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Page 148

| Oil. |

| For effective circuit interruption, oil should have the following properties: |

| 1. High dielectric strength |

| 2. Freedom from acid, alkali, or sulphur |

| 3. Low viscosity to aid in arc cooling |

| 4. Low freezing point so as to remain fluid in outdoor temperatures |

| 5. Resistance to emulsion so that accidental water will separate from it and any carbon from the arcs will settle out |

| 6. A specific gravity that will not permit ice to rise through it and float. |

| Although the requirements for circuit breaker oil may be somewhat different from those for transformer oil, the same oil will satisfy both applications. |

| Porcelain Bushings |

| Porcelain bushings are solid porcelain cylinders that surround the conductors (Fig. 8-19). They are used for moderate voltage breakers (to about 20,000 V) of relatively small interrupting capacity where the repulsion effects on the bushings (caused by short circuits within the capacity of the breaker) are relatively limited and the solid porcelain will have sufficient mechanical strength. Smaller procelain bushings may have smooth sides, but larger ones, and those for use outdoors that will be exposed to the elements, especially rain, are corrugated or provided with petticoats to increase the creepage distances or leakage paths between the energized terminal and the tank. |

| Figure 8-19 Solid porcelain bushing. |

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