In modern power systems, the transformer plays an indispensable role in the transmission and distribution of electrical energy. Among the many transformer types, the dry‑type transformer has become the preferred power equipment for high‑rise buildings, rail transit, data centers, new energy projects, and many other fields, thanks to its outstanding advantages in safety, environmental friendliness, and low maintenance.
A dry‑type transformer, by definition, is a transformer whose core and windings are not immersed in insulating oil. Unlike traditional oil‑immersed transformers, dry‑type transformers use air or solid insulating materials (such as epoxy resin) as the dielectric medium, completely eliminating the risk of oil leakage and enabling truly green power supply. This article provides a systematic exposition of dry‑type transformers from three core perspectives: structural features, working principles, and typical applications, offering readers a comprehensive understanding of this critical power device.
As a large‑scale enterprise integrating R&D, manufacturing, trade, and services, Xinhong Electrical (Jiangsu Xinhong Electrical Equipment Co., Ltd.) has been deeply engaged in the power industry for over 15 years, specializing in the production of three‑phase epoxy resin cast dry‑type transformers from 30 kVA to 6300 kVA. The following content combines industry‑standard technologies with Xinhong Electrical’s practical experience to present a complete technical picture of dry‑type transformers.
The structural design of a dry‑type transformer directly affects its performance, reliability, and service life. A complete dry‑type transformer consists of four core components: the core, windings, insulation system, and cooling system.
The core is the magnetic circuit of the transformer, responsible for conducting magnetic flux. The core of a dry‑type transformer is typically made of high‑quality grain‑oriented cold‑rolled silicon steel sheets, which are stacked to reduce hysteresis losses and eddy‑current losses. In structural design, the mainstream process adopts a 45° fully mitered lap joint and step‑lap stacking technology, allowing magnetic flux to flow smoothly along the joint direction of the steel sheets, effectively reducing no‑load losses and noise levels.
Xinhong Electrical’s dry‑type transformers use high‑permeability, low‑loss silicon steel sheets. The core legs are tightly bound with high‑strength insulating tape, and the core surface is sealed with insulating resin for moisture and rust protection, ensuring long‑term stable operation in various environments.
Windings are the key components for voltage transformation, consisting of high‑voltage windingsand low‑voltage windings. Conductor materials are typically copper or aluminum, with copper being the industry’s first choice due to its excellent conductivity (electrical conductivity γ = 56).
In terms of winding technology, the most advanced method today is the epoxy resin vacuum casting process – under vacuum conditions, the windings are cast with a filler‑containing epoxy resin system and glass fiber reinforcement to form a solid, bubble‑free insulation structure. This process ensures that the thermal expansion coefficient of the insulation layer closely matches that of the copper conductor, giving the coils excellent resistance to impact, temperature variations, and cracking.
Xinhong Electrical’s dry‑type transformer products use Class F insulated copper conductors as the winding material, with glass fiber and epoxy resin composite as the insulation layer. For high‑ and low‑voltage coils, round copper wire, flat copper wire, or copper foil is used respectively to meet different capacity requirements.
The insulation system of a dry‑type transformer is the fundamental feature that distinguishes it from oil‑immersed transformers. Common insulation methods include epoxy resin casting and Nomex paper insulation. Epoxy resin casting completely encapsulates the windings in resin, offering advantages such as moisture resistance, dust protection, and high mechanical strength – it is the mainstream choice for large‑capacity dry‑type transformers today.
DMD insulation material is used between windings as an interlayer barrier, and the ends are sealed and cured with resin after winding to ensure insulation reliability. Overall, the insulation system gives dry‑type transformers inherent safety, non‑flammability, fire resistance, and pollution‑freecharacteristics, allowing them to be installed directly at load centres.
The cooling methods for dry‑type transformers are divided into natural air cooling (AN) and forced air cooling (AF). Natural air cooling relies on air convection for heat dissipation – it is simple in structure and noise‑free, suitable for small‑capacity transformers. Forced air cooling uses fans to accelerate airflow, which can increase the transformer’s output capacity by approximately 50%, making it suitable for large‑capacity or overload operation scenarios.
In winding design, the uniform and dense arrangement of honeycomb‑shaped cooling ductsensures excellent heat dissipation and further enhances overload capability.
The working principle of a dry‑type transformer is based on the law of electromagnetic induction. Its core logic can be summarised as the energy conversion process of “electricity generates magnetism, magnetism generates electricity.”
When the primary winding (input side) is connected to an AC power supply, an alternating current flows through the winding. This alternating current, passing through the core, generates an alternating magnetic flux that forms a closed magnetic circuit. When this alternating flux links with the secondary winding (output side), an electromotive force is induced in the secondary winding according to Faraday’s law of electromagnetic induction, thus producing a voltage at the output terminals.
The primary and secondary sides are coupled magnetically without any direct electrical connection, so dry‑type transformers inherently provide electrical isolation, effectively ensuring electrical safety.
The voltage transformation relationship of a transformer follows a simple and precise physical law: voltage is proportional to the number of turns in the winding. That is, when the secondary winding has more turns than the primary, the output voltage increases (step‑up transformer); when the secondary has fewer turns, the output voltage decreases (step‑down transformer).
Meanwhile, current is inversely proportional to the number of turns – a winding with more turns carries less current, and a winding with fewer turns carries more current. This law ensures that while changing the voltage, the transformer also achieves impedance matching, allowing efficient power transmission between different voltage levels in the power system.
Under ideal conditions, the input power of a transformer equals the output power (neglecting losses). This means that when voltage increases, current decreases correspondingly; when voltage decreases, current increases correspondingly. It is this fundamental principle that enables high‑voltage transmission (low current, low losses) and low‑voltage distribution (safe electricity use) to work together in a single power system.
Thanks to their safety, environmental friendliness, and low maintenance, dry‑type transformers are widely used in many fields. Their main application scenarios include:
High‑rise buildings, hotels, hospitals, schools, and similar places have extremely high requirements for fire safety. The oil‑free, non‑combustible, and non‑explosive nature of dry‑type transformers makes them the preferred choice for power distribution in these venues. The transformers can be installed directly in basements or floor‑level electrical rooms close to load centres, saving significant floor space without the need for a separate transformer room.
Subways, light rail, and other rail transit systems have stringent demands on power supply reliability and safety. Dry‑type transformers have been widely adopted in all 44 cities in China that have operating urban rail transit systems. Xinhong Electrical’s dry‑type transformer products have also been successfully deployed in numerous domestic rail transit projects, contributing to the power security of urban public transportation.
As the infrastructure of the digital economy, data centres require extremely high power supply continuity and safety. Dry‑type transformers, due to their fire‑safe characteristics, can be installed indoors within the data centre, close to power distribution equipment, effectively shortening power supply distances and improving reliability.
In wind power, photovoltaic, and other new energy generation projects, dry‑type transformers are widely used in step‑up grid‑connection stages. By 2022, dry‑type transformers had been applied in a cumulative total of 85 wind farm projects and 163 photovoltaic power station projects across China. Xinhong Electrical’s product line covers diverse new energy requirements, providing solid power equipment support for green energy development.
In industrial fields such as chemicals, steel, and cement – especially in harsh environments with high temperatures, dust, and humidity – the protective capabilities and reliability of transformers are critical. Epoxy resin cast dry‑type transformers excel in these scenarios due to their excellent moisture and dust resistance and high short‑circuit withstand capability.
In addition, dry‑type transformers are also widely used in airports, ports, CNC machinery, UPS power supplies, medical equipment, frequency converters, and many other areas. Their applicable voltage levels cover 6 kV, 10 kV, 20 kV, and 35 kV, with capacity ranges from 30 kVA up to several MVA.
Jiangsu Xinhong Electrical Equipment Co., Ltd. (Xinhong Electrical) is a large‑scale enterprise integrating R&D, manufacturing, trade, and services, specialising in industrial electrical equipment. With over 15 years of production and R&D experience in the power industry, the company offers three‑phase epoxy resin cast dry‑type transformers from 30 kVA to 6300 kVA.
Xinhong Electrical’s dry‑type transformer products feature the following core advantages:
Safe and reliable – oil‑free design, fire‑proof and explosion‑proof, pollution‑free, can be installed directly at load centres
High efficiency and energy saving – low‑loss design, meeting modern green power requirements
Epoxy resin vacuum casting – advanced process ensuring excellent insulation performance and high mechanical strength
Customised solutions – non‑standard customisation available to meet diverse application needs
Global presence – products exported to many countries and regions worldwide
Whether for rail transit, data centres, new energy power stations, or high‑rise buildings and industrial distribution, Xinhong Electrical delivers professional and reliable dry‑type transformer solutions.
As an indispensable key device in modern power systems, the dry‑type transformer is increasingly replacing traditional oil‑immersed transformers in a growing number of applications, thanks to its significant advantages of safety and fire resistance, environmental friendliness, and low maintenance. From the physical principles of electromagnetic induction, to the sophisticated design of core and winding structures, and to the diverse real‑world applications, the dry‑type transformer embodies the deep accumulation of power electronics technology.
With the rapid development of green buildings, smart grids, new energy, and other industries, dry‑type transformers are continuously evolving towards higher efficiency, lower noise, and greater intelligence. As a professional manufacturer in this field, Xinhong Electrical will continue to be driven by innovation, providing global customers with safe, efficient, and environmentally friendly dry‑type transformer products and solutions, supporting the sustainable development of the power industry.
