IEEE C57.105-1978

1 Scope
2 Electrical Connections
  2.1 Primary and Secondary Systems
  2.2 Delta and Y Connections
  2.3 Zigzag-Connected Winding
  2.4 T-T Connections
  2.5 Terminal Markings, Phase Relations, and Paralleling
  2.6 Connection of the Neutral
3 Magnetic Circuits
  3.1 General Transformer Design
  3.2 3-Phase Transformer Core Configuration
  3.3 Magnetic Circuit Effects on 3-Phase Transformer Behavior
4 Harmonic Currents and Voltages
  4.1 Exciting Current Harmonics
  4.2 Harmonic Generation
  4.3 Flow on 3-Phase System
  4.4 Telephone Noise
5 Primary Faults
  5.1 Types and Clearing of Faults
  5.2 Ground Faults
  5.3 Open Conductor Faults
6 Unbalanced Loads and Secondary Ground Faults
  6.1 Phase-to-Neutral Loads
  6.2 Phase-to-Phase Loads
  6.3 Secondary Faults
7 Ferroresonance
  7.1 Qualitative Description
  7.2 Transformer Connections Highly Susceptible to Ferroresonance
  7.3 Measures to Minimize the Probability of Ferroresonance with
      Ungrounded Primary Connection
  7.4 Transformer Connections Least Susceptible to Ferroresonance
  7.5 Measures to Minimize the Probability of Ferroresonance with
      Grounded Primary Connections
  7.6 Bibliography
8 Unsymmetrical Banks and Special Connections
  8.1 T-Connected
  8.2 Circulating Delta Currents
  8.3 Grounded Delta Secondary
  8.4 Open-Delta Secondary
  8.5 Open-Y primary to 4-Wire 208 V Service
  8.6 Effect on Voltage Balance
9 References and Bibliography
  9.1 General
  9.2 Ferroresonance
  9.3 Special Connections

Describes connections in 3-phase distribution systems. Distribution systems are characterized by primary voltages up to and including 34.5 kV, usually have a preponderance of connected transformers with low-voltage windings below 1000 V and furnish electric service to consumers.