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 MIL-HDBK-1012/1
d) The neutral conductors for all supplementary power sources,
such as generators and isolation transformers and as defined in NFPA 70,
Section 250-5(d), are required to be grounded to the G2 power and frame ground
plate. NFPA 70, Section 250-91(C) permits additional grounds. These
additional neutral grounds must be connected to the same point on the neutral
as the G2 ground connection.
e) Three-phase delta-wye isolation transformers are required at
most sites to eliminate objectionable ground currents. In many cases this
function can be combined with voltage-stepdown requirement. These
transformers will be specified in the BESEP. Since the purpose of these
transformers would be defeated by interconnecting primary and secondary
neutrals, it is required that only three wires (no neutral wire) be run from
the source to the primary windings. A single new neutral and safety ground is
required to be established by connecting the secondary neutral directly to the
G2 power and frame ground plate in accordance with NFPA 70, Sections 250-23(a)
and 250-26(a). Electrostatic shields in isolation transformers must be
connected to the source safety ground lead and not directly to either neutral.
Insulated conduit bushings are required to isolate source and load safety
grounds.
8.12.3.4 Power Sources. The technical power distribution systems for
oceanographic facilities were designed to be supplied from redundant technical
power busses energized by continuously-running diesel engine-driven
alternators. These busses provide an essentially continuous source of well-
regulated power and only stable loads are permitted. Specifically, cyclic
loads are not permitted on busses serving technical equipment. Non-technical
or commercial power sources were used for technical power only in emergency or
otherwise exceptional circumstances. As a conservation measure, these sites
are being converted to use commercial power continuously with engine
alternators used only for emergency power as described in Section 5.3.
Emergency power sources are required to be able to support each
site continuously and indefinitely. This requirement plus the need for
separating technical and cyclic loads means that at least three engine
alternators are normally required at each site. UPS Systems are required to
filter commercial power and support critical loads during transitions to and
from emergency power. Figure 5 shows the typical power plant and distribution
system required. Any site specific requirements shall be stated in the BESEP.
a) Load requirements are contained in the BESEP and are normally
stated in terms of the existing maximum demand load and the anticipated future
demand load for each of the components of the operational load as defined in
Section 5.3(b). These loads are normally given in volt-amperes. A power
factor of 0.85 is normally assumed for technical load power calculations.
b) Installed power capacity requirements are based on the total
known future load requirements plus a nominal 25 percent allowance for
unanticipated growth.
c) Steady-state load voltage requirements are normally 120/208V
plus or minus 3 percent at the technical equipment input terminals. Transient
excursions must not exceed plus or minus 5 percent from any point within the
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