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Page 91

| voltage. The low-voltage portion of the autotransformer is therefore insulated to withstand this high voltage. But, while this may protect the transformer, it does not protect the connected load appliances. |

| Another disadvantage of the autotransformer stems from its comparatively lower impedance which causes short-circuit currents of greater magnitudes to flow through it during fault conditions. hence, the autotransformer must be built very ruggedly to withstand the greater mechanical stresses produced, or external impedances should be connected in the circuit to limit the magnitude of these short-circuit currents, or a combination of both. |

| Autotransformer Connections |

| Autotransformers may be used on both single-phase and polyphase circuits, including phase transformation. The single-phase transformation has already been discussed and illustrated in Fig. 6-1. Two-phase transformation from two-phase to two-phase circuits are merely two single-phase applications, one for each of the two phases. |

| Another connection (Fig. 6-2) known as the T-connection, and somewhat similar to the Scott connection for two-winding transformers, may be used for both three-phase transformations and for transformations from three-phase to two-phase, or vice-versa. |

| Figure 6-2 T-connection of auto-transformers. (A) Three-phase to three-phase, three wire. (B) Three-phase to two phase, three wire. |

| Voltage Regulators |

| A voltage regulator is used to maintain the voltage of a circuit, and is essentially a special application of an autotransformer. The voltage in the portion of the winding which is added or subtracted in an autotransformer is made variable, so the outgoing voltage may thus be kept approximately at the rated value. These are two types of voltage regulators commonly used, and the principle of operation of both is the same as for the autotransformer. |

| One type of voltage regulator, called an induction-voltage regulator (Fig. 6-3 on page 92) has a primary which is used as a high-voltage winding |

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