Thermal Aging Properties of 500 kV AC and DC XLPE Cable Insulation Materials

Abstract

Despite similar material composition and insulation application, the alternating current (AC) cross-linked polyethylene (XLPE) and direct current (DC) XLPE materials cannot replace each other due to different voltage forms. Herein, this work presents a systematical investigation into the effects of thermal aging on the material composition and properties of 500 kV-level commercial AC XLPE and DC XLPE materials. A higher content of antioxidants in the AC XLPE than in the DC XLPE was experimentally demonstrated via thermal analysis technologies, such as oxidation-induced time and oxidation-induced temperature. Retarded thermal oxidation and suppression of space charge effects were observed in thermally aged AC XLPE samples. On the other hand, the carbonyl index of DC XLPE dramatically rose when thermal aging was up to 168 h. The newly generated oxygen-containing groups provided deep trapping sites (~0.95 eV) for space charges and caused severe electric field distortion (120%) under −50 kV/mm at room temperature in the aged DC XLPE samples. For the unaged XLPE materials, the positive space charge packets were attributed to the residue crosslinking byproducts, even after being treated in vacuum at 70 °C for 24 h. Thus, it was reasoned that the DC XLPE material had a lower crosslinking degree to guarantee fewer crosslinking byproducts. This work offers a simple but accurate method for evaluating thermal oxidation resistance and space charge properties crucial for developing high-performance HVDC cable insulation materials.

Structural Changes and Very-Low-Frequency Nonlinear Dielectric Response of XLPE Cable Insulation under Thermal Aging

“…FTIR is an effective technique to analyze chemical changes in the molecular chain structure of XLPE cables. For unaged XLPE, there are usually four characteristic bands in the FTIR spectrum with wavenumbers of 720 cm −1 , 1460 cm −1 , 2840 cm −1 and 2915 cm −1 , corresponding to the rocking of methylene groups, wag vibration of methylene groups, stretching vibration of methyl groups and methylene groups, respectively [ 26 ].…”

“…As the aging temperature increased to 120 °C and 150 °C, the four bands decreased gradually, which could be a result of the scission of the molecular chain inside XLPE. It can be seen that the reflection peaks around 800 cm −1 , 1020–1090 cm −1 and 1260 cm −1 obviously increase with aging degree [ 26 ]. Furthermore, the absorption peak at the wavenumber of 1720 cm −1 corresponding to carbonyl (-C=O) appears when the aging temperature reaches 120 °C and the intensity increases gradually with the thermal aging process, which means that the number of carbonyl groups increases [ 27 , 28 ].…”

Polymers and Nanotechnology for Industry 4.0

“…PE is frequently used for manufacturing zip lock bags, bottles, food containers, food crates, stretch film, tape, pallets and plastic sheeting (Figure 1). The papers selected from the conference present widely varying types of polymers, such as polyurethane (PU) [9], cross-linked polyethylene (XLPE) [10], polycaprolactone (PCL) [11] and poly(L-lactide) (PLA) [11,12], microcapsules synthesized by the in situ polymerisation of crystal violet lactone (CVL), bisphenol A (BPA) and tetradecanol [13], polypropylene (PP) [14], and poly(3-hexylthiophene) [15]. In the following paragraphs, a concise overview of the published articles is provided in order to attract the interest of potential readers.…”

“…Another application of XLPE is in the field of high voltage direct current (HVDC) technology [17], in particular as cable insulation material. In this regard, Hang et al [10] have investigated the physical, thermal, mechanical, and space charge properties of commercial AC and DC XLPE cable materials. Thermal analysis experiments and oven aging tests were performed to assess their oxidation and thermal-oxidative aging.…”

“…The production of PP at an industrial scale comprises several stages, namely the initiation reaction where the activation occurs; the polymerisation stage, in which the chain of monomers is formed; and finally the termination stage, in which the Another application of XLPE is in the field of high voltage direct current (HVDC) technology [17], in particular as cable insulation material. In this regard, Hang et al [10] have investigated the physical, thermal, mechanical, and space charge properties of commercial AC and DC XLPE cable materials. Thermal analysis experiments and oven aging tests were performed to assess their oxidation and thermal-oxidative aging.…”