Download SECTION 16403

SECTION 16403
LOW VOLTAGE DISTRIBUTION TRANSFORMERS, DRY TYPE
403.01
GENERAL
A.
Manufacturers
Transformers used for converting the 480-Volt systems voltage to
lower voltages shall be dry type, as manufactured by Square D.
B.
Description
1.
Transformer rating and type shall be as shown in the contract
documents. All low voltage transformers shall meet the efficiency
levels established in Nema TP-1, TP-2 and TP-3 80 C
temperaure rise in conncection to energy efficient transformers in
accordance with the Claifornia Code of Regulations Title 20
requirement.
2.
Transformers shall be rated 480-Volt, 3-phase, 3-wire Delta
primary and 120/208-Volt, 3-phase, 4-wire wye secondary.
3.
Impedance shall be in accordance with NEMA Standards. All
transformers of identical KVA shall have similar impedance
ratings.
4.
Transformers, 600 volts and below, 500 KVA and below, shall be
Underwriter’s Laboratory listed and shall bear the UL label.
Transformers shall meet NEMA, IEEE, and ANSI standards.
Transformers shall be designed for continuous operation at rated
KVA, 24 hours a day, 365 days a year, with normal life expectancy
as defined in IEEE #65. This performance shall be obtainable
without exceeding 80C average temperature rise in a 40C
maximum ambient, and 4% minimum impedance
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5.
The transformer shall be capable of withstanding a zero
impedance fault, across any or all low voltage bushings, without
mechanical or electrical damage.
6.
Transformers shall have 2-2 ½% taps above and 4-2 ½% taps
below nominal rated voltage. The taps shall be set for nominal
rated voltage at the factory.
7.
The transformer shall have sound levels equal to or lower than
those established in the latest revision of ANSI Standard C89.12.7 2.
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LOW VOLTAGE DISTRIBUTION TRANSFORMERS, DRY TYPE
8.
The transformer enclosure shall meet the Underwriter’s
Laboratories specification UL506 for the following:
a. Ventilation openings, corrosion resistance, cable bending
space, grounding provisions, surface temperatures, wiring
compartment temperature rise, and terminations. The
transformer case shall be of the self-bracing type.
b. The enclosure shall be provided with lifting holes to facilitate
handling and installation without removal of any of the
enclosure components.
c. The terminal compartment shall be located in the bottom of the
transformer, below the coil-core assembly, and shall provide
for back, bottom, or side conduit entrance. Terminals shall be
plainly identified.
9.
Transformers 15 KVA and Larger shall be 80 C temperature rise
above 40 ambient unless otherwise noted.
C.
The transformer shall be constructed with core materials of a high
quality, low loss nature, in order to minimize exciting current, no-load
losses, and inter-laminar vibrations.
D.
K-RATED TRANSFORMER
K-Rated transformers shall be UL listed for use for 50 to 100% NonLinear Harmonic loads. The primary winding shall have sufficient
conductor capability to withstand the high circulating harmonic currents
which circulate in the data windings.
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1.
K-rating of the transformer shall be as shown on the contract
documents, the K-rating shall be as defined in ANSI standard
C57.110 and UL-1561.
2.
Coil Conductors shall have continuous windings with termination's
brazed or welded. Individually insulated secondary conductors
are arranged to minimize hysteresis and eddy current losses at
harmonic frequencies.
3.
The transformer shall be designed to compensate for the
additional heating effects generated by the harmonic currents of
Non-Sinusoidal loads.
4.
Winding temperature rise shall not exceed 115 C in 40 C max.
ambient.
5.
The neutral bus shall accommodate 200% of the rated current.
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LOW VOLTAGE DISTRIBUTION TRANSFORMERS, DRY TYPE
6.
7.
E.
Core flux density shall be below saturation at 10% primary over
voltage, and with Basic impulse level of 10 kV.
The transformer on impedance should be 4% minimum to limit the
let through connect to 10KA
ELECTROSTATIC ISOLATION TRANSFORMER:
The isolation transformer shall protect the system from power line
noise and transients.
1.
Electrostatic shield shall be of copper, between primary and
secondary windings. Shielding shall have low capacitive coupling
between input and output.
2.
Provide the electrostatic shield with a separate insulated ground
connection.
3.
The transformer noise rejection shall be 140db for common mode
and 60db for normal mode noise with EMF of 0.1 Gauss max.
measured at 18" from the noise suppresser.
4.
The transformer shall have efficiency of 95% at operating
frequency of +/- 2% of 60Hz, and load regulation of 3% or less
from no load to full load.
***END OF SECTION 16403***
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