DIESEL POWER
PLANTS:
A diesel
generator is the combination of a diesel
engine with an electrical generator (often called an alternator)
to generate electric energy. Diesel generating sets are used in places without
connection to the power grid or as emergency power-supply
if the grid fails. Small portable diesel generators range from about 1 kVA to
10 kVA may be used as power supplies on construction sites, or as auxiliary
power for vehicles such as mobile homes.
Generator
Rating Definitions
Standby
Rating based on Applicable for supplying emergency power for the
duration of normal power interruption. No sustained overload capability is
available for this rating. (Equivalent to Fuel Stop Power in accordance with
ISO3046, AS2789, DIN6271 and BS5514). Nominally rated.
Typical
application - emergency power plant in hospitals, offices, factories etc. Not
connected to grid.
Prime
(Unlimited Running Time) Rating: Should not be used for Construction
Power applications. Output available with varying load for an unlimited time.
Average power output is 70% of the prime rating. Typical peak demand 100% of
prime-rated ekW with 10% of overload capability for emergency use for a maximum
of 1 hour in 12. A 10% overload capability is available for limited time.
(Equivalent to Prime Power in accordance with ISO8528 and Overload Power in
accordance with ISO3046, AS2789, DIN6271, and BS5514). This rating is not
applicable to all generator set models.
Typical
application - where the generator is the sole source of power for say a remote
mining or construction site, fairground, festival etc.
Base
Load (Continuous) Rating based on: Applicable for supplying power
continuously to a constant load up to the full output rating for unlimited
hours. No sustained overload capability is available for this rating. Consult
authorized distributor for rating. (Equivalent to Continuous Power in
accordance with ISO8528, ISO3046, AS2789, DIN6271, and BS5514). This rating is
not applicable to all generator set models
Typical
application - a generator running a continuous unvarying load, or paralleled
with the mains and continuously feeding power at the maximum permissible level
8760 hours per year. This also applies to sets used for peak shaving /grid
support even though this may only occur for say 200 hour per year.
As an
example if in a particular set the Standby Rating were 1000 kW, then a
Prime Power rating might be 850 kW, and the Continuous Rating 800 kW.
However these ratings vary according to manufacturer and should be taken from
the manufacturer's data sheet.
Often a
set might be given all three ratings stamped on the data plate, but sometimes
it may have only a standby rating, or only a prime rating.
Sizing
Typically
however it is the size of the maximum load that has to be connected and the
acceptable maximum voltage drop which determines the set size, not the ratings
themselves. If the set is required to start motors, then the set will have to
be at least 3 times the largest motor, which is normally started first. This
means it will be unlikely to operate at anywhere near the ratings of the chosen
set.
Manufactures
have sophisticated software that enables the correct choice of set for any
given load combination.
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