2.6.2
Conductors
The bus phase conductors shall be of bare copper, aluminum or
aluminum-alloy, and when assembled shall withstand the specified dielectric
tests. Field joints in the conductors shall be silver-plated except that
contact surfaces of aluminum-alloy conductors may be tin plated. The
joints shall be provided with sufficient bolts to provide adequate
low-resistance contacts.
2.6.3
Enclosure
The three phase conductors with insulating supports and spacers shall be
mounted inside a common nonventilated dust tight enclosure made of sheet
metal not less than No. 14 MSG. Covers for enclosure openings shall be not
less than No. 14 MSG. The design of the enclosure shall permit the
installation and alignment of all bus sections and the completion of field
joints in the conductors before the enclosure is completely closed.
2.6.4
Grounding
All sections of the housing shall be connected to the powerhouse ground
system. Bus housing sections shall be bonded together or connected to a
common ground bus to facilitate connection to the powerhouse ground system.
The proposed method of metal-enclosed bus grounding shall be subject to
approval.
2.7
SECONDARY UNIT SUBSTATION
2.7.1
General
The secondary unit substation shall be indoor metal-enclosed secondary
selective (double-ended) type rated [13,800-480] [[_____]-480] volts,
[_____]kVA, 3-phase, 3-wire, with incoming, transforming, and outgoing
sections arranged as indicated. Except as otherwise specified or
indicated, the unit substation shall conform to the applicable requirements
of NEMA TR 1.
2.7.2
Incoming Sections
Incoming sections for terminating the high-voltage power cables shall be as
specified for Station Service Transformers.
2.7.3
Transforming Sections
The transforming section shall be metal enclosed containing ventilated dry
type (Class AA) transformers as specified for Station Service Transformers.
2.7.4
Transformer Bus Connections
The transformer low-voltage terminals shall be connected to the power
supply breakers in the adjacent 480-volt, outgoing switchgear section by
means of copper or aluminum bus with thermal and mechanical capacities
coordinated with the ratings of the 480-volt power supply circuit breakers.
The transformer high-voltage and low-voltage bus connections shall be
arranged so that the front of the transformer enclosures will line up with
the front of adjoining incoming sections and the 480-volt outgoing
switchgear section. Suitable bus transition compartments shall be provided
if required.
SECTION 16404A
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