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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]

The polyethylene terephthalate (PET) is widely used in dry-type insulation application because of its excellent insulation properties. In practice, thermal aging of PET is often encountered, but the related mechanisms and effect of thermal aging on the PET dielectric properties still remain unclear. In the present paper, we presented a systematic and comparative study on the effect of thermal aging on surface microscopic morphological characteristics, DC breakdown strength, trap depths and the apparent mobility. The results indicate that when aged at 130?C, the surface topography becomes coarser than that aged at 80?C. The polarity reversal at the PET/PET interface during the polarization indicates that the injection abilities of Al and Sc electrodes are gradually enhanced when aged at 80?C and 130?C, respectively. Moreover, the measured isothermal discharge currents during depolarization show that the trap depth corresponding to the maximum trap density increases significantly in the beginning of aging, and then it decreases gradually when aged at 80?C, but it increases evidently when aged at 130?C with increasing the aging degree. It also has been found that the apparent trap-controlled charge mobility is greatly enhanced when aged at 80?C with the increase in thermal aging degree. This enhancement is proved to be associated with the decrease in trap energy level at the PET/PET interface. Also, it can be preliminary concluded that the enhancement of DC breakdown strength (at 1500 h) is closely related to the increase in electron type trap energy and its density when aged at 130?C. [ABSTRACT FROM PUBLISHER]

Grounding resistance is an important basic index used to ensure the safety and reliability of grounding systems. In this paper, a method for grounding resistance measurement based on the fall of potential curve is proposed that can be performed using a 2–2.5D lead wire length. In this method, the potential distribution near the auxiliary current electrode is tested and is used as the main analysis and measurement parameter. Based on the relationship between the potential distribution generated by the grounding grid and the current electrode, the grounding resistance of the grounding grid can be deduced. First, the voltages between the grounding grid and the earth surface potential near the current electrode are measured; then, the ground potential rise (GPR) of the grounding grid is calculated through theoretical analysis and numerical calculation; and finally, the grounding resistance is calculated by dividing the potential by the test current. This method avoids the complex task of accurate compensation point location required for traditional measurement methods, and can be performed easily and quickly using a short lead wire. Measurement results from spot testing show that the proposed method can meet the accuracy requirements of engineering testing. [ABSTRACT FROM AUTHOR]

The MIE (Minimum Ignition Energy) characterizes the danger of a kind of combustible gas and its ignition behavior, and the antistatic test for the non-metallic materials is of great value to mining industry. This paper describes an antistatic level testing system for the non-metallic materials used in mines, and the methods to calculate the MIE of the ignition system, electromagnetic energy and scale the antistatic grade are also presented in details. According to the structure of the antistatic level testing system, the model to calculate the electromagnetic energy of the ignition system is set up firstly, then the MIE and electromagnetic energy before and after ignition are computed respectively. The ignition energy coupling coefficient is defined to indicate the ratio between the energy used for ignition and the total electromagnetic energy, based on which the quantity of triboelectric charge produced by the testing material can be obtained. The numerical relation between the ignition energy coupling coefficient and electrode gap is investigated, for the system described in the paper the threshold of ignition energy coupling coefficient increases from 0.42 to 0.77 when the gap distance increases from 1 mm to 5 mm. The system designed in the paper can be used to test the possibility of ignition and explosion for non-metallic devices used in mine, and the safety limit space for different material can be determined. In addition, it also offers reference for the scaling of triboelectric charge. [ABSTRACT FROM PUBLISHER]