Driven by the global “carbon peak and carbon neutrality” goals, China’s energy efficiency standard system for power transformers is evolving at an unprecedented pace. On April 29, 2024, the State Administration for Market Regulation and the National Standardization Administration jointly released the new GB 20052-2024 “Minimum allowable values of energy efficiency and energy efficiency grades for power transformers” , which came into effect on February 1, 2025, replacing the previous GB 20052-2020 standard. As core equipment in the power industry, the energy efficiency of power transformers directly affects the overall energy consumption of transmission and distribution systems. This article systematically reviews the energy efficiency grading system under the new national standard and provides insights into the application and selection of high-efficiency energy-saving transformers.
GB 20052-2024 is the only mandatory energy efficiency standard for power transformers at the national level. Previously, the National Development and Reform Commission and the State Administration for Market Regulation had included power transformers in the catalogue of energy efficiency label products, requiring all products on the market to bear a unified energy efficiency label and complete registration. The release of the new standard further strengthens the market access threshold for power transformers and provides a clear technical basis for promoting green transformation in the industry.
The scope of GB 20052-2024 has been significantly expanded compared to the previous version. The new standard covers the following three categories: three-phase 10kV voltage class, oil-immersed distribution transformers and dry-type distribution transformers with rated capacities from 30kVA to 2500kVA; oil-immersed power transformers with voltage classes from 35kV to 500kV and rated capacities of 3150kVA and above; and three-phase 6kV to 35kV transformers for new energy power generation (photovoltaic, wind power, energy storage). In addition, three-phase 66kV voltage class transformers with rated capacities from 3150kVA to 20000kVA for new energy power generation are newly added. The new standard excludes gas-filled transformers, tower-mounted transformers and nacelle transformers.
According to GB 20052-2024, the energy efficiency of power transformers is uniformly divided into three grades, with Grade 1 being the highest, corresponding to the lowest no‑load and load losses. The measured no‑load loss and load loss of each grade at rated capacity must not exceed the limits specified in the standard’s appendix. For capacity ratings not listed, linear interpolation is applied.
Grade 1 energy efficiency: Represents the most advanced energy-saving technology in China’s transformer market, with the lowest no‑load and load losses. Products of this grade offer the most significant energy-saving effect over long‑term operation and outstanding life‑cycle cost advantages. They are widely used in high‑demand scenarios such as data centers, new energy power stations and key State Grid projects.
Grade 2 energy efficiency: A balanced grade between Grade 1 and Grade 3, achieving a good trade‑off between loss control and manufacturing cost. Suitable for general industrial and commercial power distribution projects, it is the mainstream product grade in the market, combining energy-saving benefits with economic feasibility.
Grade 3 energy efficiency: The minimum mandatory market access level, with no‑load and load losses higher than those of higher grades. It can be used in budget‑limited or low‑load applications, but the total cost of ownership over the long term may not be lower. It is gradually being replaced by higher‑efficiency products.
It should be noted that there is a direct correspondence between energy efficiency grades and transformer model designations, but the model alone does not absolutely guarantee the grade. Purchasers should always rely on actual test reports.
Grade 1 oil‑immersed transformers are represented by the S22 series, covering voltage classes from 10kV to 35kV. The S22 series adopts optimised core and winding designs to effectively reduce core loss, winding loss and tank stray loss. The core uses high‑grade cold‑rolled grain‑oriented silicon steel to achieve ultra‑low loss characteristics with refined magnetic circuit design. For example, the S22‑M‑50/10‑NX1 model has a total loss of only 0.678kW, while the S22‑M‑400/10‑NX1 model has a total loss of 3.427kW.
Grade 2 oil‑immersed transformers are represented by the S20 series, which strikes an ideal balance between loss control and manufacturing cost, suitable for most industrial and commercial distribution applications.
Grade 3 oil‑immersed transformers are represented by the S13 series. Notably, under the new GB 20052-2024 standard, the S13 type has been downgraded from Grade 2 under the previous standard to Grade 3, now an entry‑level product that only meets basic operational requirements. For companies seeking long‑term energy savings, Grade 1 or Grade 2 products are strongly recommended.
For dry‑type transformers, Grade 1 is represented by the silicon‑steel SCB18 series and the amorphous‑alloy SCBH19 series. The SCB18‑800kVA dry‑type transformer, built with epoxy resin cast windings, offers excellent insulation and moisture resistance, effectively withstanding harsh environments such as humidity and dust. It also features strong overload capacity and flame‑retardant properties, making it ideal for commercial buildings, industrial plants, data centers, subways and airports – places where space is valuable and high power supply reliability is required.
Grade 2 dry‑type transformers are represented by the SCB14 series. Grade 3 is represented by the SCB13 series; similarly to oil‑immersed products, SCB13 is now classified as an entry‑level Grade 3 product under the new standard.
Correctly identifying transformer energy efficiency grades is crucial for users. Some manufacturers sell products with “positive deviation” – the declared model corresponds to a certain grade, but the actual losses are higher than the standard limits due to “marginal design” plus manufacturing tolerances. Therefore, when selecting a transformer, in addition to the model, always check the factory energy efficiency test report and the national unified energy efficiency label, and choose a reliable supplier with a complete technical certification system. Xinhong Electrical consistently adheres to high production standards. All our products are designed, manufactured and tested strictly in accordance with GB 20052-2024, ensuring that no‑load loss and load loss fully meet or exceed the standard limits, providing customers with reliable power transformer products.
A key revision in GB 20052-2024 compared to the previous version is the addition of energy efficiency limit requirements for 6kV, 10kV, 35kV and 66kV transformers used in new energy power generation (photovoltaic, wind power, energy storage) . The new standard formally brings these wind, solar and storage‑supporting transformers – previously not covered by the energy efficiency management system – into the framework, providing a unified technical basis for production, procurement and application.
In terms of specific technical requirements, taking a 35kV oil‑immersed new energy generation transformer as an example: Grade 3 no‑load loss is reduced by 30% compared to the same model under GB 6451-2015; Grade 2 further reduces both no‑load and load losses by 5% relative to Grade 3; Grade 1 further reduces no‑load loss by 10% while keeping load loss the same as Grade 2 – comprehensively pushing new energy supporting power equipment towards higher efficiency.
This expansion accurately responds to China’s rapidly growing new energy installed capacity and the fast development of energy storage, marking a milestone in the standardisation and energy‑saving promotion of new energy grid‑connected supporting power equipment.
China’s transformer industry continues to expand. According to statistics, the output value of China’s transformer industry exceeded RMB 300 billion in 2025, accounting for more than 50% of global production. The proportion of energy‑saving transformers in operation increased by 10 percentage points compared to 2020. At the same time, the total in‑service capacity of power transformers nationwide is approximately 16,000 GVA, with annual electrical energy losses of about 250 billion kWh, accounting for roughly 40% of the country’s transmission and distribution losses – representing significant potential for efficiency improvement.
On the policy front, the National Development and Reform Commission and the National Energy Administration have clearly required that by 2025, grid companies must completely phase out old high‑loss distribution transformers such as S7 and S8 types, as well as products that have been in operation for more than 25 years and fail to meet the market access level. The proportion of energy‑saving and higher‑grade transformers in operation nationwide must increase by more than 10 percentage points compared to 2021. The recently issued “Implementation Plan for High‑Quality Development of Energy‑Saving Equipment (2026–2028)” by four ministries including the Ministry of Industry and Information Technology further proposes that by 2028, the proportion of newly added energy‑saving transformers should exceed 75%, and the proportion of in‑service energy‑saving transformers should reach 15%. The tri‑ministry “Work Plan for Stabilising Growth of the Power Equipment Industry (2025–2026)” also explicitly requires “improving the energy efficiency levels of motors, transformers and distribution equipment”, guiding the industry to fully align with Grade 1 and Grade 2 energy efficiency standards.
As energy efficiency standards continue to tighten and green manufacturing policies deepen, China’s power transformer market is accelerating its transformation towards high efficiency, energy saving and low carbon. For industrial users, commercial real estate operators and new energy project developers, choosing high‑efficiency power transformers not only helps reduce long‑term operating electricity costs but also represents an important step in fulfilling social responsibility and enhancing corporate green competitiveness.
Xinhong Electrical remains committed to technological innovation and quality first. We closely follow the latest developments in China’s power transformer energy efficiency standards and continue to launch oil‑immersed and dry‑type transformer products that meet GB 20052-2024 Grade 1 and Grade 2 standards, providing global customers with efficient, reliable and low‑carbon power system solutions. For more product information or energy efficiency selection advice, please feel free to contact us.
