Arc-Strangler loadbreaking device with NX
®
fusing
NX
®
full-range current-limiting fuses up to 15.5 kV can
be ordered with an integral Arc-Strangler
®
loadbreaking
device. These in-air devices are mounted on the faceplate
of the transformer. The Arc-Strangler device has the same
operating characteristics as the basic NX clip-style fuse,
along with loadbreaking capabilities.
The Arc-Strangler loadbreaking device is a spring-loaded
sliding sleeve that extinguishes the arc drawn between the
mounting contacts and the fuse conductor when the fuse
is opened while load current is flowing. All magnitudes
of current through the continuous current rating of the
fuse can be interrupted positively and safely under proper
conditions. A pull-ring at the top of the fuse assembly (for
hotstick operation) and a hinge at the bottom complete the
loadbreak device.
Arc-Strangler switchblades
Switchblades with integral Arc-Strangler loadbreaking
devices are available for use in NX type fuse mountings.
Arc-Strangler switchblades are designed to break load
current only (up to 200 A) and do not incorporate a fuse of
any type for overload or fault interruption.
Surge arresters
Surge arresters are used in three-phase pad-mounted
transformers to protect underground distribution equipment
and cable from overvoltage surges. During steady state
conditions, line-to-ground voltage is applied continuously
across the arrester terminals. When surges occur, the
arrester immediately limits the overvoltage to the required
protective level by conducting the surge current to ground.
Upon passage of the surge, the arrester returns to its initial
state, conducting minimal leakage current.
Surge arresters should be installed only on systems where
the power frequency voltage at the arrester does not
exceed published maximum continuous operating voltage
(MCOV) values.
The transformer should not be tested (impulse or applied
potential) with the arrester connected. If connected during
impulse tests, the arrester will clamp the discharge voltage
applied by the test equipment. If the arrester is connected
to the transformer during an applied potential test, there is
a possibility that the arrester will be damaged. Disconnect
surge arresters before tests are performed on the
transformer. Arresters should be reconnected immediately
after tests are completed.
Under-oil MOV arrester
Eaton’s Cooper Power series heavy-duty distribution-class
under-oil MOV arrester is designed to be mounted inside
the transformer tank (see Figure 25). Internal, under-oil
mounting of the arrester prevents shortened arrester life
due to surface contamination, wildlife damage, vandalism,
or moisture ingress.
Under-oil arresters are designed to operate when
submerged in oil. It is recommended that the average oil
temperature not exceed 90 °C and that the maximum oil
temperature not exceed 125 °C.
Figure 25. Heavy-duty distribution-class under-oil MOV
arrester.
WARNING
Hazardous voltage. Can cause severe injury, death, or
damage to equipment. Depending on configuration,
Arc-Strangler fuses or switchblades may be energized
even when in the “open” position. Refer to catalog
section 240-60 for further information.
WARNING
Hazardous voltage. Can cause severe injury, death, or
damage to equipment. De-energize transformer from a
remote upstream source before servicing or operating
surge arresters or disconnect switches. Check that all
transformer terminals and bushings have zero voltage.
Ground transformer following industry accepted safe
grounding practices.
CAUTION
Excessive test voltage can damage surge arresters.
Disconnect surge arresters before running impulse or
applied potential tests on the transformer.
17Three-phase pad-mounted compartmental type installation and maintenance instructions MN202001EN August 2015
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