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

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

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