This paper presents the influence of three different voltage stabilizers, 4-n-propylbenzoic acid, 2-methoxyphenylboronic acid, and 3-aminobenzoylmethylamide, on the insulation properties of cross-linked polyethylene (XLPE). The 1 wt % voltage stabilizers are blended with XLPE by a solution method, and then the samples are prepared via a hot pressing method. Electrical and physicochemical properties of the XLPE blends are analyzed by space charge, DC resistivity, DC breakdown strength, thermally stimulated depolarization current, Fourier transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry experiments. It is found that the addition of the voltage stabilizers enhances the DC resistivity and DC breakdown strength of the XLPE, which also inhibits the accumulation of space charges in the XLPE. The results show that the XLPE blend with the addition of 4-n-propylbenzoic acid has the lowest conduction current and a 23.3% increment in the DC breakdown strength compared to that of the reference XLPE among the used voltage stabilizers. Moreover, it is found that the melting properties and thermal stability of the XLPE are not affected by the addition of the voltage stabilizers. The XLPE blend with 4-n-propylbenzoic acid exhibits a uniform trap depth distribution, which facilitates the migration of the space charge to the anode and reduces the electric field inside the sample bulk. Quantum chemical calculations demonstrate that the matching ability of the electron-withdrawing and electron-donating groups of the three voltage stabilizers effectively enhances the electrical properties of the XLPE. In contrast, the 4-n-propylbenzoic acid has the lowest unoccupied molecular orbital energy level, which can effectively buffer the high-energy electrons and increase the DC breakdown strength. A charge carrier transport mechanism is also proposed to explain the effect of the voltage stabilizer on the space charge movement in the tested samples.

This paper presents the effects of the filler type and testing temperature on the charge dynamics and thermal properties of the epoxy resin. The micro‐nano hybrid composites with different content of the micro and nano aluminum nitride (AlN) fillers are fabricated. The morphology of micro‐nano hybrid composites is characterized. Electrical testing and thermal analysis methods are adopted to analyze its electrical and thermal performance. The results show that the space charge accumulation is suppressed and the charge decay process is facilitated in the hybrid composites. The electrical performances of the hybrid composites are enhanced by the nano‐fillers. The apparent mobility and activation energy are decreased with nano‐AlN fillers in the composites at the high temperature. The glass transition temperature and thermal stability of the materials is improved with the nano‐AlN. A hypothetical mechanism is proposed to explain the charge carrier injection and transport of the composites at different temperatures.

This research investigates the optimal region to achieve balanced thermal and electrical insulation properties of epoxy (EP) under high frequency (HF) and high temperature (HT) via integration of surface-modified hexagonal boron nitride (h-BN) nanoparticles. The effects of nanoparticle content and high temperature on various electrical (DC, AC, and high frequency) and thermal properties of EP are investigated. It is found that the nano h-BN addition enhances thermal performance and weakens electrical insulation properties. On the other side, under HF and HT stress, the presence of h-BN nanoparticles significantly improves the electrical performance of BN/EP nanocomposites. The EP has superior insulation properties at low temperature and low frequency, whereas the BN/EP nanocomposites exhibit better insulation performance than EP under HF and HT. The factors such as homogeneous nanoparticle dispersion in EP, enhanced thermal conductivity, nanoparticle surface modification, weight percent of nanoparticles, the mismatch between the relative permittivity of EP and nano h-BN, and the presence of voids in nanocomposites play the crucial role. The optimal nanoparticle content and homogenous dispersion can produce suitable EP composites for the high frequency and high temperature environment, particularly solid-state transformer applications.

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The effect of adding electron-buffering voltage stabilizer (1 wt% maminobenzoic acid) on the electrical tree-induced degradation of cross-linked polyethylene (XLPE) was studied at high temperatures. The electrical tree inception, growth, and partial discharge characteristics were simultaneously analyzed at 30, 50, and 70 C, respectively. The results showed that the growth rate of electrical tree and partial discharge activity as well as the discharge repetition rate, significantly increased with the temperature for pure XLPE and XLPE stabilizer blend. However, the XLPE stabilizer blend exhibited higher tree inception voltage, lower tree growth rate, and partial discharge activity than pure XLPE. The addition of the voltage stabilizer reduced the carbon layer thickness in the tree channel and offered higher resistance to the electrical tree growth. Surface potential decay demonstrated that the voltage stabilizer addition decreased the trap energy level, but increased the shallow trap density of the XLPE. Quantum chemical calculations showed that the voltage stabilizer enhanced the ability to buffer the high-energy electrons in the XLPE. A high-energy electron buffering mechanism was also proposed to explain the effect of voltage stabilizer on the electrical treeing and partial discharge activity in the XLPE at high temperatures.

This paper investigates the influence of voltage stabilizer and nanofiller addition on the insulation performance of the cross-linked polyethylene (XLPE). The test samples of XLPE/stabilizer blends consisting of 1 wt% maminobenzoic acid, XLPE nanocomposites consisting of 0.5 wt% nano MgO and XLPE hybrid composite consisting of both voltage stabilizer and nanofillers were prepared. Various physicochemical and electrical properties were measured to analyze the performance of prepared samples. The obtained results show that the addition of nanofillers deteriorates the electrical insulation performance of the XLPE. On the other hand, the voltage stabilizer addition proves to be suitable for enhancing the electrical insulation performance of the XLPE. Meanwhile, the hybrid XLPE composites have shown medium behavior. The voltage stabilizer addition reduces, but the nanofillers increase the space charge density inside the XLPE compared to pure XLPE. It is also found that the dispersion of the voltage stabilizer in the material is uniform, whereas the nanofillers are aggregated. Furthermore, both additives slightly improve the thermal stability of the XLPE. The trap level theory based on quantum chemical calculation is proposed to explain the influence mechanism of the additives on the XLPE.

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