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The impulse voltage wave invading a transformer is not the double exponential impulse wave (DEIW) specified by the IEC but a non‐standard waveform with oscillation attenuation characteristics, and this fact leads to doubts about the scientificity and optimality of insulation coordination. A key solution for this issue is the establishment of an equivalent relationship between the measured non‐standard impulse voltage wave and the DEIW. In this study, a test platform of multiparameter impulse voltage was set up. Then, the authors obtained the 50% breakdown voltage (U50%) of the oil‐impregnated paper (OIP) for transformer under the bipolar oscillatory attenuated impulse wave (BOAIW) and the DEIW with different waveform parameters. The effects of waveform parameters on the breakdown characteristics of the OIP were finally revealed. On the basis of experimental data and several mathematical methods, the authors established the U50% prediction mathematical models for the OIP under the BOAIW and DEIW. Based on the prediction models and the microfluctuation characteristics of measured overvoltage's waveform parameters, the authors proposed a method for evaluating the waveform equivalence. The characteristics of voltage amplitude and change rate were regarded as the two key factors for the waveform equivalence of this method. [ABSTRACT FROM AUTHOR]

The development of high‐voltage direct current circuit breaker (HVDCCB) has progressed rapidly. One of the major reasons for the failure of a circuit breaker is the metallic particle contamination. An enhanced mathematical model is proposed to simulate the motion dynamics of a spherical copper particle in the break of sulphur hexafluoride (SF6)[AQ ID=Q2] HVDCCB. By linking COMSOL and MATLAB, the interaction between particle motion and electric field distribution and plastic random movement in the collision process is considered. The effects of voltage magnitude and particle size on the particle motion are discussed. By means of statistical methods, the obtained findings show that, as voltage magnitude decreases or particle size increases, the particle–anode collision frequency decreases, and the particle–anode collision region increases in the x‐direction but decreases in the y‐direction. The accuracy of the proposed model is verified by experimental observations via high‐speed video camera. [ABSTRACT FROM AUTHOR]

This study presents a method for the estimation of soil structure based on genetic algorithm (GA), which can reveal actual soil structures through the experimental curve of apparent resistivity that was measured near the ground grid. GA involves the use of the errors produced by the experimental and theoretical curve of soil apparent resistivity to achieve soil structure optimisation. In this study, new soil structures were generated by GA, and finite element method (FEM) was used to compute the theoretical curve of apparent resistivity under these soil structures. The relative position of ground grid and the measurement profiles was considered in FEM, which can reveal the true measurement site. Compared with present methods, the proposed method that combines FEM and GA can adapt to a solution domain of complex geometry shape while ground grid and soil exist simultaneously. Thus, the proposed method can handle the experimental curve which is influenced by the grounding system. In addition, the solution accuracy of the soil parameters was reasonably established and thus allowed the algorithm to exhibit convergence within 50 generations. [ABSTRACT FROM AUTHOR]

The working current of DC grounding electrodes is constantly increasing with the rapid development of high‐voltage direct current systems. Thus, the temperature rise of grounding electrode conductors is increasingly becoming an important safety factor. Therefore this study measured the soil temperature characteristics of water content and resistivity; established an electric heat coupling finite element model for DC grounding electrodes that is based on current field and temperature field theories to analyse the temperature changes in common DC grounding electrodes. In contrast to traditional models, the proposed model realises electric heat coupling field calculation by considering the mutual influence of temperature rise and soil parameters. The results show that the soil resistivity increases with increasing temperature and the soil resistivity change further influence the temperature changes of the grounding electrodes. The change in grounding electrode temperature rise is not steady and includes a sharp growth stage. [ABSTRACT FROM AUTHOR]

The wide variety of lightning stroke characteristics and the modifying effects of power system components result in a diversity of intrusive lightning voltage waveshapes that stress transformers. These are not the traditional standard lightning impulses with a waveshape of 1.2/50 μs. Therefore the applicability of the standard lightning impulse voltage to power transformer testing has been questioned, and the overvoltage used in the test on transformers should be in accordance with the lightning overvoltage measured in the field. In this study, a lightning overvoltage monitoring system was installed in a 110 kV air‐insulated substation, and the lightning overvoltages from 2007 to 2012 have been measured. Analysis was conducted on the measured data, which indicated that bidirectional oscillatory lightning waveforms rose up in the measured overvoltages. Using the energy method, the bidirectional oscillatory lightning waveform was reformulated into double exponential waveform, and the characteristic parameters, such as peak amplitude, front time and tail time, of the measured data were statistically analysed. [ABSTRACT FROM AUTHOR]