Unit Substation Transformer – Integrated, efficient, and the heart of reliable power distribution.
01 General
1.1 Project Description
1500 kVA unit substation transformer was delivered to USA in 2025. The rated power of the transformer is 1500 kVA with KNAN cooling. The high voltage is 5D kV with ±2*2.5% tapping range (NLTC), the low voltage is 0.48Y/0.277 kV, they formed a vector group of Dyn1.
The electrical substations are compact power distribution devices that integrate primary switchgear, a three-phase power transformer, and secondary distribution equipment into a single, close-coupled assembly. It is designed to step down utility distribution voltages to levels suitable for in-plant or commercial building distribution, and is suitable for both indoor and outdoor installations. With its close-coupled design, the transformer can be placed near the load center, significantly reducing cable and busway lengths, which in turn lowers line losses and exposure to faults while improving voltage regulation and service continuity. Compared to conventional substation layouts, its compact footprint saves substantial installation space, reduces on-site construction and transportation costs, and lowers long-term maintenance expenses through simplified accessories. The unit substation transformer fully complies with ANSI, IEEE, and NEMA standards, ensuring complete electrical and mechanical coordination. As an option, the transformer can be filled with FR3™ natural ester fluid-a renewable, vegetable-oil-based dielectric with a high fire point and excellent environmental properties-while conventional mineral oil remains available for applications with standard requirements. With its high reliability, efficiency, and flexible configuration, the unit substation transformer is widely used in industrial facilities, commercial buildings, utility substations, and critical infrastructure networks where space, safety, and performance are essential.
1.2 Technical Specification
1500 kVA electrical substations specifications type and data sheet
| Delivered to | USA |
| Year | 2025 |
| Type | unit substation transformer |
| Standard | IEEE |
| Rated Power | 1500 kVA |
| Frequency | 60HZ |
| Phase | 3 |
| Cooling Type | KNAN |
| Primary Voltage | 5D kV |
| Secondary Voltage | 0.48Y/0.277 kV |
| Winding Material | Copper |
| Vector Group | YNyn0 |
| Impedance | 5.75%±7.5% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | 1.545 kW |
| On Load Loss | 10.54 kW |
1.3 Drawings
1500 kVA electrical substations diagram drawing and size.
02 Manufacturing
2.1 Core
| Core uses CRGO silicon steel, perfectly matched to 1500kVA, 5.0/0.48kV, Dyn1, 60Hz (no‑load loss 1.545kW, load loss 10.540kW). Design & manufacturing comply with IEEE C57.12.34-2022, C57.12.00-2021 & C57.12.90-2021. Tests confirm: max turns ratio deviation +0.16% (well below 0.5%), losses and impedance meet guaranteed values. Quality: five‑step step‑lap process reduces eddy losses and noise; core clamped and coated against moisture/rust. Highlights: step‑lap cuts no‑load current ~12% and transverse leakage >50%; 45° mitered joints smooth flux steering. |  |
2.2 Winding
 | HV winding with 2×2.5% on‑load taps (5 taps), LV Y‑connected 480V/277V + neutral. Test results (see table below) show LV resistance unbalance 1.11%, HV max unbalance 0.80%; insulation resistance & magnetic balance all passed. Quality: high‑purity copper, Class F (155°C) insulation, vacuum vapour‑phase drying. Highlights: continuous/interleaved HV design, foil/helical LV windings, reinforced end clamping for short‑circuit withstand.
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2.3 Tank
Tank designed with stiffeners; tested at +50kPa and -67kPa. Results (see tables): after release, permanent deflection ≤0.03mm at all 10 points, no damage – both tests passed. Quality: high‑grade steel, 100% weld inspection, separate pressure test before assembly. Highlights: optimised rib layout, controlled welding heat input, gasket design against oil leakage & moisture ingress.
Positive pressure test (50kPa):
| Point | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| Initial (mm) | 1.50 | 1.50 | 1.50 | 1.50 | 1.30 | 1.50 | 1.50 | 1.50 | 1.20 | 1.50 |
| After pressure applied (mm) | 2.19 | +3.00 | +3.00 | 2.72 | 2.10 | 1.72 | 2.07 | 1.94 | 2.15 | 1.98 |
| After pressure released (mm) | 1.51 | 1.52 | 1.52 | 1.51 | 1.51 | 1.51 | 1.51 | 1.52 | 1.52 | 1.50 |
| Permanent deflection (mm) | 0.01 | 0.02 | 0.02 | 0.01 | 0.01 | 0.01 | 0.01 | 0.02 | 0.02 | 0.02 |
Vacuum test (-67kPa):
| Point | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
| Initial (mm) | 1.51 | 1.52 | 1.52 | 1.51 | 1.51 | 1.51 | 1.51 | 1.52 | 1.52 | 1.52 |
| After vacuum applied (mm) | 0.71 | -0.00 | -0.00 | -0.00 | 0.78 | 1.12 | 0.89 | 1.01 | 0.85 | 0.92 |
| After vacuum released (mm) | 1.49 | 1.49 | 1.50 | 1.48 | 1.49 | 1.49 | 1.49 | 1.49 | 1.49 | 1.50 |
| Permanent deflection (mm) | 0.02 | 0.03 | 0.02 | 0.03 | 0.02 | 0.02 | 0.02 | 0.03 | 0.03 | 0.01 |
2.4 Final Assembly
 | Assembly: core‑coil lowering, vacuum oil treatment, bushing/accessory installation, Dyn1 lead configuration. Semi‑finished tests (after drying, before tanking) all passed: insulation resistance, turns ratio (max dev. 0.16%), phase relation (Dyn1), winding resistance, impedance (5.75%), magnetic balance. Quality: each step recorded, oil vacuum‑filtered, tap‑changer operation verified. Highlights: vacuum drying & impregnation, precision jigs for core‑tank clearance, torque‑wrench tightening of all connections. |
03 Testing
Tests cover electrical, mechanical & insulation performance per IEEE C57.12.00-2021 & C57.12.90-2021.
| Test Item | Test Result | Conclusion |
| Insulation resistance (HV‑GND, LV‑GND, HV‑LV, core‑frame) | Pass | Pass |
| Turns ratio deviation | <0.2% per tap | Pass |
| Phase relation | Dyn1 | Correct |
| Winding resistance unbalance | LV 1.11%, HV 0.80% | Excellent |
| Short‑circuit impedance | 5.75% | Meets guaranteed value |
| Magnetic balance test | 3‑phase voltage balanced | Pass |
| Positive pressure test (50kPa) | Permanent deflection ≤0.02mm | Pass |
| Vacuum test (-67kPa) | Permanent deflection ≤0.03mm | Pass |
| Tank visual inspection | No damage | Pass |
04 Packing and Shipping
4.1 Packing
| Custom wooden crates, ISPM15 heat‑treated wood for customs clearance without fumigation. Reliability verified by pre‑shipment inspection & vibration simulation. Quality: six‑way strapping + anti‑slip pads (movement <2mm), cushioning material, moisture/rust protection. Highlights: centre of gravity & lifting points marked, 100% pre‑pack inspection, spare parts in same crate. |  |
4.2 Shipping
 | Sea/land transport matched to destination; traceable via contract & serial numbers. Follows Incoterms & export regulations; pre‑shipment inspection satisfies customs. Reliability validated by vibration simulation. Quality: weather‑proof “do not tip/drop” labels, loading inspection, full shipping documents & COO. Highlights: eco‑friendly materials, shock indicators on large units, packing list/weight list/dimension drawing provided. |
05 Site And Summary
In summary, this 1500kVA electrical substations delivers exceptional electrical performance, proven mechanical robustness, and full compliance with IEEE C57.12.34-2022. With core and winding losses meeting guaranteed values, voltage ratio deviation below 0.2%, winding resistance unbalance as low as 1.11%, and tank permanent deformation under pressure/vacuum tests limited to ≤0.03mm, it offers a reliable, low life‑cycle cost solution. Rigorous semi‑finished and final testing – from insulation resistance to magnetic balance and tank deformation – ensures every unit leaves the factory ready for demanding utility applications. Choose SCOTECH as your trusted partner to build a smarter, more resilient electrical infrastructure.
