Search

Nanocomposite (NC) polymers are commonly employed because of their high breakdown strength, but the underlying mechanism of this phenomenon is not well understood. In the present study, specimens of polyethylene terephthalate (PET) films coated with epoxy resin (EP) and filled with nano-SiO 2 and Si 3 N 4 at concentrations of 0, 0.5, 1, 2, 5 and 10 wt % were subjected to DC and impulse voltages to breakdown. The effects of the types of nano-fillers and concentrations on the dielectric properties, crystallinity, and space charge trap characteristics were investigated on the breakdown strength. The experimental results show that improved DC breakdown strength of a sandwich structure of PET/nano-EP film is obtained even at 10 wt%, which is attributed to the effect of increased trap density for deep traps. In addition, to experimentally establish the dominant factors during impulse breakdown, a systematic theoretical model was used to account for the variations of impulse breakdown performance. It is concluded that the frequency-dependent dielectric characteristics plays an important role in determining the absorption of activation energy for trapped electrons, which affects the instantaneous insulating performance of NC polymers. [ABSTRACT FROM AUTHOR]

As the core component of composite insulation for dry-type high-voltage equipment, polytetrafluoroethylene (PTFE) films are subjected to high temperatures and complex electric fields. Therefore, this study explores the effects of electric field and temperature on the space charge characteristics of double-layered PTFE films based on the measurement of space charge distribution in double-layered PTFE films under different DC voltages and temperatures using the pulsed electro-acoustic measurement system. Results show that more charges accumulated in the PTFE sample subjected to a positive electric field during polarization and the space charges dissipated more rapidly during depolarization compared with those subjected to a negative electric field. The existence of a PTFE/PTFE interface increased the density of trap and deepened the trap. The positive charges that accumulated at the PTFE/PTFE interface during polarization gradually held a dominant position with the increase of temperature. Finally, the formation of charge in the PTFE/PTFE interface mainly depended on two factors. When the applied DC voltage was not large, the charge formation was mainly dominated by the Maxwell-Wagner polarization effect. When the voltage increased to a certain threshold, the charge formation was mainly caused by the charge injection and migration characteristics. [ABSTRACT FROM AUTHOR]

Polyimide film (PI) is widely used as dry-type smoothing reactor insulation for ultra-high voltage direct current (UHVDC) projects. In practice, the temperature of a central conductor can reach 80 °C to 100 °C at the rated power flow. Thus, the inner insulation composed of PI sustains these high temperatures. In this study, the space charge characteristics of PI at different temperatures (40 °C, 60 °C, and 80 °C) and thermal aging degrees (336, 500, 1000, and 1500 h) were examined with an improved pulsed electro-acoustic (PEA) measurement system to investigate the effects of temperature and thermal aging on dielectric performance. The apparent trap depths corresponding to various aging degrees were obtained according to the space charge decay dynamics at the interface. Results indicate that positive charges likely accumulate within the bulk of the material because of the thermal aging of homogeneous materials. The polarity of space charge at the interface also changes from positive to negative as aging degree increases. The space charge decay dynamics at the interface further shows that the trap energy increases as the thermal aging degree increases. The amount of residual space charge also increases remarkably as the electric strength and aging degree increase. The electric field distortion is closely related to temperature, thermal aging degree, and electric strength. [ABSTRACT FROM AUTHOR]