TM5-811-1/AFJMAN
32-1080
(2) Three-phase transformers, delta wye con-
circuit breakers are preferred. Metal enclosed
nected, are preferred in lieu of single-phase trans-
circuit breakers or fused interrupting switches
formers, size permitting, where the load can be
may be allowed depending upon the application
served by a single three-phase transformer and
and economics. Metering and relaying require-
where the transformer can be easily repaired or
ments are the same as (1) (c) and (d) above.
replaced upon failure of any winding and the load
Automatic reclosing relays shall be installed on
can be interrupted during such repair period.
each overhead feeder circuit. Automatic reclosers
(3) Four single-phase units may be provided
and sectionalizers shall be utilized on overhead
where such spare capacity is required for 100
circuits as called for in the coordination short-
percent spare transformer capacity on site. Multi-
circuit study.
ple installation of like substations for two or more
(3) Operating equipment for breakers:
blocks of load at the same general installation
(a) For substation capacity above 2,000
shall employ three-phase transformers in parallel
kVA, ac capacitor trip and ac solenoid close.
or through secondary bus tie.
(b) For substation capacity above 2,000
e. Foundations and fencings.
kVA, ac capacitor trip and ac solenoid close, or
(1) Foundations and equipment pads. Con-
crete.
battery trip and close.
b. Arresters. Station class is preferred, consider-
(2) Fencing. Chain link, eight feet in height
topped with three strands of barbwire and com-
ation should be given to gapless types such as zinc
plete with "High Voltage" signs.
oxide, metal oxide varistor (MOV).
(3) Fence gates for vehicles, minimum width,
c. Voltage regulator. Step-feeder voltage regula-
ten feet. Personnel gates, minimum width, three
tor with by-pass gang operated switch on second-
feet.
ary bus only. At the supply point, a three-phase
(4) Sufficient working space shall be provided
transformer with automatic load tap changers may
so that transformers can be maintained and moved
be provided.
into and out of an area without disturbing adja-
d. Transformers.
cent transformers or any fixed equipment.
(1) Single-phase, self-cooled with provisions to
f. Polychlorinated Byphenyls. Polychlorinated
increase capacity if externally cooled, delta wye if
byphenyls (PCB) contaminated transformers shall
connected for three-phase service. Nonflammable
be disposed of in accordance with the requirements
liquid or epoxy insulation is preferred; however,
of the Environmental Protection Agency (EPA) as
high-fire-point liquid or oil insulation may be
they are removed from service.
provided if it is approved by the HOST/REQ CMD.
4-16
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