Against the backdrop of global efforts to promote energy saving, emission reduction, and carbon neutrality, distribution transformers – as the most fundamental equipment in power systems – have seen their energy efficiency become a focal point of international attention. In recent years, major economies worldwide have successively introduced mandatory minimum energy performance standards for distribution transformers.

China has accordingly updated its national standard GB 20052 Minimum allowable values of energy efficiency and energy efficiency grades for three-phase distribution transformers, imposing stricter requirements on both no‑load loss and load loss. The upgrading of transformer energy efficiency grades directly drives continuous improvement in the performance of core materials.

 

In this context, Baosteel's independently developed low‑iron‑loss grain‑oriented silicon steel grades B18R065 and B20R070, with their excellent electromagnetic properties and stable processing characteristics, have been successfully applied in the volume production of Tier 1 energy‑efficient distribution transformers.

 

As an authorised channel partner of Baosteel, GNEE Steel can stably supply both of these grades of grain‑oriented silicon steel, offering transformer manufacturers an efficient and reliable material solution.

 

This article systematically presents the development principles, performance parameters, and practical application results of these two products, providing a reference for transformer manufacturers in material selection and design.

 

 

1. Overview of High‑Efficiency Distribution Transformer Development

In recent years, to effectively reduce power losses in transmission and distribution and cut CO₂ emissions, major countries and regions have successively issued or revised mandatory high‑efficiency distribution transformer standards:

• Japan has implemented the "Top Runner Program" since 2014, continuously raising the efficiency benchmarks for transformers;
• The European Union enforced the Ecodesign Regulation – Tier 2 for transformers in 2021, setting higher thresholds for no‑load and load losses;
• The United States implemented a new DOE standard for distribution transformers in 2024, comprehensively upgrading efficiency requirements;
• China has repeatedly revised GB 20052, adding energy efficiency grades, raising the minimum allowable values, and classifying transformers into three grades: Tier 1, Tier 2, and Tier 3.

 

Manufacturing energy‑saving distribution transformers requires not only advanced design concepts and sophisticated production equipment, but also high‑quality core materials. At present, transformer cores mainly use thin‑gauge grain‑oriented silicon steel and iron‑based amorphous alloys. Although amorphous alloys exhibit extremely low no‑load loss, they have limitations in terms of producible width, toughness, moisture resistance, and magnetostriction, which affect quality consistency and general applicability.

 

In the field of grain‑oriented silicon steel, leading international producers such as Nippon Steel have introduced grades 23ZDKH075 and 20ZDKH070, while JFE offers 20JCSE070. Domestically, Baosteel, after more than ten years of independent R&D, has fully mastered the entire process technology for grain‑oriented silicon steel and built a complete product family covering thicknesses from 0.18 mm to 0.35 mm.

 

Among these, the thin‑gauge premium grades have achieved stable volume production and have been successfully applied in Tier 1 energy‑efficient distribution transformers. Baosteel has thus become one of the very few global producers capable of simultaneously supplying 0.20 mm and 0.18 mm high‑permeability grain‑oriented silicon steel in volume.

 

2. Principles of Material Development

The typical thicknesses of grain‑oriented silicon steel are 0.23 mm, 0.27 mm, and 0.30 mm, with a silicon content of about 3.0 %. The microstructure exhibits a strong Goss texture, with the easy magnetisation direction aligned parallel to the rolling direction, resulting in high magnetic induction along the rolling direction. During magnetisation, magnetic domains are formed, and the surface insulating coating serves both electrical insulation and magnetic domain refinement.

 

 

The main technical approaches to reducing iron loss in grain‑oriented silicon steel include three aspects:Improve the grain orientation degree; the product surface is smooth without base coating; the thickness is reduced to 0.15~0.20 mm, and the silicon content is increased to 3.4%~3.5%.

Core loss consists of hysteresis loss (\(P_h\)), eddy current loss (\(P_e\)) and anomalous loss (\(P_a\)): • Hysteresis loss: affected by crystal structure, impurities, internal stress, grain size and other factors; • Eddy current loss: strongly correlated with sheet thickness, with the formula expressed as

Anomalous loss: the residual portion of total core loss after deducting the above two losses.

Total eddy current loss considering anomalous loss:

Hysteresis Loss Formula:

Total Loss Formula:

Thickness reduction can lower eddy current loss and total core loss, whereas domain refinement will increase hysteresis loss.

Meanwhile, sheet thinning tends to cause unstable secondary recrystallization, strip breakage during production and other defects, which requires strict control over chemical composition and the entire manufacturing process.

 

3. Performance of New Products B18R065 and B20R070

Baoshan Iron & Steel has developed low-core-loss grades B18R065 and B20R070 by adopting technologies including innovative chemical composition control, induction heating, high-tension coating and laser scribing:

 

The electromagnetic properties of B20R070 are basically equivalent to foreign 0.2 mm 070-grade products.

 

Mechanical property comparison: No significant differences exist between B18R065, B20R070 and B23R075. The shearing process shall be strictly controlled to guarantee processing quality.

 

Table 1 Mechanical Property Indicators of Thin-Gauge Grain-Oriented Electrical Steel

Grade	Tensile Strength (Longitudinal) / MPa	Yield Strength (Longitudinal) / MPa	Elongation (Longitudinal) / %	HV1
B23R075	352	330	12	200
B20R070	348	327	11	192
B18R065	345	322	14	189

 

4. Application Advantages of B18R065 and B20R070 in High‑Efficiency Transformers

 

GB 20052 is a mandatory national standard that requires significant reductions in no-load loss and load loss, making ultra-low core-loss electrical steel the optimal material choice.

 

Taking the optimized design of a 630 kVA energy-saving distribution transformer as an example: upgrading the grain-oriented electrical steel grade allows the transformer to be designed with a higher magnetic flux density, which reduces the cross-sectional area of the iron core.

 

This further cuts down the weight of windings, transformer tanks, insulating oil and other components, resulting in a more compact overall structure and a 3%~4% improvement in cost performance. Therefore, B18R065 and B20R070 serve as the preferred core materials for high-efficiency transformers.

 

5. User Application Performance

 

Test results of Class 1 energy efficiency distribution transformer Model S-M-315/10-NX1 developed in cooperation with transformer manufacturers:

• B18R065: Its no-load loss is 13% lower than the standard value, with a noise level of only 42 dBA. All technical indicators exceed the specified standard requirements.
• B20R070: Its electromagnetic performance is equivalent to that of imported 0.2 mm grade 070 electrical steel.

Table 2 Test Parameters of S-M-315/10-NX1 Class 1 Energy Efficiency Distribution Transformer with Different Core Materials

Core Material Grade	No-Load Loss / W		Load Loss / W		No-Load Current / %		Noise Level / dBA
	Standard	Measured	Standard	Measured	Standard	Measured	Standard	Measured
B18R065	340	298301	3065	29462931	0.35	0.21	48	4142
B20R070	340	329332	3065	29452877	0.35	0.190.21	48	-
Imported 0.2 mm Grade 070	340	325327	3065	29632960	0.35	0.150.16	48	-

 

6. Conclusions and Outlook

The continuous upgrading of mandatory high‑efficiency distribution transformer standards worldwide has become a key driver for the ongoing improvement of core material performance. The successive revisions of China's GB 20052 explicitly guide transformer manufacturing towards lower losses and higher reliability, creating broad application opportunities for thin‑gauge premium grain‑oriented silicon steels.

 

With its fully self‑developed process technology, Baosteel's B20R070 and B18R065 grades have reached internationally advanced levels and have achieved volume application in Tier 1 energy‑efficient distribution transformers. In particular, transformers using B18R065 have demonstrated no‑load losses more than 13 % below the standard limit, marking a significant breakthrough for domestic materials in high‑grade energy‑efficient transformer applications. Baosteel has become the world's first producer capable of simultaneously supplying 0.20 mm and 0.18 mm high‑permeability grain‑oriented silicon steel in volume.

 

Looking ahead, Baosteel will continue to expand the production capacity of 0.20 mm and 0.18 mm thin‑gauge grain‑oriented silicon steels, further improve product consistency and surface quality, and accelerate the development of next‑generation products with even lower iron loss and higher magnetic induction, providing stronger material support for ongoing transformer efficiency upgrades.

 

 

GNEE Steel, as an authorised distributor of Baosteel grain‑oriented silicon steel, maintains long‑term stock of the full range of thin‑gauge high‑permeability grades, including B18R065 and B20R070. We offer slitting, shearing, and other processing services, backed by professional technical support. We welcome all transformer manufacturers to enquire or visit our facility. We are committed to providing you with high‑quality products and satisfactory service.

 

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