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Page 227

| Figure 12-7 Effects of voltage surges on transmission line. |

| characteristics of the point of discontinuity are such that the reflected wave is superimposed on the original surge wave and the crest voltage is double the original value at the point of discontinuity. In Fig. 12-7B, the characteristics of the point of discontinuity are such that the reflected wave is subtracted from the original wave. |

| 3. An arrester will not necessarily prevent a surge from striking or entering the equipment to be protected. Its function is to discharge fast enough after the surge has been applied to prevent the surge voltage from having enough time to damage the insulation of the equipment to be protected. |

| 4. The effectiveness of an arrester depends on, in addition to its internal characteristics, the ability of the ground connection to discharge the abnormal current to the ground. |

| 5. The fulfillment of the arrester's primary function, which is to prevent excessive voltage stress on protected equipment, requires the coordination of the equipment's insulation characteristics with the arrester's protective characteristics. |

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