A three-phase \(34.5-\mathrm{kV}\) feeder supplying a 3.5-MVA load is protected by \(80 \mathrm{E}\) power fuses in each phase, in series with a recloser. The time-current characteristic of the 80E fuse is shown in Figure 10.43. Analysis yields maximum and minimum fault currents of 1000 and \(500 \mathrm{~A}\), respectively,

(a) To have the recloser clear the fault, find the maximum clearing time necessary for recloser operation.

(b) To have the fuses clear the fault, find the minimum recloser clearing time. Assume that the recloser operating time is independent of fault current magnitude.

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Time in seconds 0.5 0.3 0.2 0.1 0.06 0.03 0.02 0.01 T T Minimum melting time 300 500 1 Current limiting 80E power fuse 34.5 kV 60 Hz 25 C ambient Maximum clearing time 1000 Current in amperes 2000 L L L 5000