TM5-811-1/AFJMAN
32-1080
CHAPTER 2
ELECTRICAL POWER REQUIREMENTS
2-1. General.
formers, and all equipment associated with distri-
bution of electrical power to utilization equipment.
The most feasible method of supplying and distrib-
Realistic demand factors will be calculated in
uting electrical power will be determined by first
early design stages to provide an economical, cost
quantifying the electrical power requirements (or
effective system while insuring that items of
maximum demand load) for the installation. In the
equipment and materials are adequate to serve
early design stages, this demand should be based
existing, new, and future load demands. Demand
on area or population; in later design stages,
factors utilized in later design stages will docu-
summation of individual building connected loads
ment and reflect the number, the type, the duty
modified by suitable demand and diversity factors
rating (continuous, intermittent, periodic, short
will be used. For early stages, use of kW, kVA,
time, and varying), and the wattage or voltampere
and hp interchangeably on a one to one basis is
rating of equipment supplied by a common source
of power, and the diversity of operation of equip-
sufficiently precise. During final design, hp will be
ment served by the common source. No more than
converted to kVA; and kVA may be multiplied by
ten percent spare capacity will be considered dur-
the estimated power factor to obtain kW if re-
ing design unless spare capacity is authorized by
quired. The calculation of full load amperes will
follow-on projects approved for construction in
utilize kVA.
later years. Demand factor is defined as the ratio
2-2. load Estimation.
of the maximum demand (largest demand during a
specified time period) to the total connected load.
Load estimation requires analysis of load charac-
c. Diversity factor. Diversity factors will be ap-
teristics and will take into account the demand
plied to the demand loads when calculating the
factor relationship between connected loads and
required ampacity of service and feeder conduc-
the actual demand imposed on the system.
a. Preliminary loads. The load data given in
tors, distribution transformers, and all other distri-
bution system equipment. Typical diversity factors
table 2-1 will be used to compute preliminary
are given in table 2-2 and an illustration of their
estimates of the expected maximum demands and
use is shown in a demand flow relationship in
electrical energy usage. These values allow compu-
figure 2-1. This illustration indicates the load at
tations to be made for either population or build-
substation "X" would be 1/2.24 or 0.45 times the
ing area. Per capita loads are for an average
summation of the demands based on the given
daytime population.
b. Demand factor. Demand factors will be ap-
data. Since utilities calculate loads on a less
conservative basis, diversity factors for main elec-
plied to connected loads when calculating the
trical supply stations on military installations will
required ampacity of conductors, capacity of trans-
Table 2-1. Typical Demands and Usages.
Per capita
Per 1,000 square feet
Maximum
demand
Usage per year
Maximum
demand
Usage per year
Installation
kW
kWh
kW
Service
kWh
1.0-3.0
7,500-25,000
0.5-2
Development & Readiness
5,000-20,000
Forces
0.5-1.2
3,000- 6,000
1-5
5.000-25.000
Army
0.6-1.2
2,500- 7,500
1-3
Command
Training & Doctrine
5,000-20,000
1.5-2.5
7,000-10,000
2-4
Logistics Command
10,000-20,000
Military Airlift Command
1.0-2.5
5,000-10,000
2-3
Air Force
5,000-15,000
3,000- 6,000
Tactical Air Command
0.5-2.0
2-5
Base
10,000-20,000
1.0-1.5
4,000- 6,000
2-5
Training
10,000-20,000
2-1
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