page_252

< previous page | page_252 | next page >

Page 252

| Auxiliary Relays.. |

| Auxiliary relays are those that operate in association with equipment, devices, or other relays in the performance of some function or functions and that are usually actuated by them. They come in many shapes, forms, and types, and no attempt will be made here to discuss them all. Some of their functions will be shown schematically in subsequent figures. |

| An elementary diagram of a protective relay connected to a circuit breaker is shown in Fig. 13-12. When the breaker opens, the auxiliary switch of the breaker interrupts the trip circuit to prevent burning of the relay contacts. |

| Figure 13-12 Protective relay and circuit breaker. |

| Large circuit breakers are usually electrically operated, being closed by a closing coil and opened by a trip coil that trips a latch. Breakers may also be operated manually by means of a control switch that closes the circuit both for opening and closing them. Together with indicating devices, all employ auxiliary switches of some kind, and the entire assembly is usually referred to as a control circuit. A typical dc control circuit, including a number of auxiliary switches, is shown in Fig. 13-13. The purposes of this assembly are as follows: |

| 1. To open the trip circuit outside the relay since relay contacts usually cannot carry the heavy tripping current required. |

| 2. To light the proper signal-indicating lights: green for open and red for closed. |

< previous page | page_252 | next page >