Howard HI-102 Overhead Transformer - Manual (Page 16)

Document 2.4.95, Revision 0
May. 2013
16
Fluid-Filled Overhead Distribution Transformers
Replacement fuses should have the proper rating
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
The optional internal weak-link fuse is a fluid-im-
mersed expulsion fuse that is designed to isolate the
transformer from the distribution system in the event
of an overload or an internal transformer fault on the
load side of the fuse. The fuse is mounted at the
bottom of the high-voltage bushing or in some cases
on a terminal block located on the multiple-voltage
switch or between the high-voltage bushing and the
high-voltage coil. The presence of a weak-link fuse, if
provided, will be indicated on the transformer name-
plate.
Fuses can be accessed by removing the transformer
cover or, if a handhole is provided, by removing the
handhole cover. When accessing the fuse, observe
the precautions and instructions discussed in “Open-
ing the Transformer Tank.”
Partial-Range Current-Limiting Fuse
The optional partial-range current-limiting fuse is
designed to limit the energy released by a low-im-
pedance (high-current) internal fault and reduce the
likelihood of violent transformer failure. A weak-link
expulsion fuse is normally installed in series with the
partial-range current-limiting fuse. The purpose of
the weak-link expulsion fuse is to clear a high-imped-
ance fault or overload. When properly applied, the
partial-range current-limiting fuse will operate only
for internal transformer faults. When a partial-range
current-limiting fuse has operated, the transformer
should be considered faulted and removed from ser-
vice. The presence of a partial-range current limiting
fuse, if provided, will be indicated on the transformer
nameplate.
Surge Arrester
The optional surge arrester is used to protect the
transformer from damage due to over-voltage tran-
sients (such as lightning surges), which propagate
through the distribution system. Surge arresters may
be provided as an externally-mounted device or as
an internal fluid-immersed device. The surge arrester
should be installed only on systems where the power
frequency voltage at the arrester does not exceed
the arrester’s published maximum continuous oper-
ating voltage (MCOV) value.
External Surge Arrester
The external arrester line-lead and tank grounding
connections should be checked to ensure they are
tight before placing the transformer in service. Refer
to Table 3 for torque guidelines.
▲
! WARNING
FAILURE TO FOLLOW THE INSTRUCTIONS
BELOW COULD RESULT IN DEATH OR SERIOUS
PERSONAL INJURY, AND COULD ALSO RESULT
IN DAMAGE TO THE EQUIPMENT.
• De-energize the transformer from a remote
location and make sure all transformer
terminals and bushings have zero voltage
before connecting or servicing surge
arresters.
• Disconnect all surge arresters before
performing impulse, induced-potential or
applied-potential tests.
Disconnect the external surge arrester line-lead
before performing impulse, induced-potential or
applied-potential tests; otherwise, the arrester may
be damaged. Reconnect the surge arrester after
testing and before placing the transformer back into
service.
Internal Surge Arrester
The optional internal metal-oxide-varister (MOV)