Document 2.4.126, Revision 4
October 2017
10
Three-Phase Padmounted Distribution Transformers
Avoid locating the transformer in corrosive areas.
Remove any shipping braces and packing material
that may have been installed at the factory.
Verifying Enclosure Integrity
Three-phase compartmental padmounted
transformers are designed and constructed to be
tamper resistant according to the requirements
of IEEE Standard C57.12.28 or C57.12.29, as
applicable, and therefore need not be located
in a restricted area. Do not modify the tank or
terminal compartment in such a way that it will
compromise tamper resistance. If for any reason
modifications must be made to the tank or terminal
compartment that compromise tamper resistance,
the transformer must then be located in a restricted
area. Such modifications of may void the warranty.
Consult with the Howard Industries Transformer
Division before making any modifications to the
transformer.
Grounding
The transformer must be permanently grounded
according to applicable local and national codes.
Ground the transformer by using ground pads or
nuts located at the base of the front panel in the
terminal compartment. Do not use hold-down
bolts, pipe connections or any other fittings for
ground connections. A proper low-resistance ground
connection is necessary for safe operation.
Transformers with a grounded wye high-voltage
winding and a wye low-voltage winding are
designed for electric distribution systems that
have a grounded neutral. All windings designed for
grounded neutral operation must be permanently
and solidly grounded to the system neutral.
High-Voltage and Low-Voltage Connections
Before making high-voltage and low-voltage line
connections, check to make sure that all mating
connector surfaces are clean and smooth.
Connections must be tightened appropriately to
prevent overheating and possible failure of the
connection. Refer to the nominal torque guidelines
contained in Table 3. Connections should be made
with care to avoid placing undue stress on the
bushings.
High-Voltage Connections
Three-phase padmounted transformers with
live-front construction are usually supplied with
externally-clamped porcelain high-voltage bushings
for connection to the high-voltage source. Bushings
are supplied with tin-plated eye-bolt or spade
terminals that are suitable for connection to both
aluminum and copper conductors.
Three-phase padmounted transformers with dead-
front construction are supplied with universal
bushing wells, one-piece (integral) bushings or
universal bushing wells with factory-installed
inserts. One-piece (integral) bushings and bushing
inserts are designed to interface with insulated
elbow connectors, and can be supplied for either
load-break or non load-break operation.
When transformers are supplied with bushing wells
only, inserts must be installed in the field before
cable connections can be made. Bushing well
inserts must compatible with the universal bushing
well. Do not use incompatible or improperly
rated inserts, or equipment damage might occur.
When installing inserts, follow the manufacturer’s
instructions accompanying the insert.
On transformers with dead-front construction,
grounding caps must be installed on all unused
high-voltage bushings before energizing.
DANGER
Do not make any modifications to the
transformer that might compromise its
tamper resistant construction. FAILURE TO
FOLLOW THIS INSTRUCTION WILL RESULT IN
DEATH OR SERIOUS PERSONAL INJURY, AND
DAMAGE TO THE EQUIPMENT.
DANGER
The transformer must be properly grounded
at all times. FAILURE TO FOLLOW THIS
INSTRUCTION WILL RESULT IN DEATH OR
SERIOUS PERSONAL INJURY, AND DAMAGE
TO THE EQUIPMENT.
