Degradation and Lifetime Prediction of Epoxy Composite Insulation Materials under High Relative Humidity

Area of Science:

• Materials Science
• Electrical Engineering
• Polymer Chemistry

Background:

• Insulation failure in distribution switchgear, particularly composite epoxy materials, is a significant cause of component damage.
• Elevated temperatures and high humidity accelerate the degradation of these critical insulation systems.

Purpose of the Study:

• To investigate the aging behavior of diglycidyl ether of bisphenol A (DGEBA)/anhydride/wollastonite composite insulation materials.
• To establish failure criteria and predict the service lifetime of these materials under specific environmental stresses.

Main Methods:

• Composite epoxy insulation materials were prepared using casting and curing techniques.
• Accelerated aging experiments were conducted at 75°C/95% RH, 85°C/95% RH, and 95°C/95% RH.
• Material, mechanical, thermal, chemical, and microstructural properties were analyzed, with tensile strength and infrared carbonyl bond absorption used as failure indicators.

Main Results:

• Tensile strength decreased by 50% and ester carbonyl bond absorption reduced to approximately 28% at material failure points.
• A lifetime prediction model estimated the material's service life at 25°C and 95% RH to be 33.16 years.
• Degradation was attributed to hydrolysis of epoxy ester bonds, forming organic acids that reacted with filler calcium ions, compromising the resin-filler interface.

Conclusions:

• Hydrolysis of epoxy resin ester bonds is the primary degradation mechanism under combined heat and humidity stress.
• The reaction between organic acids and filler ions leads to interface destruction, increased surface hydrophilicity, and reduced mechanical strength.
• The developed lifetime prediction model provides valuable insights for assessing the durability of composite epoxy insulation in switchgear.