Powering smart underground grids with 2500 kVA residential electrical transformers built for efficiency and safety
01 General
1.1 Project Description
In 2025, we delivered two 2500kVA residential electrical transformers to a client in the United States to support a modern underground power distribution system. Built to meet IEEE Std C57.12.34-2022 and DOE 2016 energy efficiency standards, this pad mounted transformer offers high reliability, energy savings, and long-term environmental benefits.
The unit features a loop feed, dead front design, ensuring safe operation and easy maintenance in compact urban environments. It uses FR3 natural ester oil, a fire-safe, biodegradable insulating fluid ideal for residential, commercial, and institutional installations where safety and sustainability are critical.
With a sealed enclosure and side-mounted low voltage flange outlet, this residential electrical transformer is optimized for underground cable connections in smart grid upgrades, business districts, industrial parks, and utility substations. Its compact footprint and quiet operation make it ideal for locations with strict space and noise restrictions.
By combining high efficiency (99.53%), robust insulation, and flexible voltage adjustment, this unit provides a reliable, low-maintenance power solution tailored to North America’s demanding grid applications.
1.2 Technical Specification
2500kVA residential electrical 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 | 34.5 Kv |
| Secondary Voltage | 0.63 Kv |
| Vector Group | YNyn0 |
| Winding Material | Aluminum |
| Impedance | 5.75% |
| Efficiency and Losses Standard | DOE 2016 |
| Efficiency | 99.53 % |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | 2.4 KW |
| On Load Loss | 15.79KW |
1.3 Drawings
2500kVA residential electrical transformer drawing and weight details
02 Manufacturing
2.1 Core
The core consists of three main legs and two auxiliary legs. Magnetic flux flows through both main and auxiliary legs, providing extra paths that improve flux closure. This design ensures stable operation under unbalanced load and no-load conditions, reducing vibration and noise. The five-leg core runs quietly and reliably, making it ideal for urban distribution and commercial use where low noise and high reliability are required. |  |
2.2 Winding
 | The residential electrical pad mounted transformer uses low-voltage foil winding and high-voltage wire winding with flat aluminum conductors for improved performance and reduced losses. The coil is made of aluminum for its conductivity and light weight. In the image, a worker tightens pressing plate screws to secure the coil, preparing for the next pressing step. This ensures tight compression, enhances mechanical stability, reduces vibration, and boosts reliability and efficiency during operation. |
2.3 Tank
The three-phase residential electrical transformer features a sealed mild steel tank with a bolted cover, powder-coated in RAL 9003 white for corrosion resistance. Equipped with lifting lugs and jacking pads for easy handling. It passes a 50kPa pressure leak test for 12 hours with no leakage or deformation, ensuring reliable sealing and structural integrity. |  |
2.4 LV Flanged Side-mounted Bushings
 | The three-phase pad mounted transformer features a low voltage flanged side outlet design, allowing easy and secure connection to underground cables. The side-mounted LV terminals are protected by a sealed cable box, ensuring safe, space-efficient installation in urban distribution networks and commercial power systems. |
2.5 Final Assembly
Core & Coil Assembly Tank Preparation Assembly Positioning HV Side Integration Vacuum Filling Monitoring Installation Final Wiring & Testing |  |
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-relationTest：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 50KPa shall be conducted for 12h without leakage. No permanent deformation.
- Insulation Resistance Measurement
| No. | Test Item | Unit | Acceptance Values | Measured Values | Conclusion |
| 1 | Resistance Measurements | % | Maximun resistance unbalance rate | 4.58 | Pass |
| 2 | Ratio Tests | % | The deviation of voltage ratio on the principal tapping: ≤0.5% Connection symbol: YNyn0 | 0.01% ~ 0.03% | Pass |
| 3 | phase-relation tests | / | YNyn0 | YNyn0 | Pass |
| 4 | No-load losses and excitation current | / | I0 :: provide measured value | 0.18% | Pass |
| P0: provide measured value（t:20℃） | 2.281kW | ||||
| 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 | 6.00% | ||||
| Pk: measured value | 15.091kW | ||||
| Pt: measured value | 17.372 kW | ||||
| Efficiency not less than 99.53% | 99.55% | ||||
| 6 | Applied Voltage Test | kV | LV: 10kV 60s | No collapse of the test voltage occurs | Pass |
| 7 | Induced Voltage Withstand Tes | 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：50kPA | No leakage and no Damage | Pass |
| Duration：12h | |||||
| 9 | Insulation Resistance Measurement | GΩ | HV-LV to Ground : | 1.40 | / |
| LV-HV to Ground: | 1.53 |
04 Packing and Shipping
05 Site And Summary
SCOTECH is honored to have delivered pad-mounted transformers to our U.S. client, contributing to their power distribution needs with reliable and efficient solutions.
With a focus on meeting IEEE and DOE standards, our team carefully designed, manufactured, and tested these residential electrical transformers to ensure performance and durability. This project was a collaborative effort, and we appreciate the trust our client placed in us.
As a company committed to continuous improvement, we strive to refine our engineering expertise and service capabilities to support global energy infrastructure. We look forward to future opportunities to provide sustainable and high-quality transformer solutions to partners worldwide.
Thank you for choosing SCOTECH-we remain dedicated to excellence in power technology and customer satisfaction.
