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| smaller and have less losses than a corresponding two-winding transformer. Its relationship between voltage ratio, current ratio, and turn ratio is the same as for two-winding transformers. |

| 3. Autotransformer connections may be the same as for two-winding transformers. They may be connected in either delta or wye, but may not be connected in combination of these. They may also be used for three-phase to two-phase transformation (Fig. 6-2). |

| 4. Voltage regulators are a particular application of the autotransformer. The voltage in the portion of the winding which is added or subtracted is made variable, as the outgoing voltage may be kept at approximately rated value. In the induction regulator (Fig. 6-3), this portion of the coil can be rotated with reference to the major coil, so that the voltage induced in it can vary as the coils deviate from parallel positions. In a second type, the portion of the coil whose voltage is to be added or subtracted is equipped with taps; selecting the proper tap adds or subtracts more or less voltage to or from the incoming voltage so that the output voltage may be kept at approximately the rated value (Figs. 6-5 and 6-6). |

| 5. Transformers are also used for metering and relaying purposes, when only a small portion of the original values need be used (Fig. 6-7). These are known as potential transformers (PT) for measuring voltage; and current transformers (CT) for measuring a current. PT's are connected in parallel with the main supply circuit (Fig. 6-8), while CT's are connected in series (Fig. 6-9); relative polarity of primary and secondary windings of these transformers is also necessary. The capacity of these transformers is usually very small; and be of dry or oil filled types. |

| 6. PT's have small output and high accuracy, they have small regulation or voltage drop, the windings are also compensated to give its exact ratio at some specified rated burden. CT's also have small output and high accuracy. The primary may be one or a few turns and insulated for line voltage, the insulated conductor itself may serve as the primary passing through the core around which the secondary windings are wound. Because of the high turn ratio usually met in CT's, it is possible to obtain an unsafe high voltage across the secondary terminals. The regulation is so designed that the voltage drops very rapidly as the burden is connected to it. For safety reasons, the terminals of the CT's should be short-circuited when instruments are not connected to them; instruments should first be connected before the short-circuit strap is removed. |

| 7. Series street lighting employs types of transformers including a constant-current transformer (Fig. 6-10), where the primary and secondary coils move away or closer to each other on the iron core causing the secondary voltage to change, but delivering an essentially constant value of current. Other two-winding transformers are used to supply an individual light |

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