In the transient process of power grid faults,the transferring distortion of current transformer(CT)can seriously affect relay protection performance.Under these conditions,it is difficult to analyze the ferromagnetic...In the transient process of power grid faults,the transferring distortion of current transformer(CT)can seriously affect relay protection performance.Under these conditions,it is difficult to analyze the ferromagnetic characteristic of the magnetizing branch in the transient equivalent circuit of CT.The Jiles-Atherton hysteresis model(J-A model),which is widely used in digital simulations,can accurately describe the hysteresis and saturation process of the core characteristics;however,to acquire the parameters of the J-A model of current transformers in practical use is still a challenging problem.In this paper,physical tests based on a practical CT and parameter identification are presented to solve the problem.The basic hysteresis loops of P,PR,and TPY class of practical current transformers are obtained through physical tests.Thus,the J-A model parameters are identified using a hybrid genetic/simulated annealing algorithm,based on which transient simulation models of different class CTs are constructed.The effectiveness of the proposed method is verified via dynamic physical simulation tests.A typical accident is analyzed based on these models.展开更多
The current research about the flow ripple of axial piston pump mainly focuses on the effect of the structure of parts on the flow ripple. Therein, the structure of parts are usually designed and optimized at rated wo...The current research about the flow ripple of axial piston pump mainly focuses on the effect of the structure of parts on the flow ripple. Therein, the structure of parts are usually designed and optimized at rated working conditions. However, the pump usually has to work in large-scale and time-variant working conditions. Therefore, the flow ripple characteristics of pump and analysis for its test accuracy with respect to variant steady-state conditions and transient conditions in a wide range of operating parameters are focused in this paper. First, a simulation model has been constructed, which takes the kinematics of oil film within friction pairs into account for higher accuracy. Afterwards, a test bed which adopts Secondary Source Method is built to verify the model. The simulation and tests results show that the angular position of the piston, corresponding to the position where the peak flow ripple is produced, varies with the different pressure. The pulsating amplitude and pulsation rate of flow ripple increase with the rise of pressure and the variation rate of pressure. For the pump working at a constant speed, the flow pulsation rate decreases dramatically with the increasing speed when the speed is less than 27.78% of the maximum speed, subsequently presents a small decrease tendency with the speed further increasing. With the rise of the variation rate of speed, the pulsating amplitude and pulsation rate of flow ripple increase. As the swash plate angle augments, the pulsating amplitude of flow ripple increases, nevertheless the flow pulsation rate decreases. In contrast with the effect of the variation of pressure, the test accuracy of flow ripple is more sensitive to the variation of speed. It makes the test accuracy above 96.20% available for the pulsating amplitude of pressure deviating within a range of ~6% from the mean pressure. However, with a variation of speed deviating within a range of ±2% from the mean speed, the attainable test accuracy of flow ripple is above 93.07%. The model constructed in this research proposes a method to determine the flow ripple characteristics of pump and its attainable test accuracy under the large-scale and time-variant working conditions. Meanwhile, a discussion about the variation of flow ripple and its obtainable test accuracy with the conditions of the pump working in wide operating ranges is given as well.展开更多
GIS中的隔离开关在操作过程中由于断口重复击穿会产生特快速瞬态过电压(very fast transient overvoltage,VFTO)。VFTO幅值高、波前陡,严重威胁电气一次绝缘,并会产生电磁干扰问题。目前,实际工程中除采用带投切电阻的隔离开关抑制VFTO...GIS中的隔离开关在操作过程中由于断口重复击穿会产生特快速瞬态过电压(very fast transient overvoltage,VFTO)。VFTO幅值高、波前陡,严重威胁电气一次绝缘,并会产生电磁干扰问题。目前,实际工程中除采用带投切电阻的隔离开关抑制VFTO外,还可以采用磁环型阻尼母线对VFTO进行抑制。为了保证GIS的可靠性,磁环型阻尼母线抑制性能的优劣至关重要。为此,亟需研究提出一种在试验室进行磁环抑制效果的评定方法。文中针对磁环型阻尼母线的抑制性能,设计了专门的抑制性能试验回路,该试验回路中主要包含套管、阻尼电阻、放电间隙、磁环型阻尼母线、GIS短母线、VFTO传感器以及VFTO测量系统。该试验回路的额定电压为1100 kV,回路中的套管和母线可承受的额定工频电压为1100 kV,阻尼电阻的阻值为560Ω或1500Ω,放电间隙可以通过电极间距的调整产生不同等级的放电电压值和放电陡波,陡波上升时间可以达到30 ns。应用该试验回路在试验室进行模拟试验的方法检验磁环型阻尼母线的抑制效果,试验结果表明,该试验回路可以完成磁环型阻尼母线抑制效果的检验,可以定量地给出抑制效果的优劣。该方法可以推广到其他电压等级的GIS产品中,有助于推动实现磁环型阻尼母线的工业化设计、制造及检验。展开更多
In view of the anisotropy,heterogeneity and stress-sensitive permeability in low permeability reservoirs,an analytical well test model was established by introducing the concept of permeability modulus.This model cons...In view of the anisotropy,heterogeneity and stress-sensitive permeability in low permeability reservoirs,an analytical well test model was established by introducing the concept of permeability modulus.This model considered the permeability stress-sensitivity,wellbore storage effect,and the skin effect.The perturbation technique and Laplace transformation were used to solve the mathematical model analytically in Laplace space,and the bottom-hole pressure type curves were plotted and analyzed in real space by using the Stehfest numerical inversion.展开更多
BACKGROUND: Recent researches demonstrate that damage of executive function is an early manifestation of vascular cognitive disorder. OBJECTIVE: To investigate the executive functions of patients with transient isch...BACKGROUND: Recent researches demonstrate that damage of executive function is an early manifestation of vascular cognitive disorder. OBJECTIVE: To investigate the executive functions of patients with transient ischemic attack (TIA). DESIGN: Case control. SETTING: Department of Neurology, the First Affiliated Hospital of Xinxiang Medical College. PARTICIPANTS: A total of 83 TIA patients (46 males and 37 females, aged 32 - 74 years) were selected from Department of Neurology, the First Affiliated Hospital of Xinxiang Medical College from July 2005 to December 2006. The diagnosis of TIA was established by the criteria of cerebrovascular diseases made by the Fourth National Cerebrovascular Disease Meeting. In these cases, forty-five patients (54%) were involved in internal carotid artery, and thirty-eight patients (46%) were involved in vertebral basilar system. Fifty healthy adults (Control group: 28 males and 22 females, aged 32 - 74 years) were chosen from retiree in community and family of patients. All of them were right-handedness, without cerebrovascular disease, cerebral trauma, inborn oligophrenia, and heating and visual disorders; also they had no anxiety and depression nearly one week. In addition, all the subjects cooperated with examination. METHODS: After TIA diagnosis, all patients received neuropsychological examination, including attention and inhibition, working memory, flexibility, planning and diversion, based on Stroop tests (C and CW) and the Wisconsin card sorting tests (WCST). ① WCST test: The edition revised by Nelson was used. We would take the times of sorting, incorrect response, persistent incorrect response, and randomly incorrect response as the index of evaluation.② Stroop tests: The edition revised by Trenarry was used and this test had two types: form color and form color-word. Their incorrect response and response time were recorded for data analysis in the end. MAIN OUTCOME MEASURES: Results of WCST test and Stroop tests. RESULTS: A total of 83 TIA patients and 50 healthy subjects were involved in the final analysis. Items of Stroop tests, including response time of Stroop-C test, incorrect response of Stroop-C test, response time of Stroop-CW test and incorrect response of Stroop-CW test, and items of WCST, including incorrect response, persistent incorrect response and random incorrect response, between internal carotid artery system and vertebral basilar artery system were (93.87±24.39) s, 3.16±3.97, (228.46±68.13) s, 12.91 ± 10.56, 55.42± 20.38, 26.58± 10.41, 28.62±11.22; (96.76±24.75) s, 3.89±4.77, (223.46±72.54) s, 18.71 ± 13.80, 52.47 ±22.25, 28.82± 16.20, 23.39±9.72, respectively; this was higher than those in the control group [(52.10± 12.18) s, 1.68± 1.97, (134.86±34.15) s, 4.22±4.21, 32.46± 17.97, 14.42±8.47, 18.24± 10.24, P 〈 0.05 - 0.01]. Times of sorting of WCST between internal carotid artery system and vertebral basilar artery system were obviously lower than those in the control group (8.27±2.73, 8.66±2.77, 11.22±2.41, P 〈 0.01). However, there were no significant differences between internal carotid artery system and vertebral basilar artery system (P 〉 0.05). CONCLUSION: Patients with TIA have executive dysfunctions, and the dysfunctions have no difference between internal carotid artery system and vertebral basilar artery system.展开更多
基金supported by the Key project of smart grid technology and equipment of national key research and development plan of China under Grant 2016YFB0900600。
文摘In the transient process of power grid faults,the transferring distortion of current transformer(CT)can seriously affect relay protection performance.Under these conditions,it is difficult to analyze the ferromagnetic characteristic of the magnetizing branch in the transient equivalent circuit of CT.The Jiles-Atherton hysteresis model(J-A model),which is widely used in digital simulations,can accurately describe the hysteresis and saturation process of the core characteristics;however,to acquire the parameters of the J-A model of current transformers in practical use is still a challenging problem.In this paper,physical tests based on a practical CT and parameter identification are presented to solve the problem.The basic hysteresis loops of P,PR,and TPY class of practical current transformers are obtained through physical tests.Thus,the J-A model parameters are identified using a hybrid genetic/simulated annealing algorithm,based on which transient simulation models of different class CTs are constructed.The effectiveness of the proposed method is verified via dynamic physical simulation tests.A typical accident is analyzed based on these models.
基金Supported by National Basic Research Program of China(973 Program,Grant No.2014CB046403)National Key Technology R&D Program of the Twelfth Five-year Plan of China(Grant No.2013BAF07B01)
文摘The current research about the flow ripple of axial piston pump mainly focuses on the effect of the structure of parts on the flow ripple. Therein, the structure of parts are usually designed and optimized at rated working conditions. However, the pump usually has to work in large-scale and time-variant working conditions. Therefore, the flow ripple characteristics of pump and analysis for its test accuracy with respect to variant steady-state conditions and transient conditions in a wide range of operating parameters are focused in this paper. First, a simulation model has been constructed, which takes the kinematics of oil film within friction pairs into account for higher accuracy. Afterwards, a test bed which adopts Secondary Source Method is built to verify the model. The simulation and tests results show that the angular position of the piston, corresponding to the position where the peak flow ripple is produced, varies with the different pressure. The pulsating amplitude and pulsation rate of flow ripple increase with the rise of pressure and the variation rate of pressure. For the pump working at a constant speed, the flow pulsation rate decreases dramatically with the increasing speed when the speed is less than 27.78% of the maximum speed, subsequently presents a small decrease tendency with the speed further increasing. With the rise of the variation rate of speed, the pulsating amplitude and pulsation rate of flow ripple increase. As the swash plate angle augments, the pulsating amplitude of flow ripple increases, nevertheless the flow pulsation rate decreases. In contrast with the effect of the variation of pressure, the test accuracy of flow ripple is more sensitive to the variation of speed. It makes the test accuracy above 96.20% available for the pulsating amplitude of pressure deviating within a range of ~6% from the mean pressure. However, with a variation of speed deviating within a range of ±2% from the mean speed, the attainable test accuracy of flow ripple is above 93.07%. The model constructed in this research proposes a method to determine the flow ripple characteristics of pump and its attainable test accuracy under the large-scale and time-variant working conditions. Meanwhile, a discussion about the variation of flow ripple and its obtainable test accuracy with the conditions of the pump working in wide operating ranges is given as well.
基金support from the National 973 Program (Grant No. 2006CB705808)PetroChina Young and Middle Aged People Innovation Fund (Grant No. 07E1016)+1 种基金PetroChina Science & Technology Innovation Fund (Grant No. 2008D-5006-02-09)Science & Technology Innovation Fund of Southwest Petroleum University (Grant No. 2007XJZ010)
文摘In view of the anisotropy,heterogeneity and stress-sensitive permeability in low permeability reservoirs,an analytical well test model was established by introducing the concept of permeability modulus.This model considered the permeability stress-sensitivity,wellbore storage effect,and the skin effect.The perturbation technique and Laplace transformation were used to solve the mathematical model analytically in Laplace space,and the bottom-hole pressure type curves were plotted and analyzed in real space by using the Stehfest numerical inversion.
基金High-educational Talents Starting Foundation of Xinxiang Medical College
文摘BACKGROUND: Recent researches demonstrate that damage of executive function is an early manifestation of vascular cognitive disorder. OBJECTIVE: To investigate the executive functions of patients with transient ischemic attack (TIA). DESIGN: Case control. SETTING: Department of Neurology, the First Affiliated Hospital of Xinxiang Medical College. PARTICIPANTS: A total of 83 TIA patients (46 males and 37 females, aged 32 - 74 years) were selected from Department of Neurology, the First Affiliated Hospital of Xinxiang Medical College from July 2005 to December 2006. The diagnosis of TIA was established by the criteria of cerebrovascular diseases made by the Fourth National Cerebrovascular Disease Meeting. In these cases, forty-five patients (54%) were involved in internal carotid artery, and thirty-eight patients (46%) were involved in vertebral basilar system. Fifty healthy adults (Control group: 28 males and 22 females, aged 32 - 74 years) were chosen from retiree in community and family of patients. All of them were right-handedness, without cerebrovascular disease, cerebral trauma, inborn oligophrenia, and heating and visual disorders; also they had no anxiety and depression nearly one week. In addition, all the subjects cooperated with examination. METHODS: After TIA diagnosis, all patients received neuropsychological examination, including attention and inhibition, working memory, flexibility, planning and diversion, based on Stroop tests (C and CW) and the Wisconsin card sorting tests (WCST). ① WCST test: The edition revised by Nelson was used. We would take the times of sorting, incorrect response, persistent incorrect response, and randomly incorrect response as the index of evaluation.② Stroop tests: The edition revised by Trenarry was used and this test had two types: form color and form color-word. Their incorrect response and response time were recorded for data analysis in the end. MAIN OUTCOME MEASURES: Results of WCST test and Stroop tests. RESULTS: A total of 83 TIA patients and 50 healthy subjects were involved in the final analysis. Items of Stroop tests, including response time of Stroop-C test, incorrect response of Stroop-C test, response time of Stroop-CW test and incorrect response of Stroop-CW test, and items of WCST, including incorrect response, persistent incorrect response and random incorrect response, between internal carotid artery system and vertebral basilar artery system were (93.87±24.39) s, 3.16±3.97, (228.46±68.13) s, 12.91 ± 10.56, 55.42± 20.38, 26.58± 10.41, 28.62±11.22; (96.76±24.75) s, 3.89±4.77, (223.46±72.54) s, 18.71 ± 13.80, 52.47 ±22.25, 28.82± 16.20, 23.39±9.72, respectively; this was higher than those in the control group [(52.10± 12.18) s, 1.68± 1.97, (134.86±34.15) s, 4.22±4.21, 32.46± 17.97, 14.42±8.47, 18.24± 10.24, P 〈 0.05 - 0.01]. Times of sorting of WCST between internal carotid artery system and vertebral basilar artery system were obviously lower than those in the control group (8.27±2.73, 8.66±2.77, 11.22±2.41, P 〈 0.01). However, there were no significant differences between internal carotid artery system and vertebral basilar artery system (P 〉 0.05). CONCLUSION: Patients with TIA have executive dysfunctions, and the dysfunctions have no difference between internal carotid artery system and vertebral basilar artery system.