TM
5-811-1/AFJMAN
32-1080
trical supply system sectionalizing for operation
systems will also be described relative to adequacy
and maintenance will be defined, together with a
and dependability, along with other applicable data
description of switching and redundant circuits
covered in the requirement for engineering studies.
d. Design computations. Computations will be
required to meet or optimize system availability.
Any provisions for communication circuits to be
provided to indicate that materials and systems
installed by others, either aerially or underground,
are adequate, but not over-designed, and are cor-
will be described.
rectly coordinated. Computations will be provided
(5) Underground justification. The basis for
for (but not limited to) conductor sizing, cable
design will justify proposed underground construc-
pulling, strength requirements (structures, poles,
tion by citing either criteria or authority for
concrete pads, supports, etc.), pole line span
waiver of criteria.
lengths, generator and transformer capacities,
(6) Work performed by others. If functional
switch and switchgear ratings, and protective de-
adequacy of the design is contingent on work to be
vice selection. Load flow and voltage drop calcula-
performed by the Using Agency or the local util-
tions will be provided for new distribution sys-
ity, the basis for design will describe the limits of
tems, feeders where large loads are being added,
such work and the responsible agency.
and for line extensions where loads are being
b. Electrical generating plants. Wherever elec-
placed on lines far from the substation or other
tric generating plants are required, pertinent data
source. Short-circuit and protective device calcula-
will be included in the basis for design.
tions will be provided for new substations, distri-
(1) Loading. The estimated connected load,
bution feeders from existing substations, and
maximum demand, average demand, minimum
where new facilities requiring protective devices
demand, number of units proposed, their kW rat-
are to be installed. The calculations should provide
ings, and reasons for the selection of these units
adequate conductor and equipment short-circuit
will be indicated.
withstand-ampacity and demonstrate coordination
(2) Prime mover specifications. The class of
under the upstream devices. Protective device cal-
plant, type of starting system, type and grade of
culations are mandatory when relay and circuit
fuel, and approximate storage capacity will be
breaker trip settings must be determined. Situa-
covered. The type of plant, whether completely
tions where system coordination is not achievable
manual, fully automatic, or semiautomatic, with
will be noted. Short circuit and protective device
reasons for the selection will be noted.
c a l c u l a t i o n s will be in accordance with TM
(3) Voltage selection. The selected voltage and
5-811-14 and IEEE STD 242. Grounding system
reasons for the choice will be given. If commercial
calculations will be performed in accordance with
electrical power is not provided, the reasons why
IEEE Std 242 and Std 80.
commercial power is not used will be stated. If
1-10. Service Conditions.
operation in parallel with the serving utility is
Temperature, humidity, and other climatological
planned, a written utility company statement is
necessary affirming agreement with this mode of
factors as well as altitude will require special
design techniques at some installations. Design
operation.
(4) Frequency and voltage regulation. Fre-
techniques will comply with the standards listed
quency and voltage regulating requirements, in-
in table l-l.
a. Artic conditions. Basic engineering practices
cluding requirements for parallel operation, will
governing design and construction of electrical
be listed. A statement will be made that standard
power systems in temperate areas will be applied to
equipment is to be specified; where special equip-
arctic and subarctic zones. Modifications, as neces-
ment such as precise electrical power equipment is
sary, in accordance with TM 5-349, TM 5-852-5,
proposed, this special equipment will be fully
and AFM 88-19, will be made to combat snow and
justified. The additional cost of special equipment
ice above ground and permafrost conditions in
will be covered.
(5) Cooling and heat recovery systems. The
underlying subsoils. Methods used in temperate
zones for installing electrical distribution poles are
type of cooling system and reason for selection is
adequate in most cases; occasionally, special pole
required, along with a description of the type of
construction techniques, using cribs and tripods or
waste heat recovery, if any. An explanation is
blasting or drilling into the permafrost, will be
required to justify not utilizing waste heat.
c. Main electric supply stations. Where a main
required. Utilidors, which are usually rigid, insu-
lated, and heated conduits with either crawl- or
electric supply station is provided, the utility's
walk-through space for servicing and which are
system will be described including the utility's
usually installed underground, may also be used.
recommendations. Where pertinent, the utility's
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