What is a Dry Type Transformer : Types and Its Factors
There are various types of electrical devices or components available where some of them operate with the same frequency although the transformer is required for different voltage otherwise current requirements. The main function of a transformer in an electrical circuit is to increase or decrease currents/voltages. There are different types of transformers available in the market but the “Dry Type Transformer” is recommended due to some benefits as inexpensive, more efficient and they have safety features. These transformers also called cast resin type transformers. These kinds of transformers are applicable in indoors otherwise outdoors like a commercial, utility, industrial applications.
What is Dry Type Transformer?
Definition: Dry-type transformer is a completely stationary solid-state device and it needs less maintenance to provide problem-free service. This transformer doesn’t contain any moving parts. Not like liquid fill transformers, this transformer use simply high-temperature insulation systems as they are very safe environmentally. These transformers give a secure and consistent power source that doesn’t need fire-resistant vaults, the emitting of toxic gasses otherwise catch basins. These safety factors will allow these transformers to install in different applications where fire safety is required like schools, buildings, hospitals, factories, chemical industries.
This transformer does not use a liquid-like silicone otherwise oil to cool the core as well as coils. These transformers are isolation devices like air-cooled because the case of this device is ventilated to permit air to supply as well as cool the coils.
Types of Dry Type Transformers
There are different types of dry-type transformers available in the market like the following.
Open Wound Transformer
VPI-Vacuum Pressure Impregnated
VPE-Vacuum Pressure Encapsulated
Cast Coil
Open Wound Transformer
As the name suggests, this type of transformer is named based on its manufacturing process. The process involves heating the coils of the transformer, dipping them in varnish, and then baking them. This “dip and bake” method ensures a robust and reliable insulation for the coils.
VPI (Vacuum Pressure Impregnated)
These transformers are typically used in commercial and industrial applications. They include insulation materials that can withstand high temperatures. The manufacturing process involves using materials that resist extremely high temperatures. VPI transformers are treated with a polyester sealant that is moisture-resistant and are commonly produced using a vacuum force impregnation technique.
VPE (Vacuum Pressure Encapsulated)
VPE transformers use a silicon-based resin instead of polyester. This results in a thick varnish coating that provides excellent resistance to humidity, salt, and other harsh environmental conditions, making them suitable for more demanding environments.
Cast Coil
Cast coil transformers are known for their reliability in extreme weather conditions and require minimal maintenance. They can withstand high short circuits, making them ideal for applications in harsh environments where liquid-filled units were previously used. Nowadays, they are extensively used in ships, tunnels, nuclear plants, cranes, and mining industries.
Important Factors in Transformer Design
When designing transformers, several critical factors must be considered:
- Type of Insulation
- Life Expectancy
- Core Material Selection with Minimal Hysteresis Loss
- Level of Insulation
- Losses
- Winding Material Selection
- Regulation
- K-factor
- Overloading
- Testing
In dry-type transformers, insulation breakdown is the most frequent failure, leading to severe faults like earth faults or phase-to-phase winding faults. Insulation condition can be determined through various tests, as dissolved gas analysis (common in oil-type transformers) is not applicable for dry types. Key tests include:
- Partial discharge tests
- Insulation resistance tests
- Frequency response analysis
- Polarization index tests
- Thermographic surveys
- Dielectric loss angle measurement
- Acoustic emission tests
Advantages of Dry Type Transformers
- Pollution-free
- Suitable for contaminated and damp areas
- Simple installation
- Long-lasting due to dielectric heating and low thermal expansion
- Protects property and people
- High resistance to short circuit currents
- Low side clearance
- Excellent performance
- High capacity to support overloads
Disadvantages of Dry Type Transformers
- Expensive
- Difficult maintenance
- Fire risks if coils are not properly cleaned
- Maintenance requires deactivation and downtime
- High electrical losses
- Cooling system needed to control heat-induced losses
- High operating noise, unsuitable for some indoor applications
Applications of Dry Type Transformers
- Gas, chemical, and oil industries
- Environmentally sensitive water protection areas
- Forests
- Inner-city substations
- Indoor and underground substations
- Renewable generation
FAQs
- What is the difference between dry type and oil type transformer?
- Dry type transformers use air for cooling, whereas oil type transformers use oil.
- How do you test a dry-type transformer?
- By measuring winding resistance, voltage ratio, phase displacement, load loss, etc.
- Which oil is filled in a transformer?
- Insulating oils with high insulating properties.
- Why is the oil used in a transformer?
- To protect the core and winding as they are completely immersed within the oil.
- What is DGPT in a transformer?
- DGPT stands for detection of gas, pressure, and temperature in transformers.
In summary, dry type transformers are highly favored for their size, insulation, fire risk mitigation, maintenance ease, and installation cost benefits compared to other transformers.