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Page 117

| Figure 7-7 Connections of opposition method for temperature test. |

| Compromise Short-Circuit Method |

| One winding, usually the secondary, of the transformer under test is short-circuited, similar to the connection for the impedance test, shown in Fig. 7-5. A current is circulated in the other winding which will give an impedance loss equal to the sum of the core loss and the normal impedance loss. (See also Impedance Tests and Transformer Losses previously discussed.) |

| With each method, it is necessary to obtain the winding resistances both when the transformer is cold and after the oil heating is stabilized. The hot transformer is temporarily disconnected while the resistance test is made. (See Resistance Tests at beginning of chapter.) The final temperature of the windings is calculated from the formula: |

| The temperature rise of the windings is found by subtracting the final ambient temperature from the final winding temperature, found above. The oil temperature rise is found by subtracting the final ambient temperature from the final oil temperature. |

| Connections for testing three single-phase transformers or for a three-phase transformer when the windings can be connected in delta is shown in Fig. 7-8. |

| High-Voltage Test |

| Those tests in which high voltage may be applied are usually associated with the insulation of transformers. |

| The object of this test is to show that the insulation in the transformer winding is adequate. A higher than rated voltage is applied between the |

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