Howard HI-104 Single-Phase Pad Transformer - Manual (Page 25)

Document 2.4.96, Revision 0
March, 2013
25
Single-Phase Pad-Mounted Compartmental-Type Distribution Transformers
Refer to “Sampling and Testing the Fluid” for the fluid
sampling.
Automatic Pressure Relief Valve
The automatic pressure relief valve (PRV) is designed
to relieve excessive tank pressure that might occur
during normal operation of the transformer. The
valve consists of a self-resealing, spring-loaded dia-
phragm. Some PRV types may include a re-settable
visual flag to indicate that the valve has operated.
When gas pressure in the tank exceeds the PRV’s
specified limit, the gas pressure will cause the valve
to open, venting the excess pressure. After the
internal pressure decreases below the PRV reseal
rating, the valve will automatically close and reseal
the transformer. For PRV’s equipped with a visual
indicating flag, the flag must be manually reset.
When specified, PRV’s are provided with optional
switch contacts, which can be used to provide a
remote alarm.
▲
! WARNING
FAILURE TO FOLLOW THE INSTRUCTIONS
BELOW COULD RESULT IN DEATH OR SERIOUS
PERSONAL INJURY, AND COULD ALSO RESULT
IN DAMAGE TO THE EQUIPMENT.
The cause of PRV activation should always be in-
vestigated, since pressure venting may indicate
a potential problem inside the transformer.
Internal Fault Detector
The optional Internal Fault Detector (IFD) is a me-
chanical sensor that activates when sudden pres-
sure from an internal arcing fault occurs inside
the transformer. If an internal fault occurs, the IFD
releases a visible, non-resettable orange signal flag.
This signal flag alerts crews that the transformer is
faulted and should not be re-energized. Be aware
that the IFD is not a disconnect device. It provides
only a visual indication that an internal fault has oc-
curred. Personnel should read and follow the instruc-
tions provided by the IFD device manufacturer for
proper operating procedures and safety information.
▲
! WARNING
FAILURE TO FOLLOW THE INSTRUCTIONS
BELOW COULD RESULT IN DEATH OR SERIOUS
PERSONAL INJURY, AND COULD ALSO RESULT
IN DAMAGE TO THE EQUIPMENT.
• Do not re-energize a transformer if the IFD
has operated.
• Do not attempt to reset the orange signal
flag.
• Always assume that a transformer might be
faulted, even if the IFD has not operated.
• Never rely solely on the IFD as an indicator of
transformer condition.
• The IFD is a visual indicator only. It is not an
electrical disconnect device, and should not
be relied on as such.
The IFD also includes a standard pressure relief
valve that is integrated into the sensor to relieve
excessive tank pressures that might occur during
normal operation of the transformer. The valve can
be operated manually using the pull-ring.
The IFD incorporates a removable shipping lock for
transportation and storage. The shipping lock must
be removed after transformer installation. Always
transport IFD-equipped transformers with the ship-
ping lock installed to prevent accidental operation of
the device.
High-Voltage Bushings
Single-phase pad-mounted transformers with dead-
front construction are provided with externally-
clamped universal bushing wells only, one-piece
(integral) bushings or universal bushing wells with
factory-installed bushing inserts. One-piece bush-
ings and bushing inserts are designed to interface
with separable insulated elbow connectors, and can
be provided as either load-break or non load-break
devices. When transformers are provided with bush-
ing wells only, inserts must be installed by the user
before cable connections can be made. High-voltage
terminations may be configured for radial feed (one
termination) or loop feed (two terminations).
Single-phase pad-mounted transformers with live-