Distribution transformer guide

Distribution Transformer Guide

Distribution Transformer Division Athens, Georgia Jefferson City, Missouri June, 1979 Revised March, 2002

ISO 9001 CERTIFIED

Foreword
The purpose of this guide is to assemble fundamental information concerning common ratings, connections, and applications of distribution transformers. The information presented is a summary of these fundamentals and isintended as a reference for those who deal occasionally with distribution transformer applications. This guide does not purport to cover all aspects of selection and application; if questions arise or further details are required, contact ABB Inc.

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Index I. General

Page A. Application ................................................................................ 4 B. Physical Description................................................................. 4 C. Protection and Accessories ...................................................... 11

II. Performance
A. B. C. D. E. F. G. H. I. J. K. Designation of Winding Voltage Ratings ................................. Polarity ...................................................................................... Terminal Designations.............................................................. Short Circuit Ratings ................................................................ Sound Level Ratings ................................................................ Tolerance Definitions ................................................................ Impedance Calculations........................................................... Efficiency Calculations ............................................................. Regulation Calculations ........................................................... Performance Example .............................................................. Secondary Fault Current—120/240 Volt Systems ................... 17 20 21 22 22 23 23 24 24 26 27

III. Three-Phase Transformers and BanksA. Application Considerations ...................................................... 34 B. Summary of Common Connections ......................................... 41 C. Common Three-Phase Banks Using Single-Phase Transformers ........................................................................... 48

IV. Loading
A. B. C. D. Paralleling................................................................................. Delta-Delta Bank Loading ........................................................ Overloading .............................................................................. Single-Phase and Three-Phase Loading of Symmetrical and Unsymmetrical Transformer Banks .......................................... E. Dedicated Motor Loads............................................................ 51 51 52 53 66

V. Voltage Unbalance
A. B. C. D. Effects of Voltage Unbalance ................................................... Voltage Unbalance Definitions ................................................. Causes of Voltage Unbalance ................................................. Voltage Unbalance With Three-Phase Loading ...................... 1. Delta-Delta andFloating Wye-Delta Banks ........................ 2. Open-Delta Banks ............................................................... 71 71 73 73 74 75

VI. Reference Data
Solid and Concentric Stranded Aluminum and Copper Conductors .................................................................................... Temperature Correction Factors for Resistance of Aluminum Conductors.................................................................................... Logarithm Tables ........................................................................... Nominal direct-Current Resistance, Ohms per 1000 Feet, at 20°C and 25°C of Solid and Concentric Stranded Conductors .... Natural Functions of Angles .......................................................... Typical Isokeraunic Map...