As wind power, photovoltaic (PV), and energy storage projects continue to expand, the transformer—as the core equipment connecting the power generation system to the grid—directly impacts project efficiency, system reliability, and return on investment. Unlike traditional power transmission and distribution scenarios, renewable energy projects involve a large number of power electronic devices such as inverters and converters, generating significant harmonic currents and short‑term impact loads. This places higher demands on transformers regarding harmonic resistance, overload capability, and environmental adaptability. Xinhong Electrical, with its deep expertise in renewable energy transformers, provides professional solutions for wind, PV, and energy storage applications worldwide. Our products cover a maximum voltage of 35kV and are certified with CEand ISO9001, ensuring stable and reliable quality. This article systematically reviews the key selection points and core parameters for each scenario, helping engineers and project decision‑makers make optimal choices.
Wind power projects are divided into onshore and offshore types, each with different requirements for transformers.
The capacity of a wind turbine step‑up transformer should be selected based on the rated apparent power of the wind turbine generator. Industry practice typically adopts a “one turbine, one transformer” unit connection. For example, in a 100MW wind project, a single 6.25MW turbine paired with a 6900kVA compact substation transformer is a mature configuration.
The maximum voltage of dry‑type or liquid‑immersed transformers for wind power step‑up shall not exceed 35kV and must comply with GB/T 1094.1 and GB/T 1094.11. GB/T 1094.16‑2025, a dedicated standard for wind power transformers (published in August 2025, effective February 2026), specifies rating, electrical performance, and testing requirements – an important reference for selection. The low‑voltage side connecting a single turbine to the collection system is typically 0.69kV or 0.96kV, stepped up to 10kV or 35kV collection voltage.
Wind turbine transformers are installed either inside the tower or as compact substations. Tower‑mounted units face special requirements for impact load resistance, overvoltage tolerance, heat dissipation, and vibration resistance. Offshore wind projects are even more demanding, requiring resistance to humid, salty environments and high‑frequency vibrations. For offshore wind, compact and lightweight nacelle transformers have become mainstream – for example, 35kV, 10‑12MVA products are already in use.
Wind turbine transformers should preferably use Class H (180°C) insulation systems with a protection rating of at least IP54. In coastal areas, anti‑corrosion coatings for salt fog and condensation removal devices are essential.
The most critical transformer equipment in a PV power plant is the PV step‑up compact substation, which performs the key task of stepping up the low‑voltage output from PV inverters to the voltage required at the grid connection point.
The capacity of a PV compact substation should be slightly larger than the total inverter output capacity, typically with a 10‑20% margin to cope with morning/evening solar output fluctuations. For example, for a 3MW PV system with a total inverter output of about 3.2MW (considering 10% losses), the transformer capacity should be ≥3.2MVA, with a 10‑15% redundancy recommended. If the PV capacity exceeds 5MW, a 10kV/35kV step‑up compact substation is recommended to reduce energy losses. The main transformer of a PV plant can be designed according to GB/T 50797, with capacity selected based on the maximum continuous output power of the PV array unit.
The input voltage of the compact substation must match the output voltage of the PV array, while the output voltage must meet grid connection requirements – the maximum shall not exceed 35kV. For example, mainstream 182mm cells output 600V‑1000V; if the grid connection requires 35kV, the high‑voltage side of the compact substation should be rated 35kV. Some projects use a 0.8kV/10.5kV step‑up scheme.
Energy efficiency directly affects power generation revenue. National regulations mandate that newly purchased transformers must be at least energy efficiency Class III (S13). Class II (S14) or Class I (S20) is strongly recommended. The higher procurement cost is typically recovered within 2‑5 years through electricity savings. For a 1MVA compact substation, a Class I transformer reduces annual losses by about 20,000 kWh compared to a Class III product. Selection should consider total cost of ownership over the entire lifecycle, incorporating 25‑year operating losses into the comparison.
Intelligent compact substations integrate temperature sensors and partial discharge sensors, supporting the Modbus protocol for connection to SCADA systems. Remote monitoring and fault alerts via IoT platforms can reduce maintenance frequency by more than 50%.
PV inverters are the main source of harmonics. The D,yn11 vector group is strongly recommended.Compared to Yyn0, Dyn11 improves the attenuation of 3rd harmonic currents by 92%, effectively reducing additional heating and losses caused by non‑sinusoidal currents. At the same time, the K‑factor should be evaluated (typically K=10; for high‑harmonic scenarios K=13 is recommended) to ensure sufficient harmonic tolerance margin.
Residential/commercial & industrial PV: Minimum protection rating IP54, suitable for roof or ground installation.
Utility‑scale PV plants: Protection rating IP65 required, with anti‑salt‑fog and anti‑corrosion coatings. In desert or high‑altitude areas, forced air cooling or liquid cooling systems are necessary.
Energy storage systems mainly use bidirectional step‑up transformers and auxiliary isolation transformers – the former for energy exchange between the storage system and the grid, and the latter for electrical isolation within the system.
Energy storage isolation transformers must support bidirectional operation – stepping down during discharge to supply the grid or load, and stepping up during charge to feed back to the battery system. The voltage level must precisely match the PCS output and the grid connection point, with a maximum voltage not exceeding 35kV. Small residential scenarios suit 6kVA‑50kVA, commercial & industrial storage suits 110kVA‑800kVA, and utility‑scale storage suits 1000kVA‑2000kVA.
Energy storage systems have short‑term impact characteristics during charge/discharge. Industry experience indicates that the main transformer capacity should be increased by about 20% after connecting an energy storage system. Step‑up transformer capacity should be strictly configured as “maximum discharge power × 1.2 margin” (e.g., 5MW storage requires a 6.5MVA step‑up transformer) to ensure stable operation under full impact load.
Low‑harmonic isolation design effectively suppresses grid pollution and improves the power quality of PV inverters and energy storage systems. After connecting an energy storage system, short‑circuit current may increase by 7.6%‑11.8%; short‑circuit withstand capability must be rechecked during selection to ensure reliable protection device operation.
Low‑voltage auxiliary transformers (for station service power) in wind‑solar‑storage projects should be evaluated from six dimensions: capacity, voltage level, insulation class, protection rating, connection method, and efficiency – ensuring precise matching with system operating conditions. A typical auxiliary transformer broadens the input voltage adaptation range to 500V‑1200V and stably outputs 400V ±5% to power various auxiliary equipment reliably.
Renewable energy plants generally experience short‑term impact loads (inverter start‑up, fault ride‑through, etc.). A 10‑15% margin above rated capacity is recommended. For energy storage, a margin of at least 20% is suggested. If a transformer operates continuously near its overload limit, insulation life halves for every 6°C temperature rise – thus, capacity margin is not redundancy but a safety foundation.
Total harmonic distortion (THD) in renewable energy systems can reach 5‑15%, much higher than in conventional grids (THD <3%). Traditional single‑disc windings struggle with high‑order harmonics. Interleaved or continuous winding structures effectively reduce additional losses and eddy‑current heating and should be prioritized.
Due to harmonics, voltage fluctuations, and harsh outdoor environments, renewable energy projects should prioritize Class F (155°C) or Class H (180°C) insulation systems. Higher thermal class insulation materials help extend equipment life and reduce maintenance replacement costs.
Keep track of renewable energy subsidies and carbon reduction policies in different countries: China follows GB 20052; Europe and the US refer to IEC 60076 efficiency tiers. Selection should be based on 25‑year total cost of ownership (TCO), comprehensively analyzing procurement price, maintenance costs, and energy loss expenses to avoid choosing low initial cost at the expense of high energy losses. Xinhong Electrical products meet international mainstream efficiency standards, offering customers the best value.
Xinhong Electrical renewable energy transformers are strictly certified with CE (meeting EU safety and electromagnetic compatibility requirements) and ISO9001 (quality management system), ensuring full‑process quality control from design and production to delivery. The maximum voltage is strictly controlled within 35kV, covering the vast majority of commercial, industrial, and utility‑scale renewable energy projects worldwide. No additional certifications are required for export to the EU and many other countries that recognize the CE mark, providing reliable assurance for project exports.
Xinhong Electrical has many years of experience in the renewable energy transformer field, with product lines covering wind, PV, and energy storage applications, offering one‑stop services from capacity selection to lifecycle maintenance.
Full‑scenario product portfolio: Includes oil‑immersed transformers, dry‑type transformers, compact substations, and isolation transformers, suitable for projects from 1MW to 500MW, with a maximum voltage of 35kV.
Technology leadership: High‑grade oriented silicon steel and 99.99% oxygen‑free copper windings; compliant with both GB/T 1094 series and IEC 60076 series standards; supports extreme temperatures from -30°C to 70°C.
Intelligent operation platform: Built‑in sensors and IoT architecture enable real‑time temperature monitoring, fault alerts, and remote management, significantly reducing maintenance costs.
International certifications: Products are certified with CE and ISO9001, sold in more than 30 countries and regions worldwide.
Professional delivery service: Full‑process support from initial solution design and customized production to on‑site commissioning and after‑sales service.
Whether you are preparing a new utility‑scale PV plant, a distributed wind power project, or a commercial & industrial energy storage system, Xinhong Electrical is ready to be your most reliable partner on the road to energy transition with reliable products and professional service. Please visit our official website for more product information and technical data, or contact our engineering team for a customized selection solution.
