MIL-HDBK-1191
load on any transformer exceeds the no fan rating. The temperature indicator
and the current relay will activate the cooling fans. If the fans are not
activated when the temperature indicator and/or the current relay exceed the
manufacturer's setting, and alarms will be sounded so load shedding can be
initiated. Each transformer must carry a 10 percent overload for short periods
of time without fans.
(b)
If a service entrance transformer fails, off line for maintenance,
or the normal bus receives no power from any one of the service entrance
transformer feeders, the fans on the remaining two service entrance
transformers will be automatically activated allowing 100 percent of the total
hospital load to be assumed. There is no time delay in the load shifting to
the remaining two transformers.
(c)
Where each transformer of the multi-ended network substation is
sized for no fan application, each transformer will be sized to carry not less
than 50 percent of the full hospital demand and spare load (linear and
nonlinear) growth capacity. Each transformer feeder serving the normal bus
will be equipped with an alarm to indicate power loss from that feeder to the
normal bus.
(d)
The transformers in the multi-ended network substation will be
identical and impedance matched.
52 DEVICES. The 52 devices (AC power circuit breaker devices, draw-out
5.
type) will be sized to support the transformer capacity.
(a)
The equipment will be laid-out in a manner which allows load
center expansion, without requiring replacement. New sections can be added to
either end of the load center.
(b)
The main load center bus will be sized for not less than the sum
of the three transformer kva rating.
GROUND FAULT. Ground fault protection for medical facilities will
6.
conform to those requirements in NFPA-70 and 99, and MIL HDBK-1191.
STANDARDS. All metering will read true RMS, and the protective relays
7.
and devices will comply with IEEE standards.
10-32
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