The Extra-Low Frequency Dielectric Analysis Method for Evaluating Byproducts of Cross-Linked Polyethylene Cable Insulation Materials

Cross-linking byproducts in the cross-linked polyethylene (XLPE) cable insulation material significantly affect the insulation properties of XLPE, and the non-destructive detection method for cross-linking byproducts during cable degassing process still faces great challenges. This work develops an extra-low frequency (ELF) dielectric analysis method based on time-dependent polarisation current for non-destructive detection of byproducts in XLPE. The effects of single byproduct of acetophenone and cumyl alcohol on the ELF dielectric properties of XLPE are studied separately. The ELF associated static permittivity and the dielectric loss of XLPE rise as the content of the single byproduct increases, and the α relaxation (10⁻⁴–10⁻³ Hz) and β relaxation (10⁻³–10⁻² Hz) of XLPE are observed. Ionisation of acetophenone occurs above electric field strength of 20 kV, whereas ionisation tends to saturate above 50 kV. The optimal field strength for ELF dielectric testing of XLPE is determined to be 20–50 kV. Furthermore, the degassing factor is proposed to accurately determine the removal of byproducts. Based on these, the non-destructive detection of degassing of XLPE cable is achieved. The proposed ELF dielectric analysis method enables the non-destructive detection of byproducts in cables, opening a new avenue for cable degassing effect evaluation.