page_150

< previous page | page_150 | next page >

Page 150

Figure 8-21
Sulphur-Hexafluoride filled
bushing for sulphur
hexafluoride circuit breaker.
(Courtesy, Westinghouse
Electric Co.)

| center are subjected to greater electrostatic stresses than the outer layers. The metal foil between the layers forms a series of condensers that tend to even out and equalize the stresses among the layers. Such construction permits operation at higher voltages with less material, at lower cost, and with better performance. |

| Sulphur Hexafluoride Bushing.. |

| In the sulphur hexafluoride breaker, the hollow porcelain bushing is opened to the main breaker tank and filled with sulphur hexafluoride gas to serve as insulation (Fig. 8-21). There is no organic insulation to break down. Since the porcelain is under low pressure, it maintains the gas flowing outward in the event of a pin hole or crack, thereby preserving the insulating qualities of the bushing until repairs can be made. |

| Insulation Coordination |

| The insulation associated with the several parts of the circuit breaker must not only withstand the normal operating voltages imposed on them, but must also be able to withstand the higher voltage surges resulting from lightning or from switch operations. The insulation from the energized parts to ground (tanks, supports, and the like), or from one pole to another, where more than one pole exists in the same tank, must be strong enough to withstand the voltages produced by the impulses at these points. |

< previous page | page_150 | next page >