Classes of Insulation in Dry Type Transformers
Class A:
- Temperature limit: 105°C
- Basic insulation class
- Suitable for less demanding applications
Class B:
- Temperature limit: 130°C
- Improved heat resistance compared to Class A
- Used in moderate temperature environments
Class F:
- Temperature limit: 155°C
- Widely used in industrial applications
- Offers higher temperature resistance than Class B
Class H:
- Temperature limit: 180°C
- High-performance insulation
- Suitable for demanding environments with elevated temperatures
Class R:
- Temperature limit: 220°C
- Most heat-resistant class
- Used in extreme conditions where other classes may fail
Insulation Materials for dry type transformer
Fiberglass laminates and sheets
Fiberglass laminates and sheets serve as core, barrier, and structural insulation in dry type transformers. 3240 epoxy and GPO-3 are common fiberglass laminates used in transformer construction.
3240 epoxy, a fiberglass-reinforced laminate, offers high mechanical strength and electrical insulation. It functions as core insulation and structural components. Its heat and chemical resistance make it suitable for harsh environments.
GPO-3 (glass polyester grade 3) is a flame-retardant fiberglass laminate with high-temperature resistance. It acts as barrier insulation between windings and provides structural support.
PET film and polyimide film
PET (polyethylene terephthalate) film, known as Mylar, possesses high dielectric strength and temperature resistance. Its thin, durable nature makes it suitable for insulating individual wire turns in transformer windings. PET film maintains insulating properties under high temperatures and electrical stress.
Polyimide film, often called Kapton, offers superior heat resistance, withstanding temperatures up to 400°C.
Both PET and polyimide films excel in cylinder insulation design. Their flexibility allows for smooth, uniform layers around cylindrical cores. These films can be combined with other insulating materials to create composite structures meeting specific voltage and temperature requirements. The low moisture absorption rates of PET and polyimide films contribute to dry type transformer stability.
Prepreg DMD
Prepreg DMD combines PET film and epoxy resin to form a robust low voltage layer insulation for dry type transformers. This composite material offers superior electrical and mechanical properties, making it ideal for low voltage windings.
Prepreg DMD provides high insulation strength compared to traditional materials. Its composition allows for improved thermal conductivity, dissipating heat more effectively within the transformer.
The material’s flexibility and ease of application streamline the manufacturing process. The epoxy resin component bonds layers together, creating a cohesive insulation structure. This reduces partial discharge risks and enhances the transformer’s overall dielectric strength.
Glass fiber mesh, cloth, and tapes
Glass fiber mesh reinforces windings mechanically. It wraps around coils, enhancing structural integrity and preventing deformation from electromagnetic forces. The mesh’s open structure facilitates heat dissipation, maintaining optimal transformer performance.
Glass fiber cloth provides layer insulation between windings. Its tight weave creates a reliable electrical breakdown barrier while remaining flexible. Manufacturers often combine it with other insulating materials for robust insulation systems.
Glass fiber tapes bind transformer cores. They secure core laminations, reducing vibration and noise. These tapes also insulate between the core and windings.
Aramid papers
Aramid papers, including Nomex and NHN, are key insulation materials in dry type transformers. These papers serve multiple functions: turn, layer, barrier, core, lead, and spacer insulation. Their exceptional thermal and electrical properties make them indispensable in transformer design.
Sheet molding compound
Sheet molding compound (SMC) for high-voltage coil pads enhances dry type transformer insulation. SMC combines chopped glass fibers, polyester resin, and mineral fillers. It offers excellent electrical insulation, mechanical strength, and thermal stability.
SMC can be more expensive than some alternatives and requires specialized manufacturing processes. However, its performance benefits often justify its use in high-voltage dry type transformers, particularly in applications demanding reliability and longevity.
Polyester tapes
Polyester tapes serve critical functions in dry type transformer insulation, specifically for coil binding and core insulation. These tapes are widely used due to their superior electrical and mechanical properties. They withstand high temperatures and provide reliable insulation throughout the transformer’s operational life.
In coil binding applications, polyester tapes secure windings and maintain their shape. This prevents movement and potential short circuits during operation. Manufacturers apply these tapes in multiple layers, creating a robust barrier against electrical breakdown.
For core insulation, polyester tapes act as an effective barrier between the core and windings. They prevent electrical contact and reduce core heating risks. These tapes are often used in combination with other insulating materials to achieve optimal performance.
Varnishes, epoxies, and resins for sealing and impregnation
Varnishes are used for dipping or vacuum pressure impregnation of coils. They penetrate windings deeply, improving heat dissipation and increasing dielectric strength. Epoxies provide superior mechanical strength and excellent adhesion. Manufacturers often use them to encapsulate entire coil assemblies, creating a robust barrier against moisture and contaminants.
Resins, including polyurethane and silicone-based compounds, offer versatile sealing and impregnation options. They can be applied through casting, potting, or vacuum impregnation. These materials exhibit good thermal conductivity and flexibility, making them suitable for various operating conditions.
FAQs
How Often Should Dry Type Transformer Insulation Be Inspected?
Dry type transformer insulation should be inspected annually. More frequent inspections are necessary for harsh environments or frequent overloads.
Can Insulation Class Be Upgraded in Existing Dry Type Transformers?
Upgrading insulation class in existing dry type transformers is typically not feasible. Higher temperature ratings usually require replacing the entire transformer with one specifically designed for a higher insulation class.
What Environmental Factors Most Affect Dry Type Transformer Insulation Longevity?
Temperature, humidity, and contaminants primarily affect dry type transformer insulation longevity. High temperatures accelerate aging, moisture reduces dielectric strength, and pollutants cause chemical degradation.
How Does Insulation Class Impact the Overall Cost of a Dry Type Transformer?
Higher insulation classes increase transformer costs due to superior materials and manufacturing.
