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Page 78

| Figure 5-10 Three, single-phase transformers additive polarity, connected D-Y. |

| parallel as shown in Fig. 5-10. Single-phase 120 volt loads are connected between each of the three secondary phases and neutral, while three-phase power loads are connected to the three secondary phases receiving its supply at 208 volts. |

| In some cases, the secondary coils are not paralleled but brought out as in other connections to supply a 240/416 volt, three-phase power supply, with the three common connections not connected to a separate neutral or ground. Small single-phase 120 volt requirements may be supplied by bringing out the midpoint of one of the transformers, establishing it as a separate neutral, as in other cases mentioned above. |

| In large power transformers, the delta-wye connection is often used for step-up transformers. The wye high-voltage connection provides a neutral for grounding the high-voltage circuit; it also results in a lower voltage per transformer than would be the case for a delta connection, with a smaller number of high voltage turns and lessened insulation requirements. The angular displacement between incoming and outgoing voltages should be considered before paralleling the stepped-up voltage line with other lines. |

| Wye-Delta Connection |

| This connection is often used to supply large three-phase power loads at 240 volts from a wye primary system. As in other types of connections, small single-phase 120 volt requirements may be supplied by bringing out the midpoint of the secondary winding of one of the transformers, as shown in Fig. 5-11. |

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