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Figure 3-6 Unit pole closing
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TM-5-6120-250-12 Substation Trailer Mounted 500 KVA AC 4160-416Y/240V 208Y/120V 3 Phase 50/60 Hertz Manual
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Figure 3-7. Tap changer
Section VI. MAINTENANCE OF TRANSFORMER
transformer nameplate.  A table on the transformer
3-12. General
nameplate gives the voltages and current rating for each
Instructions contained in this section are for operator's
tap position.
information and guidance in maintenance of the
transformer.
WARNING
WARNING
The tap-changer must not be operated while
Solid insulation surrounding an energized
the  transformer  is  energized.  Serious
conductor and power apparatus must never
personal injury and / or damage to the
be replied upon to provide protection to
transformer may result.
personnel.
e. To change taps remove the tap changer cap (1,
a.  The external surfaces should be inspected at
fig. 3-7) by removing the two hex head bolts (4). With
regular intervals.  If they show weathering is taking
the cap removed, the tap position can be observed
place the surfaces should be cleaned and repainted.
through a slot in the indicator cams (3). Use a wrench to
turn the hex head drive mechanism (2).
The
b.  Check the pressure gage to make sure the
mechanism must be rotated through 5 / 6 of a turn to
transformer seal is being maintained. The gage reading
make a change of one tap.
Although the drive
should vary as the transformer temperature changes
mechanism can be turned continuously in either
and should normally indicate a positive pressure. A lack
direction placing the wedge in any one of six different
of any change in readings with changes in temperature
positions, only five positions are numbered for use as
is an indication of a leak in the transformer seal and
shown on the transformer nameplate. The unnumbered
should be investigated. Check and make sure vent
position should not be used. After the desired change
valve and sample valve are fully closed.
has been made, make sure that the cap gasket is in
good condition and replace the cap.
c. The meters and gages should be inspected to
gee that all are in good condition, registering properly
NOTE
and have no broken or cracked glass, scarred, or
The slots in the two indicator cams must
damaged cases and are tightly mounted.
coincide before the cap can be seated
d. The wedge-type tap changer provides a means
properly. This is to insure that the cap is
of c(hanging the voltage ratio of a de-energized
not replaced until the tap changer is on
transformer without breaking the transformer seal. It is
position.
It  also  serves  to  align  an
shipped  in  place  and  is  set  on  the  position
appropriate position number on the cap with
corresponding to the rated voltage shown on the
the arrow on the mounting flange. Secure
the cap with its two hex head bolts.
3-11

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