Howard HI-102 Overhead Transformer - Manual (Page 20)

Document 2.4.95, Revision 0
May. 2013
20
Fluid-Filled Overhead Distribution Transformers
Drain Valve and Sampling Device
The drain valve and sampling device permit draining
the transformer fluid and sampling the fluid for
testing purposes. The valve is located near the
bottom of the transformer tank. Refer to “Sampling
and Testing the Fluid” and “Draining and Filling the
Tank” for the fluid sampling and draining procedures.
Automatic Pressure Relief Valve
The automatic pressure relief valve (PRV) is
designed to relieve excessive tank pressure that
might occur during operation of the transformer.
The valve consists of a self-resealing, spring-loaded
diaphragm. Some PRV types may include a re-
settable visual flag to indicate that the valve has
operated.
When pressure in the tank exceeds the PRV’s
specified limit, the 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.
▲
! WARNING
FAILURE TO FOLLOW THE INSTRUCTIONS BE-
LOW COULD RESULT IN MINOR OR MODERATE
PERSONAL INJURY, AND COULD ALSO RESULT
IN DAMAGE TO THE EQUIPMENT.
The cause of PRV activation should always be
investigated, since pressure venting may indicate
a potential problem inside the transformer.
Internal Fault Detector
The Internal Fault Detector (IFD) is a mechanical
sensor that activates when sudden pressure 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
provides only a visual indication that a fault has
occurred. It is not an electrical disconnect device.
▲
! 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, and should
not be relied on as an electrical disconnect
device.
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. Refer to
information elsewhere in these instructions
regarding operation of an automatic pressure relief
valve.
The IFD incorporates a removable shipping lock
for use during transportation and storage. The
shipping lock must be removed after the transformer
is installed. Re-install the shipping lock if the
transformer must be relocated. Always transport
IFD-equipped transformers with the shipping lock
installed to prevent accidental operation.
Bushings and Terminals
Tin-plated eye-bolt or spade terminals are provided
as specified by IEEE standards and are suitable for
connection to either aluminum or copper conductors.
High-voltage and low-voltage connections should be
made as indicated on the transformer nameplate.
Clean and properly tighten all terminal connections
to ensure a low-resistance connection and prevent
overheating. Refer to torque guidelines contained
in Table 3. Ensure that there is sufficient electrical
clearance between all live parts, including both
phase-to-phase and phase-to-ground clearances.