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1.6 De-rating:
The AC alternators are selected so that they are suitable
for operation in ship engine rooms with an ambient
temperature of up to 45°C. However the diesel engine will
be affected by high temperature and humidity.
Engine de-rating must be applied;
•
Should the generating set is installed in an acoustic
housing or for that matter any restricted area where
the fan in the generator is the only means of moving
the air. When Beta Marine acoustic housings are used
output will be de-rated by 10%.
•
The conditions of installation differ from the standard
conditions set out in standard ISO 3046, i.e. 100 kPa
barometric pressure, 27°C cooling and combustion
air temperature and 60% relative humidity. Generally
for marine applications only temperature need be
considered when de-rate is usually taken as 2%
(3% for turbocharged engines) for every 5°C (or part
thereof) above 30°C.
1.7 Power Factor:
Power factor is often the cause of much misunderstanding
and is a function of the load NOT the generator. However
generators are designed to cope with loads at various
power factors. Standard machines are designed to cope
with loads having power factor between 0.8 and unity
being rated by the makers at 0.8 power factor. Some
very small machines are designed and rated for unity
power factor loads only. A typical unity power factor load
would be a heater element (resistive load). A system
incorporating a larger electric motor could have a running
power factor nearer to 0.8.
Beta Marine Ltd sell equipment producing 'POWER' and
the units of power are kilowatts. To change kVA into kW
multiply by the power factor. As previously stated the
ratings of our generating sets are given in kVA at 0.8
power factor. To obtain the kW rating of the generating set
multiply the kVA x 0.8.
By way of an example for a 30 kVA load: A generating
set offered on our price list at 33 kVA will drive a system
having a rating of 30 kVA where the system power
factor is 0.8. However if the system power factor is unity
(perhaps all heating and lighting) the kW rating of the
system will be 30 x 1 = 30 kW the 33 kVA set will not
power it because its rating will only be 33 x 0.8 = 26.4 kW.
Consequently a set having a rating of 38.5 kW at 0.8
power factor = 30.8 kVA will be required. (38.5 x 0.8 =
30.8 kW).
This is a simple example not a detailed explanation and is
intended for guidance only. The above refers to electrical
kW. The relationship between mechanical kW of the
engine and electrical kW of generator output depends on
the efficiency of the generator and any other driven items.
All of our generating sets are fully load tested against
a unity power factor load, that is at their kW rating. All
sets are also tested to prove that they will provide a 10%
overload in accordance with ISO requirements.
For maximum output, continuous output and typical load
please refer 'Technical Specification' pages 12 to 29.
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