page_177

< previous page | page_177 | next page >

Page 177

| 6. Before draining oil (or other fluid) to maintain elements of a breaker, its condition may be determined by checking the resistance across each set of contacts, by visual and dielectric test of the oil, and by the speed and smoothness of the closing of the contacts using a graphic travel indicator. Resistance (Fig. 9-9), Megger (Fig. 9-10), and power-factor tests (Fig. 9-11) may be used to check the condition of the bushings. |

| STUDY QUESTIONS |

| 1. What is meant by the trip-free feature of a circuit breaker? |

| 2. What is meant by the antipump feature of a circuit breaker? |

| 3. What type of mechanisms are employed in the operation of circuit breakers? |

| 4. How are circuit breakers opened? How are they closed? |

| 5. What three elements of a circuit breaker require special care in their maintenance? |

| 6. What is meant by the throwing of oil? |

| 7. How should the oil in a circuit breaker be checked? |

| 8. What three tests should be made to determine the condition of a circuit breaker? |

| 9- What precautions must be taken to insure a continuous electric supply for the reliable operation of circuit breakers? |

| 10. What is a Megger and where is it used? |

< previous page | page_177 | next page >