GE Industrial Solutions Seconday Substation Transformer - Manual (Page 8)

8
certain Supply jobs for older transformers, 12-
inch fans may also be mounted below the
bottom headers blowing upward. On those
mounted under the headers, a swivel-type
bracket is provided in order to permit
installation of the fan on the required center
line.
WIRING
After the fans are mounted, the fan wiring is
to be installed as indicated on the Outline
drawing and Connection Diagram. When the
fans are divided into two or more banks,
separate cabling will be provided for each
bank. Make sure water-tight seals are
established where cables enter the various
fittings. Cables are to be clamped to the
cooling tubes and fan guards.
MAINTENANCE
A periodic inspection should be made of
the forced-air cooling equipment to be sure it
is in satisfactory operating condition. Motor
bearings are permanently lubricated and
sealed at the factory and require no
maintenance.
Do not paint fan blades. Doing so except
under controlled conditions will frequently
cause the blades to become dynamically
unbalanced. When placed in operation, the
imbalance will then set up excessive vibration
which can eventually lead to destruction of
the blade.
TAP CHANGER
GE-PROLEC small power transformers use
de-energized tap changers that are used to
change the voltage ratio when the transformer
is de-energized.
The tap changer is provided with stop
notches, a position indicator for avoiding
faulty positions and a hole for a lock to
prevent un-authorized operations. It is
shipped in place, and is set on the position
corresponding to the rated voltage shown on
the transformer nameplate.
THERMOMETER
A dial-type thermometer is standard
equipment on most transformers. It is
mounted in a well in the transformer and
therefore can easily be removed. The
thermometer reads top-oil temperature.
The thermometer also has a drag pointer
which indicates maximum temperature
reached. This drag pointer is reset by
drawing the magnet (chained to the
thermometer) across the face of the
thermometer.
A thermometer with alarm contacts is an
optional extra. These contacts can be used
to sound an alarm, control fans and/or
actuate circuit breakers when preset
temperatures are reached.
LIQUID-LEVEL INDICATOR
The magnetic liquid-level gauges are
composed of two subassemblies. The
internal float mechanism and flange is first
bolted to the tank flange with a gasket seal.
The bezel assembly which contains dial and
pointer is next screwed to the flange. Motion
of the float inside the tank is transmitted from
internal shaft to the pointer shaft by polarized
magnets, located each side of the flange.
Because of the seal, no liquid or gas is lost
even if gauge glass is broken.
The liquid-level gauge can also be provided
with microswitch for alarm circuits.
METHOD OF DRYING
TRANSFORMERS
Excess moisture can curtail transformer life.
GE-PROLEC removes moisture from the
insulating system during manufacturing by
loading the core and coil assembly into a
drying oven and baking it for over 12 hours
maintaining the internal temperature at
120°C. This process takes part prior to the
vacuum and liquid filling process.