Powering Safe & Efficient Energy Distribution
Three-Phase Padmount Transformers are essential medium-voltage distribution units used throughout the United States for safe and efficient power delivery in underground electrical networks. Designed for outdoor installation on a concrete pad, these transformers feature a tamper-proof, compartmentalized enclosure that protects energized components and meets stringent ANSI/IEEE and NEMA standards for public safety and reliability. Liquid-filled with mineral oil or biodegradable dielectric fluids, they step down primary voltages from utility distribution lines to usable secondary levels for commercial, industrial, and large residential loads while offering robust performance across diverse environments.
Available in a wide range of kVA ratings and configurations, three-phase padmount transformers support balanced power delivery, enhanced surge protection, and flexible installation options for campuses, business parks, data centers, and municipalities. Their compact, weather-resistant design makes them a preferred choice for modern U.S. power infrastructure.
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Product Name |
Pad-Mounted Distribution Transformer |
|
Voltage Class |
15 / 25 / 35 kV |
|
Power Rating |
45 – 10000 kVA |
|
Cooling |
ONAN / KNAN |
|
Insulating Fluid |
Mineral Oil / R-Temp / FR3 / Other |
|
Mounting |
Pad-mounted, Dead-front or Live-front |
|
Standards |
IEEE C57.12.00, DOE 2016, ANSI C57.12.28, NEMA TR-1 |
| Feature | Item | Details |
|---|---|---|
|
Tank Access |
Bolted cover |
45–1000 kVA |
|
|
Welded cover with handhole |
1500–7500 kVA |
|
Security |
Three-point latching door |
For high-voltage cabinet |
|
Lightning Protection |
Lightning arrester provisions |
Live-front units |
|
Nameplate |
Laser-scribed anodized aluminum |
Durable and permanent |
|
Fluid Access |
One-inch drain valve with sampler |
In low-voltage compartment (45–7500 kVA) |
|
|
One-inch upper fill plug |
Standard fluid fill |
|
Pressure Management |
Automatic pressure relief device |
Built-in |
|
Cabinet Depth |
20″ / 24″ / 30″ cabinet |
Based on rating: 20″ (45–1000 kVA), 24″ (1500–7500), 30″ (34.5 kV) |
|
Installation |
Removable sill |
Easier transformer placement |
|
Internal Divider |
Steel divider between HV and LV compartments |
Electrical separation |
|
Bushings |
RTE 15/25 kV 200 A (HTN) bushing wells |
Dead-front |
|
|
RTE 15/25/35 kV 200 A integral bushings |
Dead-front |
|
|
Cooper wet-process porcelain bushings |
Live-front |
|
Lifting Hardware |
Lifting lugs |
4 included |
|
Grounding |
Stainless steel ground pads |
45–500 kVA |
|
|
NEMA 2-hole ground pads |
750–7500 kVA |
|
Hardware |
Stainless steel cabinet hinges and mounting studs |
Corrosion-resistant |
| Accessories | Item | Details |
|---|---|---|
|
Monitoring |
Liquid level gauge |
Optional auxiliary contacts |
|
|
Pressure vacuum gauge |
Analog type |
|
|
Dial type thermometer |
Optional auxiliary contacts |
|
Switching |
On/Off loadbreak switches (1–3) |
Manual switches |
|
|
4-position loadbreak switch |
V-blade or T-blade |
|
|
Delta–wye switch |
Manual or automatic |
|
|
Kyle® VFI |
Vacuum Fault Interrupter |
|
Bushings & Inserts |
6/8/10-hole LV spade |
45–500 kVA |
|
|
12/16/20-hole LV spade |
750–2500 kVA |
|
|
LV bushing supports |
Enhanced terminal protection |
|
|
RTE 15/25 kV 200 A bushing inserts |
High-voltage |
|
|
RTE 15/25 kV 200 A feedthru inserts |
|
|
|
RTE HTN bushing wells with removable studs |
|
|
|
RTE 15/25/35 kV 600 A one-piece deadbreak bushings |
|
|
Safety |
Hexhead captive bolt |
Tamper-resistant |
|
|
High-voltage warning signs |
OSHA/ANSI compliant |
|
Hardware/Mechanical |
Ground connectors |
Stainless steel |
|
|
Drain/sampling valve (HV side) |
Optional |
|
|
Breaker mounting provisions |
Optional |
|
|
Touch-up paint |
Color-matched |
|
|
Stainless steel nameplate |
Optional |
|
|
Stainless steel tank base/cabinet/sides/sill |
Enhanced corrosion protection |
|
|
Service entrance (2″) in sill or cabinet side |
Cable routing |
|
Gas System |
Nitrogen blanket |
With bleeder and purge valve |
|
Windings |
All copper windings |
Optional upgrade |
|
Fluid Fill |
Globe type upper fill valve |
Alternate to std. fill plug |
|
Certifications |
Factory Mutual approved |
Optional |
|
Efficiency |
K-Factor rated transformer |
For non-linear loads |
The transformer core is designed for high efficiency using rectangular wound configurations, ensuring low excitation current, minimal core losses, and quiet operation. Cores are available in five-leg or triplex configurations and are constructed from precision-cut, grain-oriented silicon steel laminations. Each lamination is fully annealed after cutting, and core stacking is done with tight joint alignment to eliminate corner gaps. This results in superior performance with reduced ferroresonance susceptibility and better efficiency at loading levels above 50% compared to amorphous core alternatives. Stacked core designs are also available upon request.
Transformer coils are engineered for compactness, mechanical rigidity, and electrical balance, in compliance with ANSI C57.12.26 standards. Coils are hydraulically pressed and baked, bonding wire and insulating paper into a solid structure with high dielectric and short-circuit strength (certified per ANSI C57.12.90). Diamond-pattern epoxy-coated paper enhances mechanical strength and allows coolant to flow freely. Primary windings are made from varnished or paper-insulated copper or aluminum wire, flattened during winding to increase surface contact and space efficiency. Secondary coils use full-width aluminum strip with burr-free edges and are insulated with epoxy-diamond paper between each layer. All insulation levels meet ANSI C57.12.00 standards.
Cooper Power Systems transformers are available with a range of dielectric coolants, including standard mineral oil and specialized fluids like R-Temp and Envirotemp® FR3. These fluids are degassed and tested for dryness and dielectric strength prior to filling. R-Temp fluid is a less-flammable, biodegradable coolant with superior dielectric strength, suitable for installation next to or inside buildings. Envirotemp FR3 is a natural ester-based, biodegradable fluid with enhanced fire safety and food-grade additives. All fluids are treated under strict quality control protocols to ensure longevity and performance.
Moisture removal is critical to transformer performance and lifespan. Cooper’s advanced vacuum processing simultaneously heats and dries transformer components, removing internal moisture and air. By energizing the coils under shorted conditions, internal heating drives moisture to the surface, where it is removed via vacuum. Degassed insulating fluid is added under vacuum, ensuring full saturation of coils and insulation. This method surpasses hot air dry-out systems by achieving consistently low residual moisture levels, maximizing dielectric integrity and minimizing corona risk.
Tank assemblies are built from cold-rolled precision-cut steel and pressure-tested to 7 psig without distortion. Tanks include rolling bases, jack pads, and lifting hooks. For units up to 1000 kVA, a bolted cover allows for internal cleaning and repainting before final assembly, minimizing contamination. Covers are domed for moisture run-off and secured with high-strength bolts concealed by a protective cover guard. Tank interiors are painted light gray to improve internal visibility.
The cabinet design incorporates patented high-security features exceeding ANSI standards. A three-point latch and concealed stainless steel hinges secure the low-voltage compartment. Access is restricted with a tamper-proof silicon bronze pentahead bolt. Cabinets are available in 20″, 24″, or 30″ depths depending on kVA rating and accessories. Full-height doors open 120° and include stops for service convenience.
A multi-stage finishing process exceeds ANSI corrosion protection standards. An eight-stage phosphate pretreatment improves paint adhesion, followed by three layers of electro-deposited epoxy primer (E-coat). A polyester powder topcoat (P-coat) provides impact and abrasion resistance, finished with a UV-resistant urethane clear coat.
Enhanced Public Safety – Fully enclosed, tamper-resistant steel cabinets with dead-front construction reduce exposure to live components.
Reliable Three-Phase Power – Delivers balanced and consistent power for commercial buildings, industrial facilities, and utility distribution.
Ideal for Underground Distribution – Designed specifically for underground electrical networks common across U.S. urban and suburban areas.
Compliance with U.S. Standards – Manufactured to meet ANSI/IEEE, NEMA, and UL standards required by American utilities.
Wide kVA & Voltage Range – Available in multiple kVA ratings and voltage configurations to match diverse load requirements.
Durable Outdoor Performance – Weather-resistant construction supports long service life in varied U.S. climates.
Liquid-Filled Cooling Efficiency – Uses mineral oil or eco-friendly dielectric fluids for effective cooling and improved efficiency.
Space-Saving Design – Ground-level installation eliminates the need for poles or vaults, improving site aesthetics.
Low Maintenance – Sealed tank design minimizes servicing and operational downtime.
Utility Power Distribution – Widely used by U.S. electric utilities for safe and efficient underground medium-voltage distribution.
Commercial Complexes – Ideal for shopping centers, office buildings, hotels, and mixed-use developments requiring reliable three-phase power.
Industrial Facilities – Supports manufacturing plants, warehouses, refineries, and processing units with balanced, high-capacity power delivery.
Data Centers – Provides stable and continuous three-phase power essential for mission-critical IT infrastructure.
Educational Campuses – Commonly installed in universities, schools, and research centers with underground electrical networks.
Healthcare Facilities – Supplies dependable power to hospitals and medical centers where reliability and safety are critical.
Large Residential Developments – Used in apartment complexes and housing communities to maintain aesthetics and safety without overhead lines.
Municipal Infrastructure – Powers water treatment plants, transportation hubs, and public facilities across U.S. cities.
Three-phase padmount transformers by Premier Transformer in the USA deliver reliable, efficient power distribution for commercial, industrial, and utility applications. Designed for durability and safety, these transformers feature tamper-resistant enclosures, advanced insulation systems, and compliance with ANSI, IEEE, and DOE standards. Premier Transformer offers custom-engineered solutions to meet specific voltage, kVA, and installation requirements, ensuring optimal performance in demanding environments. Manufactured domestically with strict quality control, each unit is built for long service life, minimal maintenance, and dependable operation. Customers benefit from responsive engineering support, competitive lead times, and proven expertise in three-phase padmounted transformer design and manufacturing excellence.
