S11-1250kva/11/0.4KV Three-Phase Low-Loss Oil-immersed Transformer
May 21, 2026
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At GNEE, we are a direct manufacturer of oil-immersed and dry-type transformers, serving power utilities, EPC contractors and industrial users worldwide since 2008. Our modern production workshops and strict quality control ensure every unit meets IEC 60076 standards.
Today, we focus on our most trusted product: the 1250kVA/11/0.4KV three phase oil-immersed transformer. This medium-capacity power transformer is widely used in utility substations, industrial power distribution systems, commercial buildings and renewable energy projects. Designed with all-copper windings, ultra-low losses and a PEI of 99.61%, this transformer delivers stable performance, strong overload capacity and long service life.
Technical Specifications – 1250kVA Three Phase Oil-Immersed Transformer
The 1250kVA three phase oil-immersed transformer steps down primary voltage at 11kV to secondary voltage at 0.4kV (400V) - the standard level for industrial equipment. Below are its key parameters:
| Parameter | Specification |
|---|---|
| Rated Capacity | 1250 kVA |
| Phase | Three-phase |
| Primary Voltage | 11 kV |
| Secondary Voltage | 0.4 kV (400V) |
| Frequency | 50/60 Hz |
| Vector Group | Dyn11 (customizable) |
| Impedance Voltage | 4% – 4.5% |
| Winding Material | All-copper (high-purity oxygen-free copper) |
| Core Material | Grain-oriented silicon steel |
| Cooling Method | ONAN |
| Insulation Medium | Mineral oil (No.25/45) |
| PEI | ≥ 99.61% |
| Dimensions (L×W×H) | 1800 × 1560 × 1650 mm |
| Net Weight | ~3500 kg |
This 0.4KV three phase oil-immersed transformer efficiently powers industrial plants, commercial complexes and residential communities.
Core Components of a High-Efficiency 1250kVA Oil-Immersed Transformer
Understanding the components explains why this 1250kVA oil-immersed transformer achieves such high performance.
High-Quality Silicon Steel Core
The iron core is the magnetic circuit. It is made of grain-oriented cold-rolled silicon steel sheet with step-lap core technology, which minimizes no-load loss, no-load current and noise. This contributes directly to the ultra-low losses and 99.61% PEI rating.
All-Copper Windings – Key to Low Losses
The windings are the electrical circuit. This 1250kVA three phase oil-immersed transformer uses all-copper windings for both HV and LV sides. Copper offers lower resistivity than aluminum, resulting in substantially reduced load losses (I²R losses). Copper windings also provide superior short-circuit withstand strength and allow short-term overload to 150% of rated capacity for up to two hours.
Oil Tank, Cooling System and Accessories
- Tank: Wide-steel plate construction with a folded design minimizes welding seams and prevents oil leakage.
- Cooling: ONAN (Oil Natural Air Natural) with wide-plate radiators.
- Accessories: Oil conservator, bushings, tap changer (off-circuit or on-load), Buchholz gas relay, pressure release valve, Pt100 temperature monitor and oil level gauge. These ensure safe, reliable and maintenance-friendly operation.
Advantages of the 0.4KV Three Phase Oil-Immersed Transformer
Ultra-Low Loss Design
The combination of a high-quality silicon steel core and all-copper windings yields no-load and load losses significantly lower than conventional designs. For S13 series models, typical no-load loss is ~855W and load loss ~9500W.
Exceptional Efficiency – PEI 99.61%
With a PEI of 99.61%, this 0.4KV oil-immersed transformer exceeds European ecodesign Tier 2 energy efficiency regulations. Higher efficiency means lower operating costs and reduced carbon footprint over its 25+ year life.
Strong Short-Circuit Withstand and Moisture Resistance
The robust cylindrical winding structure ensures balanced ampere-turn distribution, minimizing mechanical stresses during short-circuit events. The hermetically sealed IP65 design is dustproof and moisture-proof, requiring minimal maintenance.
Conclusion – Your Reliable Power Solution
The 1250kVA/11/0.4KV three phase oil-immersed transformer combines all-copper windings, ultra-low losses and a robust oil-immersed design to deliver reliable, efficient power distribution. With a PEI of 99.61% and overload capacity to 150%, it is the optimal choice for industrial and commercial applications.
📞 Ready to order your 1250kVA three phase oil-immersed transformer?
Contact GNEE today for a competitive quote, technical datasheet and free consultation.
What is the current of 1250 kVA transformer?
Therefore, 1250kva transformer allows 1804A current to work for a long time, and the maximum continuous current is so large, but it is allowed to overload for a short time, and the overload is related to the overload time.
What is the impedance of a 1250 kVA transformer?
Key specifications include copper windings, maximum losses of 1850/11000 watts, 6.15% impedance, and maximum temperature rises of 45/55 degrees Celsius. The transformer has three limbs and uses spiral and continuous disc winding designs.
What is the load capacity of a 1250 kVA transformer?
The weight of the 1250 kVA transformer is 11,090 lbs. The load loss at rated voltage is less than 12,000W, and the no-load losses are less than 2,000W. The efficiency of the 1250 kVA transformer is 99.24%.
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