scholarly journals Breakdown Characteristics of Long Air Gap at Different Frequency Based on Series Resonance

2021 ◽  
Vol 2143 (1) ◽  
pp. 012051
Author(s):  
Zhengyong Hu ◽  
Peng Xu ◽  
Wenlong Tan ◽  
Kai Gao ◽  
Lv Cui
Keyword(s):  
Breakdown Voltage ◽  
Discharge Voltage ◽  
Air Gap ◽  
Series Resonance ◽  
Streamer Corona ◽  
Vector Machines ◽  
Power Frequency ◽  
The Difference ◽  
Experimental Researches ◽  
Reasonable Use

Abstract In today’s rapid economic development, with the development of science and technology, higher requirements have been put forward in the economic operation of the system. This requires various departments to make more reasonable use of existing energy and equipment, and to ensure quality. Meet all aspects of supply with more energy-saving and more economical operation methods. Therefore, more and more attention has been paid to the research on the method of predicting the breakdown voltage of the air gap. Although domestic and foreign scholars have used power frequency test transformers to carry out a large number of long air gap experimental researches, the research on the breakdown voltage of long air gaps based on the principle of vector machines is still blank. In this paper, a vector machine test device is used to study the breakdown discharge characteristics of a long air gap at two frequencies of 229Hz and 68Hz. Comparing the test phenomena at different frequencies, it is found that the initial discharge voltage of the streamer corona is lower when the frequency is 229Hz, and the discharge phenomenon before breakdown is more intense, and the quality factor will be significantly reduced due to the violent discharge. At the same time, under the same test conditions, the breakdown voltage at 229Hz is lower than that at 68Hz, and as the air gap increases, the difference between the two is greater. The experimental results show that the breakdown voltage of the long air gap based on the vector machine is different when the frequency is different, and the safety distance of the field withstand voltage test should be evaluated according to the experimental data under the vector machine condition to ensure the safety of the test.

scholarly journals Study on Partial Discharge Characteristics of C6F12O Mixed Gas

2021 ◽  
Author(s):  
Xiajin Rao ◽  
Dajian Li ◽  
Xiaofei Xia ◽  
Yi Su ◽  
Yufeng Lu ◽  
...  
Keyword(s):  
Breakdown Voltage ◽  
Low Voltage ◽  
Partial Discharge ◽  
Buffer Gas ◽  
Mixing Ratio ◽  
Mixed Gas ◽  
Discharge Characteristics ◽  
Power Frequency ◽  
The Difference ◽  
Inception Voltage

Abstract The greenhouse effect of SF6 increasingly limits its application in various gas insulated equipment. C6F12O combines the advantages of insulation resistance, safety and environmental protection. When mixed with buffer gas, C6F12O is considered to have potential application prospects in medium and low voltage equipment. In this paper, about the partial discharge characteristics of the mixed gas, an experimental study was carried out. The partial discharge initiation voltage and discharge extinction voltage of mixed gas under power frequency voltage are measured and compared with the breakdown voltage. The results show that with the increase of mixing ratio, the partial discharge initiation voltage and extinction voltage of mixed gas gradually increase, and the effect of gas pressure on high mixing ratio is obvious. The difference between the partial discharge inception voltage and the breakdown voltage is larger than that of pure N2. The research in this paper can provide an important reference for the application, operation and protection of C6F12O mixed gas in medium and low voltage equipment.

scholarly journals Lightning Impulse Breakdown Voltage of Rice Bran Oil for Transformer Application

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 5084
Author(s):  
Mardhiah Hayati Abdul Hamid ◽  
Mohd Taufiq Ishak ◽  
Nur Sabrina Suhaimi ◽  
Jaafar Adnan ◽  
Nazrul Fariq Makmor ◽  
...  
Keyword(s):  
Weibull Distribution ◽  
Electric Fields ◽  
Breakdown Voltage ◽  
Rice Bran ◽  
Rice Bran Oil ◽  
Transformer Oil ◽  
Uniform Field ◽  
Testing Methods ◽  
Lightning Impulse ◽  
The Difference

Transformer oil does not only serve as an insulating liquid, but also in removing heat from the windings and cores. Mineral oil (MO) has been widely used in transformers for more than 150 years. Recently, researchers have attempted to search for alternative insulating oils due to the possibility that MO will run out in the future together with the concern on fire safety and environmental pollution. Among the potential oils is rice bran oil (RBO). This work presents the studies of the lightning impulse (LI) of RBO behavior under various electric fields, gap distances and testing methods. The electrical performances of LI tests show that RBO and Palm Oil (PO) have lower LI breakdown voltage than MO under both uniform and non-uniform electric fields. However, the difference in LI breakdown voltages between RBO, PO and MO are slightly small which is less than 20%. In addition, there is no significant effect in the various testing methods under both uniform field and non-uniform field where the percentages of difference are less than 12% and 8% respectively. The data of LI breakdown voltage were statistically analysed to predict the withstand voltage and 50% breakdown voltage of oil samples by using Weibull distribution. The Weibull distribution of MO, PO and RBO has well fit with the fitting line. Finally, the relationship between LI voltages under a non-uniform field with various parameters of PO and RBO was obtained and proposed. From this work, it can be concluded that RBO shows promising results to be considered as an alternative to MO in transformer applications.

The impact of different parameter sets on the classification of asteroid types

2021 ◽  
Author(s):  
Hanna Klimczak ◽  
Wojciech Kotłowski ◽  
Dagmara Oszkiewicz ◽  
Francesca DeMeo ◽  
Agnieszka Kryszczyńska ◽  
...  
Keyword(s):  
Gradient Boosting ◽  
Support Vector ◽  
Multilayer Perceptrons ◽  
Machine Learning Methods ◽  
Vector Machines ◽  
Science Centre ◽  
The Difference ◽  
The Impact

<p>The aim of the project is the classification of asteroids according to the most commonly used asteroid taxonomy (Bus-Demeo et al. 2009) with the use of various machine learning methods like Logistic Regression, Naive Bayes, Support Vector Machines, Gradient Boosting and Multilayer Perceptrons. Different parameter sets are used for classification in order to compare the quality of prediction with limited amount of data, namely the difference in performance between using the 0.45mu to 2.45mu spectral range and multiple spectral features, as well as performing the Prinicpal Component Analysis to reduce the dimensions of the spectral data.</p> <p> </p> <p>This work has been supported by grant No. 2017/25/B/ST9/00740 from the National Science Centre, Poland.</p>

scholarly journals Effect of oxygen on power frequency breakdown voltage and decomposition characteristics of the C5F10O/N2/O2 gas mixture

RSC Advances ◽  
2019 ◽  
Vol 9 (33) ◽  
pp. 18963-18970 ◽  
Author(s):  
Yue Zhang ◽  
Xiaoxing Zhang ◽  
Yi Li ◽  
Yalong Li ◽  
Qi Chen ◽  
...  
Keyword(s):  
Breakdown Voltage ◽  
Carbon Deposition ◽  
Environmentally Friendly ◽  
Gas Mixture ◽  
Power Frequency ◽  
New Type ◽  
High Insulation ◽  
Effect Of Oxygen

C5F10O gas mixture is a SF6 potential substitute with high insulation strength and is a new type of environmentally friendly insulating gas. By adding oxygen to C5F10O gas mixture, insulation strength can be improved and carbon deposition can be suppressed.

scholarly journals Thermal Characteristics of Positive Leaders under Different Electrode Terminals in a Long Air Gap

Energies ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 4024 ◽  
Author(s):  
Du ◽  
Tang ◽  
Li ◽  
Zou ◽  
Ma ◽  
...  
Keyword(s):  
High Speed ◽  
Thermal Characteristics ◽  
Video Camera ◽  
Air Gap ◽  
Radius Of Curvature ◽  
Gas Temperature ◽  
Gas Density ◽  
Interference Fringes ◽  
High Speed Video Camera ◽  
The Difference

The thermal characteristics of the positive leader discharges occurring under the different electrode terminals in a 1 m rod-plate air gap were studied quantitatively using Mach–Zehnder interferometry and a high-speed video camera. When disturbed by the discharge channel, the interference fringes are distorted because of the change in the refractive index of air, which is related to the gas density. Therefore, the gas temperature and gas density distribution in the leader channel can be retrieved from the offset of the interference fringes. Based on these results, the thermal characteristics of the leader channel were studied under different electrode terminals with a radius of curvature of 2.5 mm and 5 mm for cone electrodes and a diameter of 40 mm for a spherical electrode. The results show that the gas temperature in the leader channel increased while the gas density decreased as the radius of curvature of the electrode terminal decreased. Additionally, a smaller radius of curvature leads to a larger thermal diameter, but the difference in the thermal diameter is not obvious; for the terminals used in this paper, the difference is within 2 mm.

scholarly journals Spectrum Analysis and Optimization of the Axial Magnetic Gear with Halbach Permanent Magnet Arrays

Energies ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 2003
Author(s):  
Fang Hu ◽  
Yilan Zhou ◽  
Hesong Cui ◽  
Xiao Liu
Keyword(s):  
Permanent Magnet ◽  
Axial Force ◽  
Spectrum Analysis ◽  
Parametric Analysis ◽  
Air Gap ◽  
Torque Density ◽  
Output Torque ◽  
Magnetic Gear ◽  
The Difference ◽  
Force Calculation

In order to study the contribution of each harmonic to the output torque and axial torque of the axial magnetic gear with Halbach permanent magnet arrays (HAMG), torque and axial force calculation formulas of the HAMG are proposed based on the air-gap flux density distribution of the HAMG. Because of the difference of the air-gap flux densities at different radii, two simplified torque and axial force calculation formulas are proposed and compared. To improve the torque capability of the HAMG, parametric analysis of eight dimensional parameters is firstly conducted. By parametric analysis, six parameters such as the inner radius have been found to have obvious impact on the output torque and output torque density of the HAMG. The optimization using Maxwell software is then executed for maximizing the output torque density of the HAMG. The output torque density of the optimized HAMG is improved from 78.1 kNm/m3 to 93.3 kNm/m3 with an increase of 19%. Furthermore, spectrum analysis is also presented to illustrate the significant output torque improvement based on the torque calculation formulas.

scholarly journals Predicting the Loose Zone of Roadway Surrounding Rock Using Wavelet Relevance Vector Machine

2019 ◽  
Vol 9 (10) ◽  
pp. 2064 ◽  
Author(s):  
Yang Liu ◽  
Yicheng Ye ◽  
Qihu Wang ◽  
Xiaoyun Liu ◽  
Weiqi Wang
Keyword(s):  
Relevance Vector Machine ◽  
Surrounding Rock ◽  
Prediction Errors ◽  
Test Results ◽  
Factors Affecting ◽  
Relevance Vector Machines ◽  
Five Factors ◽  
Vector Machines ◽  
Practical Engineering ◽  
The Difference

By applying the Wavelet Relevance Vector Machine (WRVM) method, this research proposes the loose zone of roadway surrounding rock prediction. Based on the theory of relevance vector machine (RVM), the wavelet function is introduced to replace the original Gauss function as the model kernel function to form the WRVM. Five factors affecting the loose zone of roadway surrounding rock are selected as the model input, and the prediction model of the loose zone of roadway surrounding rock based on WRVM is established. By using cross-validation method, the kernel parameters of three kinds of wavelet relevance vector machines (RVMs) are calculated. By comparing and analyzing the root mean square (RMS) error of the test results of each predictive model, the advantages and accuracy of the model are verified. In practical engineering applications, the average relative prediction errors of the Mexican relevance vector machine, the Morlet relevance vector machine and the difference of Gaussian (DOG) relevance vector machine models are accordingly 4.581%, 4.586% and 4.575%. The square correlation coefficient of the predicted samples is 0.95 > 0.9, which further verifies the accuracy and reliability of the proposed method.

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