Page 41 - Uninterruptible Power Supplies

Standby Power Generating Sets
Standby Power Generating Sets 39

using surplus oxygen in the exhaust gases to do so. The latter uses a plat-
inum and rhodium catalyst which, in addition to oxidizing carbon monox-
ide and hydrocarbons, reduces nitrous oxides to nitrogen and oxygen. It
requires a stoichometric air/fuel ratio for proper operation and is not at
present applicable to diesel engines used for standby generation purposes.
Catalytic converters do not operate until heated to their operating
temperature, which is of the order of 200–300°C. Converters cannot
change the particulate material in the exhaust gases but it has been
claimed that by oxidizing the sticky hydrocarbons associated with it,
the particulate material is changed to a dry powder which is much less
damaging environmentally. This feature is useful as it offers the
advantage that the particulate material adheres only temporarily to
the catalytic surfaces.

Control Systems

The control system coordinates the operation of the various controls
built into the generating set. Over many years the control system has
developed from an assembly of hard-wired relays, indicator lamps, and
meters to a small modular system with a programmable controller,
push buttons, and an alphanumeric display. It is normally powered
from the starter battery, but for the very highest class of installation a
dedicated control battery and charger may be provided.
While the control of engine speed and generator voltage are undoubt-
edly part of the control system, these two functions are invariably per-
formed directly by the speed governor and the voltage regulator. The
speed governor and voltage regulator may interact with the control
module for load and kVAr sharing, and for synchronizing purposes,
which leaves the modular controller to perform other functions such as:

■ Monitor the voltage and frequency of the normal supply
■ Control the engine start and shut down sequences
■ Open and close the switching devices controlling the normal and
standby supplies, where appropriate initiate load shedding and apply
the load to the generator in steps
■ Monitor any warning alarms originating from the generating set and
take appropriate action
■ Monitor any shut down alarms originating from the generating set
and take appropriate action
■ Where a telemetry system is installed, transmit data to, and receive
instructions from, the base station

The above functions are considered in detail in the following sub-
sections.

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