ac aging and space-charge characteristics in low-density polyethylene polymeric insulation

Abstract

In the present work efforts have been made to investigate the influence of ac aging on space-charge dynamics in low-density polyethylene ͑LDPE͒. LDPE films with 200 µm were aged under various electric stress levels at 50 Hz for various times at ambient temperature. Space-charge dynamics in the samples after aging were monitored using the pulsed electroacoustic technique. It has been revealed that the space charge under ac aging conditions is related to the level of the applied field, duration of the voltage application, as well as the electrode materials. By comparing with the results of unaged sample the results from aged sample provide a direct evidence of changing trapping characteristics after ac aging. Negative space charge is present in the bulk of the material and the total amount of charge increases with the aging time. The amount of charge increases with the applied field. Charge decay test indicates that the charges are captured in deep traps. These deep traps are believed to form during the aging and related to change caused by injected charge. By using different electrode materials such as gold, brass alloy, and polyethylene loaded with carbon black, it was found that the electrode has an important role in the formation of charge, hence subsequent changes caused by charge. The charge dynamics of the aged samples under dc bias differ from the sample without ac aging, indicating changes brought in by ac aging. Chemical analysis by Fourier transform infrared spectroscope and Raman microscope reveals no detectable chemical changes taken place in the bulk of the material after ac aging. Finally, the consequence of the accumulation of space charge under ac conditions on the lifetime of the material has been discussed. The presence of deeply trapped space charge leads to an electric stress enhancement which may shorten the lifetime of the insulation system.

Space charge characteristics of multi-layer oil-paper insulation under different DC voltages

“…Detection of acoustic pressure waves allows one to determine charge distribution across the sample. The principle of the PEA can be seen in many literatures [1,2]. The voltage profile in the present study is shown in Figure 2.…”

Influence of Electrical Aging on Space Charge Dynamics of Oil-Impregnated Paper Insulation under AC-DC Combined Voltages

“…Detection of acoustic pressure waves allows the determination of charge distribution across the sample. The details of PEA technique are documented in literature [23,24].…”

Space Charge Behavior of Oil-Impregnated Paper Insulation Aging at AC-DC Combined Voltages

“…Acoustic pressure wave is detected and determine charge distribution across the sample. Details of the PEA technique are documented in literatures [6,24].…”