Smarter Grids Start Here – Pad-Mounted Transformers for a Resilient Energy Future.
01 General
1.1 Project Description
1250 kVA three phase pad mounted transformer was delivered to America in 2025. The rated power of the transformer is 1250 kVA with kNAN cooling. The primary voltage is 12.47GrdY/7.2 kV with ±2*2.5% tapping range (NLTC), the secondary voltage is 0.6Y/0.347 kV, they formed a vector group of YNyn0.
This Pad-Mounted Transformer is a high-performance power distribution equipment specifically designed for modern smart grids, integrating eco-friendly safety, lightning protection, and compact intelligence into one system. It is ideally suited for critical power applications including urban grids, industrial parks, commercial centers, and renewable energy power stations.
As a core component of power distribution systems, this product utilizes high-performance FR3 natural ester insulating oil, overcoming the limitations of traditional mineral oil with its ultra-high flash point, exceptional environmental compatibility, and extended service life. Equipped with built-in lightning arresters, it effectively suppresses lightning strikes and switching overvoltages, providing 24/7 protection for the grid. The fully enclosed tank design features explosion-proof, moisture-resistant, and anti-corrosion properties, capable of stable operation in extreme environments ranging from -40°C to +50°C, even under harsh conditions such as typhoons, heavy rain, and sandstorms.
Furthermore, this product supports smart upgrades with optional online monitoring systems that collect real-time data on oil temperature, load conditions, partial discharges, and other critical parameters. Through IoT technology, it enables remote monitoring and fault prediction, contributing to the development of efficient, low-carbon, and highly reliable smart distribution networks.
1.2 Technical Specification
1250 kVA pad mounted transformer specifications type and data sheet
| Delivered to | America |
| Year | 2025 |
| Type | Pad mounted transformer |
| Standard | IEEE StdC57.12.34-2022 |
| Rated Power | 1250 kVA |
| Frequency | 60HZ |
| Phase | 3 |
| Feed | Loop |
| Front | Dead |
| Cooling Type | KNAN |
| Primary Voltage | 12.47GrdY/7.2 kV |
| Secondary Voltage | 0.6Y/0.347 kV |
| Winding Material | Aluminum |
| Angular displacement | YNyn0 |
| Impedance | 5.75% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | 1.41 kW |
| On Load Loss | 9.05 kW |
| Accessories | Standard Configuration |
1.3 Drawings
1250 kVA pad mounted transformer diagram drawing and size.
02 Manufacturing
2.1 Core
This pad-mounted transformer features an advanced three-phase five-limb core structure, consisting of three main core limbs (for phase windings) and two additional return yokes. This design offers the following key advantages:
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2.2 Winding
 | This 1250kVA 12.47/0.6kV pad-mounted transformer features a layered winding structure with aluminum-wound high-voltage (HV) windings and aluminum foil-wound low-voltage (LV) windings. The HV side employs layered aluminum wire windings with insulated conductors, ensuring both electrical strength and thermal performance. The LV side uses continuously wound aluminum foil for compact construction, high short-circuit resistance, and optimized axial heat dissipation. The design balances reliable insulation, mechanical robustness, and reduced weight/cost, meeting the compact and efficient requirements of outdoor pad-mounted transformers. |
2.3 Tank
| The tank is formed by welding high-strength mild steel. The tank body is sandblasted for rust removal and then coated with anti-corrosion paint to ensure long-term corrosion resistance outdoors. Reinforcing ribs are designed on the tank wall to enhance mechanical strength, and the heat dissipation area is optimized. Primary seams use automated submerged arc welding or CO₂ gas shielding to ensure leak-proof joints. |  |
2.4 Final Assembly
 | 1. Winding Mounting: Insert the three windings onto the core column 2. Core Assembly: Stack silicon steel laminations layer by layer 3. Clamp Installation: Secure top/bottom clamps with high-strength bolts 4. Lead Connection: The leads connected to the pressure regulating switch and the leads of the high and low voltage bushings |
03 Testing
| No. | Test Item | Unit | Acceptance Values | Measured Values | Conclusion |
| 1 | Resistance Measurements | % | Maximun resistance unbalance rate | 2.13 | Pass |
| 2 | Ratio Tests | % | The deviation of voltage ratio on the principal tapping: ≤0.5% Connection symbol: YNyn0 | -0.12% ~ 0.09% | Pass |
| 3 | phase-relation tests | / | YNyn0 | YNyn0 | Pass |
| 4 | No-load losses and excitation current | / | I0 :: provide measured value | 0.32% | Pass |
| P0: provide measured value（t:20℃） | 1.272kW | ||||
| 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 | 5.87% | ||||
| Pk: measured value | 8.883kW | ||||
| Pt: measured value | 10.155kW | ||||
| Efficiency not less than 99.45% | 99.48% | ||||
| 6 | Applied Voltage Test | kV | HV: 34kV 60s LV: 10kV 60s | No collapse of the test voltage occurs | Pass |
| 7 | Induced Voltage Withstand Test | 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 : | 2.39 | / |
| LV-HV to Ground: | 2.53 | ||||
| HV&LV to Ground | 1.40 |
04 Packing and Shipping
05 Site And Summary
Our pad-mounted transformers deliver reliable power distribution with compact design, high efficiency, and robust durability, ideal for solar farms, urban grids, and industrial applications.
• Rugged Performance: sealed tank for harsh environments
• Smart Monitoring: Optional IoT sensors for real-time load/temperature tracking
• Global Support: Standardized production with flexible customization
Committed to safe and sustainable energy solutions – contact us for technical specs or project support!
