The dry type transformer is an electrical transformer which transfers electrical energy from one circuit to another without using liquid insulation such as mineral oil. It uses air and solid insulating materials, such as epoxy resin, varnish or other insulating systems, for electrical insulation and heat removal.

What Is a Dry Type Transformer?

Dry Type Transformer A transformer that uses air and solid insulation rather than insulating liquid for its primary insulation and cooling system.Its main electrical job is the same as other transformers: electromagnetic induction is used to transfer electrical energy from the primary winding to the secondary winding, changing the voltage level.

A typical dry type transformer consists of:

· Magnetic core

· High-voltage winding

· Low-voltage winding

· Solid insulation system

· Cooling system

· Clamping and supporting structure

· Terminals and connection components

· Temperature monitoring equipment

· Optional enclosure and protection devices

For example, a transformer may convert: 13.8 kV → 480Y/277 V or 11 kV → 400/230 V depending on the requirements of the electrical distribution system.

The major difference between a dry type transformer and an oil immersed transformer is the insulation and cooling method. Oil immersed transformers use insulating liquid to provide both insulation and heat transfer, while dry type transformers use air together with solid insulation materials.

This oil-free construction makes dry type transformers particularly useful in buildings and installations where liquid-filled equipment may create additional fire protection, containment, or environmental considerations.

IEC 60076-11:2018 specifically covers dry-type power transformers and includes requirements related to electrical, thermal, environmental and fire-performance considerations.

How Does a Dry Type Transformer Work?

The working principle of the dry type transformer is based on the electromagnetic induction.
When the AC voltage is applied to the primary winding, an alternating current flows through the winding and creates an alternating magnetic flux in the transformer core.
The magnetic flux flows through the core and couples with the secondary winding. The secondary winding will induce a voltage . Faraday 's law of electromagnetic induction says that.

The relationship between the primary and secondary voltage is approximately determined by the turns ratio: V₁ / V₂ ≈ N₁ / N₂

· V₁ = Primary voltage

· V₂ = Secondary voltage

· N₁ = Number of primary turns

· N₂ = Number of secondary turns

A transformer reduces the voltage if the primary winding has more turns than the secondary winding.
If the primary winding has less turns than the secondary winding the transformer increases the voltage .

Main Types of Dry Type Transformers

There is no single construction suitable for every application.

The most common dry type transformer types include cast resin transformers, vacuum pressure impregnated transformers, and open-wound or ventilated dry type transformers.

1. Cast Resin Transformer

A cast resin transformer uses epoxy resin to encapsulate or cast the transformer windings.

The solid resin insulation provides electrical insulation while also protecting the windings against moisture, dust, pollution and other environmental influences.

Cast resin transformers are widely considered for:

· Commercial buildings

· Industrial plants

· Hospitals

· Data centers

· Airports

· Railway systems

· Indoor substations

· Solar power plants

· Battery energy storage systems

· High-humidity environments

One of the important benefits of cast resin technology is that the resin system physically protects the winding insulation system.
This can be of value in service where moisture, dust or contamination may otherwise affect winding insulation.

2. VPI Dry Type Transformer

A Vacuum Pressure Impregnated (VPI) Transformer is one in which a vacuum- pressure impregnation process is used to force insulating varnish into the winding insulation system.
During manufacture the windings are treated under controlled vacuum and pressure conditions which allow the insulating material to penetrate the winding structure.

VPI transformers are commonly used in:

· Industrial facilities

· Commercial power distribution

· Motor control systems

· Infrastructure projects

· Large electrical installations

VPI technology is different from cast resin construction in structure of insulation and process of manufacture. The correct choice depends on environmental conditions, voltage level, capacity, mechanical requirements and project specifications.

3. Open-Wound Dry Type Transformer

Open-wound transformers have an air insulated winding structure, usually coated with varnish or other insulation.
They may be considered for relatively clean and controlled indoor environments where the transformer does not require the additional environmental protection of a fully encapsulated winding.
Because of their simpler construction they may be suitable for some general purpose applications.

Dry Type Transformer Types Comparison

The actual performance depends on the transformer design, insulation system, manufacturing process and the applicable specifications, not only on the name of the technology.

Dry Type Transformer Cooling

Dry type transformers, compared to oil immersed transformers, are unable to use transformer oil to take heat away from the windings and core.
No, heat is distributed through air instead.Cooling arrangements are generally:
AN – Air Natural
Natural air circulation dissipates heat from the transformer.
This is used generally when the transformer is operated at its normal rated conditions.
AF — Air Force
Fans are employed to improve the airflow over the transformer.
If the transformer is designed and rated to operate in this mode, the forced-air cooling could lead to an increase in the available capacity of the transformer for the specified operating conditions.

Cooling design is particularly important in:

· Data centers

· Industrial plants

· High-load commercial buildings

· Solar power systems

· Battery energy storage systems

· High ambient-temperature environments

The installation room must also provide sufficient ventilation.

Advantages of Dry Type Transformers/Why are dry type transformers widely used in modern electrical distribution systems?

The answer depends on the application, but several characteristics make them desirable.
1. Oil-Free Design
The most obvious difference is the lack of transformer oil.
The oil filling and the oil leakage from the transformer itself can be eliminated and the indoor installations can be made simpler.
2. Reduced Fire Hazard
A dry type transformer does not use mineral oil as its insulating medium. Therefore, there is no transformer oil that can leak or be involved in an oil related fire.
This property is particularly important for installations inside buildings.
But "oil-free" is not "fire-proof." Electrical equipment can still fail, overheat or have insulation failure so appropriate protection and installation practices are still required.
3. Needs Little Attention
A dry type transformer does not need routine oil sampling, oil filtration or oil replacement.
Regular maintenance includes:

• Cleaning

• Air Circulation

• Electrical connections

• State of insulation

• Monitoring of temperature

• Operation of fan Mechanical Inspection

This may mean less need for routine maintenance than with liquid filled transformers.
4. Benefits to the Environment
There is no transformer-oil leakage because the unit has no insulating oil.
This can be useful for buildings in sensitive locations, or buildings where oil containment would otherwise have to be taken into account.
5. Indoor installation possible
Dry-type transformers are often selected for:

• Electrical rooms

• Commercial buildings

• Hospitals

• Schools

• Shopping centers

• Data-centres

• Airports

• Industrial buildings

Since they contain no oil they can be more readily incorporated into indoor power distribution systems.
6. Good resistance to environmental effects
Cast resin dry type transformers can offer good protection against moisture, dust and contamination.
They are useful for demanding industrial and infrastructure environments if specified properly.
7. Simple Installation
Dry type transformers can be designed in different ways for:

• Distribution of low voltage

• High voltage distribution

• Three phase systems 

• Systems of renewable energy 

• Power system industrial

• Power Distribution Building

Where Are Dry Type Transformers Used?

Dry type transformers continue to find wider application as buildings and industrial facilities demand reliable, safe electrical distribution.
Commercial Buildings
Dry type distribution transformers are generally used for: 

• Office buildings 

• Hotels
• Shopping malls 

•High-rise buildings 

•Airports
·Business complexes
An important consideration is the ability to locate the transformer close to electrical loads without bringing transformer oil into the building.
Industrial Buildings
Dry type transformers can be used to supply factories: 

• Engines

• Manufacturing pipelines

• Pumps Compressors

• HVAC equipment

• Automation systems

• Machines_ (machinery)

Special consideration can be given to industrial projects for dust, temperature, harmonics, motor starting and continuous loading.
Data Center
Data centers need very reliable electrical distribution.
Dry-type transformers are used for: 

Distribution of utilities UPS systems 

Mechanical systems 

Critical loads Auxiliary systems
Efficiency, harmonic loading, temperature monitoring, noise, redundancy and short-circuit performance all need to be considered by buyers when choosing a transformer for a data center.
Medical Centers
Hospitals have demanding electrical needs and often place a strong emphasis on fire safety and reliability.
When specified properly, dry type transformers can be used for building distribution, medical facilities and auxiliary power systems.
Renewable Energy
Dry type transformers are also employed in renewable energy systems.
Common applications include: 

·Solar photovoltaic system 

· Wind-power systems Energy storage (batteries) 

· Decentralized generation Commercial renewable energy projects
IEEE C57.159 covers the use of both liquid-immersed and dry-type transformers for distributed photovoltaic power generation systems.
EV Charging Infrastructure
Rapid deployment of electric vehicle charging stations is helping drive the need for transformers that can handle high and sometimes highly variable electrical loads.
If the charging infrastructure is installed inside commercial or industrial facilities, you can consider dry type transformers.

How to Choose the Right Dry Type Transformer

Selecting a dry type transformer should begin with the electrical system rather than the product catalog.

1. Determine Transformer Capacity

The first parameter is normally the required kVA or MVA rating.

Common distribution transformer ratings include:100 kVA、160 kVA、250 kVA、315 kVA、400 kVA、500 kVA、630 kVA、800 kVA、1000 kVA、1250 kVA、1600 kVA、2000 kVA

The appropriate rating depends on present load, future expansion, load factor and required spare capacity.

2. Confirm Primary Voltage

The primary voltage must match the upstream electrical system.

Typical medium-voltage levels may include:6 kV、10 kV、11 kV、13.8 kV、15 kV、20 kV、22 kV、33 kV

Actual voltage requirements vary by country and utility system.

3. Confirm Secondary Voltage

The secondary voltage must match the downstream distribution equipment.

Common examples include:

· 400/230 V

· 415/240 V

· 480Y/277 V

· 480 V

· 600 V

The manufacturer should confirm the exact connection, phase configuration and frequency.

4. Choose Single-Phase or Three-Phase

The three phase dry type transformer is a common configuration for commercial and industrial power distribution.
Single-phase transformers may be better suited for certain residential, commercial or specialty applications.

5. Select the Insulation Technology

Consider whether the project requires:

· Cast resin

· VPI

· Open wound

The choice should reflect environmental conditions, fire requirements, maintenance expectations, capacity and project specifications.

6. Consider Ambient Conditions

The transformer design may need to account for:

· Ambient temperature

· Altitude

· Humidity

· Dust

· Salt contamination

· Indoor/outdoor installation

· Seismic conditions

IEC 60076-11:2018 specifically includes considerations related to altitude, climatic classes and seismic classification.

7. Evaluate Harmonic Loads

Modern electrical systems may contain nonlinear loads such as:

· Variable-frequency drives

· UPS systems

· Data center equipment

· EV chargers

· Solar inverters

· Power electronics

Harmonic current can increase transformer heating and affect transformer loading capability.
IEEE C57.110 provides procedures for evaluating transformer capability to supply nonsinusoidal load currents.

Important Dry Type Transformer Specifications

When requesting a quotation from a dry type transformer manufacturer, buyers should provide as much technical information as possible.

Frequently Asked Questions About Dry Type Transformers

1.What is dry type transformer ?
A dry type transformer is a kind of electrical transformer that does not use liquid insulation such as mineral oil. It insulates the windings with air and solid insulation materials and disperses heat.
2. Major types of dry type transformer are:
The main technologies are cast resin transformers, VPI transformers and open-wound dry type transformers.
3. Is dry type transformer better than oil immersed transformer?
Neither technology is superior across the board. Dry type transformers are preferred for indoor applications, fire sensitive environments and applications where oil-free equipment is desired. For other applications, especially some utility and high-capacity ones, oil-immersed transformers may be more appropriate.
4. Are the dry type transformers fire proof?
Dry type transformers do not use transformer oil, and therefore do not have the oil-related fire risk of liquid filled transformers. These are still electrical equipment and require proper protection, installation and operating practices however.
5. Do you need oil for dry type transformers?
No . The dry type transformer does not require transformer oil for its primary insulation system .
6.Can dry type transformer be placed outdoors?
Dry type transformers can be placed outdoors if they are designed for outdoor use and have the proper protection for the environment. The enclosure, insulation system, temperature, humidity, pollution level and other site conditions should be considered.
7. What is the life of dry type transformer ?
The service life is affected by insulation quality, temperature, loading, environmental conditions, maintenance and manufacturing quality. Transformers properly designed and operated will give long term service.
8.What is cast resin transformer?
Cast resin transformer A dry type transformer whose windings are encapsulated or cast with resin insulation, often epoxy resin. The resin serves electrical insulation and environmental protection purposes.
9.What is the difference between dry type transformer and cast resin transformer?

"Dry type transformer" is a generic term. A cast resin transformer is a specific kind of dry type transformer, whose windings are encapsulated in resin.
10. What should be included in a dry type transformer quotation request?
Please provide at least:

• Rated output power 

• Voltage in primary 

• Voltage secondary 

• Frequency

• Number of stages 

• Operating environment

• Cooling requirements 

• Standard applicable 

• Impedance constraints

• Tap range 

• Enclosure requirements

• Delivery destination

The more detailed the technical specification, the more precise the producer's quotation will be.

Why Choose Shandong Future Electric for Dry Type Transformer?

Choosing the right dry type transformer manufacturer is as important as choosing the right transformer specifications. For overseas distributors, contractors, EPC companies, utilities and industrial buyers, transformer quality, customization capability, delivery reliability and technical support all directly impact on project performance.
Shandong Future Electric Co., Ltd. is a custom transformer manufacturer, providing factory manufacturing and technical support for international power distribution projects and overseas B2B customers.

Factory-Direct Transformer Manufacturing

Shandong Future Electric is a transformer manufacturer, so you get direct factory production and technical support. This allows overseas buyers to communicate specifications directly with the engineering and production teams instead of having to rely solely on intermediaries.

We can produce for a variety of transformer applications and voltage levels, so customers are welcome to talk about capacity, voltage ratio, insulation system, cooling method, enclosure, accessories and other project-specific requirements before production.

Customized Dry Type Transformer Solutions

Projects are different and require different transformer configurations.

We can cater for bespoke requirements including:

Voltage and rated capacity

Connection of Three-phase Transformer

Dry type insulation solutions or cast resin

need for cooling

Rising temperature

Resistance

Touch Range

Conditions on enclosure and security

Setting up the terminal

Installation environment

Technical specifications of the Project

For overseas B2B customers, our engineering team can also check the technical specifications and drawings before production to ensure that the proposed transformer meets the actual project requirements.

Quality Control and International Standards

Besides the name plate rating, many factors affect the performance of a transformer. Long term reliability is affected by core materials, winding construction, insulation, assembly, testing and temperature control.
Shandong Future Electric adopts controlled manufacturing and testing procedures for transformer production, and can provide relevant technical documents and factory test reports according to project requirements.
We can coordinate transformer designs for international projects to the applicable IEC and other regional standards, based on the destination market and project specification.

Support for Global B2B Projects

We provide our transformers to our customers in international markets for use in applications such as:
Industrial plant

• Business Buildings

• Projects - Infrastructure & Utility

• Renewable energies systems

• Distribution networks

• Works of construction

• Commercial & Industrial substations

We have experience with overseas customers and we know that a successful transformer order is not only about manufacturing the equipment. Also important parts of the project are the technical communication, documentation, packaging, transportation and after-sales support.

Export Packaging and Delivery Support

Transformers are heavy electrical equipment that require proper protection during international transportation.
We provide export packaging to protect transformers from impact, vibration, moisture, dust and handling hazards during transportation.
Shipping support may include: 

• Depending on project requirements

• Export wooden boxes or steel packing

• Internal protection materials

• Shipping marks and customer brand

• Product literature

• Reports of Factory Testing

• Customs papers

• Technical manuals

This helps overseas buyers efficiently manage the process from factory production to final delivery.

One Supplier for Different Transformer Requirements

Shandong Future Electric provides a diverse range of transformer solutions, enabling customers to consolidate different transformer needs with one experienced manufacturing partner.

We provide the following range of products:

• Three Phase Oil Immersed Transformers

• Three Phase Dry Type Transformers

• Box Type Transformers

• Single Phase Oil Immersed Transformers

Whether you are sourcing a standard dry type distribution transformer or developing a customized transformer solution for a specific project, our team can work with your technical specifications and application requirements.

Looking for a Reliable Dry Type Transformer Supplier?

If you are searching for a dry type transformer manufacturer or supplier for an international project, send us your transformer requirements.
Please provide the following information, where known:
Rated Power + Primary Voltage + Secondary Voltage + Frequency + Phase + Installation Environment + Applicable Standard
Our engineering team can then review the requirements and provide a suitable transformer configuration, technical proposal and quotation.
Shandong Future Electric Transformer Solutions for World Power Distribution.