Transformer Connections

COURSE DESCRIPTION
The purpose of this unit is to teach the common types of transformers and how they are connected. Basic concepts of transformers and primary systems are covered as well as single-phase connections. Single-phase distribution transformers can be interconnected to provide three-phase power in a number of different ways, providing a utility with the flexibility of meeting a variety of customer needs. This program demonstrates and explains how three-phase delta connections and three-phase wye connections are made. This program also explains how to make delta-wye, wye-delta, and open bank connections.


COURSE GOALS

  • Identify the characteristics that are common to most single-phase overhead transformers.
  • Explain the difference between delta and wye primary systems.
  • Demonstrate how to make single-phase transformer connections.
  • Demonstrate how three single-phase transformers can be connected in a delta configuration on both the primary and secondary sides.
  • Demonstrate how three single-phase transformers can be connected in a wye configuration on both the primary and secondary sides.
  • Illustrate a three-phase, three-wire, delta secondary connection.
  • Illustrate a three-phase, four-wire, delta secondary connection.
  • Illustrate a three-phase, four-wire, wye secondary connection.
  • Use phasor diagrams to illustrate three-phase delta-delta and three-phase wye-wye transformer connections.
  • Demonstrate and explain how three-phase delta-wye and wye-delta connections producing 30 degrees of angular displacement are made.

  • Demonstrate and explain how open connections are made.
  • Recognize and use phasor diagrams for delta-wye, wye-delta, and open connections.

 
SUBJECTS AND OBJECTIVES
Transformer Basics

  • Define the term “transformer” and identify some common types of overhead distribution transformers.
  • Describe the designations that are commonly used to identify primary and secondary bushings.
  • List and explain basic information found on a transformer nameplate.

Primary Systems

  • Differentiate between delta and wye primary systems.
  • Recognize and explain the phasor diagrams used to illustrate delta and wye systems.
  • List and explain basic requirements for connecting transformers to delta and wye systems.

Single-Phase Transformer Connections

  • Demonstrate and explain how single-phase transformers can be connected to supply single-phase service.

Three-Phase Primary Connections

  • Demonstrate and explain a three-phase delta primary connection using three single-phase transformers.
  • Demonstrate and explain a three-phase wye primary connection using three single-phase transformers.

Delta Secondary Connections

  • Demonstrate and explain how to make delta secondary connections.
  • Illustrate how to connect three single-phase transformers to supply a three-phase, three-wire delta secondary.
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  • Illustrate how to connect three single-phase transformers to supply a three-phase, four-wire delta secondary.
  • Identify some of the secondary voltages that are typically found on three-phase, three-wire and three-phase, four-wire delta-connected transformer banks.

Wye Secondary Connections

  • Demonstrate and explain three-phase, four-wire, wye secondary connections.
  • Identify some of the secondary voltages that can be supplied from a three-phase, four-wire, wye-wye connected bank.

Introduction To Three-Phase Banks

  • Describe the basic requirements for connecting units together to form a three-phase bank.
  • Explain connection principles and theory using phasor diagrams.
  • Demonstrate and explain that delta-wye and wye-delta three-phase connections have angular displacements of 30 degrees.

Delta-Wye Connections

  • Demonstrate and explain how a three-phase, delta-wye connection producing 30 degrees of angular displacement is made using subtractive-polarity transformers.

Wye-Delta Connections

  • Demonstrate and explain how a three-phase wye-delta connection producing 30 degrees of angular displacement is made.

Alternative Connections

  • Demonstrate and explain phasor diagrams and angular displacement using alternative connections.
  • Demonstrate and explain how an alternative delta-delta three-phase connection producing 180 degrees of angular displacement can be made.
  • Demonstrate and explain how an alternative wye-delta three-phase connection producing 210 degrees of angular displacement can be made.

Open Banks

  • Demonstrate and explain an open delta-open delta connection producing 0 degrees of angular displacement.
  • Demonstrate and explain an open wye-open delta, three-phase connection producing 30 degrees of angular displacement.