IEEE C57.105-1978

This guide concerns transformer 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. The characteristics of the various transformer connections and possible operating problems under normal or abnormal conditions are treated. All combinations of Δ and Y, grounded and ungrounded, T connected, zigzag, and certain special connections are considered. Only two-winding transformers are included. Phasing procedures and loading practices are not covered. Guides for loading of oil-immersed and dry-type transformers are available in publications of the American National Standards Institute: American National Standard C57.91-1974, Appendix to C57.12.00-1973, Guide for Loading Mineral Oil-Immersed Overhead-Type Distribution Transformers with 55°C or 65°C Average Winding Rise; American National Standard C57.92-1962, Appendix to C57.12 Standards, Guide for Loading Oil-Immersed Distribution and Power Transformers; and American National Standard C57.96-1959, Appendix to C57.12 Standards, Guide for Loading Dry-Type Distribution and Power Transformers, respectively.



New IEEE Standard - Superseded. The characteristics of the various transformer connections and possible operating problems under normal or abnormal conditions are treated for three-phase distribution systems. These 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. All combinations of Delta and Y, grounded and ungrounded, T connected, zigzag, and certain special connections are considered. Only two-winding transformers are included. Phasing procedures and loading practices are not covered.