Typical Pad Spec






(Dead Front Construction)




         1.1 WORK INCLUDED

Provide liquid immersed, self cooled, pad-mounted transformer(s) in accordance with the following specifications.

         1.2 STANDARDS

These transformer(s) shall be designed, manufactured and tested in accordance with the  applicable portions of the latest versions of ANSI, NEMA and IEEE standards including:

•ANSI C57.12.00, Standard for General Requirements for Distribution, Power and Regulating Transformers and Shunt Reactors,

•ANSI C57.12.26, Requirements for Three Phase Self Cooled Compartmental Type Pad-Mounted Transformers (Dead Front Construction)

•ANSI C57.12.27, Conformance Requirements for Liquid Filled Distribution Transformers Used in Pad-Mounted Installations, Including Unit Substations

•ANSI C57.12.28, Pad-Mounted Equipment - Enclosure Integrity

•ANSI C57.12.70, Terminal Markings and Connections for Distribution and Power Transformers,

•ANSI C57.12.80, Terminology for Power and Distribution Transformers,

•ANSI C57.12.90, Test Code for Liquid Immersed Distribution, Power and Regulating Transformers,

•ANSI C57.92, Guide for Loading Mineral Oil Immersed Power Transformers Up to and  Including 100 MVA with 55°C or 65°C Average Winding Rise,

•ANSI/IEEE 386, Standard for Separable Connectors and Bushings.

         1.3 SUBMITTALS

Provide submittals for all transformers supplied under these specifications. The submittal shall be clear and legible and include the following.

•Complete outline and arrangement drawings for the transformer showing plan and elevation views. A nameplate drawing and electrical wiring and connection diagrams for all applicable accessories are to be provided. Catalog cuts and descriptive literature are to be included for the transformer and all accessories.

•Certified Test Reports as outlined in paragraph 1.6 FACTORY TESTS are to be provided after testing is complete, prior to shipment.

•Instruction Manuals as outlined in paragraph 1.4 INSTRUCTION MANUALS are to be provided with the as built drawings, prior to shipment.


The Instruction Manuals shall include as a minimum, details of the transformer and of serviceable components and accessories. The Instructions shall describe receipt, handling, care, inspection, installation, operation and maintenance of the transformer and accessories.


The manufacturer shall have a thoroughly documented, written quality assurance and inspection program. This shall be available to the Engineer upon request. All test equipment shall be calibrated and traceable to the National Bureau of Standards.

         1.6 FACTORY TESTS

Tests shall be performed in accordance with all applicable standards including ANSI C57.12.90, latest edition. All tests listed in Table 16 of ANSI C57.12.00, Routine Design and Other Tests for Liquid Filled Transformers and one full wave quality control impulse test shall be performed on each transformer. The tests shall include:

•1. Resistance Measurement Test,

•2. Ratio Test,

•3. Polarity and Phase Relation Tests,

•4. No-load and Excitation Current Tests,

•5. Dissipation Factor Test (Capacitance Bridge Method)

•6. Impedance Voltage and Load Loss Test,

•7. Applied and Induced Potential Tests,

•8. Pressure / Leak Test (minimum of 7 psi for 24 hrs. on tank and radiators),

•9. One Full Wave Quality Control Impulse Test.

Certified copies of all test reports shall be provided upon completion of the tests, prior to shipment.


The transformer(s) to be provided shall be the standard catalog products of manufacturers regularly engaged in the manufacture of this type of product. The transformer(s) shall represent product types which shall have at least ten years of satisfactory use. Transformer shall be Pacific Crest Transformers type PMT or approved equal.

         1.8 WARRANTY

The manufacturer shall warrant the product for a period of not less than eighteen (18) months from the date of shipment or twelve (12) months from the date of energization, whichever occurs earliest.


The transformer(s) shall be compartmental pad mount type, inhibited Type II mineral oil filled, for outdoor service.


•A. KVA: as shown on the plans

•B. Phase: 3

•C. Liquid type: Type II mineral oil

•D. Temperature rise: 65°C

•E. Cooling: OA

•F. Altitude, above sea level: (           ) ft.

•G. Frequency: 60 hZ

•H. Winding conductor: aluminum

•I. High voltage:              volt,       kV BIL

•J. High voltage connection: delta

•K. De-energized taps: 2±2.5%

•M. Impedance: 4.5% minimum

•N. Low voltage: 480/277 volt, 30 kV BIL

•O. Low voltage connection: wye.


When facing the transformer the high voltage compartment shall be on the left. The primary bushings shall be 200 amp deep well bushings. The installing contractor shall be responsible for providing the inserts and elbows. The low voltage on the right is to be provided with molded epoxy spade terminals with NEMA hole spacing. The installing contractor shall be responsible for providing suitable cable terminations.
Two (2) ANSI two-hole ground pads are to be provided on the base. A stainless steel connection diagram and nameplate shall be provided. The tap changing mechanism for de-energized operation shall be wall mounted in the primary compartment with external, padlockable operating handle. Lifting lugs and jacking pads designed to lift the transformer complete with liquid shall be provided.

         2.3 ACCESSORIES

The following accessories are to be included with the transformer:

  1. 1. 1" drain and sampling valve,

  2. 2. liquid level gauge,

  3. 3. dial type thermometer with resettable maximum indicator,

  4. 4. upper filter press connection and fill plug,

  5. 5. pressure relief valve,

  6. 6. pressure vacuum gauge,

  7. 7. (4) external tank hold down brackets,

  8. 8. gas sample / pressure test connection,

  9. 9. 1" upper fill / filter press connection,

  10. 10. non PCB label,

  11. 11. standard pad mount green paint.


This section describes the construction requirements for the design, manufacture and testing of outdoor, three phase, liquid filled, self cooled, compartmental, tamper resistant pad mount type distribution transformers.

         3.1 The transformer(s) shall be compartmental type, self cooled, and tamper resistant for mounting on a pad. The transformer(s) primary is to be dead front and arranged for radial feed. The unit shall restrict the entry of water (other than flood water) into the compartments so as not to impair it's operation. There shall be no exposed screws, bolts or other fastening devices which are externally removable.

         3.2 The transformer(s) shall consist of a transformer tank and full height, bolt-on high and low voltage cable terminating compartments located side-by-side separated by a rigid metal barrier. Each compartment shall have separate doors, designed to provide access to the high voltage compartment only after the low voltage door has been opened. There shall be an additional fastening device to open the high voltage compartment door after the low voltage door is open. The low voltage door shall have a handle operated, three point latching mechanism designed to be secured with a single padlock. A hex head bolt shall be incorporated into the low voltage door latching mechanism. Both doors shall be equipped with lift-off stainless steel hinges and door stops to secure the them in the open position. Doors are to be mounted flush with the cabinet frame. The high voltage compartment door shall be provided with key interlock mounting provisions so that the door cannot be opened unless it's respective switch has been locked open. The interlock is to be provided by the switchgear manufacturer for field mounting on the transformer.

         3.3 Compartment sills, doors and covers shall be removable to facilitate cable pulling and installation. Compartments shall be designed for cable entry from below and shall be sized to the minimum dimensions of ANSI C57.12.26. The low voltage compartment shall include factory mounted 600 amp molded case breaker.

         3.4 The transformer(s) is to be rated for continuous operation at full load at 65°C temperature rise with a 24 hour average ambient temperature of 30°C without loss of life expectancy. The transformer(s) and all current carrying parts shall also be designed to operate at 65°C.

         3.5 The self cooled transformer(s) shall be designed with an average sound level not to exceed those defined in NEMA. This will be in accordance with the audible sound level test procedure as outlined in NEMA.

         3.6 The transformer(s) shall be two winding type of circular coil construction using flat strip low voltage conductor and a round or rectangular high voltage conductor. All windings shall be of aluminum. The layer to layer insulation shall consist of thermally upgraded Shellac Craft diamond epoxy coated paper rated for operation at 65°C rise, 80°C hot spot.

         3.7 The core shall be of the three legged stacked core design. High grade, grain oriented non-aging silicone coated core steel is to be utilized. Magnetic flux densities are to be kept well below saturation to allow for a minimum of 10% over voltage excitation.

         3.8 The core frame shall be designed to provide maximum support of the core and coil assembly. The core frame shall be welded or bolted to ensure maximum short circuit strength. The core and coil assembly are to be designed and manufactured to meet the short circuit requirements of ANSI C57.12.90.

         3.9 The core and coils are to be baked at 250°F to dry the unit and thermally set the epoxy. A Dissipation Power Factor test is to be performed to insure that moisture content has been minimized. Immediately after the drying process the core and coils are to be tanked and placed under a full vacuum. After the unit has been under a full vacuum for several hours the unit is to be filled with the appropriate cooling medium.

         3.10 Transformers supplied with "less flammable" liquids shall be designed and manufactured to meet the requirements of the UL classification for less flammable fluids per NEC 450-23.

         3.11 The transformer(s) shall be of the sealed tank construction of A36 grade mild steel with sufficient strength to withstand a pressure of 7 psi without permanent distortion. The tank shall be designed to permit rolling or skidding in any direction. The cover shall be domed to shed water and is to be welded with a bolted and gasketed handhole. Transformers supplied with "less flammable " liquids, (high molecular weight hydrocarbon fluid or silicone) shall be manufactured to withstand 12 psig without rupture. The transformer shall remain sealed for a top oil temperature range of -5°C to +105°C. Flat cooling panels in a common header on the back, sides or front shall be provided when required.

         3.12 The transformer(s) is to be shipped as a unit requiring only anchoring to the pad and termination of high and low voltage cables. The required amount of liquid is to be factory installed. Any contacts required by this specification are to be wired in rigid steel conduit or liquidtite to within 18" of the contact and to a terminal block mounted in the low voltage compartment on the steel divider.

         3.13 The transformer manufacturer shall certify that the transformer(s) is Non-PCB, containing no detectable PCBs. Do not provide high flash point liquids including askarel, or other liquids including tetrachlorethylene, perchlorethylene, chlorine compounds, or halogenated compounds.

         3.14 When high voltage taps are specified, full capacity taps shall be provided with a tap changing mechanism designed for de-energized operation. The padlockable tap changer operator shall be located within the primary compartment.

         3.15 When a primary switch is required, as shown on the plans, the switch is to be oil immersed with hook stick operating handle located in the primary compartment. The two position, gang operated, spring-loaded toggle switch is to be rated 200 amp continuous and load break, 15 kV, 95 kV BIL, 10 kA symmetrical momentary and fault close.


The transformer(s) shall be thoroughly cleaned prior to painting. The tank and all metal parts shall be shot blasted to white metal and immediately primed with at least 1.5 mils of rust inhibiting primer. After assembly all parts shall be steam cleaned with a phosphatizing agent prior to applying the finish coat. The finish coat shall consist of a minimum of 3 mils of high gloss alkyd enamel paint. The transformer(s) is to be painted pad-mount green.


Acceptance of the transformer(s) is contingent upon satisfactory meeting these specifications and tests as specified herein.