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15 Transformer Connections Dan D. Perco Perco Transformer Engineering 15.1 Introduction..................................................................... 15-1 15.2 Polarity of Single-Phase Transformers........................... 15-1 15.3 Angular Displacement of Three-Phase Transformers.................................................................... 15-2 15.4 Three-Phase Transformer Connections......................... 15-2 Double-Wound Transformers . Multiwinding Transformers . Autotransformers Connections . Interconnected-Wye and Grounding Transformers . Phase-Shifting Transformers 15.5 Three-Phase to Six-Phase Connections....................... 15-10 15.6 Paralleling of Transformers........................................... 15-10 15.1 Introduction In deciding the transformer connections required in a particular application, there are so many considerations to be taken into account that the final solution must necessarily be a compromise. It is therefore necessary to study in detail the various features of the transformer connections together with the local requirements under which the transformer will be operated. The advantages and disadvantages of each type of connection should be understood and taken into consideration. This section describes the common connections for distribution, power, HVDC (high-voltage dc) converter, rectifier, and phase-shifting transformers. Space does not permit a detailed discussion of other uncommon transformer connections. The information presented in this section is primarily directed to transformer users. Additional information can be obtained from the IEEE transformer standards. In particular, reference is made to IEEE Std. C57.12.70, Terminal Markings and Connections for Distribu- tion and Power Transformers; C57.105, Application of Transformer Connections in Three-Phase Distribution Systems; C57.129, General Requirements and Test Code for Oil-Immersed HVDC Con- verter Transformers; C57.18.10, Practices and Requirements for Semiconductor Power and Rectifier Transformers; C57.12.20, Overhead-Type Distribution Transformers; and C57.135, IEEE Guide for the Application, Specification, and Testing of Phase-Shifting Transformers. 15.2 Polarity of Single-Phase Transformers The term polarity as applied to transformers is used to indicate the phase relationship between the primary and secondary windings of a given transformer or to indicate the instantaneous relative direction of voltage phasors in the windings of different transformers. This facilitates rapid and accurate connections of transformers in service. Transformer manufacturers have agreed to standardize the marking of terminals 2006 by Taylor & Francis Group, LLC. to indicate their polarit y. For a sing le-phase, two-w inding transformer, the hig h-voltage ter- minals are labeled H1 and H2, while the low- voltage terminals are labeled X1 and X2. When transformers are to be operated in parallel, like- marked terminals are to be joined together.... View Full Document

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