Document 2.4.128, Revision 3
October, 2017
25
Network Transformer Instruction Manual
water and other possible contaminants before
proceeding with the filling process
2. Pump from the bottom of the storage container.
To prevent bubbles in the fluid, do not allow air to
enter the pump intake.
3. Place the discharge hose at the bottom of the
transformer tank below the fluid surface to
prevent aeration and the introduction of bubbles.
4. Pump and fill the transformer tank slowly. Fill
the tank to fill line marked on inside of the
transformer tank. If the fill line mark cannot
be viewed, use the indication on the fluid level
gauge (if supplied) or fill to the bottom of the fill
plug on the other side of the transformer tank.
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. Either of the above
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 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 bolted 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, being
careful to avoid hot fluid that could be
expelled from the 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.
The following procedure should be used to reinstall
the hand-hole cover.
1. Replace the gasket, if damaged.
2. Re-install the hand-hole cover. Re-
install fasteners according to the torque
recommendations in Table 3. After tightening
all fasteners, re-torque each one to ensure
proper torque.
3. Pressurize the headspace to 3-4 PSIG and
check for fluid leaks. This pressure should be
maintained for at least four hours.
When the internal inspection is complete, reseal the
tank and re-fill with fluid (if any was removed prior
to inspection). The gas space should be filled with
dry air or dry nitrogen to 2 PSIG. Contact the Howard
Industries Transformer Division, if any internal
damage is found during the internal inspection.
Torque Guidelines
Tables 3 through 6 below contain recommended
torque values for tightening various connections
on the transformer. Connections with gaskets or
those involving rubber components (such as high-
voltage busing inserts) will normally relax after initial
tightening. Nominal torque values listed below
include an allowance for normal relaxation.
Do not over-tighten any connection; otherwise,
gaskets may split due to over-compression, and
components may break. Fluid leaks may result if
