2500 kVA three-phase pad-mounted transformer-powering the U.S. energy transition with safe, efficient, and renewable-ready performance
01 General
1.1 Project Description
To support the growing demand for clean and sustainable energy in the United States, our team successfully delivered a 2500 kVA 3 phase pad mounted step down transformer in April 2025. This unit is specifically engineered for solar and wind power generation systems, providing reliable medium- to low-voltage transformation in utility-scale renewable projects.
This oil-filled step-down transformer is designed with a primary voltage of 13.8 kV and a dual secondary voltage of 0.63 kV × 2, configured in the YNd1d1 vector group. Operating at 60 Hz, it features an impedance of 5.75% and an X/R ratio of 6, ensuring stable performance in renewable energy and utility applications. The transformer includes a no-load tap changer (NLTC) with a ±2×2.5% tapping range for voltage regulation. Built with high-conductivity aluminum windings and cooled by KNAN (natural air cooling), it complies with the DOE 2016 efficiency standards, offering reliable and energy-efficient performance.
This three phase pad-mounted transformer plays a critical role in renewable energy integration, converting medium voltage (13.8 kV) power generated by solar farms or wind turbines down to 0.63 kV for direct connection to inverters or energy storage systems.
1. FR3 fluid provides enhanced thermal performance, fire safety (flash point > 300°C), and environmental benefits-ideal for clean energy zones and high fire-risk areas.
2. Dead-front construction complies with U.S. safety codes, making it suitable for installation in public-access environments and energy parks.
3. The loop feed design ensures system flexibility and reliability for distributed energy resource (DER) integration.
This 2500 kVA 3 phase pad mounted step down transformer was tailored for the U.S. energy transition market, supporting the nation’s goals to reduce carbon emissions and expand the use of renewable power. Delivered on schedule in April 2025, it reflects our commitment to energy innovation, environmental responsibility, and engineering excellence.
1.2 Technical Specification
2500 kVA three phase pad-mounted transformer specification and data sheet
| Delivered to | America |
| Year | 2025 |
| Type | Three phase pad mount transformer |
| Standard | IEEE Std C57.12.34-2022 |
| Rated Power | 2500KVA |
| Frequency | 60HZ |
| Feed | Loop |
| Front | Dead |
| Phase | three |
| Cooling Type | KNAN |
| Liquid insulant | FR3 Oil |
| Primary Voltage | 13.8 Kv |
| Secondary Voltage | 0.63*2 Kv |
| Vector Group | YNd1d1 |
| Winding Material | Aluminum |
| Impedance | 5.75% |
| Efficiency and Losses Standard | DOE 2016 |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | 2.4 KW |
| On Load Loss | 15.79KW |
| Accessories | Standard Configuration |
1.3 Drawings
2500 kVA three phase pad-mounted transformer dimensions and weight details
02 Manufacturing
2.1 Core
The 2500 kVA pad mounted transformer benefits greatly from the three-phase three-column core design, which enhances performance and efficiency. This core structure allows the transformer to share magnetic paths across all three phases, resulting in better flux balance and reduced core losses. It also contributes to a more compact and lightweight build, optimizing space utilization and lowering material costs.
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2.2 Winding
 | The transformer uses wire-wound high-voltage coil windings for even voltage distribution and strong insulation. The foil-type low-voltage winding efficiently handles high currents with reduced losses. It’s YNd1d1 vector group enhances system isolation and power quality. This design ensures reliable performance in solar and wind energy applications. |
2.3 Tank
The 2500 kVA 3 phase pad mounted step down transformer features a sealed mild steel oil tank with a durable white powder coating (RAL 9003) for corrosion resistance. A bolted cover ensures oil protection. Three rear-mounted plate radiators enhance heat dissipation by increasing surface area and promoting natural air convection, ensuring stable performance under varying loads. |  |
2.4 Final Assembly
 | During final assembly, this 2500 kVA, 13.8/0.63×2 kV pad mounted transformer designed for clean and sustainable energy applications, is equipped with six 15 kV/200 A separable high-voltage bushings, including a dedicated separate H0 neutral bushing. The low-voltage side features six resin-cast spade-type bushings with 6-hole terminals for secure cable connections. Protection components include three current-limiting fuses (CLF) to ensure reliable fault isolation. Cooling is enhanced by three sets of plate radiators, providing efficient heat dissipation to maintain optimal performance in demanding renewable energy environments. This configuration supports the U.S. clean energy market’s requirements for safety, reliability, and long-term operation. |
03 Testing
Routine Test and Testing Standard
- Resistance Measurements：According to IEEE C57.12.90-2021 Clause 5
- Ratio Tests：According to IEEE C57.12.90-2021 Clause 7
- Phase-relation Test：According to IEEE C57.12.90-2021 Clause 6
- No Load Losses and No Load Current：According to IEEE C57.12.90-2021 Clause 8
- Load Losses, Impedance Voltage and efficiency：According to IEEE C57.12.90-2021 Clause 9
- Applied Voltage Test：According to IEEE C57.12.90-2021 Clause 10.6
- Induced Voltage Withstand Test：According to IEEE C57.12.90-2021 Clause 10.5.1
- Insulation Resistance Measurement
- Leak Testing with Pressure for Liquid Immersed Transformers：The leaking test at 20KPa shall be conducted for 12h without leakage. No permanent deformation.
Test Results
| No. | Test Item | Unit | Acceptance Values | Measured Values | Conclusion |
| 1 | Resistance Measurements | % | Maximun resistance unbalance rate | 3.10 | Pass |
| 2 | Ratio Tests | % | The deviation of voltage ratio on the principal tapping: ≤0.5% Connection symbol: YNd1d1 | 0.01% ~ 0.23% | Pass |
| 3 | phase-relation tests | / | YNd1d1 | YNd1d1 | Pass |
| 4 | No-load losses and excitation current
| / | I0 :: provide measured value | 0.37% | Pass |
| P0: provide measured value（t:20℃） | 2.038kW | ||||
| the tolerance for no load loss is +10% | / | ||||
| 5 | Load losses impedance voltage and efficiency
| / | t:85℃ the tolerance for impedance is ±7.5% the tolerance for total load loss is +6% | / | Pass
|
| Z%: measured value | 5.85% | ||||
| Pk: measured value | 16.516kW | ||||
| Pt: measured value | 18.554 kW | ||||
| Efficiency not less than 99.53% | 99.54% | ||||
| 6 | Applied Voltage Test | kV | HV/: 34kV 60s LV/: 10kV 60s | No collapse of the test voltage occurs
| Pass
|
| 7 | Induced Voltage Withstand
| kV | Applied voltage (KV):2Ur | No collapse of the test voltage occurs | Pass |
| Duration(s):48 | |||||
| Frequency (HZ): 150 | |||||
| 8 | Leakage Test
| kPa | Applied pressure：20kPA | No leakage and no Damage | Pass |
| Duration：12h | |||||
| 9 | Insulation Resistance Measurement | GΩ | HV-LV to Ground : | 3.11 | / |
| LV-HV to Ground: | 3.18 | ||||
| HV&LV to Ground | 2.99 |
04 Packing and Shipping
05 Site And Summary
This 2500 kVA, 13.8/0.63×2 kV pad-mounted transformer is expertly designed to meet the growing demands of clean and sustainable energy projects in the U.S. market, especially for solar and wind power integration. With features like a YNd1d1 vector group, high-efficiency aluminum windings, and advanced cooling via plate radiators, it ensures reliable voltage transformation and stable operation in renewable energy systems.
Equipped with safety-focused dead-front construction and robust protection components, this 2500 kVA 3 phase pad mounted step down transformer complies with strict U.S. standards, making it ideal for public and utility-scale installations. Its use of environmentally friendly FR3 fluid and energy-efficient design aligns perfectly with the nationwide shift towards decarbonization and clean power.
By delivering cutting-edge, reliable transformers tailored for renewable energy, our company supports the transition to sustainable power generation, helping customers meet their clean energy goals while ensuring grid stability and operational efficiency.
