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Why Do Epoxy Bushings Outperform Porcelain Bushings?

Engineers and OEM manufacturers are increasingly specifying epoxy over porcelain for use in transformers and circuit breakers. Epoxy bushings are stronger, lighter, more durable, easier to install, and more flexible. In normal operating conditions, epoxy bushings will last 20 to 30 years. In fact, many of the epoxy bushings first made at Polycast are still in active service after nearly 50 years. Other benefits of epoxy include:

  • Epoxy is homogeneous.
    If the outside layer of an epoxy bushing becomes damaged the material underneath has the same properties as the surface and will perform equivalently. Whereas, if the outside glaze of a porcelain bushing is damaged, the bushing may have to be replaced or repaired.
  • Epoxy Bushings don’t require assembly.
    Porcelain bushings require assembly of several components to build the final product. Aside from the extra expenses associated with the build, the assembly process also increases the risk of flaws and failure in the bushing’s duty to insulate the conductors. Oil filled porcelain bushings can leak from the seal after assembly, whereas epoxy insulation is a solid body bonded to the conductor to provide the seal and has no oil content to leak.Epoxy bushings do not require assembly which saves the transformer manufacturer time, money, and reduces risk. Epoxy bushings are ready to be installed the moment they arrive.
  • Increased Design Flexibility.
    Epoxy provides more flexibility in manufacturing and design and can be molded into intricate shapes and profiles to meet the needs of your application. Epoxy tooling is less costly than porcelain which enables low number production runs for replacement parts to be more economical.

From the development of Polycast formulations to the design and manufacture of our bushings, our experienced team of chemists and engineers combine research and development with extensive testing to ensure high-quality, reliable epoxy products.

Polycast transformer and switchgear bushings are available for both indoor and outdoor applications for low to medium voltage use. Our epoxy bushings are in service in all types of environmental conditions including highly contaminated or polluted areas.

Physical performance

Polycast epoxy thermal expansion closely matches that of the copper conductor which means the bar and epoxy body of the bushing expand and contract at close rates when heated and cooled. This feature of the epoxy greatly improves bushing performance and longevity in thermal cycling due to reduced mechanical stresses. The risk of epoxy bushings leaking beyond the seal is greatly reduced, and so the risk of cracking caused by thermal shock is eliminated. In addition:

  • Polycast epoxies perform at equal or higher strength in tension and compression and are tougher than their porcelain alternatives.
  • Polycast epoxies have an equivalent impact strength to porcelain.
  • Temperature rating of 105°C is standard.
  • Epoxy bushings are not oil-filled and can not leak the bushing contents.
  • Excellent hydrophobicity performance with water absorption of < 0.1%.
  • All Polycast epoxies are UL approved and flammability rated at V0.

Electrical Performance

  • Polycast cycloaliphatic and bis-A resins formulations exceed the tracking requirements for ASTM 2303 with more than 300 min at 3.5 kV.
  • Controlled in house blending, dispersion, vacuuming, and metering of resin and hardener systems ensure void-free castings that guarantee low partial discharge levels.
  • The dielectric constant of Polycast epoxy is lower than porcelain.

Polycast specializes in a shared design approach; working with you to provide engineered epoxy solutions for the most challenging demands. As an ISO 9001:2015 certified manufacturer, we are dedicated to improving our processes to cost-effectively meet the quality and delivery requirements of our growing customer base.

Allow us to be your casting partner.
Call 1-800-665-7445 or complete the contact form to speak to our Sales or Engineering team.