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Page 37

| Connecting leads within the transformer, between coils or between coil and terminals require careful consideration because these conductors may be subjected to great stresses from the proximity of high-voltage coils and from heavy short-circuit currents which they may be called upon to carry. Such conductors often have additional insulation and bracing to minimize the possibility of breakdown. |

| Taps And Tap Changing.. |

| Often it may be desirable to change, by a relatively small amount, the ratio of a transformer. This may be done to compensate for the voltage drop in the supply source or to accommodate a specific characteristic of the connected load. The simplest method brings taps from one or both windings to a terminal board below the oil level to provide an arrangement of studs and links by which the connections may be changed (Fig. 2-19). Changes in these connections are made only when the transformer is deenergized. Sometimes, the tap changing equipment is designed so that the change of connections, under the oil, may be accomplished by the turn of a handle protruding above the oil level; it is still necessary that the transformer be deenergized. The connections from the coils to the terminal branch, the board itself, and the studs and links all must conform to the same requirements as those bushing leads and terminals. |

| Taps may be changed under loads, that is, while the transformer is energized and operating. Such applications are used where the maintenance of voltage is of paramount importance, and such units are used as voltage regu- |

| Figure 2-19 Tap changer used to adjust the turns ratio of a transformer. (A) No-load tap changer. (B) Typical internal wiring of transformer with tap changer. |

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