Investigation of space charge accumulation processes in a chemically cross-linked polyethylene for ac usage (XLPE) and a modified XLPE for dc usage (DC-XLPE) at voltage polarity reversal was carried out using pulsed electro-acoustic (PEA) measurement system. We found that a huge amount of so called packet-like charge, some of which partially increased the electric field in the material to more than twice of the average applied stress, generated in XLPE at the polarity reversal of DC stress. It enhanced the electric stress locally in the sample by almost twice of the applied average stress. On the other hand, we also found that the packet-like charge was not observed in DC-XLPE under the same experimental condition.

Space-charge characteristics of the pure epoxy resin (EP) and epoxy-based hybrid composites under square pulse waves of different polarities and frequencies at different temperatures are investigated. A specially built high-speed pulsed electro-acoustic (PEA) equipment for high-temperature testing is used. The square pulse of 40 kV/mm with different polarities and frequencies at 25 °C, 50 °C, and 80 °C, respectively, are adopted. The findings reveal that a negative electric field with a greater frequency and a positive electric field with a lower frequency can increase the space-charge accumulation. At low temperatures, there is no noticeable difference between the pure epoxy and micro-nano hybrid (MN) samples. The MN sample has fewer accumulated charges than the pure epoxy sample under the same electric field of different frequencies at different temperatures. At different temperatures, the electric field inside the pure epoxy sample distorts more severely than the MN sample, and such distortion increases with the temperature. On the other side, the electric field in the MN sample remains steady even at high temperatures. Negative electric fields have a more significant impact on average charge amounts than positive electric fields, especially at higher frequencies. A relevant mechanism is proposed to explain the results.

This work investigates the influence of aluminum nitride (AlN) fillers on the charge dynamics of epoxy resin (EP) and its hybrid composites through space charge measurements and quantum chemical calculations (QCCs). QCCs analyze the energy-level orbitals and trap parameters of the molecules under the electric field. The pure EP exhibits a homo-charge accumulation, whereas fewer charges are accumulated in the EP hybrid composites. The AlN filler addition significantly suppresses the space charge accumulation during polarization and facilitates the charge dissipation during the depolarization due to the lower trap density than the pure EP. It is found that the orbital energy level of the combined reaction of all monomers together is not a simple superposition of individual orbital energy levels of different monomers. The increased charge injection barrier height suppresses space charge injection and accumulation. The electric field significantly influences the hole traps more than the electron traps. The positive charges with low mobility are easily trapped inside hole traps compared with the negative charges with high mobility inside the electron traps. This results in positive charge accumulation during the polarization and slow decay during the depolarization. The increase of the electrostatic potential is more uniform in hybrid composites than in the pure EP, and no visible electron migration is observed. It indicates that hybrid composites remain stable under electric fields. Moreover, it is not easy for the hole to transport due to the deep trap after the charge injection, leading to limited visible space charge accumulation near the anode.

The characteristics of space charge accumulation under DC stress in glass materials were investigated using the pulsed electro-acoustic method. However, the observed signal was an incomprehensible signal. To understand the observed signal, a measurement of the glass material with a PET film, which was used as a suppression layer for charge injection, was carried out. From this measurement, it is found that hetro space charges were accumulated in glass material under DC stress. One of the reasons for the incomprehensible signal is thought to be a mismatch of acoustic impedance. Therefore, in this paper, the analysis of observed acoustic signal was carried out by calculating the signal ratio at the interface between the sample and electrodes.

In this paper, we studied the space charge phenomena of a solid polymer under thermal and electrical stresses with different frequencies and waveforms. By analyzing the parameter selection method of a protection capacitor and resistor, the newly built pulsed electro-acoustic (PEA) system can be used for special electrical stresses under 500 Hz, based on which the charge phenomena are studied in detail under positive and negative DC and half-wave sine and rectangular wave voltages. Experimental results show that the charge accumulated in the polyimide polymer under DC conditions mainly comes from the grounded electrode side, and the amount of charge accumulated with electric field distortion becomes larger in a high-temperature environment. At room temperature, positive charges tend to accumulate in low-frequency conditions under positive rectangular wave voltages, while they easily appear under high-frequency situations of negative ones. In contrast, the maximum electric field distortion and charge accumulation under both half-wave sine voltages occur at 10 Hz. When the measurement temperature increases, the accumulated positive charge decreases, with a more negative charge appearing under rectangular wave voltages, while a more positive charge accumulates at different frequencies of half-wave sine voltages. Therefore, our study of the charge characteristics under different voltage and temperature conditions can provide a reference for applications in the corresponding environments.