Question

A 3750 KVA, 69 KV - 4.16Y/2.4KV, delta-grounded wye-connected distribution substation transformer supplies two distribution feeders. Each distribution feeder is protected by three single-phase, 400A, type D reclosers. The reclosers are set to operate once on the instantaneous curve and three times on the D time delay curve. The maximum available fault current on the 4.16 KV bus is 7000A. In the event of a fault on either of the 4.16 KV distribution feeders, the reclosers should operate to lockout before the transformer high-side fuse blows. On the same log-log scale, plot the following: A.) Recloser trip characteristics referred to the high-voltage side for worst-case fault conditions on the low-voltage side of the transformer B.) The adjusted transformer withstand characteristics for worst-case fault conditions Determine the proper E-rated fuse to selectively coordinate with the low-side reclosers and protect the transformer against through faults.

          A 3750 KVA, 69 KV - 4.16Y/2.4KV, delta-grounded wye-connected distribution substation transformer supplies two distribution feeders. Each distribution feeder is protected by three single-phase, 400A, type D reclosers. The reclosers are set to operate once on the instantaneous curve and three times on the D time delay curve. The maximum available fault current on the 4.16 KV bus is 7000A. In the event of a fault on either of the 4.16 KV distribution feeders, the reclosers should operate to lockout before the transformer high-side fuse blows. On the same log-log scale, plot the following:
A.) Recloser trip characteristics referred to the high-voltage side for worst-case fault conditions on the low-voltage side of the transformer
B.) The adjusted transformer withstand characteristics for worst-case fault conditions
Determine the proper E-rated fuse to selectively coordinate with the low-side reclosers and protect the transformer against through faults.

Added by Mason F.

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