Document 2.4.128, Revision 3
October, 2017
15
Network Transformer Instruction Manual
Tap Changer
The de-energized (no-load) tap changer may be used
to adjust the voltage ratio of a transformer while it
is de-energized. It is intended to allow adjustment
of the output (secondary) voltage to the rated
value. Do not use the tap changer to raise or lower
the output voltage to any voltage other than that
indicated on the transformer nameplate. If the tap
changer is set to provide an output voltage different
from rated voltage, core saturation may result,
producing high excitation current, high core loss and
a high noise level.
WARNING
FAILURE TO FOLLOW THE INSTRUCTIONS
BELOW COULD RESULT IN DEATH OR
SERIOUS PERSONAL INJURY AND MAY ALSO
RESULT IN
DAMAGE TO THE EQUIPMENT.
• Do not operate a de-energized tap
changer unless the transformer is
completely de-energized.
• Do not re-energize the transformer unless
the tap changer handle is locked into
position.
The de-energized tap changer is located on the
main tank cover, protected by a 2-inch pipe cap. The
tap changer can be rotated by means of a special
wrench that must be inserted into the operating
mechanism. When the tap changer is not in use, the
protective cap must be installed. Apply a suitable
sealant to the threads of the coupling before
installing the cap.
Never operate a de-energized tap changer while the
transformer is energized. Tap changers normally
have five or seven tap positions, as indicated on
the tap changer dial plate and on the transformer
nameplate. A locking mechanism is provided to lock
the tap changer into position and prevent accidental
operation. Do not re-energize the transformer until
the tap changer is firmly locked into a tap position.
The wrench is keyed, so that it can be removed only
when the tap changer is properly placed into one of
the tap positions.
Unless otherwise specified, transformers supplied
with tap changers will be shipped from the factory
with the switch set to the nominal position.
Series/Multiple or Delta/Wye Switch
Transformers designed with series/multiple windings
(dual-voltage or triple-voltage) or re-connectable
delta/wye windings are provided with a de-energized
series/multiple or delta/wye switch, as indicated on
the transformer nameplate. The series/multiple or
delta/wye switch is usually located on the main tank
cover, protected by a 2-inch pipe cap. The switch can
be rotated by means of a special wrench that must
be inserted into the operating mechanism. When
the switch is not in use, the protective cap must be
installed. Apply a suitable sealant to the threads of
the coupling before installing the cap.
Never operate a de-energized series/multiple or
delta/wye switch while the transformer is energized.
A locking mechanism is provided to lock the switch
into position and prevent accidental operation. Do
not re-energize the transformer until the switch is
firmly locked into the desired position. The wrench is
keyed, so that it can be removed only when the tap
changer is properly placed into position.
Unless otherwise specified, transformers are shipped
from the factory with series/multiple and delta/wye
connections set to the highest voltage.
WARNING
FAILURE TO FOLLOW THE INSTRUCTIONS
BELOW COULD RESULT IN DEATH OR
SERIOUS PERSONAL INJURY AND MAY ALSO
RESULT IN
DAMAGE TO THE EQUIPMENT.
• Do not operate a series/multiple or delta/
wye switch unless the transformer is
totally de-energized.
• Do not re-energize the transformer unless
the series/multiple or delta/wye switch
handle is locked into position.
