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Page 63

| Figure 4-4 The Megger insulation tester. |

| Figure 4-5 Typical Megger hook-up to measure insulation resistance (A), and (B) typical indicating scale on the Megger Insulation Tester. (Courtesy, James G. Biddle Co.) |

| Figure 4-6 Megger testing of transformer winding. |

| Drying Out Transformers.. |

| These are four methods that may be used in drying out transformers: |

| 1. Internal Heat. The windings are left in the case with the oil removed and the cover left off to allow circulation of air. The low voltage winding is short circuited. A rheostat to control current is connected in series with the high voltage winding and sufficient voltage impressed to circulate enough current through the coils to maintain a temperature between 80° to 90°C. The end terminal of the winding is used, not taps, so that the current will circulate through the total winding. This |

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