Section 6:
LEVELS OF DISTRIBUTION VOLTAGE
6.1
Criteria Coverage. Distribution systems that have a medium voltage
level of 2.4 to 35 kV are covered in this section except, that for 4.16 kV
and below 400 Hz distribution systems, the criteria appears in DM-4.05.
Systems in the utilization voltage level of 600 V and below are covered in
MIL-HDBK-1004/4, Electrical Utilization Systems. Generally, the majority of
systems supplying primary distribution voltages at naval activities are of
the 15 kV class or less. However, voltages above 15 kV may be encountered as
utility voltage supplying naval installations or as distribution voltages.
In each case of distribution design, evaluate the cost of individual
distribution components and energy losses, and adopt the most economical
voltage level from an overall point of view.
6.2
System Voltages.
Electrical power may be generated at the site or
purchased.
6.2.1
Power Generated at Site.
Criteria for electric power generated at
the site is contained in DM-3.
6.2.2
Purchased Energy. Where purchased electrical power is used, adopt
the most economical voltage, taking into consideration transformers,
switchgear, control equipment, and energy losses.
6.2.2.1
2,400 V System. Use a 2,400 V system where total capacity does not
exceed 5,000 kVA, but only when utility company service is at that voltage,
and where a predominantly motor load includes motors rated at 200 hp or more.
Where such motor conditions exist, use direct connection to motor starting
equipment.
6.2.2.2
4,160 V System. Use a 4,160 V system for maximum demands not
exceeding 7,500 kVA, but only when a utility company delivers electric power
at that voltage level. Switchgear and cable at 4,160 V will give a more
economical installation than one at 2,400 V. For loads including motors of
250 hp and over, and for groups of motors up to 7,000 kVA, the 4,160 V system
may be more economical than any other voltage level.
6.2.2.3
6,900 V System. Use 6,900 V system only where the utility company
delivers energy at this level or there are other special considerations.
6.2.2.4
12,000 V to 13,800 V Systems.
These systems can be economically
used for demands of 7,500 kVA and over.
6.2.2.5
15,000 V to 34,500 V Systems. These systems can be economically
used for demands of 20,000 kVA and over, especially when the distances
involved are considerable.
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