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Page 75

| Two-Phase Transformer Connections |

| Although two-phase systems are being replaced by three-phase systems, they are being included here because many still exist. Two-phase transformation of power is usually made with two single-phase transformers connected as shown in Fig. 5-6. Transformers illustrated are additive polarity. |

| Figure 5-6 Two-phase transformer connections for: (A) 3 wire, 240 volts secondary. (B) 4 wire,240 volt secondary. (C) 5 wire, 120/240 volt secondary. |

| Three-Phase Transformer Connections |

| Three-phase transformations can be accomplished by means of three single-phase transformers or by means of a three-phase transformer. The methods of connecting the windings for three-phase transformation are the same whether the three windings of one three-phase transformer or the three windings of three separate single-phase transformers are used. The most common connections used are the delta and the star or wye described above, or combination of these. Additive polarity transformers are shown in Fig. 5-7 (on page 76); these usually represent distribution transformers while station, large, or industrial transformers are usually of subtractive polarity. Note the difference in voltage ratings of the transformers connected to the delta and wye primary supply mains. |

| Delta-Delta Connection |

| In completing the delta connections, precautions should be taken that the third transformer is connected so that its voltage will be proper in relation to the other two. Despite the polarity identification on the transformer, it sometimes occurs that they may be in error. Hence, instead of a voltage of |

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