With the global energy transition and the continuous upgrade of grid efficiency standards, the energy performance of oil-immersed distribution transformers has become a critical factor affecting both operating costs and environmental sustainability. Based on years of experience supplying power equipment to international markets, Xinhong Electrical has observed that Chinese-manufactured S‑series oil-immersed transformers – S11, S13, S20, and S22 – are increasingly becoming the mainstream choice for overseas distribution networks, industrial/commercial projects, and renewable energy power plants, thanks to their evolving core technology, low-loss design, and reliable fully-sealed construction.
This article systematically compares the technical characteristics, efficiency levels, application scenarios, and selection strategies of these four generations, helping overseas engineers and project decision‑makers make the optimal choice.
The advancement of China’s energy efficiency standards for oil-immersed transformers (GB 20052) from Level 3 to Level 1 corresponds exactly to the technological iteration of S11 → S13 → S20 → S22. Each generation brings significant improvements in core structure, no‑load loss, load loss, and total life‑cycle cost.
Today, Xinhong Electrical has mass‑produced and exported the full range of these series. All oil-immersed transformers comply with IEC 60076 and the grid codes of target countries. Custom options such as fully‑sealed corrugated tanks and natural ester (vegetable) oil are also available.
The S11 series oil-immersed transformer is the most widely used and trusted mature product in international markets today. Its main technical features include:
Fully‑sealed corrugated tank – The transformer oil is completely isolated from the atmosphere, preventing moisture absorption and oil oxidation. This enables maintenance‑free operation, ideal for remote overseas sites or projects with high maintenance costs.
Wound core or joint‑free stacked core – High‑permeability cold‑rolled silicon steel ensures a uniform magnetic circuit, reducing no‑load current by 70–85% compared to older series (e.g., S9).
Loss advantages – No‑load loss is reduced by about 30% versus older generations, with significant improvements in load loss as well.
Dyn11 vector group – Effectively suppresses third harmonics, adapts to unbalanced loads, and improves power quality.
Typical applications:
Overseas industrial and mining facilities
Rural and urban distribution networks
Commercial buildings and residential complexes
Small to medium‑sized solar/wind power projects
Xinhong Electrical offers S11 series oil-immersed transformers in capacities from 30 kVA to 2500 kVA, supporting common overseas voltage levels such as 11 kV and 33 kV, with optional off‑circuit or on‑load tap changers.
The S13 series further refines the core technology based on S11, adopting a stepped wound coreor multi‑step joint structure. No‑load loss is reduced by more than 25% compared to S11. Under GB 20052‑2020, S13 generally corresponds to Level 3 efficiency, but optimized versions can reach Level 1 – making it an excellent choice for projects that balance initial investment and long‑term electricity costs.
Key advantages:
Lower no‑load loss – For a 630 kVA unit, no‑load loss is only 570 W, a significant reduction from the same capacity in S11.
Quieter operation – Vacuum annealing reduces noise by 7–10 dB compared to S11, suitable for residential areas or noise‑sensitive zones.
High short‑circuit withstand capability – Concentric windings provide dynamic and thermal stability meeting IEC 60076‑5.
Optional vegetable oil – Xinhong Electrical can supply S13 transformers with natural ester insulating oil, offering high fire safety and biodegradability – ideal for environmentally sensitive overseas tenders.
Recommended scenarios:
International markets with efficiency subsidies or strict准入 requirements (e.g., EU, Middle East)
Industrial parks with long annual operating hours and high electricity tariffs
Standby transformers for data centers
The S20 series represents a major innovation in Chinese oil-immersed transformer technology, classified as Level 2 efficiency under the national standard. Its core is the 3D three‑phase wound core – three identical rectangular semi‑circular wound core frames assembled into a triangular three‑dimensional structure.
Technical breakthroughs:
Perfectly symmetrical magnetic circuit – Eliminates the imbalance of planar stacked cores, reducing no‑load current by 60–80%.
Extremely low no‑load loss – For a 200 kVA unit, S20 no‑load loss is only 230 W, 26% lower than S13 (~310 W).
Material savings – Continuous winding process generates almost no waste; material utilisation approaches 100%, keeping costs under control.
Compact construction – The active part forms an equilateral triangle, small and lightweight – ideal for containerised substations or city‑centre installations.
International adaptability:
The S20 series fully complies with IEC 60076. Its low‑loss characteristics provide excellent life‑cycle economics in highly commercialised electricity markets such as Europe, Australia, and Southeast Asia.
Xinhong Electrical can equip S20 transformers with intelligent sensors (oil temperature, oil level) and IoT interfaces for easy integration into overseas digital power management systems.
If the S20 is an excellent representative of high efficiency, the S22 series represents the peak efficiency level of today’s Chinese‑made oil-immersed transformers. According to the new GB 20052‑2024 standard, S22 is a Level 1 efficiency product, with the lowest no‑load and load losses in the industry.
Parameter comparison (2000 kVA as an example):
Total loss of S22: only 14.265 kW
Total loss of S13 for the same capacity: ~19.96 kW; S20: ~15.865 kW
Load loss of S22 is reduced by more than 15% compared to S13, and by 25% compared to S11
Significant advantages:
Very low operating electricity cost – For a data centre or factory running 8,000 hours/year, thousands of kWh can be saved annually.
Low carbon footprint – Significantly reduces CO₂ emissions, helping overseas projects earn green building certifications (e.g., LEED, BREEAM).
Long life & maintenance‑free – Fully‑sealed corrugated tank with high‑quality insulating oil provides a design life of ≥30 years.
Ultra‑low noise – Measured ≤58 dB, suitable for installation in office basements or near residential areas.
Typical overseas projects:
Step‑up transformers for renewable plants (solar, wind)
Transformers for battery energy storage systems
5G base stations and edge data centres
Large commercial complexes and hospitals
Xinhong Electrical provides S22 series oil-immersed transformers with type test reports from third‑party laboratories (e.g., KEMA, CESI, or local accredited labs), fully compliant with IEC 60076 – meeting the strict technical requirements of international EPC contractors.
| Parameter | S11 Series | S13 Series | S20 Series | S22 Series |
|---|---|---|---|---|
| GB 20052 efficiency level | Level 3 | Level 3 / Level 1 (high‑end) | Level 2 | Level 1 |
| No‑load loss (200kVA example, W) | ~280 | ~310 (optimised version lower) | 230 | ~180 |
| Load loss (200kVA example, W) | ~2200 | ~2600 | 2500 | 2400 |
| No‑load loss reduction vs S11 | — | 10–15% lower | 25% lower | 35% lower |
| Core structure | Planar wound / stacked core | Stepped wound core | 3D wound core | Optimised 3D wound core |
| Typical noise level | Moderate | Relatively low | Low | Ultra‑low |
| Maintenance‑free period | 10–15 years | 15–20 years | ≥20 years | ≥25 years |
| Applicable standards | IEC 60076 | IEC 60076 | IEC 60076 | IEC 60076 |
Note: Actual values vary slightly by rating – refer to Xinhong Electrical factory test reports.
Xinhong Electrical recommends the following decision logic:
S11 – Economical & Practical
Suitable for: limited budgets, annual running time <4000 hours, or as a standby transformer. Best price/performance ratio, simple maintenance.
S13 – Balanced
Suitable for: projects needing lower no‑load loss than S11 but not yet requiring the investment of a 3D wound core. May qualify for energy efficiency subsidies in some countries.
S20 – High‑Efficiency Investment
Suitable for: annual operating time >6000 hours, high electricity tariffs (e.g., Europe, Japan). Payback period typically 3–5 years.
S22 – Premium Energy‑Saving
Suitable for: projects with clear carbon neutrality goals, long‑term ownership (>20 years), and the most demanding total cost of ownership requirements. Also future‑proofs against stricter efficiency regulations.
Additionally, consider these custom options for overseas projects:
Insulating medium – Mineral oil (standard) or natural ester vegetable oil (high fire point, biodegradable).
Protection class – IP44 or higher for dusty, humid, or coastal environments.
Tap changer – Off‑circuit (standard) or on‑load (for areas with large voltage fluctuations).
Monitoring interface – Integrated sensors for oil temperature, oil level, winding temperature, partial discharge, etc.
Full range of high‑efficiency certifications – From S11 to S22, all transformers pass authoritative tests; we provide compliance reports to IEC/ANSI/IEEE standards.
Fully‑sealed maintenance‑free design – Every oil-immersed transformer comes standard with a corrugated tank or expansion radiator, solving the headache of difficult on‑site maintenance for overseas projects.
Mature natural ester (vegetable oil) application – Hundreds of vegetable oil transformers have been exported to Europe and Southeast Asia, meeting both fire safety and environmental requirements.
Smart‑grid ready – Supports MODBUS, IEC 61850 and other protocols for easy integration into smart grids.
Fast response & global logistics – We provide customised drawings, English technical documentation, and one‑stop customs coordination for overseas projects.
From S11 to S22, from planar cores to 3D wound cores – Xinhong Electrical is committed to delivering reliable, efficient, and green oil-immersed transformer solutions to customers worldwide. Whether you are an EPC contractor, a distribution network operator, or an industrial end‑user, we can match you with the optimal efficiency level and cost combination.
For detailed technical data sheets or project‑specific quotations for S11 / S13 / S20 / S22 series oil-immersed transformers, please visit the Xinhong Electrical official website or contact our technical team directly.
