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Page 125

| voltage test (Fig. 7-12) to check insulation between turns; insulation-resistance test, using Megger, to check condition of insulation; liquid insulation test to check dielectric strength of oils or askarels; bushing power-factor test (Fig. 7-13) to determine condition of bushing insulation. |

| 4. Transformer troubles from mechanical or electrical failures may be observed, the cause ascertained and remedial measure applied. Similarly, transformers may be affected by line troubles; the causes and remedies may be ascertained and applied (Table 7-2). |

| STUDY QUESTIONS |

| 1. When and why are transformers tested? |

| 2. What types of low-voltage tests are made on a transformer and why? |

| 3. What types of high-voltage tests are made on a transformer and why? |

| 4. What voltage source is used in a Megger test for testing transformers? |

| 5. What are the possible causes for a hot transformer? |

| 6. What are the possible causes of a noisy transformer? |

| 7- What are the possible causes of a bushing flashover? |

| 8. What are the possible causes of a winding failure? |

| 9. How may winding failure be detected? |

| 10. What are the possible causes of low dielectric strength of oil? |

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