MIL-HDBK-1191
10.3.7
ENGINE STARTING. Electric start will be provided on engine-
generator sets rated below 700Kw and either electric or pneumatic start will
be provided on engine - generator sets rated 700Kw through 1000Kw. For all
engine-generator units rated above 1000Kw, only pneumatic start will be
provided. Reference NFPA-99.
MANUAL TEST SWITCHES. Manual test switches will be provided for
10.3.8
each automatic transfer switch of the essential electrical system. A group of
test switches will be provided at a single point in the generator control area
and one test switch will be provided with each automatic transfer switch. The
two test switches associated with each transfer switch will be wired in series
to allow testing at either location. Testing of either individual automatic
transfer switches or the entire essential electrical system will be possible.
Each test switch will simulate a normal power source failure and
automatically cause the engine generator sets to crank, attain rated frequency
and voltage, and to transfer associated essential electrical system loads from
the normal source to the emergency source. After 30 minutes of operation in
the emergency mode, essential electrical system loads being tested will again
be automatically transferred back to the normal source. If for any reason the
generator units experience difficulty while in the emergency mode, the load
will immediately be transferred to the normal source automatically. During
this test run, nonessential hospital loads will continue to be served from
normal power supply without experiencing interruption. A manual override
switch will be installed that can be actuated to keep essential hospital loads
on the emergency source as long as desired. This switch will permit engine
generator sets to operate indefinitely beyond the 30 minute automatic transfer
restoration time.
Generator sets will be designed to
10.3.9
GENERATOR SET OPERATION.
function essentially as follows: After 30 hertz (CYCLES) following an
interruption of the normal power supply, each generator set will receive the
starting signal simultaneously, whereupon each set will automatically crank
and attain normal speed and voltage. Voltage for sensing devices to start
generator sets will be taken from each phase of the incoming normal power
terminal of each automatic transfer switch. The first generator sets to reach
preset voltage and frequency conditions will be automatically connected to the
emergency bus. System protection will be provided to prevent simultaneous
connection of non-synchronized generators to the dead emergency bus. A
priority selective device will be provided and programmed or preset to
transfer the emergency system loads from the normal bus to the emergency bus
within 10 seconds from time of NORMAL POWER interruption. The remaining unit
will automatically synchronize with the emergency bus, close the respective
generator breaker, and connect the units in parallel for normal operation.
After this, the equipment system loads will be automatically transferred to
the emergency bus by programmed or preset incremental steps. The equipment
system loads will be completely transferred within 45 seconds, based on a
priority sequence, after the generator sets are connected in parallel. Should
one or more of the generator sets fail to crank or is shutdown for any reason
during the operation, the remaining unit will be scheduled to serve only
emergency system loads and, if possible, highest priority equipment system
loads until the failed unit is energized and connected to the emergency bus.
For such a condition, a programming device will shed all or part of the
equipment loads, to keep the remaining generator within its kw rating. If the
automatic controls fail, a manual start switch will be provided to override
the automatic start of the engine-generator sets so they can be cranked,
synchronized and connected on the emergency bus.
RETURN TO NORMAL POWER SOURCE. Thirty minutes following the
10.3.10
return of a stable normal power supply, both emergency system loads and
equipment system loads will be automatically transferred to the normal power
source. An automatic timer, having an adjustable time range of from 2 to 30
minutes (set at 30 minutes), will be provided to this transfer. Following
transfer of the loads, generator sets will continue to run, unloaded, for a
10-8
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