MIL-HDBK-1191
ANNEX B
MULTI-ENDED NETWORK SUBSTATION
GENERAL. The multi-ended network (FULLY AUTOMATIC) substation (Figure
1.
10-5 and 10-6) design philosophy eliminates many switching time delays;
simplifies the monitor and control functions; standardized equipment; reduces
equipment size; provides expansion capability for future load growth and
maintains reliability, durability, and maintainability. When using the multi-
ended network or the double-ended substation to replace an existing
substation, all down stream equipment requires short circuit current
validation, and power system coordination.
NORMAL HOSPITAL SOURCE ALTERNATE DESIGN CONFIGURATION. For electrical
2.
design criteria related to power supply, see documents listed in "TABLE 10-1
APPLICABLE REFERENCES." Hospitals will be served by two primary service
feeders each connected to one side of the automatic (with alternate manual
operator) load break primary selector switch with manual load break by-pass
isolation switches that serves a multi-ended network substation (Figure 10-5).
Each feeder shall have the capacity to serve the full hospital demand plus 20
percent spare load growth, and shall be installed underground within the
hospital site. The primary selector switch with by-pass isolation switches
will have the capacity to serve not less than the sum of the three
transformer's kva rating, and have load limiting equal to the full hospital
demand plus the 20 percent spare load growth. The automatic function will
monitor both primary feeders, and if power is lost to the feeder serving the
load, the load will be transferred to the other feeder in not more than 30
cycles if power exists on that primary feeder. Service feeders will be
connected to different power sources, if available, and to two differently
routed distribution system feeders. Where two power sources are not
available, the service feeders may be connected to two different sections of a
loop system.. Transformers will normally be located outside the hospital, but
may be located within the building where practicable and economical. Multi-
ended network substation distribution systems will be designed for hospitals,
medical centers and specially designated facilities. Each transformer in the
multi-ended network transformer substation will be sized to carry 50 percent
of the full hospital demand and spare load (linear and nonlinear) growth
capacity. All transformers will be identical and impedance matched. All multi-
ended network transformer substation will have coordinated surge and fault
protection. The system protection will be selective.
AUTOMATIC PRIMARY FEEDER SELECTOR SWITCHES (APFSS). (This is not to be
3.
construed as an automatic transfer switch) The APFSS may be double-throw with
draw-out construction. The APFSS rating will be not less that the sum of the
three transformer kva ratings, and have adjustable load or fixed limiting
control (the loading control may limit the capacity to that of two
transformers). Contacts may have viewing ports for ease of contact inspection.
The APFSS will have indicator lights to identify which normal primary feeder
is connected to the load (green in color). Load transfer to either normal
primary feeder will be achieved with not more than 30 cycles of load
interruption. All APFSS will be equipped with load break by-pass isolation
switch to maintain normal primary service feeder connection or when the APFSS
is being repaired or maintained. The by-pass isolation switch can be initiated
with not more than two movements of the hand to either position regardless of
the position or condition of the APFSS. Two vacuum power circuit breakers with
load break by-pass isolation switch may be used.
4.
TRANSFORMERS.
(a)
Each service entrance transformer of the multi-ended substation
with fans is sized to carry 40 percent of the design load as to utilize
standard off-the-shelf units and increase transformer efficiency. Each of the
three transformers are equipped with forced air-cooling fans to increase the
continuous capacity rating of each transformer by 34% to 50 + percentage of
the design load when activated. The fans are automatically activated when the
10-31
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