1. Cold load pickup. After 15-min outage 200% for 0.5 s,
140% for 5 s After 4 h, all electric 300% for 5 min
2. ‘‘Damage’’ curve—75% of minimum melt.
3. Two expulsion fuses cannot be coordinated if the
available fault current is great enough to indicate an interruption of less
than 0.8 cycles.
4. ‘‘T’’-SLOWand ‘‘K’’-FAST.
5. CLFs can be coordinated in the subcycle region.
6. Capacitor protection:
. The fuse should be rated for 165% of the normal capacitor
current. The fuse should also clear within 300 s for the minimum short-circuit
current.
. If current exceeds the maximum case rupture point, a CLF
must be used.
. CLFs should be used if a single parallel group exceeds 300
kVAR.
7. Transformer
. Inrush—12 times for 0.1 s.
. 25 times for 0.01 s.
. Self protected—primary fuse rating is 10–14 times
continuous when secondary breaker is used.
. Self protected—weak link is selected to be about 2.5 times
the continuous when no secondary breaker is used (which means that minimum melt
is in the area of 4–6 times rating).
. Conventional—primary fuse rated 2–3 times.
. General-purpose current limiting—2–3 times continuous.
. Back-up current limiting—the expulsion and CLF are usually
coordinated such that the minimum melt I2t of the expulsion fuse is equal to or
less than that of the back-up CLF.
8. Conductor burn down—not as great a problem today because
loads are higher and hence conductors are larger.
9. General purpose—one which will successfully clear any
current from its rated maximum interrupting current down to the current that
will cause melting of the fusible element in 1 h.
10. Back-up—one which will successfully clear any current
from its rated maximum interrupting down to the rated minimum interrupting
current, which may be at the 10-s time period on the minimum melting
time–current curve.
11. CLF—approximately 1=4 cycle operation; can limit energy
by as much as 60 to 1.
12. Weak link—in oil is limited to between 1500 and 3500 A.
13. Weak link—in cutout is limited to 6,000–15,000
asymmetrical.
14. Lightning minimum fuse (12T-SLOW), (25K-FAST).
15. Energy stored in inductance = ½ Li2.
16. The maximum voltage produced by a CLF typically will not
exceed 3.1 times the fuse rated maximum voltage.
17. The minimum sparkover allowed for a gapped arrester is
1.5#1.414¼2.1 times arrester rating.
18. General practice is to keep the minimum sparkover of a
gapped arrester at about 2.65x arrester rating.
19. Metal oxide varistors (MOVs) do not have a problem with
CLF ‘‘kick voltages’’.
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