High-efficiency 3-phase distribution transformer ensure stable voltage and easy maintenance
01 General
1.1 Project Description
This 500kVA three phase pad mounted transformer was delivered to the United States in 2024. It is designed and tested under IEEE Std C57.12.34-2022. The transformer meets the DOE 2016 energy efficiency standard. Its efficiency is 99.35%. The primary voltage is 13.2kV, and the secondary voltage is 0.208kV. It changes high voltage to low voltage for commercial and light industrial use. It is UL listed and follows U.S. safety and performance standards.
The vector group Dyn1 guarantees balanced phase relationships and stable secondary voltage performance under load. A no-load tap changer (NLTC) provides ±2×2.5% voltage adjustment for precise regulation under varying grid conditions.
The core uses a three-limb design made of high-grade cold-rolled silicon steel laminations, minimizing core losses and noise. Aluminum windings are employed for excellent thermal conductivity, corrosion resistance, and cost efficiency while maintaining high electrical performance. The ONAN (Oil Natural Air Natural) cooling system ensures stable operation under full load without the need for forced cooling.
This transformer is used in industrial and commercial power systems. It supplies power for factories, data centers, and substations. It works well in underground and pad-mounted installations. It is made for places where space is small, and safety and reliability are important. The combination of loop feed and dead-front configuration allows uninterrupted service and easy maintenance, meeting modern grid requirements for safety and energy efficiency.
1.2 Technical Specification
500kVA three phase pad mounted transformer specification and data sheet
| Delivered to | USA |
| Year | 2024 |
| Type | Three phase pad mount transformer |
| Standard | IEEE Std C57.12.34-2022 |
| Rated Power | 500KVA |
| Frequency | 60HZ |
| Feed | Loop |
| Front | Dead |
| Phase | three |
| Cooling Type | ONAN |
| Liquid insulant | Mineral Oil |
| Primary Voltage | 13.2 kV |
| Secondary Voltage | 0.208 kV |
| Efficiency and losses | DOE 2016, 99.35 % |
| Vector Group | Dyn1 |
| Winding Material | Aluminum |
| Impedance | 4% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | 0.71 kV |
| On Load Loss | 4.1 kV |
| Accessories | Standard Configuration |
1.3 Drawings
500kVA three phase pad mounted transformer drawing and nameplate
02 Manufacturing
2.1 Core
The 500 kVA 3-phase distribution transformer has a three-phase three-limb core made of high-grade cold-rolled silicon steel. It gives low no-load loss and low noise. The core uses precise lamination and step-lap joints to lower magnetic resistance. The clamping structure helps reduce vibration. This design makes the transformer more efficient and stable during long operation. |  |
2.2 Winding
The windings are made of high-conductivity aluminum with layer winding. They use Class H insulation and tight winding gaps to improve dielectric strength. Aluminum winding gives good heat dissipation and strong resistance to short-circuit force. It also makes the transformer lighter and improves heat performance.
2.3 Tank
| The tank is a fully welded steel structure with ONAN natural oil cooling. The surface is sandblasted, then coated with primer and epoxy paint for strong corrosion protection. This design keeps the transformer reliable in outdoor and industrial use. |  |
2.4 Final assembly
 | The core and coil assembly is cleaned, inspected, and precisely aligned, with aluminum windings securely clamped and insulated. During tanking, the active part is placed into a clean oil tank, grounded, and properly positioned for stability. Accessories such as high- and low-voltage bushings, radiators, pressure relief valve, lifting lugs, and off-circuit tap changer are installed and sealed. Additional components include a bayonet fuse with CLFs, a 2-position LBOR switch, liquid level gauge, pressure vacuum gauge, dial-type thermometer, and a drain and sample valve. The transformer is vacuum-filled with mineral oil, checked for sealing integrity, and tested for electrical performance, including resistance, ratio, voltage withstand, insulation, and leak tests. After final cleaning and inspection, nameplate data and markings are verified before shipment. |
03 Testing
Testing Standard
| IEEE C57.12.00-2021 | IEEE Standard for General Requirements for Liquid-Immersed Distribution, Power, and Regulating Transformers
|
| IEEE Std C57.12.34-2022 | IEEE Standard Requirements for Pad-Mounted, Compartmental-Type, Self- Cooled, Three-Phase Distribution Transformers, 10 MVA and Smaller; High-Voltage, 34.5 kV Nominal System Voltage and Below; Low-Voltage, 15 kV Nominal System Voltage and Below |
| IEEE C57.12.90-2021 | IEEE Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformer |
Routine Test
1 Resistance Measurements
2 Ratio Tests
3 Phase-relation Test
4 No Load Losses and No Load Current
5 Load Losses Impedance Voltage and Efficiency
6 Applied Voltage Test
7 Induced Voltage Withstand Test
8 Leak Testing with Pressure for Liquid Immersed Transformers
9 Insulation Resistance Measurement
10 Oil Dielectric Test
Test Results
| No. | Test Item
| Unit | Acceptance Values | Measured Values | Conclusion |
| 1 | Resistance Measurements | % | Maximum resistance unbalance rate | 4.55 | Pass |
| 2 | Ratio Tests | % | The deviation of voltage ratio on the principal tapping: ≤0.5% Connection symbol: Dyn1 | -0.02% ~ 0.05% | Pass |
| 3 | phase-relation tests | / | Dyn1 | Dyn1 | Pass |
| 4 | No-load losses and excitation current
| / | I0 :: provide measured value | 0.25% | Pass |
| P0: provide measured value（t:20℃） | 0.638kW | ||||
| 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 | 4.12% | ||||
| Pk: measured value | 4.062kW | ||||
| Pt: measured value | 4.700 kW | ||||
| Efficiency not less than 99.35% | 99.38% | ||||
| 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 |
| Induced voltage(KV):0.416 | |||||
| Duration(s):40 | |||||
| Frequency (HZ): 180 | |||||
| 8 | Leakage Test | kPa | Applied pressure：20kPA | No leakage and no Damage | Pass |
| Duration：12h | |||||
| 9 | Insulation Resistance Measurement | GΩ | HV-LV to Ground : | 21.3 | / |
| LV-HV to Ground: | 29.8 | ||||
| HV&LV to Ground: | 25.6 | ||||
| 10 | Oil Dielectric Test | kV | ≥45 | 55.2 | Pass |
04 Packing and Shipping
05 Site And Summary
The Scotech 500kVA 3-phase distribution transformer is designed and manufactured to IEEE Std C57.12.34-2022 and DOE 2016 efficiency standards, offering 99.35% high efficiency and reliable power performance. It converts 13.2kV to 0.208kV for commercial and light industrial applications in modern power networks.
The durable welded tank, corrosion-resistant coating, and standard accessories guarantee safe and efficient operation. The standard accessories make the transformer safe and efficient. Each unit is vacuum-filled with mineral oil. It is tested for electrical performance, insulation, and leaks.
Scotech transformers give reliable, energy-saving, and low-cost power for distribution systems around the world.
