Chapter 3. Distribution Transformers

Chapter 3. Distribution Transformers - 3 Distribution...

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3 Distribution Transformers Dudley L. Galloway Galloway Transformer Technology, LLC Dan Mulkey Pacific Gas and Electric Company 3.1 Historical Background. ..................................................... 3 -2 Long-Distance Power . The First Transformers . What Is a Distribution Transformer? 3.2 Construction. ..................................................................... 3 -3 Early Transformer Materials . Oil Immersion . Core Improvements . Winding Materials . Conductor Insulation . Conductor Joining . Coolants . Tank and Cabinet Materials . Modern Processing 3.3 General Transformer Design . ........................................... 3 -8 Liquid-Filled vs. Dr y Ty pe . Stacked vs. Wound Cores . Single Phase . Three Phase . Duplex and Triplex Construction . Serving Mixed Single- and Three-Phase Loads 3.4 Transformer Connections. .............................................. 3 -11 Single-Phase Primar y Connections . Single-Phase Secondar y Connections . Three-Phase Connections . Duplex Connections . Other Connections . Preferred Connections 3.5 Operational Concerns. .................................................... 3 -13 Ferroresonance . Tank Heating . Polarity and Angular Displacement 3.6 Transformer Locations. ................................................... 3 -16 Overhead . Underground . Directly Buried . Interior Installations 3.7 Underground Distribution Transformers. ..................... 3 -17 Vault Installations . Surface-Operable Installations . Vault and Subsurface Common Elements . Emerging Issues 3.8 Pad-Mounted Distribution Transformers . .................... 3 -25 Single-Phase Pad-Mounted Transformers . Three-Phase Pad-Mounted Transformers . Live Front . Dead Front . Additional Ratings . Pad-Mount Common Elements 3.9 Transformer Losses. ......................................................... 3 -31 No-Load Loss and Exciting Current . Load Loss . Harmonics and DC Effects 3.10 Transformer Performance Model. .................................. 3 -33 Schematic . Complete Equivalent Circuit . Simplified Model . Impedance . Short-Circuit Current . Percent Regulation . Percent Efficiency 3.11 Transformer Loading. ...................................................... 3 -36 Temperature Limits . Hottest-Spot Rise . Load Cycles . Thermal Time Constant . Loading Distribution Transformers 3.12 Transformer Testing . ....................................................... 3 -37 Design Tests . Production Tests ß 2006 by Taylor & Francis Group, LLC.
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3.1 Historical Background 3.1.1 Long-Distance Power In 1886, George Westinghouse built the first long-distance ac electric lighting system in Great Barrington, Massachusetts. The power source was a 25-hp steam engine driving an alternator with an output of 500 V and 12 A. In the middle of town, 4,000 ft away, transformers were used to reduce the voltage to serve light bulbs located in nearby stores and offices (Powel, 1997). 3.1.2 The First Transformers Westinghouse realized that electric power could only be delivered over distances by transmitting at a higher voltage and then reducing the voltage at the location of the load. He purchased U.S. patent rights to the transformer developed by Gaulard and Gibbs, shown in Figure 3.1a. William Stanley, Westinghouse’s electrical expert, designed and built the transformers to reduce the voltage from 500 to 100 V on the Great Barrington system. The Stanley transformer is shown in Figure 3.1b. 3.1.3 What Is a Distribution Transformer?
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This note was uploaded on 10/19/2010 for the course ENGINEERIN ELEC121 taught by Professor Tang during the Spring '10 term at University of Liverpool.

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Chapter 3. Distribution Transformers - 3 Distribution...

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