1250 KVA Three-phase Pad-mounted Transformer-4.16*12.47/0.48 KV | USA 2025

Pad mounted transformer: built for weather, designed for safety, trusted for years.

01 General

1.1 Project Description

1250 kVA three-phase pad-mounted transformer was delivered to USA in 2025. The rated power of the transformer is 1250 kVA with KNAN cooling, they formed a vector group of Dyn1.

This three-phase pad-mounted transformer is a radial-feed liquid-filled unit engineered for dependable underground distribution. It features a dual high-voltage rating of 4.16 kV and 12.47 kV (with a 2A2B * ±2.5% de-energized tap changer), providing flexibility to accommodate different primary voltage levels. The low-voltage side is rated 480Y/277V with a 30 kV BIL, and the transformer impedance is set at 5.75% (±7.5%).

To meet modern efficiency requirements, the unit complies with DOE 2016 standards, achieving 99.46% efficiency at 50% load and 55°C reference temperature. For superior corrosion resistance in demanding environments, the tank and all external accessories are finished with a C5M heavy-duty paint system (Munsell 7GY3.29/1.5 green), ensuring long-term durability.

Application Fields

• Industrial parks and manufacturing plants – where high load demands and flexible adaptation to different primary voltages (4.16 kV or 12.47 kV) are required.
• Commercial complexes and large public buildings – such as shopping malls, hospitals, schools, and data centers, benefiting from low loss performance (DOE 2016) and long-term reliability.
• Utility distribution networks – for underground pad-mounted substations, especially where future voltage upgrades or dual-voltage supply is needed.
• Coastal and highly corrosive environments – including ports, chemical plants, and onshore collection centers for offshore wind farms, where the C5M paint system provides excellent resistance to salt spray, humidity, and industrial pollution.
• Renewable energy projects – such as large-scale PV plants or battery energy storage systems, requiring 480Y/277V secondary side interconnection and robust outdoor durability.

1.2 Technical Specification

1250 kVA pad mounted transformer specifications type and data sheet

1.3 Drawings

1250 kVA three-phase pad-mounted transformer diagram drawing and size.

02 Manufacturing

2.1 Core

The core uses high-permeability grain-oriented silicon steel with step-lap joints to achieve a no-load loss of only 1.35 kW, well below the DOE 2016 limit of 1.485 kW. This design is ideal for energy-sensitive applications such as data centers and commercial buildings. The magnetic balance test confirmed symmetrical flux distribution with no core defects, and insulation resistance from core to frame exceeded 18 GΩ. Manufacturing includes automatic stacking and strict gap control. Highlight: Low-loss core meets both DOE 2016 and IEEE C57.12.34-2022.

2.2 Winding

Aluminum windings are configured for dual high voltage (4.16 kV / 12.47 kV, Dyn1) with a ±2×2.5% de-energized tap changer, providing excellent grid flexibility. Voltage ratio deviation was measured at only -0.12% (well within ±0.5%), and HV winding resistance unbalance ≤0.16%. Lightning impulse and induced voltage withstand tests (2× voltage, 150 Hz) passed without breakdown. All windings are CNC wound and 100% tested for turn‑to‑turn insulation. Highlight: Dual HV rating + precise tap changer, fully compliant with IEEE C57.12.34-2022.

2.3 Tank

The welded MS steel tank is coated with a C5M heavy-duty paint system (Munsell 7GY3.29/1.5 green), offering over 20 years of corrosion protection for coastal and industrial environments. Under a vacuum of -67 kPa, the maximum permanent deformation was only 0.04 mm, and a 24‑hour pressure test at 20 kPa showed zero leakage. Tank manufacturing includes 100% kerosene leak check and blast cleaning to Sa2.5. Highlight: C5M coating + fully sealed welded cover – no gasket, no leaks.

2.4 Final Assembly

The transformer is assembled with ONAN cooling, mineral oil, and all required accessories: pressure relief valve (50 SCFM), liquid level gauge with contacts, thermometer with contacts, HV changeover switch, ground pads, handhole, and lifting/jacking provisions. Dissolved gas analysis (DGA) before and after testing showed zero acetylene and normal total hydrocarbons, confirming no internal discharge or overheating. Vacuum oil filling keeps moisture below 20 mg/kg. Highlight: Modular accessories and X0 neutral ground strap for easy field installation.

03 Testing

All tests follow IEEE C57.12.90-2021. Key results: insulation resistance >20 GΩ; ratio deviation -0.12%; no‑load loss 1.35 kW; load loss 9.05 kW; impedance deviation <0.5%; magnetic balance symmetrical; applied voltage (AV) and induced voltage (IVW) passed; lightning impulse passed; top oil and winding temperature rise ≤55K; vacuum deformation ≤0.04 mm; pressure sealing no leak; DGA normal. Every result meets or exceeds DOE 2016 and IEEE C57.12.34-2022 requirements. Complete test reports are archived with serial number 260110 for full traceability.

04 Packing and Shipping

4.1 Packing

The three-phase pad-mounted transformer is mounted on a formed steel base with fork pockets, pulling, jacking, and rolling provisions. It is covered with heavy-duty polyethylene tarpaulin, fitted with foam corner protectors, and shipped with a sealed wooden accessory box containing bolts, gaskets, and manuals. The packaging complies with ISTA 3E and ISPM 15 standards, ensuring safe ocean and land transport.

4.2 Shipping

The three-phase pad-mounted transformer is shipped oil‑filled (mineral oil at normal level) with all valves closed; an optional nitrogen blanket at 20 kPa is available. Each shipment includes a complete documentation package: factory test report, installation manual, outline drawing, and packing list. Anti‑rust treatment is applied to exposed machined parts, and optional shock/recorder monitors can be installed for sensitive routes.

05 Site And Summary

This 1250kVA three-phase pad-mounted transformer combines DOE 2016 efficiency (99.46% at 50% load), C5M heavy-duty corrosion protection, and dual high-voltage capability (4.16/12.47 kV). It fully complies with IEEE C57.12.34-2022, passes all routine and type tests with superior results, and is built with traceable manufacturing quality. Ideal for outdoor distribution in harsh environments, data centers, EV charging stations, and industrial parks.