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Page 258

| Dial positions 8 and 9 are not used, and default to Extremely Inverse. Note the refinements available are greater than for the same overcurrent relay, making for better coordination with other protective devices that may be involved. Typical time-current curves for instantaneous, inverse, and definite time are shown in Figures 3-16B, C, and D. |

| A functional block diagram for a more complex illustration, a multiple shot reclosing relay, is shown in Figure 3-17A and the flow chart planning each step of its operation is shown in Figure 3-17B. |

| The great investment in present electromagnetic and induction type relays, and their excellent performance, make large scale replacement economically unfeasible. Retrofit kits, however, are available that permit electronic relays to be installed in existing electromagnetic and induction type relay facilitiesthey have the same terminal connections and contact arrangement, and permit drawout chassis (where involved) to be placed into existing cases without rewiring. |

| Electronic relays for other functions, together with miniaturization technology, have been utilized in the automation of elements of the generating, transmission and distribution systems. In their operation, they are often called upon to coordinate (and be included) with the protective relays associated with the system being coordinated. The electronic relays with their greater flexibility and available memory banks facilitate such automation while insuring the reliability of the automated systems. |

| Figure 13-16B (Courtesy ABB Power T&D Co.) |

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