists of a bank of three single-phase units with each unit rated 100 MVA 50 Hz, 330/17.5 kV. (a) With good reasons, explain the most suitable connection of the windings on the high-voltage side and the low-voltage side of each three-phase transformer, respectively. (b) What are the advantages of using a bank of single-phase transformers for each three-phase unit? (c) What are the disadvantages of using a bank of single-phase transformers for each three-phase unit? (d) At a certain time, the load on one transformer (three-phase) was measured to be 200 MW at a power factor of 0.8 lagging. (1) Calculate the line current, and the phase current on the high-voltage side of the transformer. (ii) Calculate the line current, and the phase current on the low-voltage side of the transformer. (e) Due to fallure of one single-phase transformer, the two remaining single-phase trarsformers are connected in open-delta (V-V). What is the maximum load that the V-V connected transformer can supply without being over-loaded?
Transcribed Image Text:QUESTION TWO Power transformers are used in the power system to change the voltage levels to a level suitable for generation, or transmission or distribution. They are three-phase transformers, and can either be constructed as a single-unit or a bank of three single-phase units. In a hydro power station, a number of synchronous generators are used to generate electricity at 17.5 kV. The voltage is stepped up to 330 kV for transmission by parallel connected three-phase transformers. Each three-phase transformer consists of a bank of three single-phase units with each unit rated 100 MVA 50 Hz, 330/17.5 kV. (a) With good reasons, explain the most suitable connection of the windings on the high-voltage side and the low-voltage side of each three-phase transformer, respectively. (b) What are the advantages of using a bank of single-phase transformers for each three-phase unit? (c) What are the disadvantages of using a bank of single-phase transformers for each three-phase unit? (d) At a certain time, the load on one transformer (three-phase) was measured to be 200 MW at a power factor of 0.8 lagging. (1) Calculate the line current, and the phase current on the high-voltage side of the transformer. (ii) Calculate the line current, and the phase current on the low-voltage side of the transformer. (e) Due to fallure of one single-phase transformer, the two remaining single-phase trarsformers are connected in open-delta (V-V). What is the maximum load that the V-V connected transformer can supply without being over-loaded?
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