配电网单相接地故障占比较高,存在多种故障类型。如果对不同类型的接地故障进行适当的处理,能有效提高配电网的可靠性和可用性。然而,如何快速区分不同的故障类型,一直以来是一个研究热点。本研究针对高阻接地故障电流和电压特征不明显...配电网单相接地故障占比较高,存在多种故障类型。如果对不同类型的接地故障进行适当的处理,能有效提高配电网的可靠性和可用性。然而,如何快速区分不同的故障类型,一直以来是一个研究热点。本研究针对高阻接地故障电流和电压特征不明显导致的高阻接地故障检测困难的问题,提出了一种创新的解决方法,即采用迁移学习和深度残差网络对高阻接地故障进行识别。首先,提取单相接地故障后2个周期内的零序电压数据,利用小波变换将零序电压映射为二维时频图;其次,搭建深度残差网络,通过冻结底层参数实现小样本迁移,微调参数对不同的故障样本分类。为了验证算法有效性,搭建了10 k V配电网模型进行仿真。经实验证明,采用该方法可有效检测弧光高阻接地故障信号,并准确识别出这类接地故障。展开更多
In order to study how welding parameters affect welding quality and droplet transfer, a synchronous acquisition and analysis system is established to acquire and analyze electrical signal and instantaneous images of d...In order to study how welding parameters affect welding quality and droplet transfer, a synchronous acquisition and analysis system is established to acquire and analyze electrical signal and instantaneous images of droplet transfer simultaneously, which is based on a self-developed soft-switching inverter. On the one hand, welding current and voltage signals are acquired and analyzed by a self-developed dynamic wavelet analyzer. On the other hand, images are filtered and optimized after they are captured by high-speed camera. The results show that instantaneous waveforms and statistical data of electrical signal contribute to make an overall assessment of welding quality, and that optimized high-speed images allow a visual and clear observation of droplet transfer process. The analysis of both waveforms and images leads to a further research on droplet transfer mechanism and provides a basis for precise control of droplet transfer.展开更多
The wavelet approach is introduced to study the influence of the natural convection stagnation point flow of the Williamson fluid in the presence of thermophysical and Brownian motion effects. The thermal radiation ef...The wavelet approach is introduced to study the influence of the natural convection stagnation point flow of the Williamson fluid in the presence of thermophysical and Brownian motion effects. The thermal radiation effects are considered along a permeable stretching surface. The nonlinear problem is simulated numerically by using a novel algorithm based upon the Chebyshev wavelets. It is noticed that the velocity of the Williamson fluid increases for assisting flow cases while decreases for opposing flow cases when the unsteadiness and suction parameters increase, and the magnetic effect on the velocity increases for opposing flow cases while decreases for assisting flow cases. When the thermal radiation parameter, the Dufour number, and Williamson’s fluid parameter increase, the temperature increases for both assisting and opposing flow cases. Meanwhile, the temperature decreases when the Prandtl number increases. The concentration decreases when the Soret parameter increases, while increases when the Schmidt number increases. It is perceived that the assisting force decreases more than the opposing force. The findings endorse the credibility of the proposed algorithm, and could be extended to other nonlinear problems with complex nature.展开更多
文摘配电网单相接地故障占比较高,存在多种故障类型。如果对不同类型的接地故障进行适当的处理,能有效提高配电网的可靠性和可用性。然而,如何快速区分不同的故障类型,一直以来是一个研究热点。本研究针对高阻接地故障电流和电压特征不明显导致的高阻接地故障检测困难的问题,提出了一种创新的解决方法,即采用迁移学习和深度残差网络对高阻接地故障进行识别。首先,提取单相接地故障后2个周期内的零序电压数据,利用小波变换将零序电压映射为二维时频图;其次,搭建深度残差网络,通过冻结底层参数实现小样本迁移,微调参数对不同的故障样本分类。为了验证算法有效性,搭建了10 k V配电网模型进行仿真。经实验证明,采用该方法可有效检测弧光高阻接地故障信号,并准确识别出这类接地故障。
基金This work was supported by National Natural Science Foundation of China （ No. 50875088） Natural Science Foundation of Guangdong Province, China （ No. 07006479）.
文摘In order to study how welding parameters affect welding quality and droplet transfer, a synchronous acquisition and analysis system is established to acquire and analyze electrical signal and instantaneous images of droplet transfer simultaneously, which is based on a self-developed soft-switching inverter. On the one hand, welding current and voltage signals are acquired and analyzed by a self-developed dynamic wavelet analyzer. On the other hand, images are filtered and optimized after they are captured by high-speed camera. The results show that instantaneous waveforms and statistical data of electrical signal contribute to make an overall assessment of welding quality, and that optimized high-speed images allow a visual and clear observation of droplet transfer process. The analysis of both waveforms and images leads to a further research on droplet transfer mechanism and provides a basis for precise control of droplet transfer.
基金Project supported by the National Natural Science Foundation of China(Nos.51709191,51706149,and 51606130)the Key Laboratory of Advanced Reactor Engineering and Safety,Ministry of Education of China(No.ARES-2018-10)the State Key Laboratory of Hydraulics and Mountain River Engineering of Sichuan University of China(No.Skhl1803)
文摘The wavelet approach is introduced to study the influence of the natural convection stagnation point flow of the Williamson fluid in the presence of thermophysical and Brownian motion effects. The thermal radiation effects are considered along a permeable stretching surface. The nonlinear problem is simulated numerically by using a novel algorithm based upon the Chebyshev wavelets. It is noticed that the velocity of the Williamson fluid increases for assisting flow cases while decreases for opposing flow cases when the unsteadiness and suction parameters increase, and the magnetic effect on the velocity increases for opposing flow cases while decreases for assisting flow cases. When the thermal radiation parameter, the Dufour number, and Williamson’s fluid parameter increase, the temperature increases for both assisting and opposing flow cases. Meanwhile, the temperature decreases when the Prandtl number increases. The concentration decreases when the Soret parameter increases, while increases when the Schmidt number increases. It is perceived that the assisting force decreases more than the opposing force. The findings endorse the credibility of the proposed algorithm, and could be extended to other nonlinear problems with complex nature.
