Page 21 - Uninterruptible Power Supplies

Standby Power Generating Sets
Standby Power Generating Sets 19

require the compressed air cylinder to be inspected at regular intervals
by a competent person.

Failure to Start
If after cranking for the normal period of time the engine has failed to
start, manufacturers adopt one of two philosophies. The cranking time
may be extended to two or three times the normal period, or two or
three successive starts may be attempted, with a short rest period
between. The total period of time is limited by the battery capacity but
another limitation is set by the accumulation of unburnt fuel in the
cylinders, which is highly undesirable. The manufacturer’s advice
should be sought before any attempt is made to extend the cranking
period.

Batteries and Battery Chargers
The starting battery will usually be a lead acid type and although the
recombination type of lead acid battery is available for this application
the high temperatures commonly encountered in engine rooms can lead
to a short life and early battery failure. The flooded type of lead acid cell
which can be topped up at regular intervals will survive the high tem-
peratures and have a much longer life (provided it is topped up!).
The battery charger must be supplied from the distribution system
which in turn is supplied either from the normal supply or from the
standby supply, and should provide current-limited constant voltage
charging. The old-fashioned trickle charging should not be used, it tends
to cause unnecessary gassing and loss of electrolyte. The engine control
system should provide visual indication and an alarm on charger fail-
ure. The starter battery and its charger are vital engine components
and their neglect can lead to the failure of an engine to start.

Fuel Systems
Daily Service Tanks
Within the engine room there should be a daily service tank holding
sufficient fuel for say 8 hours running; for a modern diesel engine 1
liter of fuel will provide approximately 3.5 kWh of electrical energy, for
a gas turbine the fuel requirement will be greater, and 1 liter of fuel will
provide approximately 2.2 kWh of electrical energy. The underbase of a
diesel generating set is often used as a daily service tank; the arrange-
ment requires a lift pump to provide a supply of fuel to the injection
pump or pumps. The alternative is to mount a service tank at a level
above that of the engine and to rely on gravity for the supply to the

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