ETL 1110-2-533
30 Sep 94
(e) Long vertical drops using flexible bus can
accommodate relatively large displacements, but short
flexible bus connections between equipment, rigid bus
connections, and control cable connections to the
transformer can only accommodate limited motions
(Figure B-20).
Figure B-21. Transformer restrained by chock at
dam. A chock, clamped to a rail, restrains a ped-
estal-mounted step-up transformer at a dam. This
type of restraint has repeatedly proven to be an
inadequate anchorage
the support pedestal or pad rather than to the rails
(Figures B-22 and B-23). If the transformer carriage
Figure B-20. Transformer control cable damage.
is anchored to the rails, the stability and strength of
Sliding of an unanchored transformer has dam-
rail anchorage must be considered. The transformer
aged control cables and piping penetration allow-
must also be securely anchored to its carriage (Fig-
ing transformer oil to leak
ure B-24). Because of the wide variation in rail
support configurations, most retrofits must be speci-
(f) Pad supported transformers can be anchored
ally designed.
to plates that are bolted to the pad and then welded to
the transformer body. The design should ensure the
(i) Figure B-25 shows a close-up view of the
earthquake-induced inertial forces can be transmitted
inside of a wheel housing and concrete key. There is
to the pad without permitting unacceptable distortion
a very small gap between the key and the wheel
or creating a brittle failure mechanism due to prying
housing and the key has a large angle forming its
action between the connection and the anchor bolt.
upper corner. This procedure eliminates the need for
the rails to carry lateral loads, but still lacks positive
(g) Rail-mounted transformers are frequently
vertical restraint. The side of the chock is secured to
supported on top of pedestals to accommodate a cart
the rail by 1-in. bolts. The chock is secured to its
on rails running transverse to the row of transformers.
side supports by a single 1-in. bolt. Note that the
Chocks used to restrain the rail-mounted transformer
chock is cut to fit the curvature of the wheel and
are not very effective as they tend to be pushed off
extends about two-thirds of the way to the axle. The
the end of the rail (Figure B-21). Even if the chocks
massive wheel support has large gusset plates and is
restrain the transformer, the transformer can tip over
bolted to the carriage. The carriage is welded to the
in a lateral direction as there is no vertical restraint.
base of the transformer, ensuring a good load path
When pedestal-mounted transformers fall, they can
between the wheel and transformer.
severely damage radiators, bushings, surge arrestors,
bus and control cable connections, piping connections
(j) The recommended method of transformer
if they are water cooled, and the bus support struc-
anchorage for new construction is to weld the trans-
ture. Major, lengthy repairs are usually required.
former case to a steel embedment in the foundation
pad. It is important that adequate weld length be
(h) The design of retrofits for rail-mounted trans-
provided to carry the maximum expected loads and
formers must carefully consider the load path. In
that good weld penetration be achieved. The embed-
general, it is desirable to anchor the transformer to
ment must also be properly designed and installed.
B-15
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