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Page 268

| Figure 14-2 (cont.) (B) OCB fuse-link coordination. |

| mission linesis shown in Fig. 14-5A, which also illustrates zones of protection. Differential relaying is used for the protection of incoming breakers and buses. This type of protection depends on differences between incoming and outgoing currents in the breakers and buses and is not affected by faults outside these zones. |

| The breakers, however, must operate to clear faults outside these zones and must therefore coordinate with other protective devices on the circuits connected to them. Coordination here becomes more difficult as fault currents may flow to the point of fault from two or more directions. |

| One way of attacking this problem is to assume that all but a single source are disconnected and that the circuit resembles a loop. Protection can be provided by a combination of overcurrent and directional-overcurrent relays, as shown in Fig. 14-5B. This process is repeated for each source and relay |

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