Influences of Traction Load Shock on Artificial Partial Discharge Faults within Traction Transformer—Experimental Test for Pattern Recognition

Partial discharge (PD) measurement and its pattern recognition are vital to fault diagnosis of transformers, especially to those traction substation transformers undergoing repetitive traction load shocks. This paper presents the primary factors induced by traction load shocks including high total harmonics distortion (THD), transient voltage impulse and high-temperature rise, and their effects on the feature parameters of PD. Experimental tests are conducted on six artificial PD models with these factors introduced one by one. Results reveal that the maximum PD quantity and the PD repetitive rate are favorable to be enlarged when the oil temperature exceeds 80 °C or the THD is higher than 16% with certain orders of harmonic. The decline in PD inception voltage can mainly be attributed to the transient voltage impulse. The variation in central frequency of the fast Fourier transformation (FFT) spectra transformed from ultra-high frequency signals can mainly be attributed to high THD, especially when it exceeds 20%. The temperature rise has no significant influence on the FFT spectra; the transient voltage impulse, however, can result in a central frequency shift of the floating particle discharge. With the rapid development of high-speed railways, the study presented in this paper will be helpful for field PD detection and recognition of traction substation transformers in the future

Realizing simultaneously excellent energy storage and discharge properties in AgNbO3 based antiferroelectric ceramics via La3+ and Ta5+ co-substitution strategy

AgNbO3 based antiferroelectric (AFE) ceramics have large maximum polarization and low remanent polarization, and thus are important candidates for fabricating dielectric capacitors. However, their energy storage performances have been still large difference with those of lead-based AFEs because of their room-temperature ferrielectric (FIE) behavior. In this study, novel La3+ and Ta5+ co-substituted AgNbO3 ceramics are designed and developed. The introduction of La3+ and Ta5+ decreases the tolerance factor, reduces the polarizability of B-site cations and increases local structure heterogeneity of AgNbO3, which enhance AFE phase stability and refine polarization-electric field (P–E) loops. Besides, adding La3+ and Ta5+ into AgNbO3 ceramics causes the decrease of the grain sizes and the increase of the band gap, which contribute to increased Eb. As a consequence, a high recoverable energy density of 6.79 J/cm3 and large efficiency of 82.1%, which exceed those of many recently reported AgNbO3 based ceramics in terms of overall energy storage properties, are obtained in (Ag0.88La0.04)(Nb0.96Ta0.04)O3 ceramics. Furthermore, the discharge properties of the ceramic with discharge time of 16 ns and power density of 145.03 MW/cm3 outperform those of many lead-free dielectric ceramics

Terahertz-Based Insulation Delamination Defect Inspection of Vehicle Cable Terminals

Cable terminals of the high-speed Electric Multiple Units (EMUs) are prone to undertake insulation delamination defects due to their special operating conditions. Such a defect is difficult to identify and it may pose a great threat to the safety of the EMUs. To achieve accurate detection of insulation delamination defects, this paper proposes a terahertz-based approach that combines the spectrum of the terahertz wave and terahertz imaging techniques. Specifically, a synthetic multilayer composite insulation structure with an air gap is firstly built to simulate the internal delamination defect of the cable terminal. Then terahertz tests in both time and frequency domains are performed on the synthetic structure. Experimental results show that the delamination defect of the multilayer insulation structure can be quickly detected by observing the absorption spectrum in the terahertz frequency domain. The location and geometry of the defect can be preliminarily determined by the terahertz imaging and then further refined through image segmentation. In addition, the thickness of the delamination defect can be quickly calculated by the terahertz time-domain spectrum. By combining the terahertz spectrum and the terahertz imaging information, the delamination defects are quantitively detected for the multilayer composite structure or even for the EMU’s cable terminals