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| Figure 1-14 Diagram of transformer having two windings insulated from each other and wound on a common iron core. |

| cutting are the same for both coils, then each turn of each coil will have the same voltage produced in it. Therefore, to obtain the desired voltage in the second coil, the volts per turn are determined from the first coil. If a voltage of 1000 volts is applied to a coil of 1000 turns, then 1000 volts will be generated in the entire coil, each turn generating 1 volt. Now, if only a voltage of 100 volts is desired in the second coil, only 100 turns will be required as each turn generates 1 volt. |

| It must be remembered that the voltage in the second coil is an induced voltage and will therefore be displaced from the voltage in the first coil by a half cycle (Fig. 1-10). The currents will also be displaced by a half cycle as shown in Fig. 1-15. |

| Figure 1-15 Current in secondary of transformer displaced from current in primary of transformer by one-half cycle. |

| Ratio of Transformation. |

| The usual type of power transformer consists of two electrical windings placed on a common iron core, the number of turns in each winding being dependent on the desired ratio of transformation as described above. One winding, which is called the primary winding, is connected to the source from which power is supplied. The circuit to which power is delivered is connected to the other or secondary winding of the transformer. The primary and secondary windings are insulated from each other and from the iron core. Hence the transformer not only is a device by which the voltage of an ac system may be changed, but it also serves as a safety device for effectively isolating the lower voltage circuit from the higher voltage circuit. |

| The magnetic field produced by the first coil is determined by the number of amperes flowing in the turns of the coil, that is, on the ampere-turns as |

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