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Title: Partial discharge ageing of polymer insulation under combined AC and DC stress at elevated temperatures
Author: Zhao, Weijia
ISNI:       0000 0004 6423 0155
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2017
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Cable termination is the weakest part in any HV underground cable system, as defects may be left in the main insulation during the installation process. In HVDC systems, the converters produce the intended DC voltage for transmission but there may also be AC harmonics superimposed. The frequency of the AC harmonics could be in kHz range. The superimposed harmonics on the HVDC may have synergistic effects on cable insulation and may lead to further degradation in the cable insulation. In addition, for the sake of environmental protection, XLPE is no longer the suitable choice for underground cable insulation as it cannot be recycled. Thermoplastic material may be a candidate. There is little published information on the behaviour of thermoplastic materials under combined AC and DC voltages. In thermoplastic materials, HDPE film and PP film were selected as the target material to study in this project. As the properties of HDPE are similar to those of XLPE, the data obtained from HDPE was regarded as a bench-mark. It was decided to use the thermo-electrical stress to age the samples. For thermal stress, 90°C was chosen as the aging temperature for HDPE, while 90°C and 110°C were chosen for PP. For the electrical stress, AC & DC combined voltage was used to age the samples. DC voltage was 6 kV. The superimposed frequency of AC voltage was 1 kHz, 1.5 kHz, 2 kHz and 2.5 kHz. The AC/DC voltage ratio is from 10%, 30% and 50%. In this project, the effect of frequency and voltage ratio on HDPE and PP degradation under superimposed stresses was studied using the following approaches: Equivalent Phase Resolved Partial Discharge (PRPD) plots, Fourier Transform Infrared - Attenuated Total Reflection (FTIR-ATR) Spectroscopy and Dielectric Spectroscopy (DS) measurements were carried out. The performance of HDPE and PP were compared.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral