Transformers that have been system-connected should be
de-energized, grounded, and disconnected before being
opened for inspection.
If the tank seal is broken, it is recommended that a leak test
be performed to verify that the tank is properly sealed. To
leak test, remove the pressure relief device and pressurize
the headspace. The test pressure should not exceed 7 psig.
The established pressure should be maintained for at least
four hours to insure that all the seals are proper.
Bolt-On tank cover removal
Transformer tanks are factory-sealed to prevent ingress
of ambient air and moisture. Do not open under any
precipitation conditions.
1. Verify that tank is grounded. De-energize transformer
from a remote upstream source. Ground all bushings
and terminals before removing cover.
2. Thoroughly clean tank cover to help prevent contami-
nation of insulating liquid when removing the cover.
Remove all dirt, grease, and moisture.
3. From within the cabinet, remove the hardware (3/8”
nuts using a 9/16” socket) which attaches the cover
nutguard to the faceplate.
4. Relieve internal tank pressure by operating the pressure
relief valve. Remove the hardware (3/8” nuts using a
9/16” socket) which attaches the cover to the tank.
5. Gently pry the cover upward. Do not allow the cover
gasket to come in contact with the transformer insulat-
ing liquid. Allowing the gasket to contact the liquid will
make it slippery and difficult to hold in position during
cover installation. Lift cover straight up to prevent dam-
age to cover, bolts, and tank gasket.
6. Note the location and orientation (up/down) of each
gasket section as they are removed from the tank
flange so that they can be reinstalled properly.
Bolt-On tank cover installation
1. Return the gasket sections to their original positions
and orientation.
2. Re-install the cover, using 25 ft-lbs. torque to tighten
the cover hardware. After installing all the nuts, re-
torque each nut to ensure proper torque is achieved.
3. Remove the pressure relief valve and pressurize the
headspace through the pressure relief valve coupling to
ensure that there are no leaks. Test pressure should not
exceed 7 psig. Established pressure should be main-
tained for at least four hours to insure that all seals are
proper.
4. Re-install the nutguard using 25 ft-lbs. torque to tighten
nutguard access hardware.
5. Re-install pressure relief valve.
Bolt-On manhole/handhole cover removal
Transformer tanks are factory-sealed to prevent ingress
of ambient air and moisture. Do not open under any
precipitation conditions.
1. Verify that tank is grounded. De-energize transformer
from a remote upstream source. Ground all bushings
and terminals before removing cover.
2. From within cabinet, remove hardware (3/8” nuts using
a 9/16” socket) attaching manhole/handhole access
cover to cabinet.
3. Remove manhole/handhole access cover.
4. Thoroughly clean tank and manhole/handhole cover to
help prevent contamination of insulating liquid when
removing manhole/handhole cover. Remove all dirt,
grease, and moisture.
5. Relieve internal tank pressure by operating pressure
relief valve.
6. Remove hardware (3/8” nuts using a 9/16” socket)
attaching manhole/handhole cover to tank.
7. Gently pry cover upward. Do not allow cover gasket
to come in contact with transformer insulating liquid.
Allowing the gasket to contact the liquid will make it
slippery and difficult to hold in position during cover
installation. Lift cover straight up to prevent damage to
cover, bolts, and tank gasket.
8. Note location and orientation (up/down) of each gasket
section as they are removed from tank flange so they
can be re-installed properly.
Bolt-On manhole/handhole cover installation
1. Return gasket sections to their original positions and
orientation.
2. Re-install manhole/handhole, using 25 ft-lbs. torque to
tighten hardware. After installing all nuts, re-torque each
nut to ensure proper torque is achieved.
3. Remove pressure relief valve and pressurize headspace
through pressure relief valve coupling to ensure that
there are no leaks. Test pressure should not exceed 7
psig. Established pressure should be maintained for at
least four hours to ensure that all seals are proper.
4. Re-install access cover using 25 ft-lbs. torque to tighten
access cover hardware.
5. Re-install pressure relief valve.
20
Three-phase pad-mounted compartmental type installation and maintenance instructions
MN202001EN August 2015