Fuse recloser coordination: PE Power Protection practice question

A 12.47 kV feeder recloser uses fuse saving: two fast operations, then two delayed. A lateral tap downstream is protected by an expulsion fuse link. In the current range of interest, the fuse characteristics can be approximated as:

  • minimum melting: I2t=140,000 A2sI^2 t = 140{,}000\ \text{A}^2\text{s}
  • total clearing: I2t=220,000 A2sI^2 t = 220{,}000\ \text{A}^2\text{s}

The recloser's fast curve clears in 0.050 s at these currents. To account for fuse heating over the two fast operations, the utility requires the fuse minimum-melt time to be at least 1.35 times the fast-curve clearing time. The highest fault current on the lateral for which fuse saving still works is most nearly:

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