Howard HI-104 Single-Phase Pad Transformer - Manual (Page 17)

Document 2.4.96, Revision 0
March, 2013
17
Single-Phase Pad-Mounted Compartmental-Type Distribution Transformers
between its present setting and the next setting. The
index plate prevents the switch from switching more
than one position at a time. The live-line tool is then
inserted into the switch operating handle and turned
until the switch snaps into the next position. Repeat
this procedure until the switch is in the desired posi-
tion. Do not stop and reverse direction of the switch
before it has changed position, as this will damage
the switch mechanism.
▲
! CAUTION
FAILURE TO FOLLOW THE INSTRUCTIONS BE-
LOW COULD RESULT IN MINOR OR MODERATE
PERSONAL INJURY, AND COULD ALSO RESULT
IN DAMAGE TO THE EQUIPMENT.
• Do not operate a load-break switch by hand.
Operate only using a live-line tool (hot stick or
shotgun stick).
• Do not stop and reverse direction of the load-
break switch before it has changed positions.
Fuses
A blown fuse may indicate a faulted transformer. Do
not replace a blown fuse unless the cause of the
fuse operation has been identified and corrected.
Replacement fuses should have the appropriate rat-
ing and operating characteristics. Refer to the circuit
diagram on the transformer nameplate for the loca-
tion of fuses.
▲
! 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 replace a blown fuse unless the cause
of the fuse operation has been identified and
corrected.
• De-energize the transformer and ground all
terminals before replacing fuses.
• Only qualified personnel with appropriate
measurement devices should measure the
voltages on the transformer.
Internal Weak-Link Fuse
An internal weak-link fuse (also called a cartridge
fuse) is a fluid-immersed expulsion fuse, which is
designed to isolate the transformer from the distribu-
tion system in the event of an internal fault on the
load side of the fuse. On single-door style transform-
ers the fuse can usually be accessed by removing
one of the high-voltage bushings. On double-door
style transformers, the fuse is accessible through the
cover-mounted handhole. Refer to the transformer
nameplate for the fuse location. When accessing the
fuse, observe the precautions discussed in “Opening
the Transformer Tank.”
On single-door style transformers the fuse can be
usually be inspected and replaced through the front
panel using the following procedure.
1. Make sure that the transformer is completely de-
energized and that the tank and all primary and
secondary terminals are securely and effectively
grounded.
2. Vent the tank by operating the pressure relief
valve, being careful to avoid contact with any hot
fluid that might be expelled from the PRV.
3. Tilt the transformer to the rear, so that the inter-
nal fluid level drops below the bushing opening.
Alternatively, the fluid level can be lowered to
replace the fuse Refer to “Removing or Lowering
the Fluid.”
4. Remove the bushing clamping hardware and re-
move the bushing and fuse, taking care to avoid
stress on the high-voltage coil lead.
5. Unbolt the fuse and replace it with a new fuse of
the appropriate rating. Tighten the fuse mounting
fasteners according to the recommended torque
values in Table 4.
6. Clean the bushing mounting surface and inspect
the bushing gasket. Replace the gasket if dam-
aged.
7. Insert the fuse and bushing into the mounting
hole and install mounting hardware. Tighten
mounting fasteners according to the recommend-
ed torque guidelines in Table 4.
8. Level the transformer, re-attach hold-down cleats
or brackets if previously removed, and check to
make sure the bushing is not leaking fluid.
9. Energize the transformer from a remote location
and check for proper operation.