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Power Fuses

  • Power fuses, shown in Figure  in a typical transformer protective application, provide protection that is both reliable and economical. They are inexpensive—both in


    The operating procedure for power fuses is straightforward. Typically, after a fuse has operated, the load-side circuit breaker, switch, or recloser is opened. (If no load-side device is in place, the main-secondary circuit breaker or recloser is opened.) Then the line-side series disconnect is opened. Transformer inspection and maintenance can then be performed, and the fuses replaced. To restore service, the line-side series disconnect is closed to pick up transformer magnetizing current. Then the load-side circuit breaker, switch, or recloser is closed.


    As mentioned previously, the advantage to using power fuses is their relative low-cost compared to a relayed transformer protective device. Disadvantages include the difficulty in coordinating fuses for secondary-side faults and single-phasing of downstream devices in the event of a single-phase fault. Also, there is no way to implement more advanced relay schemes using differential, neutral overcurrent, or sudden pressure relays.



    ANSI/IEEE C37.91-1985; “IEEE Guide for Protective

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