Dielectric polymers are playing important roles in electrical and electronic industries. However, aging under high electric stress is a main threat to the reliability of polymers. In this work, we demonstrate a self-healing method for electrical tree damage based on radical chain polymerization, which is initiated by in situ radicals that are generated during electrical aging. Acrylate monomers contained in microcapsules will be released and flow into hollow channels after the capsules are punctured by electrical trees. Autonomous radical polymerization of the monomers will heal the damaged regions, which is triggered by radicals resulting from polymer chain scissions. After optimizing the healing agent compositions by evaluating their polymerization rate and dielectric properties, the fabricated self-healing epoxy resins showed effective recovery from treeing in multiple aging–healing cycles. We also expect the great potential of this method to heal tree defects autonomously without the need to switch off operating voltages. This novel self-healing strategy will shed light on building smart dielectric polymers with its broad applicability and online healing competence.
Guowei Hou,Yunpeng Zhang,Li Zhang,Guan Wang,Yiwei Wang
Polyimide (PI) is widely used as interturn insulation in solid-state transformers (SSTs) for its corona resistance, but its low thermal conductivity and high dielectric loss cause performance degradation under long-term high-frequency electrothermal stress. Adopting multi-dimensional modification design is an effective solution. In this paper, single-dimensional aluminum nitride (AlN) and multi-dimensional aluminum nitride and boron nitride (AlN-BN) modified PI composites were prepared. The surface of the filler was modified by polydopamine (PDA) and the KH550 silane coupling agent. Through microstructural analysis, thermal and mechanical characterization and high-frequency insulation testing, the enhancement mechanism of high-frequency insulation by the multi-dimensional modification was revealed from the aspects of thermal conductivity, dielectric properties, electrical conductivity and trap characteristics. The results show that the AlN-BN/PI composites exhibits enhancements in thermal conductivity, mechanical properties and high-frequency insulation performance. At 10 wt%, the thermal conductivity of AlN-BN/PI composites increases to 0.311 W/(m·K) (85.12% higher than pure PI and 26.42% higher than AlN/PI). Under 3 kV/20 kHz, the 10 wt% AlN-BN/PI composites achieves a corona aging lifetime of 69.12 min, (372% higher than pure PI and 42% higher than AlN/PI). The enhanced insulation performance of the multi-dimensional composites is attributed to: 1) the AlN-BN "sphere–sheet wrapping" structure constructs a thermal conduction network and mitigates dielectric mismatch and loss; 2) multi-dimensional modification enhances charge dynamics through elevated conductivity and shallow trap density, effectively suppressing electric field distortion. These findings advance insulation system optimization for solid-state transformers.
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