1) Cold load pickup - after 15 minute outage, 200% for.5
seconds, 140% for 5 seconds after 4 hrs, all electric 300% for 5 minutes
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 .8 cycles.
4) “T” - SLOW and "K” - FAST
5) Current limiting fuses can be coordinated in the
sub-cycle region.
6) Capacitor protection:
• The fuse should be rated for 165% of the normal capacitor
current. The fuse should also clear within 300 seconds for the minimum short
circuit current.
• If current exceeds the maximum case rupture point, a
current limiting fuse must be used.
• Current limiting fuses should be used if a single parallel
group exceeds 300 KVAR.
7) Transformer
• Inrush - 12 times for .1 sec.
• 25 times for .01 sec.
• Self protected - primary fuse rating is 10 to 14 times
continuous when secondary breaker is used.
• Self protected - weak link is selected to be about 2 1/2
times the continuous when no secondary breaker is used (which means that
minimum melt is in the area of 4 to 6 times rating).
• Conventional - primary fuse rated 2 to 3 times.
• General Purpose current limiting - 2 to 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 one hour.
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 second 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
amperes.
13) Weak link - in cutout is limited to 6000 to 15000
asymmetrical.
14) Lightning minimum fuse (12T-SLOW), (25K-FAST).
15) Energy stored in inductance = ½ Li2
16) The maximum voltage produced by a C.L. fuse typically
will not exceed 3.1 times the fuse rated maximum voltage.
17) The minimum sparkover allowed for a gapped arrester is
1.5 x 1.414 = 2.1 times arrester rating.
18) General practice is to keep the minimum sparkover of a
gapped arrester at about 2.65 x arrester rating.
19) MOVs do not have a problem with CLF “kick voltages”.
No comments:
Post a Comment