When businesses and facilities demand reliable power distribution without compromising safety, the dry type transformer stands out as a premier solution. Unlike older technologies that rely on combustible insulating fluids, these transformers use air or solid insulation to deliver outstanding performance in sensitive environments. As industries push toward greener, more sustainable operations, understanding the full capabilities of a dry type transformer becomes essential for engineers, facility managers, and procurement professionals. This guide from Delong Electric Co., Ltd. explores every critical aspect of this technology, from working principles and product variants to selection criteria and real-world applications. Whether you are upgrading a data center, equipping a hospital, or designing a renewable energy plant, the information below will help you make an informed decision. Throughout this article, we will also highlight why Delong Electric has become a trusted name among the many types of transformer manufacturers worldwide.

A dry type transformer is a static electrical device that transfers energy between two or more circuits through electromagnetic induction, using air or solid insulating materials instead of liquid oil. In contrast to oil-immersed units, the windings and core of a dry type transformer are encased in materials such as epoxy resin or vacuum-pressure-impregnated (VPI) compounds. This construction eliminates the risk of fluid leaks, making the transformer inherently safer for indoor installations. The most common variant, the cast resin type transformer, features windings that are cast under vacuum in epoxy resin, providing excellent mechanical strength and moisture resistance. Another widely adopted design is the VPI transformer, where the windings are impregnated with varnish under vacuum and pressure to enhance dielectric properties. Both designs comply with international standards like IEC 60076 11, which specifies performance and safety requirements for dry-type apparatus. Because no oil is involved, maintenance routines are simpler, and environmental hazards are greatly reduced. For many modern facilities, this combination of safety and reliability makes the dry type transformer the preferred choice over conventional liquid-filled units.

At the heart of every dry type transformer lies Faraday's Law of electromagnetic induction. An alternating current in the primary winding creates a changing magnetic flux in the laminated steel core, which induces a voltage in the secondary winding. The ratio of turns between the primary and secondary windings determines whether the voltage is stepped up or stepped down. Unlike oil-filled designs that rely on liquid for both insulation and heat dissipation, the dry type transformer uses natural or forced air circulation to remove heat generated by core losses and copper losses. In smaller units, natural convection (AN) draws cool air through the windings and expels warm air from the top. Larger transformers often employ forced air cooling (AF) using fans to increase the thermal capacity. The absence of oil not only simplifies the cooling system but also eliminates the need for expansion tanks, radiators, and leak containment structures. This direct cooling approach, combined with robust solid insulation, allows the transformer to operate reliably in dusty or humid environments where oil maintenance would be problematic. Because the entire assembly is enclosed in a ventilated or sealed housing, the system remains safe from combustion risks and requires no periodic fluid testing or disposal.

Making the right choice among the various types of transformer requires a clear understanding of how dry type and oil-immersed units compare across the dimensions of safety, maintenance, environmental impact, and application flexibility. Regarding fire safety, the dry type transformer offers a decisive advantage because it contains no combustible oil, making it suitable for installation inside buildings, near people, or close to sensitive equipment. Oil-immersed transformers, while efficient at high capacities, pose fire and spill risks that necessitate special vaults and containment systems. Maintenance for a dry type transformer is minimal: periodic cleaning of air vents, inspection of connections, and thermographic checks are usually sufficient. Oil-immersed units demand regular oil sampling, filtration, and sometimes replacement of gaskets and bushings. Environmentally, the cast resin type transformer and VPI transformer are far greener because they eliminate the risk of soil or water contamination from oil leaks; they also contain fewer hazardous materials at end-of-life. In terms of installation, dry type transformers can be placed close to loads, reducing the length and cost of low-voltage cabling, while oil-filled units are often relegated to outdoor substations or dedicated rooms. For capacity and voltage extremes, oil-immersed designs still dominate in very large power transformers, but for the vast majority of commercial, industrial, and institutional applications up to dozens of MVA, the dry type transformer is more than capable. Finally, the total cost of ownership over a 20–30 year lifecycle often favors dry type when factoring in insurance premiums, containment infrastructure, and maintenance labor.

The SCB series of cast resin type transformers manufactured by Delong Electric represents the pinnacle of dry type technology for indoor and outdoor applications. These units feature high-voltage windings cast in epoxy resin under vacuum, which eliminates voids and ensures outstanding partial discharge performance. The SCB series complies with IEC 60076 11 standards and is available in ratings from 50 kVA to 20,000 kVA with primary voltages up to 35 kV. The cast resin construction provides excellent resistance to moisture, dust, and chemical contaminants, making the transformer ideal for harsh environments such as chemical plants and coastal areas. Fire behavior is self-extinguishing, and the resin does not produce toxic gases when exposed to flame. Users benefit from low no-load losses and quiet operation, which is critical for hospitals and office complexes. Delong Electric also offers multiple cooling options (AN and AF) to match the specific thermal demands of each installation. The SCB series can be customized with various enclosure protection levels, tap changers, and monitoring accessories, all supported by the company’s professional engineering team.

For applications that demand a balance between cost and performance, the VPI transformer from Delong Electric provides a robust alternative. In this construction method, the windings are wound with high-quality copper or aluminum conductors and then impregnated with a solvent-free varnish under vacuum and pressure cycles. This process ensures that every layer of insulation is fully saturated, eliminating air pockets and improving dielectric strength. The VPI transformer is lighter than cast resin equivalents and offers excellent mechanical integrity against short-circuit forces. It is particularly popular in mining, traction, and industrial settings where the transformer may be subjected to vibration or frequent overloads. Delong Electric's VPI units are also designed to meet IEC 60076 11 and can be supplied with weatherproof enclosures for semi-outdoor installation. Maintenance is limited to routine inspections, and the varnish system provides long-term thermal stability even in high-ambient-temperature environments. Like all Delong products, the VPI transformer can be customized in terms of voltage ratio, impedance, and tapping range.

Every dry type transformer is built around a set of core components that determine its efficiency, reliability, and lifespan. The core itself is constructed from high-grade grain-oriented silicon steel laminations, stacked to minimize eddy-current losses and hysteresis losses. The windings are typically made of either copper or aluminum; copper offers higher conductivity and mechanical strength, while aluminum provides a lighter and more economical solution. The insulation system is the defining element of a dry type design: in cast resin units, the epoxy resin serves as both the primary insulation and the mechanical support structure, while in VPI units, multiple layers of Nomex or polyester film are impregnated with varnish. The enclosure, often made of sheet steel or stainless steel, houses the active part and provides protection against contact and environmental ingress. Many dry type transformers also include tap changers (off-circuit or on-load) that allow fine adjustments to the output voltage. Additional accessories such as temperature sensors, thermostats, fans, and surge arresters can be integrated to enhance monitoring and protection. The careful selection and assembly of these components ensure that the transformer meets the efficiency classes specified in standards like IEC 60076 11 and delivers reliable service for decades.

Facilities that adopt a dry type transformer gain a range of advantages that go beyond simple electrical transformation. The most cited benefit is the elimination of fire risk: with no oil inside, there is no flammable liquid to ignite or spread flames. This safety feature alone allows dry type units to be installed in basements, rooftops, and indoor rooms without requiring expensive fire suppression systems. Low maintenance is another compelling benefit; because there is no oil to test, filter, or replace, annual inspections are limited to cleaning cooling ducts and checking electrical connections. Environmental friendliness is inherent in the design: no oil leaks mean no soil contamination, and the materials used are easier to recycle at end-of-life. The flexibility of installation is also superior: dry type transformers can be placed near the load center, reducing cable losses and improving voltage regulation. Finally, the reliability of modern dry type designs, supported by rigorous testing to IEC 60076 11, means that unscheduled downtime is rare. For facility managers and building owners, these benefits translate into lower insurance premiums, reduced operational costs, and a smaller environmental footprint.

The versatility of the dry type transformer makes it a cornerstone of power distribution in a wide range of sectors. In commercial buildings, these transformers step down utility voltage to utilization levels for lighting, HVAC, and elevators, all while being safely installed in electrical rooms within occupied spaces. Hospitals rely on dry type units to supply critical life-safety equipment, operating rooms, and imaging machines where a fire could be catastrophic. Data centers, which demand high power density and uptime, use dry type transformers to feed uninterruptible power supplies and server racks while maintaining a low fire risk profile. Industrial facilities such as factories, refineries, and chemical plants benefit from the moisture and chemical resistance of cast resin type transformer designs. Renewable energy installations, including solar farms and wind turbines, use dry type transformers to collect and step up power before transmission, leveraging their ability to handle fluctuating loads and harsh outdoor conditions. In each of these applications, the transformer's compliance with IEC 60076 11 assures operators that safety and performance benchmarks have been met. Delong Electric's products serve all of these verticals, and the company's experience across hundreds of projects ensures that each unit is tailored to the specific demands of the end user.

Choosing the right dry type transformer for a project involves evaluating several key parameters that affect both performance and cost. The apparent power rating in kVA must match the total connected load plus any planned future expansion; it is prudent to select a rating 10–25% above the calculated peak load. The primary and secondary voltage levels must align with the utility supply and the equipment being served. Three-phase configurations dominate in commercial and industrial settings, but single-phase units are still used for specific applications. The installation environment determines the required enclosure type: indoor ventilated enclosures are adequate for clean spaces, while dusty or outdoor locations may require higher ingress protection. Efficiency class and no-load/load losses should be compared, especially if the transformer will run continuously; higher-efficiency units have a higher upfront cost but lower lifetime energy bills. Compliance with standards such as IEC 60076 11 is non-negotiable for international projects. Additional features like tap changers, temperature monitoring, and forced-air cooling should be specified based on voltage regulation needs and thermal loading. Delong Electric’s engineering team assists clients at every step, from load analysis to factory acceptance testing, ensuring that every specification is met. By carefully balancing these factors, buyers can secure a transformer that delivers optimum performance for decades without unnecessary capital expenditure.

Delong Electric Co., Ltd. has built a reputation for manufacturing high-quality transformers since its founding in 2001. The company’s factory is equipped with modern winding machines, vacuum casting lines, VPI autoclaves, and fully automated test stations that verify every unit before shipment. Delong’s engineering team holds deep expertise in both cast resin type transformer and VPI transformer technologies, enabling the company to offer customized solutions that meet unique customer requirements. The company’s commitment to quality is reflected in its adherence to international standards, including IEC 60076 11, and its investment in R&D to improve efficiency and reduce material usage. Global buyers benefit from Delong’s flexible customization options, competitive pricing, and responsive after-sales support. Whether you need a standard unit or a fully engineered special design, the team can manage the entire process from initial consultation to delivery and commissioning. Delong also provides comprehensive documentation, including test reports, drawings, and manuals in multiple languages. To explore the full product range or to start a custom project, visit theProduct page or learn more about the company on the About Us page. For clients seeking tailored solutions, the Customized service page outlines the step-by-step process from specification to factory testing. You can also stay updated with the latest company developments on the News page or return to the Home page for an overview of all capabilities.

Electrical infrastructure decisions have long-term consequences for safety, operational costs, and environmental stewardship. The dry type transformer has proven itself as a superior solution for a vast array of applications, offering inherent fire safety, minimal maintenance, and flexible placement that oil-filled alternatives cannot match. With advanced designs such as the cast resin type transformer and the VPI transformer, modern dry type units deliver high efficiency and reliability in compliance with IEC 60076 11. Delong Electric Co., Ltd. stands ready to support your next project with decades of manufacturing experience, a full range of standard and custom products, and a dedication to quality that ensures trouble-free operation. By selecting Delong, you choose a partner that understands the technical and commercial realities of power distribution. For more detailed information on specifications, load calculations, and ordering procedures, please contact the Delong team directly or explore the resources available throughout the company website. Invest in a transformer that prioritizes safety, efficiency, and long-term value—choose Delong Electric for your dry type transformer needs.

A dry type transformer uses air or solid insulation materials such as epoxy resin or varnish instead of liquid oil to insulate its windings and core. The main differences are safety, maintenance, and environmental impact: dry type units pose no fire or oil-spill risk, require less routine maintenance, and are easier to install indoors. Oil-immersed transformers, while efficient at very high capacities, need fluid containment, regular oil testing, and are generally restricted to outdoor or fire-rated vaults.

The two primary categories are the cast resin type transformer, where windings are encapsulated in epoxy resin, and the VPI transformer, where windings are impregnated with varnish under vacuum and pressure. Both types meet international standards such as IEC 60076 11 and are available in a range of kVA ratings from 50 kVA up to 20,000 kVA or more.

A cast resin type transformer has its high-voltage and low-voltage windings cast in solid epoxy resin under vacuum, which eliminates air voids and provides excellent moisture and chemical resistance. It is commonly used in commercial buildings, hospitals, data centers, chemical plants, and other environments where fire safety, low maintenance, and high reliability are critical.

IEC 60076 11 is the international standard that specifies performance requirements, test procedures, thermal limits, and safety criteria for dry type transformers. Compliance with this standard ensures that a transformer has been tested for temperature rise, dielectric strength, short-circuit withstand, and sound levels, giving buyers confidence in its quality and reliability.

A VPI (Vacuum Pressure Impregnated) transformer uses a process where windings are saturated with varnish under vacuum and pressure cycles, filling all insulation voids. Its advantages include excellent dielectric strength, good mechanical robustness against short-circuit forces, lighter weight compared to cast resin designs, and cost-effectiveness for industrial and traction applications.

Yes, dry type transformers can be used outdoors provided they are housed in a weatherproof enclosure with appropriate IP rating. Many manufacturers, including Delong Electric, offer enclosures designed to protect against rain, dust, and temperature extremes. For outdoor use, a forced-air cooling system may be recommended to handle higher ambient temperatures and solar heating.

A well-designed and properly maintained dry type transformer can have a service life of 25 to 35 years or more. Factors that influence longevity include operating temperature, load profile, ambient conditions, and the quality of insulation materials. Regular inspections of cooling vents and electrical connections will help maximize the operational life of the unit.

Maintenance for a dry type transformer is minimal compared to oil-filled units. An annual inspection should include cleaning of air intake and exhaust grilles, visual checking for dust or debris, thermographic scanning of connections, and verification of cooling fan operation. Every three to five years, insulation resistance and winding temperature sensor functionality should be tested.

Calculate the total connected load in kilovolt-amperes (kVA) of all equipment fed by the transformer, then apply a demand factor based on operating diversity. Add a future-expansion margin of 10–25% and select the next standard rating. It is also important to verify that the transformer’s voltage drop and thermal capacity are adequate under peak load conditions.

Delong Electric combines two decades of manufacturing experience, advanced production equipment, and a skilled engineering team that can customize cast resin and VPI transformers to exact specifications. The company adheres to IEC 60076 11 and other international standards, offers competitive pricing, and provides responsive after-sales support. Clients benefit from a full-service partner that handles everything from design to delivery.