30 Sep 94
construction, good system layout can reduce the risk
of secondary failures.
Figure B-34. Vulnerable bus runs
(c) A strategy used by some utilities to improve
Figure B-33. Disconnect switches located above
seismic response of substations known to be vulnera-
ble is to identify and seismically "harden" a critical
path so that acceptable performance can be main-
(4) Other switchyard equipment.
tained. An example of hardening would be to replace
vulnerable live-tank circuit breakers with seismically
(a) There are many other types of high voltage
rugged dead-tank circuit breakers at critical locations
switchyard equipment that are seismically vulnerable.
to ensure the integrity of the circuit. While this is an
These include current-voltage transformers, current
effective procedure for substations designed with
some redundancy and flexibility, the relatively simple
traps. These types of equipment do not appear to be
design of high voltage elements associated with dams
used at damsites and will not be discussed in detail.
does not lend itself to this approach.
Their seismic performance can be improved by limit-
ing the relative motion between adjacent equipment
items or providing bus connections that can accom-
modate this motion. High strength porcelain can also
(1) Many types of equipment are needed for
continued operation of a dam: unit substations; motor
control centers; motors; fans; pumps; tanks; piping
(b) Bus configurations may be vulnerable to
systems; air- and motor-operated valves; heating,
earthquake damage. In one case, a taut bus from
sion systems; control consoles; etc. (Figure B-35). In
support structure on top of the power house could be
general, these items are seismically rugged, primarily
subjected to high loads if the bus support structure
because they have survived shipping loads. Some
moves (Figure B-34). A small amount of slack
items, such as pumps, have service loads that are
would eliminate the problem.
more severe than seismic loads. The seismic