Interface degradation between mandrel and sheath can cause a decrease in insulation performance and mechanical strength of composite insulators. In this study, the interface ageing properties of cycloaliphatic epoxy resin and silicone rubber composite insulator were compared. A water diffusion test was adopted to simulate the composite insulator ageing in a hot and humid environment. A four‐electrode system was built to detect leakage current at different locations (mandrel, sheath and interface), which is an important basis for evaluating insulator performance. The ageing degree of insulator could be quantitatively characterised by leakage current change. It was found that the infiltrated moisture had a great effect on insulation performance. Based on the water absorption test result, the interface performance of two insulators was mainly influenced by their sheath sealing quality. As an auxiliary evaluation method, temperature rise during the test was recorded using an infrared camera. The experiment results showed that interface degradation was the main factor for the insulation performance decrease of silicone rubber composite insulators. However, insulation level reduction of the cycloaliphatic epoxy resin was caused by the wet sheath. In addition, a model for temperature rise of cycloaliphatic epoxy resin insulators was proposed based on good correspondence between sheath material and insulation. The model incorporated multiple processes such as ageing and heating of insulators, and it can predict the early temperature rise well.
The lack of hydrophobicity transfer capability has restricted the applications of insulating materials in environments with heavy contamination. In this study, an epoxy resin insulating composite was prepared using a micro‐capsule system to achieve hydrophobicity transfer triggered by creepage discharge. The influence of the micro‐capsules on the electrical properties of insulating materials and the hydrophobicity of the test samples before and after the creepage discharge test was analysed. The results show that the poly(urea‐formaldehyde) micro‐capsules, which contained hydrogen silicone oil, have good morphology and thermal stability characteristics at temperatures below 222°C. Micro‐capsules have minor effects on the electrical properties of epoxy insulating materials. Further, the hydrophobicity transfer capability of the test piece was improved considerably compared with that of the pure epoxy insulating material. This study expands the application of micro‐capsule technology in the field of insulating materials and provides a reference for the development of next‐generation insulating materials.
To investigate how the multiphase structures affect the electrical conductivity in semicrystalline polymer composites, herein, an accurate multiphase content calculation method is proposed and verified, which combines amorphous phase information in broadband dielectric spectroscopy and crystalline phase information in differential scanning calorimetry. Taken aluminium hydroxide (ATH) filled silicone rubber as an example, it is found that the rigid amorphous fraction (RAF) corresponding to the chains constrained by crystals (RAF cry ) is not linearly increased with crystalline fraction (CF). Compared to non-isothermal crystallisation, RAF caused by ATH/silicone rubber interface (RAF int ) after isothermal crystallisation at 213 K changes little, while mobile amorphous fraction and RAF cry is attenuated and CF is strengthened. Based on the calculated structures of ATH filled silicone rubber, activation energy of conductivities during cooling is dominated by the thermal transition for conductive ions and shortened distance among the conductive ions through shrunk volumes of the amorphous phase. Our findings deepen the understanding of multiphase content in semi-crystalline polymer composites and its relationship with electrical conductivity, which can be applied in manipulating electrical performance of semi-crystalline polymers by fillers. | INTRODUCTIONBy a combination of various insulating polymers and nonconductive fillers, polymer composites are endowed with improved properties, such as insulation, mechanical strength, and heat conduction [1]. Under appropriate conditions, the polymer segments with regular structure would form crystals coexisting with the amorphous phase, namely semi-crystalline polymers. Nowadays, semi-crystalline polymer with nonconductive fillers has been extensively applied in important fields, such as electric, transportation, construction etc. [2]. In the semi-crystalline polymers composites, many different phases exist, such as rigid amorphous phase caused by crystals and interfaces, mobile amorphous phase, crystalline phase, and fillers phase [1], which is important in determining the electrical property, a key property for a broad range of applications [3]. Under weak electric field, for electrical conductivity, the insulating fillers hardly provide a conductive pathway. Crystalline phase is always considered to be more insulating than amorphous phase in polymer conductivity [4,5]. According to the classical theory, ion transport, the main conductive mechanism in insulating polymers under weak electric field, is coupled to the polymer segmental motion that is various in different amorphous phase [6]. Therefore, the multiphase content and structures are closely related to the electrical properties. Understanding the multiphase information is essential to manipulating the electrical performances in semicrystalline polymers composites.
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