With the acceleration of the global energy transition, energy storage systems (ESS) have become a core component of modern power systems. Within these systems, distribution transformers play a critical role in voltage conversion, energy transmission, and isolation protection, serving as the key link between the battery energy storage system and the grid. The deep integration of distribution transformers with energy storage significantly enhances the reliability and controllability of distribution networks, while strengthening their capacity to absorb and store renewable energy.
Among the various transformer types, the oil immersed transformer stands out in energy storage applications due to its superior heat dissipation, strong overload capability, and excellent cost‑performance ratio. This article provides a multi‑dimensional analysis of the advantages of distribution transformers in energy storage equipment, offering a practical reference for ESS project selection.
The operating conditions of battery energy storage systems (BESS) differ significantly from traditional distribution scenarios, imposing higher demands on transformers:
Bidirectional power flow – ESS must switch frequently between charging and discharging modes, requiring transformers to support efficient and stable bidirectional energy transfer.
Frequent load fluctuations – When participating in peak shaving, frequency regulation, and other grid services, ESS experience repeated charge/discharge cycles and sharp load changes, demanding excellent surge withstand capability and thermal stability.
Complex harmonic environment – The power conversion system (PCS) in ESS generates substantial harmonic currents; transformers must have strong harmonic tolerance to avoid local overheating and additional losses.
Long‑term reliable operation – Most energy storage plants are unattended, so transformers must provide stable operation with minimal maintenance.
Oil immersed transformer units use insulating oil as both cooling medium and insulation material. Heat generated during operation is absorbed by the oil and dissipated through natural or forced circulation to radiators and then to the ambient environment. This oil‑immersed design delivers excellent thermal dissipation, effectively extending insulation life even under continuous heavy loads and bidirectional operation.
In comparison, cast resin transformer products have relatively poor thermal cooling performance due to the low thermal conductivity of resin materials. Under the thermal shock caused by frequent charge/discharge cycles in ESS, the thermal management advantage of oil‑immersed transformers becomes particularly evident.
During peak shaving and emergency support, ESS often require transformers to withstand short‑term loads far exceeding their rated capacity. Oil immersed transformer units offer excellent thermal inertia and overload margin, capable of handling short‑duration high‑current surges and frequent load swings. This makes them an ideal choice for energy storage, especially in applications such as distribution‑level storage that demand rapid response.
For example, distribution‑level storage can provide 40‑100 kW of support to a 11kV/0.4kV distribution transformer, effectively reducing peak load by 10‑25%. In such scenarios, the high overload capability of oil‑immersed transformers has been thoroughly validated.
When comparing oil immersed transformer vs cast resin transformer, oil‑immersed types generally offer higher efficiency and lower losses. They perform excellently in both no‑load and load losses, with strong lightning surge withstand capability and robust short‑circuit endurance, delivering significant energy savings.
Research data indicate that cast resin transformer losses are typically higher than those of liquid‑insulated options, and their use‑phase environmental impact is also greater. For energy storage projects, transformer efficiency directly affects round‑trip efficiency and overall return on investment.
At the same rated capacity, an oil immersed transformer is generally more compact and requires a smaller footprint than a Dry transformer. Liquid‑insulated designs allow for more space‑saving configurations, which is especially valuable for space‑constrained storage projects such as containerised ESS. A compact design not only saves valuable installation space but also reduces civil works costs.
In terms of cost, the oil immersed transformer has a clear price advantage over both cast resin transformer and Dry transformer options. The per‑unit‑capacity cost is lower, and the initial investment is smaller.
Over the full life cycle, oil‑immersed transformers offer significant total cost of ownership (TCO) savings, thanks to their 15‑20 year service life and low maintenance requirements.
Energy storage projects are often deployed outdoors or in harsh environments. The fully sealed design of oil immersed transformer units enables reliable operation under extreme conditions such as high temperature, high humidity, and high altitude. Fully sealed oil‑immersed transformers use corrugated tanks or other elastic structures to accommodate oil expansion, making them suitable for a wide range of outdoor and severe‑weather installations.
As a global powerhouse in transformer manufacturing, China is home to a large number of professional oil immersed transformer manufacturers. The domestic oil‑immersed transformer industry has formed a complete supply chain, covering material supply, production, R&D, and after‑sales service, all at world‑leading levels.
Among these oil immersed transformer manufacturers, Xinhong Electrical (Jiangsu Xinhong Electrical Equipment Co., Ltd.) is dedicated to producing a full range of oil‑immersed transformers, covering voltage classes from 6kV, 10kV, 20kV to 35kV, with capacities from 30kVA to 3000kVA. The company offers customised services, providing tailor‑made transformer solutions to meet specific customer requirements.
When selecting transformers for energy storage systems, the comparisons of oil immersed transformer vs cast resin transformer and oil immersed transformer vs Dry transformer are unavoidable decision points.
The main advantages of cast resin transformer and Dry transformer units lie in their oil‑free design, which provides enhanced fire safety – making them suitable for indoor locations with strict fire protection requirements, such as hospitals, airports, and commercial areas. In addition, dry‑type transformers are maintenance‑free and environmentally friendly.
However, for energy storage applications, the overall advantages of the oil immersed transformerare more pronounced:
| Comparison Dimension | Oil Immersed Transformer | Cast Resin / Dry Transformer |
|---|---|---|
| Heat Dissipation | Excellent (oil circulation) | Moderate (air cooling; resin has poor thermal conductivity) |
| Overload Capability | High | Moderate |
| Efficiency | High | Relatively lower |
| Footprint | Compact | Larger |
| Initial Investment | Low | High |
| Environmental Adaptability | Excellent (fully sealed outdoor type) | Limited (better suited for indoor) |
| Service Life | 15‑20 years | Comparable |
Therefore, provided that fire safety requirements are met, energy storage systems can preferentially adopt oil immersed transformer units to fully leverage their comprehensive advantages in cost, energy consumption, and environmental adaptability.
As energy storage projects scale up, prefabricated substation manufacturers are increasingly integrating distribution transformers with storage systems. Prefabricated substations incorporate transformers, switchgear, protection, and control systems into modular, factory‑pre‑engineered designs.
This integrated approach transforms the substation from a site‑built structure into a factory‑produced unit, greatly shortening construction timelines. Xinhong Electrical stays at the forefront of this trend, offering prefabricated substations and complete electrical equipment solutions that are widely used in conventional power grids, renewable energy (including wind, solar, and storage), and many other fields.
In real‑world applications, the value of oil immersed transformer units in energy storage projects has been well demonstrated.
In a distribution transformer station in Dongtai, Jiangsu, with a photovoltaic penetration rate of 106%, the distribution transformer experienced reverse heavy overload. By deploying a distribution‑level storage system, the transformer load rate was controlled within 70% across all periods, and three‑phase imbalance was reduced from over 25% to within 5%. This case fully validates the synergistic potential of storage technology and distribution transformers.
In the Pudong New Area of Shanghai, the first distribution‑level storage project successfully prevented power outages caused by transformer overloading. Compared with traditional transformer capacity expansion, the storage‑based solution offered a shorter construction period, lower investment, and more flexible siting – making it a more economical grid upgrade choice.
In summary, the oil immersed transformer offers multiple advantages in energy storage equipment: excellent heat dissipation, strong overload capacity, high efficiency, compact size, low cost, and outstanding environmental adaptability. When comparing oil immersed transformer vs cast resin transformer and oil immersed transformer vs Dry transformer, the oil‑immersed type consistently delivers superior overall performance for storage applications.
As a professional oil immersed transformer manufacturer in China, Xinhong Electrical is committed to providing high‑quality oil‑immersed transformer products and solutions for energy storage projects worldwide. Our products cover voltage classes from 6kV to 35kV and can meet the diverse needs of storage projects of various scales.
As the global energy storage market continues to expand, the oil immersed transformer will play an increasingly vital role in ESS. Choosing Xinhong Electrical oil‑immersed transformers means choosing reliable, efficient, and economical power protection for your energy storage project.
For more information on the application of oil immersed transformer units in energy storage systems, or to obtain prefabricated substation solutions, please contact Xinhong Electrical.
