Howard Medium Power Substation - Manual (Page 10)

Document 2.4.06, Revision 4
June 2013 Medium Power Substation Transformers
location and Mounting
The transformer should be mounted on a level concrete
foundation of sufficient strength to support the weight
of the completely assembled transformer. If the
transformer is not level, insulating fluid may not circulate
properly through the cooling assembly, possibly causing
overheating and reduced transformer life. The mounting
location should provide for adequate ventilation and
easy access for inspection. The transformer should be
located at least 24 inches from any obstruction. When
installing transformers designed for indoor operation,
adequate air inlets and outlets must be provided for
proper cooling. Avoid locating transformers in corrosive
areas.
Opening Transformer Tank
Transformers are usually shipped sealed and should not
be opened unless necessary. Opening the transformer
will be necessary when transformers are shipped without
bushings, when internal field connections are required,
or when core ground tests are required.
DANgER : SlOWlY RElEASE INTERNAl
PRESSURE PRIOR TO REMOvING TANK
ACCESSORIES. FAIlURE TO DO SO COUlD RESUlT
IN SEvERE PERSONAl INJURY, DEATH, OR PROPERTY
DAMAGE.
DANgER : TO AvOID DEATH FROM
SUFFOCATION NEvER AllOW ANYONE TO
ENTER THE TRANSFORMER TANK UNlESS AN
ANAlYSIS OF THE AIR IN THE TANK SHOWS AT lEAST
19.5% OXYGEN. THE GAS SPACE IN AN OPERATING
TRANSFORMER USUAllY CONSISTS OF NITROGEN
GAS. WHENEvER ANYONE IS IN THE TANK, A
PERSON SHOUlD BE STATIONED AT THE MANHOlE
OUTSIDE THE TANK TO ENSURE SAFETY OF THE
PERSON INSIDE.
Transformer should not remain open for more than
24 hours at a time. If work is interrupted, the tank
should be resealed, evacuated, and filled with dry air or
nitrogen.
To prevent contamination of the transformer tank, do
not open the transformer in an unprotected area during
inclement weather or where the air may contain dirt
or other particles. Either of the above could 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 refilled 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
manhole cover.
1. Thoroughly clean the manhole cover.
Remove all moisture, dirt, and grease to
avoid contaminating the transformer’s fluid
compartment.
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 sections from the manhole
flange. Record the location and orientation of
each gasket piece, so they can be reinstalled
correctly.
The following procedure should be used to reinstall the
manhole cover.
1. Place gasket sections in their original positions
and orientations.
2. Reinstall manhole cover. Reinstall fasteners
and torque to 25 ft-lbs. After tightening all
fasteners, re-torque each one to ensure proper
torque.
3. Remove the pressure relief valve and pressurize
the headspace and check for fluid leaks. Do not
exceed 7 PSIG during this test. This pressure
should be maintained for at least four hours.
INSTAllATION
10