Document 2.4.126, Revision 4
October 2017
30
Three-Phase Padmounted Distribution Transformers
1. Pump from the bottom of temporary storage
container. To prevent bubbles in the fluid,
do not allow air to enter the pump intake.
2. Place the discharge hose at the bottom of
the transformer tank below the fluid surface
to prevent aeration and the introduction of
bubbles.
3. Pump and fill the transformer tank slowly.
Fill with fluid to fill line marked inside the
transformer tank on the interior surface
of the front panel. If the fill line cannot be
viewed, use the indication on the fluid level
gauge or sight plug (if supplied) or fill to the
bottom of the fill plug.
Opening the Transformer Tank
Transformer tanks are shipped sealed and should
not be opened unless necessary. If it is necessary
to open the tank, follow the instructions below and
observe all safety warnings.
Transformer tanks should not remain open for more
than two hours. If work is interrupted, the tank
should be resealed, evacuated, and filled with dry
air or nitrogen.
To prevent contamination of the transformer, do
not open the transformer tank in an unprotected
area during inclement weather or where the air
may contain dirt or other particles. Any of these
situations could contaminate the insulating fluid
and cause a transformer failure. The tank opening
should be protected against entry of foreign matter.
If it is necessary to remove some fluid from the
tank to allow for inspection or other work, the
transformer must be re-filled with fluid after work is
completed.
Personnel should not be permitted on top of or
inside the transformer while it is open unless they
have emptied all pockets and checked for loose
objects that might fall into the tank. All tools should
be accounted for after work is completed. It is
recommended that any tools used on top of the
transformer or inside the tank be attached with
safety cords to prevent them from being lost inside
the transformer.
Personnel must not stand directly on any electrical
insulation. Clean drop cloths should be used under
working areas in the transformer to prevent objects
from dropping into the core/coil assembly.
The following procedure should be used to remove
the hand-hole cover.
1. Thoroughly clean the hand-hole cover.
Remove all moisture, dirt, and grease to avoid
contaminating the transformer tank.
2. Relieve internal tank pressure by manually
operating the pressure relief valve.
3. Remove cover fasteners.
4. Gently pry the cover upward, making sure that
the cover gasket does not fall into the tank. Lift
the cover vertically to prevent damage to cover,
bolts, and gasket.
5. Remove the gasket from the hand-hole flange.
The following procedure should be used to re-install
the hand-hole cover.
1. Place the gasket in its original position. If the
gasket is damaged, it should be replaced.
WARNING
FAILURE TO FOLLOW THE INSTRUCTIONS BELOW
MAY RESULT IN DEATH OR SEVERE PERSONAL
INJURY, AND/OR DAMAGE TO THE EQUIPMENT.
• Before servicing the transformer, ALWAYS
de-energize the transformer from a
remote upstream source and then proceed
to ground all primary and secondary
transformer terminals following industry-
accepted safe grounding practices.
Grounding secondary terminals protects
against situations such as a standby
generator energizing transformer from the
secondary circuit.
• Release internal pressure before opening
the tank.
• Never allow anyone to enter the
transformer tank until an analysis of the
air inside the tank indicates at least 19.5%
oxygen.
• Whenever someone is inside the tank, a
person should be stationed near the hand-
hole to ensure the safety of the person
inside the tank.
