ETL 1110-2-533
30 Sep 94
replacements because of their inherent seismic
ruggedness.
Figure B-32. Earthquake damage, live-tank circuit
breakers. The porcelain columns that support the
interrupter heads on life-tank circuit breakers are
very vulnerable
Figure B-31. Manifold-mounted cooler with sup-
port structure. The cooler lower support is sub-
(b) The three phases of bulk oil circuit breakers
stantial and separate from the piping penetration.
are typically welded to a fabricated base, which is
The connection to the transformer case penetra-
often anchored with friction clips. The use of friction
tion is relatively flexible to reduce moments
clips doubles the anchor bolt load, and the clips tend
applied to the pipe flanges
to rotate around the bolt allowing the circuit breaker
assembly to move in an earthquake. A simple fix is
although performance should be improved by anchor-
to weld the end of the friction clip to the circuit
ing transformers and providing slack in flexible bus
breaker frame.
so that relative motion between adjacent equipment
items can be accommodated without overloading
(3) Disconnect switches.
porcelain elements.
(a) Disconnect switches are used to reconfigure
(2) Circuit breakers.
power system elements. If damaged, they can usually
be temporarily, and quickly, bypassed.
(a) Switchyard circuit breakers play an important
role in system protection. They can be bypassed if
(b) Post insulators used to fabricate disconnect
desired but with reduced system protection then pro-
switches have failed. Their failure can cause more
vided by other circuit breakers. Their seismic shock
severe problems after they fail when they are located
integrity depends upon design. First, existing oil
on bus structures or otherwise supported above circuit
circuit breakers are seismically rugged. However,
breakers or transformers, as falling parts from the
they are being replaced with SF6 circuit breakers
switch can damage bushings (Figure B-33). The risk
which need less maintenance and are less of an envi-
of these failures is relatively small so that retrofitting
ronmental hazard. Live-tank SF6 circuit breakers are
is probably not justified. For units that present an
seismically very vulnerable (Figure B-32). If used,
unacceptable risk, the post insulators can be replaced
they should be designed for seismic forces. Dead-
with units made of high strength porcelain. In new
tank SF6 circuit breakers should be considered for
B-19
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