Five-leg core design for superior stability and efficiency - a high-performance dead front transformer built for safe and reliable power distribution
01 General
1.1 Project Description
These 75 kVA three-phase pad-mounted transformers were made by Scotech. They were sent to the United States in 2024. They meet IEEE/ANSI standards and work well with North American distribution systems. The front-compartment, dead-front design removes exposed live parts and gives a high level of safety. It is easy to check and maintain, and all energized parts stay sealed and insulated.
The 75 kVA dead front transformer has a five-leg core made of high-grade cold-rolled silicon steel sheets with step-lap joints. It is made to meet energy-efficient equipment standards and has 99.03% efficiency. The improved magnetic circuit and low-loss aluminum windings help reduce energy waste. They also save money over time and protect the environment.
The transformer is designed for 2400/4180Y or 13200/22860Y grounded wye systems, operating stably under normal service conditions. It provides safe and efficient power delivery in urban, industrial, and commercial distribution networks, supporting medium- and low-voltage loop systems across North America.
1.2 Technical Specification
75kVA three phase pad mounted transformer specification and data sheet
| Delivered to | America |
| Year | 2024 |
| Type | Three phase pad mount transformer |
| Standard | IEEE Std C57.12.34 |
| Rated Power | 75 KVA |
| Frequency | 60HZ |
| Feed | Loop |
| Front | Dead |
| Phase | three |
| Number of core leg | 5 |
| Cooling Type | ONAN |
| Liquid insulant | Mineral Oil |
| Primary Voltage | 22.86GRDY/13.2 kV |
| Secondary Voltage | 0.48y/0.208 kV |
| Vector Group | YNyn0 |
| Winding Material | Aluminum |
| Impedance | ≥2.7% |
| Efficiency | 99.03% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | 280 W |
| On Load Loss | 1070 W |
| Accessories | Standard Configuration |
1.3 Drawings
75kVA three phase pad mounted transformer drawing and nameplate
02 Manufacturing
2.1 Core
| The 75 kVA pad-mounted transformer adopts a five-limb core design to ensure symmetrical magnetic flux paths, low noise, and reduced stray losses. This structure provides a closed path for zero-sequence flux under Y–Y connection, enhances short-circuit strength, and allows a more compact tank shape suitable for loop-feed dead-front configurations commonly used in North American distribution networks. |  |
2.2 Winding
 | The HV and LV windings are made of high-conductivity aluminum conductors, ensuring a balance between efficiency, cost, and thermal performance. The windings use layer and helical winding methods with tight dimensional tolerances to achieve excellent dielectric strength and low leakage reactance. Our experienced craftsmen are professionally trained to ensure that every winding is uniform, mechanically secure, and free from deformation or insulation damage. |
2.3 Tank
| All metal parts of the transformer tank and compartments are thoroughly cleaned and pretreated before painting to ensure strong adhesion and corrosion resistance. For additional anti-corrosion performance, the bottom 4 inches of the tank and compartment are coated with coal-tar epoxy or an equivalent heavy-duty protective coating, ensuring long-term resistance to moisture, soil, and harsh outdoor environments. |  |
2.4 Transformer Accessories and Terminals
The transformer is equipped with a pressure relief device, liquid level indicator, oil thermometer, and vacuum pressure gauge for safe operation and condition monitoring. These accessories help monitor internal pressure, oil level, and temperature to ensure reliable transformer performance.
The transformer is equipped with six 25 kV, 200 A high-voltage bushings designed for separable insulated connectors. The HV terminals are mounted in the front compartment on the left side of the LV bushings for convenient cable access and maintenance.
The low-voltage side is configured with four spade-type LV and neutral terminals rated at 208 A, each provided with four mounting holes to support secure cable termination.
2.5 Final assembly
 | Core and Windings Assembly Clean and inspect the core. Install windings, secure clamps and insulation supports.
Transformer Tank Installation Ensure the tank is clean and lift the transformer into place. Align position, adjust shims and supports, and clamp.
Transformer Accessories Installation Install lifting devices, pressure relief devices, oil level indicators, drain and sampling devices, handholes, locks, bolts, Bay-O-Net fuses, tap changer, and internal fault detector (IFD).
Oil Filling and Sealing Vacuum-fill oil to the standard level and check all seals for leaks.
Electrical Connections and Testing Complete high- and low-voltage connections, verify tap changer position, and perform insulation, voltage, grounding, and leakage tests.
Exterior and Identification Clean tank and radiators, inspect paint and anti-corrosion layers, and check nameplates, terminal markings, and wiring diagrams. |
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 |
Test Results
| No. | Test Item | Unit | Acceptance Values | Measured Values | Conclusion |
| 1 | Resistance Measurements | % | Maximum resistance unbalance rate≤5% | 1.16 | Pass |
| 2 | Ratio Tests | % | The deviation of voltage ratio on the principal tapping: ≤0.5% | -0.04~-0.02 | Pass |
| 3 | phase-relation tests | / | YNyn0 | YNyn0 | Pass |
| 4 | No-load losses and excitation current | / | I0 :: provide measured value
| 0.33% | Pass |
| P0: provide measured value
| 0.062kW | ||||
| 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 | 3.65% | ||||
| Pk: measured value | 1.168kW | ||||
| Pt: measured value | 1.230kW | ||||
| Efficiency not less than 99.03% | 99.14% | ||||
| 6 | Applied Voltage Test | kV | LV: 10kV 60s | No collapse of the test voltage occurs | Pass |
| 7 | Induced Voltage Withstand Test | kV | Applied voltage (KV): 40 | No collapse of the test voltage occurs | Pass |
| Duration(s):48 | |||||
| Frequency (HZ): 150 | |||||
| 8 | Leakage Test | kPa | Applied pressure：20kPA Duration：12h | No leakage and no Damage | Pass
|
| 9 | Insulation Resistance Measurement | GΩ | LV-HV to Ground | 85.2 | / |
| 10 | Oil Test | / | Dielectric Strength; | 56.1 kv | Pass |
| Moisture Content | 9.7 mg/kg | ||||
| Dissipation Factor | 0.00327% | ||||
| Furan Analysis | 0.03 mg/kg | ||||
| Gas Chromatography Analysis | / |
04 Packing and Shipping
05 Site And Summary
This 75 kVA three-phase pad-mounted transformer by Scotech was delivered to the U.S. in 2024. It has high efficiency, strong performance, and a sturdy design. The core and aluminum windings reduce energy loss. The safe, compact design makes installation and maintenance easy. It works well for urban and commercial power distribution and gives long-term value and reliable service.
