A surface discharge non-equilibrium plasma model of air-polyimide under pulsed electrical stress is established, by considering the reaction of charged particles on the dielectric surface and the secondary electron emission caused by the condition that high-energy particles bombard the material surface. The model defines the chemical reaction of air discharge by using simplified set of reactions, which greatly reduces the complexity of the model. To avoid the negative value of particle density in the process of solution, the logarithmic finite-element method is used to solve the model established, so as to implement the dynamic simulation of the surface discharge process. Also, the temporal and spatial evolution of the microparameters such as charge and electric field distribution during discharge are obtained, and the reliability of the model is verified by experiments in terms of discharge development pattern and surface charge accumulation. By comparing the development process of surface discharge under single pulse and repetitive pulses, it can be seen that surface discharge develops from needle electrode to ground electrode under both repetitive pulses and single pulse stress, but the relationship between the discharge propagation time under repetitive pulses and pulse repetition rate is a 'u' curve, and the inflection point moves to higher repetition rate region with the increase of voltage.

This paper reports the effect of DC and pulse wave voltages on space charge characteristics of polyimide material for high-frequency insulation. The pulsed electroacoustic method is used to measure the charge distribution inside the material under the pulse wave voltages with different amplitudes, polarities, frequencies and duty ratios. Comparative results show that positive charge is more likely to accumulate inside the polyimide. The amount of accumulated charge under pulse wave voltages is larger than that under DC voltages. With frequency, more space charge is accumulated under negative pulse wave voltages with a frequency above 50 Hz, while it is not larger than 100 Hz under positive voltages. The maximum distortion of electric field appears under the negative pulse wave voltage with the frequency of 500 Hz, which is 1.19 times the applied field strength. When the duty ratio of the pulse wave voltage exceeds 50%, the distribution of accumulated charge tends to be stable. The research results can provide a reference for the practical application and modification design of polyimide materials in power electronic equipment.

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.

This paper focuses on the effect of unipolar and bipolar square, sine and triangle voltages on space charge characteristics inside solid insulation based on the bipolar charge transport model. According to the model solution process and the polarization characteristics, it is found the algorithms for the model should be chosen with regard to the direction of the electric field at each subdivision inside the calculation sample. Further comparison shows that the charge amount under different conditions is mainly determined by the input power of the imposed voltage, while the migration depth of the injected charge is less than 20 μm from the sample surface. Correlation between the current injection and the charge amount indicates that the variation trends of them follow basically the same. The results under unipolar conditions are not affected by the frequency provided it is larger than 10 Hz, while the charge amount under bipolar ones is negatively correlated to the frequency. Meanwhile, the impact of the initial phase of bipolar polarization decreases rapidly with the increased simulation time. Hence, for space charge measurement inside dielectrics under such conditions, a reliable system should be established according to the polarity and waveforms of the polarization.

The insulation of high-power electronic equipment faces special electrical stresses such as square and pulse waves, but the numerical research on space charge inside the insulation under such conditions is still in the blank at present. Based on the traditional bipolar charge transport model, it is indicated that the polarization conditions with changing polarities require that the solving algorithms of the model should be selected according to the electric field direction inside the sample grid. The charge phenomena under different sample parameters and polarization conditions in the power frequency range are further simulated. It is concluded that both the total charge amounts under unipolar and bipolar conditions are affected by the polarization power, and the charge migration depth is within 20 μm. For the sample parameters, it is found that the accumulated charge amount under two types of polar polarization conditions is obviously reduced as the value of injection barrier or extraction coefficient increases. And the trapping and detrapping parameters have a greater influence under unipolar conditions. Therefore, it is necessary to select appropriate modified parameters according to the actual operating conditions when controlling the insulating performance. As for the polarization condition, it is found that the charge amount at high frequencies is unaffected by the frequency value, and a phenomenon that positive and negative charges simultaneously accumulate can be found under all the bipolar conditions with a frequency of 0.01 Hz. In addition, the simulation also indicates that the charge measurement technique needs to have a sufficiently high spatial resolution under these conditions, and the required time to measure the steady charge is relatively shorter under bipolar conditions.

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The charge phenomena under sine and half-wave sine voltages within the frequency range of 500 Hz are studied here. Based on the pulsed electro-acoustic method, the traditional circuit design under high-frequency voltages is first analysed. It is found that the selection of a 186 pF protection capacitor and a 333 kΩ protection resistor can ensure that the actual voltage applied to the sample is consistent with the expected input. Based on this design, experimental results show that the polarity of the charge accumulated in the depth of the sample is determined by that of the upper electrode. Comparison results under special voltages with different amplitudes and frequencies indicate that the amount of accumulated charge under sine voltages are larger than those under positive and negative half-wave sine and DC conditions, and the samples under lower-frequency conditions show more charge accumulation. The maximum electric field strengths appear at 90 and 270 degrees of the sine voltage with a frequency of 10 Hz, and their values are 68.55 and 81.82 kV/mm, respectively. Therefore, the charge characteristics are easily affected by the voltage's waveform and frequency parameters. The results obtained here can provide guidance for the application of insulating materials under special voltage environments.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

The resolution performance of space charge measurement method determines its application environment and measured information, which has put forward higher temporal and spatial resolution requirements for the charge evaluation of electronic equipment insulation. Based on the ellipsometry detection principle and the photoelastic effect of the sensor, a novel optical method for space charge measurement is proposed. The potentials of the method in terms of single measurement with high signal-to-noise ratio, terahertz bandwidth and nanometer spatial resolution are analyzed. By deriving the mathematical relationship of the signal transmission, it is indicated that the light intensity difference measured by the system can linearly present the elastic force generated from space charge. Based on the built ellipsometry detection system, it is found that the detected signal from the sensor can quickly track the imposed elastic waves with different amplitudes and frequencies, which verifies the feasibility of the crucial detection part and the fast measurement speed of the proposed method. Further simulation results indicate that the refractivity performance of the sensor under the effect of elastic waves can present the deformation variation with a spatial resolution of 2 nm. Therefore, the given explorative research can provide the key theoretical basis and experimental verification for the proposed method.