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| 5 Principal Transformer Connections |

| A transformer may be connected in a number of different ways, depending upon the purpose of its installation. There are several ways of connecting a single transformer to the power supply, and also of connecting it to the load. Two or more transformers may be connected in different combinations to meet different requirements. |

| Polarity |

| Unlike direct current, there are no fixed positive and negative poles in alternating current, and hence, transformers cannot have fixed positive and negative terminals. |

| The relative direction in which primary and secondary windings of a transformer are wound around the core determines the relative direction of the voltage across the windings. In a single-phase transformer, if the direction of the applied voltage at any instant is assumed, as from a to b in Fig. 5-1, the direction of the voltage across the secondary circuit will be either from c to d or d to c, depending on the relative direction of the windings. |

| Since it is essential, if two or more transformers are to be connected together, to know the relative direction of the voltage of each transformer, certain conventions have been established for designating the polarity of a transformer. |

| The designation of polarity may be illustrated by Fig. 5-1. If one high-voltage lead is connected to the adjacent opposite low-voltage lead (say a to |

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