2.7.5
Outgoing Section
The outgoing section shall be an indoor metal-enclosed 480-volt power
circuit breaker switchgear assembly, with drawout type circuit breakers, as
specified for 480-volt Station Service Switchgear.
2.8
STATION SERVICE TRANSFORMER
2.8.1
Type and Rating
The station service transformers shall be indoor ventilated dry-type,
self-cooled, NEMA Class AA, with 150 or 220 degrees C 30 limiting
temperature insulation and shall conform to the applicable requirements of
IEEE C57.12.01, [ANSI C57.12.50] [ANSI C57.12.51], IEEE C57.12.91, and NEMA
TR 1. The transformers shall be rated [_____]kVA, 3-phase, 60-Hz,
[13,800-480 volts], [[_____]-480 volts] and the windings shall be
connected delta-delta. The transformer impedance shall be [_____] percent
subject to ANSI standard tolerance. The transformer shall be designed to
carry rated load continuously without exceeding 80 degrees C (Class 150
degrees C) or 150 degrees C (Class 220 degrees C) 176 degrees F (Class 302
degrees F) or 302 degrees F (Class 428 degrees F) temperature rise above 40
degrees C 104 degrees F ambient temperature when installed in its
ventilated sheet metal enclosure and cooled by natural air circulation.
2.8.2
Core and Coils
The core, coils and metal enclosure of the transformer shall be rigidly
attached to a structural steel base suitable for moving the complete
transformer by the use of rollers. Jacking facilities and removable
lifting eyes shall be provided on the core and coil assembly. The core
laminations shall be free from burrs which may puncture the insulation
between laminations and shall be securely fastened to prevent excessive
vibration in normal service or displacement under short-circuit conditions.
Four 2-1/2 percent full-capacity taps, 2 above rated voltage and 2 below
rated voltage, shall be provided in the high-voltage windings, and suitable
means shall be provided for changing the taps while the transformer is
de-energized. The terminal board shall be accessible through a door or
removable panel in the enclosure. All transformer leads and taps shall be
securely braced to prevent displacement or injury during transit or
installation and under short-circuit condition. Wiring for transformer
accessories shall be adequately supported to prevent breaking of the
conductors due to vibration of the transformer and shall be connected to
accessible terminal blocks.
2.8.3
Enclosure
The transformer shall be provided with a ventilated sheet steel enclosure
as specified for 480-volt Station Service Switchgear, except that a formed
enclosure of not less than No.13 MSG may be used. Doors or removable
panels shall be provided in the enclosure to permit access to the
transformer, and suitable removable lifting eyes or other approved means
shall be provided to permit lifting the enclosure alone and also the
complete transformer by the use of a crane. The enclosure shall be
adequately braced and stiffened on the inside, and shall be coated with
sound-deadening material if necessary, so that the audible sound level of
the enclosed transformer when operating at rated load will not exceed the
value permitted in Table 0-3 of NEMA TR 1.
SECTION 16404A
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