page_231

< previous page | page_231 | next page >

Page 231

| surge voltage) to the voltage class (capability to withstand this normal voltage continuously) decreases as the latter increases. The reason is that as the operating voltages become higher and higher, the effect of a surge voltage becomes less and less. Note also that the BIL for distribution class insulation is less than that for power class, that is, the BIL for utility equipment is less than for consumer equipment. This difference takes into account that a failure from a surge should preferably occur on the facilities of the utility geared to handle them. |

| Distribution class arresters are usually restricted to electric distribution circuits (Fig. 12-10A). Power class arresters find application at electric stations and transmission lines as well as consumer equipment (Fig. 12-10B). |

| Figure 12-10 (cont.) (B) impulse characteristics of power class arresters. (Courtesy, McGraw Edison Co.) |

< previous page | page_231 | next page >