A Note On Single-Pole Switching; Opening And Removing The Fuse - S&C PMH Instructions For Operation Manual

S&C Source-Transfer PMH Pad-Mounted Gear
Outdoor Distribution (14.4 kv and 25 kv)
SWITCHING WITH UNI-RUPTER — Continued

A Note on Single-Pole Switching

In single-pole switching of ungrounded-primary three-
phase transformers or banks (or single-phase trans-
formers connected line-to-line), circuit connections or
parameters may, in some cases, produce excessive
overvoltages. In particular, for the following applica-
tions above 22 kv, single-pole switching by any
means—including Uni-Rupter—should be performed
only under the conditions stated in italics:
•
Switching unloaded or lightly loaded delta-con-
nected or ungrounded-primary wye-wye connected
three-phase transformers or banks (or line-to-line
connected single-phase transformers), rated 150 kva
or less three-phase, or 50 kva or less single-
phase—or of any kva rating when combined with
unloaded cables or lines—where maximum system

Opening and Removing the Fuse

Before proceeding with the instructions on opening and
removing the fuse, refer to the "DANGER" on pages 4
and 5.
Ç
DANGER
When working in the high-voltage compartments,
always maintain proper clearance from energized
components. Failure to maintain proper clear-
ance will result in serious injury or death.
Always use an S&C Grappler (Catalog Number
4423) attached to a suitable universal pole (1 ¹ ⁄₄ inches
in diameter) to handle barriers and to install, remove,
open, or close fuses. The universal pole must be at
least 4 feet long (S&C Catalog Number 4451R2-E, or
equal) for 14.4-kv gear or at least 6 feet long (S&C Cata-
log Number 4452R2-E, or equal) for 25-kv gear.
Use an S&C Grappler attached to and in line with a
suitable universal pole to perform the procedures listed
below:
1. Open the appropriate fuse-compartment door and
secure it with the door holder. See Figure 12. The adja-
cent door should be closed and latched to minimize
exposure to high voltage.
2. If optional inner barrier panels (Catalog Number Suffix
"-G7") are furnished, loosen the pentahead bolts and
remove the panel.
Then remove only the barrier associated with the
fuse to be opened, using the Grappler for this purpose.
See Figure 13.
663-503 INSTRUCTION SHEET
Page 20 of 35
August 14, 1995
Ç
WARNING
operating voltage exceeds 22 kv. Single-pole switch-
ing should be performed only if each phase is car-
rying 5% load or more, or if the transformer or
bank is temporarily grounded at the primary neu-
tral during switching.
•
Switching loaded or unloaded ungrounded-primary
wye-delta connected three-phase transformers or
banks—alone or combined with unloaded cables or
lines—where maximum system operating voltage
exceeds 22 kv. Single-pole switching should be per-
formed only if each phase is carrying 5% load or
more and if the lighting-load phase is always
switched open first (or switched closed last); or if
the transformer or bank is temporarily grounded
at the primary neutral during switching.
3. With the Grappler prongs pointed downward, insert
the longer prong into the pull ring of the fuse. See
Figure 19.
Figure 19. Grappler, as positioned for opening stroke, with
longer prong inserted in the fuse pull ring.
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With Micro-AT Control
S&C ELECTRIC COMPANY
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