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  •   Advantages of Underground Cables vs Overhead Lines   There are a number of advantages associated with undergrounding of the transmission line across the development which include the following: Reduced visual impact by removing tower No. 11 in the centre of the development and th...
  •   System short circuits may occur across any two or even three lines, or, if the neutral Point is solidly earthed, between any one line and the earthed neutral the effect of a System short circuit is to produce over currents, the magnitude of which is Dependent on the short-circuit level of ...
  •   Corona   A corona is a partial discharge and takes place at the surface of a transmission line conductor when the electrical stress, that is, the electric field intensity (or surface potential gradient), of a conductor exceeds the breakdown strength of the surrounding air. In such a...
  •     with fire associated with power transformers or oil-filled reactors, where the consequences can be particularly serious and extensive because of the large volume of oil that can catch fire and spread widely (Fig). For more details on protection against fire   ...
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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.

     

    Reference:

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

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