from within the system. Such power users shall be properly fused or
furnished with circuit breakers to protect power sources and supplies from
overloads or faults. Power sources and power supplies shall be distributed
into functional groups and protected from overloads or faults such that a
power failure in one group does not cause power failure to the remainder of
the control system. The system shall take appropriate control action and
initiate an alarm contact upon partial power failure. Tripout of a circuit
breaker or opening of a fuse due to control equipment failure or wiring
fault in a control loop shall disable the loop in which the failure
occurred and place the final drive in the manual mode and initiate an alarm
contact. Fuses, breakers, and fuse or breaker panels shall be readily
accessible and clearly identified. Provide input filters for noise
suppression, as required. Where internal dc power supply buses are
utilized, furnish two full-capacity power supplies for each bus voltage and
auctioneer their outputs to ensure no control upsets if one supply or its
source fails. Power one supply from source "A" or "B" is distributed
internally to individual circuit cards or individual transmitters or
converters which have separate dc power supplies, provide an automatic
transfer switch to switch to the backup source upon primary source failure.
Furnish manual reset feature and provide an alarm contact on transfer.
Provide circuit isolation and monitoring to permit removal of faulty
supplies during operation.
2.12.2.4
Operating Stations
Operating stations will be remote mounted on the control panelboard in the
central steam plant control room. Furnish operating station with an
individual mounting rack to permit simple and quick removal from the panel.
Wiring to the system cabinets shall be by a prefabricated plug-in cable.
Operating stations shall contain dials, switches, lights, and indicators
necessary to operate the system by either manual or automatic mode.
Stations shall not contain computing or logic elements which are a part of
the control loop except for operator-system interface. Station shall have
the following features, as applicable, depending upon their purpose in the
a.
Manual-automatic selector switch or push buttons.
b.
Dedicated indicating meters displaying only one variable, and
marked in appropriate engineering units where applicable.
Indicating lights displaying manual or automatic status of the
control loop. Lights displaying status of the switch are not
acceptable.
c.
Set point dials calibrated and marked in appropriate engineering
units.
d.
Deviation meter.
e.
Position meter indicating the actual final drive element position
over its full range, and not the loading signal.
f.
Raise and lower control for manual operation.
Manual, set point, or indicator stations which have specified functions
shall have no extraneous or ineffectual indicators, switches, or lights.
The station shall be tailored to its purpose. Tag operating stations with
a unique number, as specified. Provide an engraved nameplate on each
operating station identifying the service such as spray dryer outlet
SECTION 15864N
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