مصنع مخصص للمحولات من النوع الجاف للحصول على حلول طاقة موثوقة

What is a dry-type transformer?

The definition of dry-type transformer is based on the physical state of the insulating medium - the insulating medium around its winding is a gas (usually air) or a dry solid compound, rather than a liquid dielectric. The word 'dry' in the name accurately reflects that the transformer does not contain any liquid insulation or cooling medium inside. In practical construction, the iron core and winding are not immersed in insulating oil, but are protected by solid materials such as epoxy resin, casting resin, vacuum pressure impregnation process, or high-temperature varnish coating for insulation; Its cooling method is air circulation, whether relying on natural convection or forced ventilation, without using circulating oil or other fluids. This definition clearly distinguishes dry-type transformers from liquid filled transformers, which rely on mineral oil, synthetic esters, or silicone oil as insulation and heat dissipation media.

Reference Standards

IEC 60076-11:     Dry-type power transformers up to 72.5 kV

IEEE C57.12.01: General requirements for dry-type distribution and power transformers

IEEE C57.12.52: Sealed dry-type power transformers, 501 kVA and higher

IEEE C57.12.91: Test code for dry-type distribution and power transformers

Technical Parameters

Typical Rating Ranges

Key Performance Parameters

Internal structure of Dry-type transformers:

The internal structure of dry-type transformers consists of several core components, each of which can work together to achieve excellent electrical performance, mechanical strength, and thermal management performance.

1. Magnetic core

Magnetic cores are usually made of laminated electrical steel (silicon steel) or other ferromagnetic materials. The stacked layers are insulated from each other to effectively reduce eddy current losses and hysteresis losses. According to specific design requirements, the geometric shape of the magnetic core can be rectangular, circular, or elliptical.

2. Winding

The winding consists of a primary winding and a secondary winding, usually made of copper or aluminum conductors. Copper has better conductivity than aluminum (with a resistivity of γ=56 for copper and 36 for aluminum), but aluminum is often used in cost sensitive applications.

The high voltage (HV) and low voltage (LV) windings are arranged concentric around the iron core, separated from each other by insulating partitions or air gaps.When winding, precision is emphasized to effectively reduce losses and ensure a relatively uniform distribution of magnetic flux.

3. Insulation system

The insulation system of dry-type transformers is not only provides electrical insulation for the windings, but also plays a role in mechanical support. The common insulation processes mainly include the following:

l Epoxy resin casting (resin casting): Use epoxy resin to completely seal the entire winding, which can effectively prevent moisture, dust, and resist the effects of mechanical stress.

l Vacuum Pressure Impregnation (VPI): In an alternating environment of vacuum and pressure, H-grade polyester resin is used to impregnate the winding. After processing, the dielectric strength, mechanical strength, and thermal stability of the winding will be significantly improved.

l Vacuum Pressure Encapsulation (VPE): The VPE process uses a thicker insulation coating, which is thicker than VPI, so it has better durability and is less prone to problems in wet, polluted and other situations.

4. Clamping structure

The clamping structure is used to fix the winding and iron core components, providing necessary mechanical strength and ensuring precise alignment of each component. It can be equipped with cooling channels or ventilation holes inside to achieve air circulation.

5. shell

The entire set of components is installed in a casing, which has three options: ventilated, non ventilated, and sealed, depending on the on-site environment. Ventilation type uses natural convection or forced air cooling to dissipate heat; Non ventilated type is specifically designed for harsh environments with high levels of conductive dust, corrosive gases, or flammable and explosive materials.

Product Classification of Dry-type transformers

Dry-type transformers can be classified according to several criteria:

1. Classification by Construction Type:

2.Classification by Insulation Technology:

3.Classification by Cooling Method

4.Classification by Phase Configuration

1. Classification by Phase Configuration

• Single-phase: Nominal power typically 15–833 kVA
• Three-phase: Nominal power typically 15–7500 kVA

2. Classification by Enclosure Type

• Ventilated: Allows air circulation through ventilation openings
• Non-ventilated: Completely enclosed design for harsh environments
• Sealed: Hermetically sealed for flood-prone or contaminated environments

Product Features

There are significant differences in product features between dry-type transformers and oil immersed transformers:

1. Insulation and Cooling

• Solid insulation media: The main insulation media include epoxy resin, casting resin, VPI treated materials or varnish coatings that can provide electrical insulation.  
• Air cooling: The heat dissipation effect is mainly achieved through natural convection (AN type - natural air cooling) or fan forced circulation (AF type - forced air cooling).

2. Construction Characteristics

• No liquid storage tank: Dry type transformers do not require oil storage tanks, so the overall size is smaller and the weight is lighter.  
• Visible iron core and winding: The biggest structural difference between dry-type transformers and oil immersed transformers is that dry-type transformers can directly visually inspect the iron core and coil components.  
• Small footprint: The dry-type transformer has a compact structure and is very suitable for installation environments with limited for example indoor.

3. Safety and Environmental Features

• Self extinguishing: The solid insulation material inside the dry-type transformer has flame retardancy and self extinguishing properties, and will not release toxic gases under arc conditions.
• No oil leakage risk: There is no risk of oil leakage for the dry-type transformers due to they have no oil tank, thus avoiding environmental pollution hazards.  
• No need for fire safety vault: dry-type transformers can be directly installed in the load center without the need for special additional fire extinguishing systems.

4. Performance Features

• High mechanical strength: Dry type transformers have better short-circuit resistance than oil immersed transformers.  
• Low partial discharge: Dry type transformers have a longer service life and minimal partial discharge activity.  
• Moisture resistance: Dry type transformers can work in humid environments of relative humidity exceeding 95%.  
• High insulation level:excellent short-circuit and lightning withand capabilities for the dry-type transformers.

Product Advantages

1. Safety Advantages

Reduce fire risk: Dry type transformers can significantly reduce the risk of fire and explosion due to the absence of flammable insulation oil.  

Self extinguishing characteristics: The solid insulation material of dry-type transformers has flame retardant properties, which can prevent electrical fires from occurring.  

Not releasing toxic gases: Dry type transformers do not produce harmful gases even under arc conditions.

2. Environmental Advantages

Environmental Protection: Dry type transformers have no risk of oil leakage or spillage, avoiding groundwater pollution problems.  

Recyclable: After the end of the service life of dry-type transformers, 90% of the waste materials can be recycled.  

No need for special anti overflow: Dry type transformers do not require anti overflow containers.

3. Operational Advantages

Low maintenance requirements: Dry type transformers do not require liquid testing, oil filtration, and only occasional visual inspections.  

Long service life: Most dry-type transformers have an operating life of over 20 years.  

Low installation cost: Dry type transformers have fewer installation restrictions and can be installed in most environments, especially without the need for groundwater protection requirements.  

Can be directly installed in the load center: dry-type transformers are installed in positions close to the load to reduce line loss costs.

4. Application Flexibility

Indoor applicability: Dry type transformers can be installed indoors without considering fire safety requirements.  

Adaptability to harsh environments: Dry type transformers can provide sealed tanks, ensuring safe operation even in urban pipelines that are susceptible to flooding.  

Wet environment operation: Dry type transformers have moisture-proof design and can still operate normally under high humidity conditions.