Precision Engineered for Peak Performance – Substation Transformers.
01 General
1.1 Project Description
3750/4250 kVA substation transformer was delivered to America used for Balling Building, ASB & Bin&Mixing in 2025. The rated power of the transformer is 3750/4250 kVA with KNAN/KNAF cooling. The primary voltage is 13.8 kV with ±2*2.5% tapping range (NLTC), the secondary voltage is 0.48/0.277 kV, and they formed a vector group of Dyn1.
Our unit substation transformer is a robust and intelligent power solution designed for superior performance and reliability in modern electrical grids. Equipped with a pressure vacuum gauge, liquid level gauge (with alarm contacts), and liquid temperature indicator, it ensures continuous monitoring of critical parameters for safe operation. Advanced protection features such as a pressure relief device, fault pressure relay, and lightning arrester safeguard against internal faults and external surges. An optimized cooling system with fans and radiators maintains thermal stability, while integrated marshalling box and CT box enable seamless control and measurement. For enhanced mobility, wheels facilitate easy installation and positioning. Engineered for durability and efficiency, this transformer delivers uninterrupted power distribution for utilities, industries, and renewable energy systems-where innovation meets reliability.
1.2 Technical Specification
3750/4250 kVA substation transformer specifications type and data sheet
| Delivered to | America |
| Year | 2025 |
| Type | Substation transformer |
| Standard | ANSI C57.12.00 |
| Rated Power | 3750/4250 kVA |
| Frequency | 60HZ |
| Phase | 3 |
| Cooling Type | KNAN/KNAF |
| Primary Voltage | 13.8 kV |
| Secondary Voltage | 0.48/0.277 kV |
| Winding Material | Copper |
| Angular displacement | Dyn1 |
| Impedance | 7% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | ≤3.5kW |
| On Load Loss | ≤29.8kW |
1.3 Drawings
3750/4250 kVA substation transformer diagram drawing and size.
02 Manufacturing
2.1 Core
The substation transformer core is constructed from high-grade, grain-oriented silicon steel laminations, meticulously stacked to minimize eddy current losses and ensure optimal magnetic flux distribution. The laminated design significantly reduces hysteresis loss, while the step-lap joint configuration enhances mechanical stability and noise reduction. Each core is precision-engineered to provide low no-load current, high permeability, and exceptional thermal performance, ensuring efficient energy transfer even under heavy load conditions. The core’s robust structure is further insulated with a durable coating to prevent short-circuiting, delivering long-term reliability in demanding power distribution applications.
2.2 Winding
 | The low-voltage winding utilizes precision-engineered foil-wound construction to achieve excellent current distribution, mechanical strength, and thermal dissipation. Meanwhile, the high-voltage winding adopts layer-wound copper conductors with interleaved insulation paper, ensuring superior dielectric strength and short-circuit resistance. Both windings incorporate radial cooling ducts and transposition techniques to minimize eddy current losses, guarantee long-term reliability under heavy loads and harsh operating conditions. |
2.3 Tank
| The tank is constructed from high-strength welded steel plates with anti-corrosion treatment, ensuring robust mechanical protection and long-term durability. Tank design incorporates reinforced ribs and lifting lugs for enhanced rigidity and safe handling during installation. The tank features a fully sealed construction with gasketed bolted covers, preventing oil leakage while allowing easy access for maintenance. Internally, it houses strategically positioned baffle plates to optimize oil circulation and heat dissipation, while external radiators or cooling fins are integrated for efficient thermal management. Special provisions such as grounding terminals, oil sampling valves, and corrosion-resistant paint finish comply with IEEE standards, making it adaptable to harsh outdoor environments. |  |
2.4 Final Assembly
 | The substation transformer undergoes a precision assembly process that integrates the core, windings, tank, and accessories into a unified system. The grain-oriented silicon steel core is first assembled with pre-insulated laminations, then precisely aligned with the LV foil and HV layer windings. The windings undergo thorough drying treatment to ensure optimal insulation performance before being mounted onto the core. The core-coil assembly is then carefully lowered into the corrosion-resistant steel tank, where cooling radiators, bushings, and control boxes are installed. Critical components such as the pressure relief device, temperature gauges, and marshalling boxes undergo final wiring and functional testing. The fully assembled unit receives vacuum oil filling, followed by rigorous tests. |
03 Testing
| No. | Test Item | Unit | Acceptance Values | Measured Values | Conclusion |
| 1 | Resistance Measurements | % | Maximum resistance unbalance rate | 5.61 | Pass |
| 2 | Ratio Tests | % | The deviation of voltage ratio on the principal tapping: ≤0.5% | -0.18~-0.10 | Pass |
| 3 | Phase-relation tests | / | Dyn1 | Dyn1 | Pass |
| 4 | No-load losses and excitation current | % | I0 :: provide measured value | 0.24 | Pass |
| kW | P0: provide measured value | 3.053 | |||
| / | the tolerance for no load loss is +0% | / | |||
| 5 | Load losses , impedance voltage, total losses and efficiency | / | t:85℃ the tolerance for impedance is +7.5% the tolerance for total load loss is +0% | / | Pass |
| % | Z%: measured value | 7.48 | |||
| kW | Pk: measured value | 29.277 | |||
| kW | Pt: measured value | 32.330 | |||
| % | Efficiency not less than 99.34% | 99.36 | |||
| 6 | Applied Voltage Test | / | HV:34kV 60s LV: 10kV 60s | No collapse of the test voltage occurs | Pass |
| 7 | Induced Voltage Withstand Test | / | Applied voltage (KV):0.96 | No collapse of the test voltage occurs | Pass |
| Duration(s):40 | |||||
| Frequency (HZ): 180 | |||||
| 8 | Insulation Resistance Measurement | GΩ | HV-LV to Ground: | 8.43 | Pass |
| LV-HV to Ground: | 3.97 | ||||
| HV&LV to Ground: | 8.16 | ||||
| 9 | Leakage Test | / | Applied pressure：50kPA | No leakage and no Damage | Pass |
| Duration：12h | |||||
| 10 | Temperature-rise test | K | Top oil ≤45K Winding average≤50K | 42.96 47.70 48.70 | Pass |
| 11 | Oil Test | kV | Dielectric Strength Measured value ≥ 45 kV | 56.7 | Pass |
| mg/kg | Moisture Content | 183.2 | |||
| % | Dissipation Factor | 3.654 | |||
| mg/kg | Furan Analysis | / | |||
| / | Gas Chromatography Analysis | / |
04 Packing and Shipping
4.1 Packing
The substation transformer is securely packaged in a custom-built wooden crate designed for optimal protection during transit and storage. The heavy-duty timber frame is constructed with reinforced corners and steel banding to withstand rigorous handling. Critical components (bushings, gauges, valves) are individually wrapped with shock-absorbing foam and moisture-resistant materials before being secured within the crate. The transformer body is mounted on a steel skid base inside the wooden enclosure, with vibration-damping pads placed at all load-bearing points. The crate features removable panels for inspection while maintaining structural integrity, and includes desiccant packs to control humidity. Exterior markings clearly display handling instructions, center of gravity warnings, and international shipping symbols in compliance with ISPM 15 regulations.
4.2 Shipping
The substation transformer, securely packed in a custom wooden crate, will be transported under CIF (Cost, Insurance, and Freight) terms to the Port of Minneapolis. The shipment process begins with loading the crated transformer onto a heavy-duty truck using forklifts at the manufacturing facility, ensuring proper weight distribution and securing with anti-slip fastenings. The truck then delivers the unit to the departure port, where it is carefully loaded into an ISO-standard open-top or flat-rack container for ocean freight. Throughout the voyage, the container will be monitored for shocks, tilt, and humidity, with marine insurance covering all risks until arrival at Minneapolis. The buyer assumes responsibility for customs clearance and final inland delivery upon the transformer’s discharge at the destination port.
05 Site And Summary
As the heart of power systems, our Substation Transformers deliver unmatched reliability, innovative engineering, and rigorous quality standards to enable efficient energy conversion worldwide. From precision manufacturing to smart protection systems, from stringent testing to secure logistics, we ensure every unit operates flawlessly under demanding conditions.
Whether for grid modernization or renewable integration, our transformers stand as your trusted partner. Powering the future, we illuminate the world together.
Contact us for customized solutions – let’s energize progress!
