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Why do some Epoxy (polymer) Transformer Bushings fail?

We all know that how troublesome it is when a bushing fails on a transformer in the field. In addition to incurring significant costs to replace the bushing, there is the question of the transformer supplier’s reputation as well as being subject to possible penalties imposed by customers suffering power interruptions.

 

The correlation between the chemical composition of the inorganic filler content and the mechanical values of an epoxy system


There are three main factors that would be considered when formulating an epoxy or urethane system for adhesives, potting and encapsulation applications.

Why Fish Eyes develop in an Epoxy or Polyurethane Coating?

When a coating is applied to a substrate that is contaminated with low surface energy particles such as oil, wax, grease, or silicone, fish eyes may develop in the coating as it is applied. These fish eyes are produced because the coating is unable to wet out the contaminated area.

A Quick Check List to Determine the Cause of Cracking in an Epoxy or Urethane Cast Component:

If the problem is recent, the Number 1 step is to check if anything has changed in your process. Do not assume! Check! - Take the show me how you do it approach!

 

Basic Considerations for Encapsulating Magnetic Components using Epoxy or Polyurethane Systems

 

Things to keep in mind:

  • Polyurethanes tend to have shorter pot life and, as a rule, exhibit more shrinkage during cure
  • Unfilled product tend to have higher CTE’s which may result in broken wires, cracked cores and / or a change in filled products exhibit less shrinkage, lower CTE and better thermal conductivity.
  • In most cases, the pot life (working time) can be adjusted by a slight alteration in the chemistry, with Epoxy systems having a wider range in this regard.

 

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