MIL-HDBK-1004/2A
5.1.1.1 Type of System Supplied. Usually substations either supply
secondary (utilization) voltages to buildings, or primary (distribution)
voltages to large areas of a naval facility.
5.1.1.2 Location. Substations are located indoors or outdoors for utili-
zation voltage service and outdoors normally for distribution voltage service.
5.1.2
Definitions. Definitions used by organizations which prepare
standards on switchgear (ANSI, IEEE, NEMA) differ from those that
manufacturers use. To provide a common basis for terms used in this handbook
and in NFGS-16321, Interior Transformers, NFGS-16335, NFGS-16462, Pad-Mounted
Transformers, and NFGS-16465, Interior Substations, the definitions of Table
5 are given. Except as noted, all usage in this manual and corresponding
NFGS's agrees with the definitions of IEEE Standard 100, IEEE Standard
Dictionary of Electrical and Electronic Terms.
5.1.3
Typical Substation Layouts. For typical substation layouts, see
Figures 2, Compartmental-Type Transformer Installation, 3, Radial-Type
Articulated Secondary Unit Substation Installation, 4, Secondary Unit
Substation Grounding, and 5, Preferred Design for a Transmission to
Distribution (Primary) Substation.
5.2
Indoor Unit Substations. Articulated unit substations with a
primary voltage of 15 kV or less may be installed indoors. Substations are
normally of the secondary unit type except where 2,400 V or 4,160 V secondary
distribution is used to serve large motor loads. Pad-mounted compartmental-
type units should generally be restricted to exterior locations.
5.2.1
Preliminary Considerations. Ensure material and equipment conforms
to NFGS-16465 based on consideration of the following:
5.2.1.1 Location. Make a selection of the number of unit substations and
their locations based on the most economical balance between the cost of a
secondary distribution system and the cost of transformers, switchgear, and a
primary distribution system. Install load centers where they are economical
for small concentrated loads. Integral transformer load centers do not
involve great installation expense. Dry types may be located in the same room
with loads; they provide good voltage regulation and have minimum energy
losses.
5.2.1.2 Capacity. Transformers larger than 500 kVA for 208Y/120 V building
service are not permitted. Similarly, do not specify transformers in ratings
of over 1,000 kVA or in exceptional cases larger than 1,500 kVA for 480Y/277 V
building service and only where functionally required. The use of smaller
transformers supplying larger loads adds flexibility and reliability to the
system. Shore-to-ship service may require larger transformers. Transformers
rated 1,500 kVA or larger should utilize secondary busway where a connection
to a nonintegral secondary switchgear section is required unless such a
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