To determine the demand load for a
of combinations of lights and motors.
particular
building
the
following
The required generator capacity may be
equation is used:
found by the following equation:
Demand load = connected load x demand
Generator capacity (KW) = generator
factor
factor x sum of individual demands in
KVA
In design problems the demand factor
will have to be selected on the basis
Where: KVA = kilo-volt-amperes
or
of the type of structures to be
1,000 volt-amperes.
served. For this course, table 2 will
be used to obtain demand factors.
Table 3 gives generator
factors
for
use in this course.
(2) Generator
factor.
As
explained above, each facility within
Table 3.
Generator Factors
the installation will have its own
maximum demand.
In addition, the
installation as a whole will have a
maximum demand. It is improbable that
all buildings in an installation would
require their demand loads at the same
time.
Thus the demand load for the
installation is usually less than the
sum of individual facility demand
loads.
The ratio of the maximum
demand of the whole group to the sum
of the individual maximum demands is
called the generator factor.
The
generator factor is usually expressed
b. Capacity.
One factor to be
as a function of the total amounts of
light and motor loads within the
considered in determining generator
entire installation.
If the total
requirements is that there are always
demand load within an installation is
several
possible
generator
combinations which will supply the
comprised solely of light loads, it
required generator capacity, but some
may be said that a good possibility
exists that all the individual demand
of these selections are inefficient.
loads may be required at the same
It is possible to select one large
time.
In such an installation, for
generator to supply the total required
capacity.
However, this selection
example, the early evening hours would
becomes
inefficient
during
periods
be a period where all facilities might
be in operation, such as messhall,
such as the early morning hours, when
barracks, theater.
Thus, all lights
the required power will be reduced
might be required at the same time.
considerably.
Since the generator
will run at a constant output, much
Conversely, it is safe to assume that
more power would be supplied than is
not all the motor loads, in an
installation
containing
only
such
actually required.
Another factor to
loads, would be required at precisely
be considered is that enough excess
the same moment.
Most motors are
generator capacity should be provided
(usually by a standby generator) to
operated intermittently, so it is
supply maximum demand when the largest
improbable
that
all
would
be
in
operation at the same time.
Many
generator is out of service because of
intermediate cases, of course, exist
maintenance or repair.
In isolated
where
the
power
using
facilities
areas where generators are placed at a
single location, the standby generator
consist of some combination of lights
is
permanently
connected
to
the
and motors.
Thus a full range of
generator factors exists for the range
1-10
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