Correlation between Terahertz Dielectric Properties of XLPE and Its Composition Structure during Electrothermal Aging

Abstract

The electrothermal aging process of cross-linked polyethylene (XLPE) insulation has been an essential factor for the reliability of high-voltage (HV) cables, but the underlying mechanism remains a puzzle. In this paper, the dielectric properties in the terahertz domain of sliced XLPE samples from an HVDC cable are investigated at an electrothermal aging duration up to 1500 h. It is found that with the increase in aging time, the real part and imaginary part of the complex permittivity decrease and increase, respectively. To explain the dielectric phenomenon, chemical changes and crystallinity are characterized by Fourier transform infrared spectrum (FTIR) and differential scanning calorimetry (DSC), respectively. It is proven that declined crystallinity is positively correlated with the real part of complex permittivity by using effective medium theory. Furthermore, by comparing the terahertz dielectric response of unaged and aged XLPE samples in different temperatures, the appearance of small polar molecules has been proven to be responsible for the rise of the imaginary part of complex permittivity.

Electric Field Assist on Enhancing the Electrical Breakdown Strength of Cross-Linked Polyethylene for Power Cable Insulation

“…The secondary melting curve of the sample was considered to eliminate the influence of the thermal history on the measurement results. The crystallinity ( X C ) is often obtained as follows: X C = Δ H m Δ H m 0 × 100 % where Δ H m is the melting enthalpy of the sample, Δ H m 0 is the melting enthalpy of the sample at 100% crystallinity, and Δ H m 0 = 289.3 J/g.…”

“…Cross-linked polyethylene (XLPE) is the common insulating material for the commercially extruded HVDC cables. 5 Reducing the imperfections in XLPE is the most traditional strategy for enhancing the electrical breakdown strength. 6,7 However, it is not always feasible to improve purity in an economical or practical way today, as the cleanliness of XLPE has been developed to an extremely advanced level.…”

“…Cross-linked polyethylene (XLPE) is the common insulating material for the commercially extruded HVDC cables . Reducing the imperfections in XLPE is the most traditional strategy for enhancing the electrical breakdown strength. , However, it is not always feasible to improve purity in an economical or practical way today, as the cleanliness of XLPE has been developed to an extremely advanced level. , In recent years, extensive work has been carried out to improve electrical breakdown strength via nanotechnology. − For example, the doping of inorganic nanoparticles (MgO, Al 2 O 3 , SiO 2 , etc.)…”

Aging and life control of cross-linked polyethylene as cable insulation material

“…由于XLPE绝缘材料的结构特征, 其内 部存在大量陷阱来捕获电荷 [14][15][16] , 当电荷积累量 足够多时, 可能会产生局部放电, 导致聚合物链断 裂甚至降解, 从而引起电缆的绝缘性能在宏观层面 上的失效, 造成重大的断电事故 [17] . 根据电缆的运 行年限, 电缆的寿命一般为30年, 但许多电缆的运 行年限已经接近甚至超过了服役年限 [18] . 而产生 晶 相 [19] .…”

Enhanced DC Breakdown Strength of XLPE via Denser Cross-Linking Network Formation with Liquid Polybutadiene

“…Differential scanning calorimetry (DSC) was employed to investigate the crystallinity and lamella thickness. 1 DSC was conducted under a nitrogen atmosphere with a temperature range of 20−200 °C and a heating rate of 10 °C/min.…”