Detection and localization of partial discharge are very important in condition monitoring of power cables, so it is necessary to build an accurate recognizer to recognize the discharge types. In this paper, firstly, a power cable model based on FDTD simulation is built to get the typical discharge signals as training samples. Secondly, because the extraction of discharge signal features is crucial, fractal characteristics of the training samples are extracted and inputted into the recognizer. To make the results more accurate, multi-SVM recognizer made up of six Support Vector Machines (SVM) is proposed in this paper. The result of the multi-SVM recognizer is determined by the vote of the six SVM. Finally, the BP neural networks and ELM are compared with multi-SVM. The accuracy comparison shows that the multi-SVM recognizer has the best accuracy and stability, and it can recognize the discharge type efficiently.
Background Tourniquet pain is the most prominent problem in ankle surgery, and there is no proper method to predict it. It was reported that pain sensitivity questionnaires could evaluate the pain sensitivity of subjects. Its potential to predict tourniquet pain in ankle surgery is constructive and meaningful. Methods One hundred and twenty patients undergoing ankle surgery were included in this study. The pain sensitivity questionnaire (PSQ) and self-rating anxiety scale (SAS) were completed before the operation. The methods included an ultrasound-guided popliteal sciatic, a femoral nerve block, and a proximal thigh tourniquet. The pressure of the tourniquet was set according to the systolic blood pressure (SBP + 100 mmHg). A visual analogue scale (VAS) was used to assess the tourniquet pain. Also, the onset time of tourniquet pain ≥4 VAS units was recorded. Results The PSQ-total and PSQ-minor scores were significantly correlated with the onset time when the tourniquet pain ≥4 VAS units ( r = −0.763, r = −0.731, P < 0.001). The PSQ-total score <6.5 group gave significantly lower ratings for items 3, 4, 14, and 16 in the PSQ survey compared to the PSQ-total score ≥6.5 group ( P < 0.05). Patients with high pain sensitivity have a higher need for analgesic drugs ( P < 0.001). PSQ-total score ≥6.5 (OR = 185.8, 95% CI = 39.8–1,437.6, P < 0.001), sex (male, OR = 0.11, 95% CI = 0.018–0.488, P < 0.05), and age (OR = 0.92, 95% CI = 0.842–0.995, P < 0.05) were risk factors for reporting a tourniquet pain ≥4 VAS units within 30 min. Conclusion The PSQ score is found to be correlated with intraoperative tourniquet pain. In addition, sex and age also affect the time of having intraoperative tourniquet pain.
With the development of ultra-high voltage transmission technology, the Hybrid Reactive Power Compensation method (HRPC) which utilizes series compensation and controllable high resistance can be widely used. Therefore, the study on the influence of HRPC on GIS shell' s TEV is significant. Based on simplified equivalent model of GIS shell grounding, the simulation analysis of the TEV waveform and frequency characteristics before and after the installation of HRPC are carried out. In both conditions of grounding that HRPC and GIS are connected to some and different grounding grids, the relationship between the amplitude of the TEV main frequency oscillation and the installation position of the HRPC are analyzed, Besides, the influence of the SCSR entrance capacitor and the series compensation capacitance on the corresponding amplitude of the TEV main frequency is analyzed as well. The results show that, compared with the case of non HRPC, the TEV oscillation of the GIS is more severe after the installation of HRPC, the peak value of TEV does not change notably, and the amplitude of the TEV main frequency has been greatly improved. With the increase of the distance between HRPC and GIS, the amplitude of the TEV main frequency decreases. The TEV main frequency amplitude increases with the equivalent capacitance of SCSR, and does not change with the variation of the earth capacitance.
The DC bias of AC transformer will be caused by grounding electrode which pour DC into the ground, DC bias is affected by the ground condition near the ground electrode, the parameters of power equipment and lines, and the operation mode of power grid, among which the geodetic parameters near the ground electrode are uncertain factors. In this paper, a method of estimating geodetic parameters is proposed. The probability statistics of moments of random variables are obtained according to the probability distribution of random factors or random disturbances. The uncertain parameters are estimated such as earth resistivity and equivalent area, and the error analysis of uncertain factors is completed. The simulation validation of the estimation method is carried out, and the variation of the ground potential with uncertainties is given, which provides data support for the calculation of DC bias in the expansion of DC project.
Polypropylene (PP) shows great potential to replace cross-linked polyethylene (XLPE) as the next generation of insulation materials for power cable. To understand the operation characteristics, this paper studied the temperature distribution and ampacities of PP-based power cable. The differences in temperature distribution between the XLPE and PP cables was compared by solving a magnetic-thermal-flow field coupling model for a 110kV power cable. And the ampacities of the two cables were studied with different laid methods in the soil, pipeline and trench. The results show that XLPE has a better heat dissipation due to the greater thermal conductivity, whereas the PP cable has a higher ampacity and stronger short-time overload current withstand due to the higher temperature tolerance. If thermal conductivity increase, the ampacity of PP cable would be further improved. However, the thermal conductivity of PP has a saturation effect on the increase in cable ampacities. Under soil, pipeline and trench laying conditions, the ampacity of PP cables is 8.5%, 9.5% and 6.3% higher than that of XLPE cables, respectively. The application of PP as cable insulation can significantly increase the transmission capacity of cables without structural changes.
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