APPENDIX C
SINGLE PHASE UNDERGROUND TRANSFORMERS
SINGLE PHASE UNDERGROUND TRANSFORMER
PART 1 - GENERAL
1.01
DESCRIPTION
A. This specification provides the requirements for the design manufacturing and testing of
three phase, 60 Hertz, liquid-filled, self-cooled, vault-type distribution transformers.
B. This specification applies to all the electrical and mechanical features of three phases
12,000 volt primary, 60 Hz, liquid-filled, self-cooled, underground-type vault transformer
for installation in below ground enclosures, which will be subject to occasional flooding.
The transformers are intended to be operated while completely submerged in water, and/or
require minimum effort to re-establish service after a flood. The successful bidder shall
provide all work and material to design, fabricate, test, and deliver the specified equipment
along with any drawings, manuals, or other documents required.
C. The vendor shall furnish underground transformers as specified herein and in the
Transformer Equipment Schedule.
D. Bidders shall be required to submit bid with product cut sheet with ratings and listed
dimensions (hard and soft copy). All sub-surface transformer, 1000KVA and below shall
fit into a deepened #7 box (4’6”x8’6”x7’6”).
1.02
REFERENCES
A.
IEEE C57.12.00, IEEE Standard General Requirements for Liquid Immersed
Distribution, Power, and Regulating Transformers.
B.
IEEE C57.12.10, Safety Requirements for Transformers 230 kV and Below.
C.
IEEE C57.12.24, Underground-Type Three-Phase Distribution Transformers.
D.
IEEE C57.12.32, IEEE Standard for Submersible Equipment – Enclosure Integrity.
E.
IEEE C57.12.70, Terminal Markings and Connections for Distribution and Power
Transformers.
F.
IEEE C57.12.80, Standard Terminology for Power and Distribution Transformers.
G.
IEEE C5.7.12.90, Standard Test code for Liquid-Immersed Distribution, Power,
and Regulating Transformers and IEEE Guide for Short-Circuit Testing of
Distribution and Power Transformers.
H.
IEEE 386, IEEE Standard for Separable Insulated Connector Systems for Power
Distribution systems above 600V.
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1.03
I.
ASTM D3487, Standard Specification for Mineral Insulating Oil.
J.
ASTM D6871, Standard Specification for Natural (Vegetable Oil) Ester Fluids
Used in Electrical apparatus.
SERVICE CONDITIONS
The equipment shall be capable of operating in accordance with the nameplate rating as
shown on design drawings when operated under the service conditions and defined in
referenced standards. The transformer shall be designed for frequent or occasional
submerged operation.
1.04
SUBMITTALS
A. The manufacturer shall submit with their bid the following technical information on each
transformer size/rating being proposed:
1) A dimensioned outline drawing showing maximum dimensions and location of
exterior mounted devices.
2) Transformer net weights (approximate).
3) The following performance data:
• Rating
• Temperature rise at rated load
• Guaranteed No-load and Guaranteed total losses
• Percent regulation at rated load – 100% power
• Percent regulation at rated load – 80% power
• Percent impedance
B. The manufacturer shall submit a copy of their quality assurance manual used in the
manufacture of the equipment being supplied. The quality assurance information shall
include the certification process for welding performed by shop personnel.
C. It shall be expressly understood that the technical information submitted with the bid, as
furnished by the successful manufacturer, shall constitute guarantees, with variance only
insofar as allowable by applicable ANSI, IEEE, and other Industry Standard tolerances.
D. Losses quoted should be realistic values based on experience with tested designs, and
therefore can be guaranteed with certainty for the units to be supplied.
1.05
SEISMIC REQUIREMENTS
A. The equipment, accessories, and supporting structures should be designed such that there
will be no damage, and the equipment should remain operational, during and following an
earthquake with a base motion of 0.25g horizontal and 0.20g vertical, acting
simultaneously.
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B. The primary steady state stresses shall be within the allowable working stress limits
accepted as good practice and set forth in the appropriate design standards. The primary
steady state stresses shall include those originating from gravity loads, operating loads,
and operating temperatures and should be combined with the seismic stresses.
PART 2 - PRODUCTS
2.01
GENERAL
A. The transformer shall be built, tested, and delivered in accordance with the industry standards
as applicable as defined in Section 1.02 unless specifically addressed otherwise in this
specification or in writing by the Engineer. The manufacturer shall be: ABB, Howard
Industry, GE or approved equal.
B. The manufacturer shall have an established welding certification and quality assurance
program in place for all performed welding in the manufacturing of the transformer.
C. The transformer rating shall be as shown on the design drawing kVA rating shall be based
on 55 degree C or 65 degree rise.
D. Windings shall be copper.
E. Transformer shall be 75KVA.
F. The high-voltage primary winding shall be:
12,000 volts
G. The insulation class shall be in accordance with IEEE C57.12.24 and IEEE C57.12.00 and
the minimum BIL rating of the primary windings and bushings shall be in accordance with
the table below.
Primary
12,000 volts
Voltage Class
15kV
BIL Rating
95 kV
H. The low voltage shall be 208 Grd Y/120 volts
I.
The insulation class shall be in accordance with IEEE C57.12.24 and IEEE C57.12.00 and
the minimum BIL rating of the secondary windings and bushings shall be in accordance
with the table below:
Secondary
Voltage Class
BIL Rating
120/240 volts
1.2 kV
30 kV
J.
The transformer shall have an externally operable manual tap changer providing full
capacity taps. Two 2-1/2% taps above and two 2-1/2% taps below are required on the
high voltage windings.
J. The transformers minimum impedances shall be specified below:
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SINGLE PHASE UNDERGROUND TRANSFORMERS
75 kVA
2.02
1.5%
Any units received with impedance values less than the listed values may be rejected by the
Engineer.
CONSTRUCTION
A. The primary high-voltage bushings, parking stands, and secondary voltage bushings and
other accessories shall be located on the cover as specified in Figure 2 of IEEE C57.12.24.
The manufacturer shall submit drawings for approval showing the location of these items
with the bid response.
B. The transformer tank shall be steel and shall have a minimum thickness of ¼ inch. The
radiators shall be carbon steel or stainless steel construction. Carbon steel radiators have a
thickness of 5/32 inch.
C. All exterior surfaces shall be coated using a system of coordinated and thoroughly tested
materials and application techniques that will assure long life under submersed or partially
submersed conditions in accordance with IEEE C57.12.32. Special attention shall be
given to welds, seams, edges, and rough spots.
D. No portion of the tank or protruding appurtenances shall trap or hold water.
E. The hand-hole shall be bolted flanged type. The hand-hole should provide accessibility to
secondary bushings and internal current limiting fuses.
F. Lifting lugs shall be designed and located on the tank to avoid interference between lifting
slings and any attachments on the transformer, and to avoid scratching or marring the
transformer coating. The transformer shall contain suitable jacking and rolling facilities.
G. All nuts, bolts, studs, and screws shall conform to the ANSI standards of pitch, thread
shapes, dimensions, and tolerances.
H. The maximum average sound level as measured per IEEE C57.12.90 shall be in
accordance with IEEE C57.12.24.
I.
Each transformer shall be supplied with six (3) primary bushing wells (1 per phase) per
IEEE C57.12.24. Each bushing well shall be rated for the primary voltage and 200ampere continuous. They shall comply with all applicable requirements and Figure 3 of
IEEE 386. The transformer primary bushing wells shall be completely protected from
paint over-spray and other contamination that may occur during manufacture or shipping.
J. Grounding pads or connecting points shall be provided near the high voltage bushings for
grounding each cable shield/neutral.
K. Secondary Connecting Equipment:
1. The transformer secondary line and neutral bushings shall be electrically rated in
accordance with section 2.01G.
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2. The secondary neutral shall be grounded using a removable connection to the
casing ground pad in accordance with IEEE C57.12.24. The connections shall be
sized for the short circuit rating of the transformer. Short circuit durations are 2
seconds minimum for transformers 1000 kVA and below.
3. Provisions shall be provided for removing the ground connection for testing
purposes on the secondary neutral for either internal or external connections.
L. Bushings for transformer secondary windings rated 208/120V:
1. The secondary voltage line bushing and neutral terminals shall be installed in
accordance with IEEE C57.12.24.
2. The neutral bushing shall be grounded externally or internally to the transformer.
2.03
ACCESSORIES AND MISCELLANEOUS
A. All standard accessories shall be supplied.
B. The transformers shall be provided with:
• Drain valves and threaded plugs
• A welded-on non gasket type magnetic liquid level indicator which will show
proper level at 25 degrees C
2.04
INSULATING FLUID
A. The transformer shall be shipped completely filled with insulating fluid. The insulating
fluid to be used shall be a FR3. Certification must be provided stating that the oil is free
of polychlorinated biphenyls (PCBs).
B. The nameplate of the transformer, or other permanent stainless steel identification, shall
specify the type of insulating fluid and that the insulating fluid is free of PCBs. The
designation on the nameplate shall read “CONTAINS NO PCB AT TIME OF
MANUFACTURE” or similar wording. Proposed similar wording shall be submitted to
the Engineer for approval.
2.05
TANK GROUNDING
Tank grounding provisions shall be provided in accordance with IEEE C57.12.24, latest
revision.
2.06
TRANSFORMER LABELING
A. All labeling shall be in accordance with IEEE C57.12.24, IEEE C57.12.70, and IEE
C57.12.00.
B. Stenciled lettering on the tank shall mark bushings and fuse designations. Decal will not
be allowed.
C. The identification of voltage connections shall be shown on the instruction on the
nameplate.
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D. An instruction nameplate of stainless steel, or other approved corrosion-resistant material,
shall be provided. This nameplate shall be securely attached to the top of the transformer
by means of stainless steel or other non-corroding material screws, rivets, or other
approved fasteners. The letters and numbers shall be stamped on the nameplate.
E. The transformer will be marked on the nameplate or on a separate permanent stainless
steel label, designating the brand name of the fluid, and stipulating that the fluid is
biodegradable.
F. Where removable current limiting fuses are used, the fuse holders shall include a warning
baffle as a precaution against energized operation of the fuse-holder.
PART 3 EXECUTION
3.01
TESTING, AND INSPECTION
A.
The applicable Design Tests in accordance with IEEE C57.12.00 shall be
successfully performed for all designs.
B.
Each transformer shall have passed the following routine tests in accordance with
IEEE C57.12.00 and C57.12.90:
1.
Resistance Measurements of all windings on the rated voltage connection.
2.
Ratio tests.
3.
Polarity and phase relation tests.
4.
No-load losses and excitation current tests.
5.
Load losses and impedance voltage.
6.
Low frequency dielectric test.
7.
Routine Impulse tests per IEEE C57.12.90 section 10.4.
8.
The completed transformer shall be pressure tested in accordance with
IEEE C57.12.24 section 7.4.1 to insure that it is free from leaks and defects.
9.
Oil dielectric tests from samples taken at the bottom of the units shall be
performed per ASTM D1816 (0.04 inch gap) after assembly is complete and
prior to shipment.
10.
Oil test results for the supplied oil in accordance with ASTM D3487 Table 1
or ASTM 6871 Table 1 shall be provided for the latest fluids shipment prior
to transformer filling.
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SINGLE PHASE UNDERGROUND TRANSFORMERS
C. A certified test report of all performed routine tests shall be supplied to the Engineer for
each unit to be delivered under this specification. Test reports should reach the Engineer
before the date of delivery of the units shipped, as this will be one of the bases of
acceptance of the shipment.
D. Accelerated aging tests on the paper insulation using shall be performed.
E. The transformers minimum impedances. The Engineer may reject any units received with
impedance values less than the listed values.
F. The owner or its representatives may at any time perform audits, inspections, or observe
the supplier’s operations.
The supplier shall cooperate and provide access to
documentation, manufacturing, or testing. The owner’s inspector shall be provided with
full access to the facilities used for manufacturing.
1. These inspections do not relieve the supplier of their responsibilities for
full compliance with all the requirements of these specifications.
2. The owner will notify the supplier of any situation where the work is
not in accordance with the requirements of these specifications.
3. All costs incurred by the supplier as a result of rejection of material
shall be considered incidental to the work. No separate payment will be
made.
3.02
SHIPPING AND PACKAGING
A. All units to be shipped in open rack type flatbed trailers. Closed van type trailers are
unacceptable and will be rejected. Stacking of objects on top of each unit is not permitted.
B. Units shall be mounted on a solid wooden pallet, or other approved pallet, for ease of
removal with forklift truck.
C. Units shall be protected during shipment so as to prevent damage to all exterior surfaces
by the hold down devices. All parts of the transformer in contact with shipping hold-down
devices should be protected to prevent chafing or other damage. Units showing damage to
the paint finish are subject to rejection by the district and corrective action by the
manufacturer.
D. Freight on board (FOB) destination – Any location within the city of San Francisco, CA.
3.03
DRAWINGS AND MANUALS
A. Drawings and technical data on the proposed transformer to be manufactured shall be
submitted to the Engineer – for review and approval prior to manufacturing or shipping.
B. These drawings shall include the following:
1. Detailed drawing of the unit showing final dimensions, clearances, and weight
2. Exterior mounted devices
3. Parts list including catalog numbers
4. Nameplate
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5. Installation, Maintenance, and Operation Instructions
6. Recommended spare parts list
7. Standard 1 year warranty
END OF SECTION
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