Common Causes of Epoxy Resin Instrument Transformer Cracking
Common Causes of Epoxy Resin Instrument Transformer Cracking
Epoxy resin instrument transformer cracking can occur during production or after years of service. The following are five common causes:
Cracks originating from metal inserts or copper bar edges — Sharp metal edges without radius (R) treatment cause stress concentration and become crack initiation points.
Batch cracking, especially in thick parts — Excessive heating rate during curing, followed by rapid cooling without a stepped curing process, creates high residual stress.
Delamination along the metal-resin interface — Insufficient preheating of coils or metal inserts, oil or dust contamination on the interface, and large differences in thermal expansion coefficient between metal and epoxy resin lead to interface stress overload.
Cracks after thermal cycling in service — Products may pass visual inspection at factory but develop cracks after cold-hot cycling at the customer site. This is delayed latent cracking caused by unreasonable curing curves and high residual stress.
Cracking at thin-wall positions — Insufficient local epoxy wall thickness, abrupt thickness changes without arc transition, and concentrated shrinkage stress cause cracks.
To prevent these issues, manufacturers should use proper radius treatment on metal inserts, stepped curing profiles, preheating of inserts, clean interfaces, and optimized wall thickness transitions. CNYIHU applies strict process control in epoxy resin APG and vacuum casting, including vacuum degassing, gelation and curing time control, and routine partial discharge testing to ensure insulation reliability. For related manufacturing details, see our Voltage Transformer Manufacturing Process and Current Transformer Manufacturing Process articles.
