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Page 272

| Figure 14-5 (cont.) (B) protection provided by overcurrent and directional overcurrent relays. (Courtesy, Westinghouse Electric Co.) |

| Actual determination of relays and settings is a more complex operation and may involve relays with special characteristics, sometimes referred to as distance or impedance relays. |

| Actual relay settings are obtained by compromises of both current and time settings, as mentioned earlier. Since calculated values of fault currents approximate relay coil settings specified in increments and time settings on inexact spring tensions, relay settings are often arrived at by cut-and-try methods. Several combinations should be tried out on paper or on computers before a final selection is made. |

| Generation-Transmission. |

| The protective zones included in the relaying schemes for generators and outgoing high-voltage transmission lines are shown in Fig. 14-6. As indicated in the diagram, the protection of generators, transformers, and transmission lines is accomplished, in this case, by differential relaying associated with the generators, buses, and breakers. Coordination with the relaying associated with the transmission lines may be accomplished by directional-overcurrent |

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