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Page 118

| Figure 7-8 Connections for temperature test of three, single-phase transformers or three-phase delta transformer. |

| winding under test and the other windings and ground. The terminals of the winding under test are connected together and to one terminal of the testing equipment. The terminals of the other windings are connected together and to the core and tank and to the other terminal of the testing equipment; this second series of connections is usually connected to ground as a safety precaution. The connection is shown in Fig. 7-9. The voltage applied is raised gradually to a predetermined value, held at that value for a predetermined time, usually 1 minute, and then reduced to a low value before the circuit is opened. The test voltage is usually about twice the rated voltage of the winding. Repeated testing may damage the winding; hence, the original acceptance test may be done at this voltage, but succeeding tests for maintenance may be held to 6070 percent of the original test. |

| Figure 7-9 Connection for high voltage test. |

| Impulse Test |

| This test is made to prove that the transformer insulation will withstand voltage surges which may be caused by lightning or switching; this includes insulation to ground, insulation between turns and windings, and the flashover |

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