The setting values of thresholds for fault feature parameters are critical in all kinds of protection schemes.When the detected feature parameter value exceeds the setting value,the protection will trip.However,the se...The setting values of thresholds for fault feature parameters are critical in all kinds of protection schemes.When the detected feature parameter value exceeds the setting value,the protection will trip.However,the setting value based conventional protection schemes sometimes cannot satisfy the protection requirements of neutral ineffectively earthed power systems(NIEPS)due to wide variations in operating conditions and the complexities of fault cases.In this paper,a novel single phase grounding fault protection scheme without threshold setting is proposed.The fault detection is achieved based on operating states rather than setting values.A fuzzy c-means algorithm is used to divide the operating state of the protected feeder into non-fault states and fault states.The cluster center of each state is then obtained by classifying the historical feature samples of the protected feeder extracted under various operating conditions into their corresponding states in a constructed multi-dimensional fault feature space.The distances between the detected feature samples and the cluster centers of the non-fault and the fault states are calculated.If the distance to the fault state is shorter than that to the non-fault state,a fault is detected.Otherwise,the feeder is considered normal.A PSCAD/EMTDC simulator is used to simulate a 35 kV NIEPS under various operating conditions,non-linear loads,and complex fault cases.Results show that the proposed single phase grounding fault protection scheme without threshold setting can protect the system correctly under all kinds of faults.展开更多
目的:观察无先兆偏头痛患者(Migraine Without Aura, MWoA)印堂、太阳、大椎、百会、风池、颊车是否存在痛敏现象,并对比经穴针刺与安慰针刺对此穴位的机械痛阈值的影响,探讨针刺对无先兆偏头痛患者痛敏的改善,并为临床治疗提供更科学...目的:观察无先兆偏头痛患者(Migraine Without Aura, MWoA)印堂、太阳、大椎、百会、风池、颊车是否存在痛敏现象,并对比经穴针刺与安慰针刺对此穴位的机械痛阈值的影响,探讨针刺对无先兆偏头痛患者痛敏的改善,并为临床治疗提供更科学的依据。方法:将50例MWoA患者随机分为经穴针刺组与安慰针刺组,并纳入25例健康受试者作为对照。研究周期共20周,其中基线期4周,治疗期4周,随访期12周。治疗期间,隔日治疗1次,每周治疗3次,连续治疗12次。主要结局指标为入组0周、4周及随访12周时患者印堂、太阳、大椎、百会、风池、颊车的机械痛阈值;次要结局指标为头痛发作次数、头痛程度、头痛持续时间。结果:MWoA患者百会、大椎、风池机械痛阈值较健康人低,差异具有统计学意义(P<0.05)。治疗4周、随访12周时,经穴针刺组患者风池、大椎机械痛阈值升高,差异具有统计学意义(P<0.05);安慰针刺组在治疗4周后、随访12周时均无明显差异(P>0.05)。经穴针刺组治疗4周、随访12周时头痛发作次数、头痛持续时间、VAS评分均下降,具有统计学意义(P<0.05)。安慰针刺组VAS得分在治疗4周、随访12周时下降;头痛发作次数、头痛持续时间在随访12周时具有差异(P<0.05)。结论:MWoA患者存在一定程度的痛觉敏化,针刺可能通过提高MWoA患者风池、大椎的机械痛域,在一定程度上减轻了患者的疼痛敏感度,改善患者头痛发作情况;且相较安慰针刺具有显著优势,对降低MWoA患者痛觉过敏有一定意义。展开更多
基金supported in part by National Natural Science Foundation of China under Grant 61233008 and Grant 51277014.
文摘The setting values of thresholds for fault feature parameters are critical in all kinds of protection schemes.When the detected feature parameter value exceeds the setting value,the protection will trip.However,the setting value based conventional protection schemes sometimes cannot satisfy the protection requirements of neutral ineffectively earthed power systems(NIEPS)due to wide variations in operating conditions and the complexities of fault cases.In this paper,a novel single phase grounding fault protection scheme without threshold setting is proposed.The fault detection is achieved based on operating states rather than setting values.A fuzzy c-means algorithm is used to divide the operating state of the protected feeder into non-fault states and fault states.The cluster center of each state is then obtained by classifying the historical feature samples of the protected feeder extracted under various operating conditions into their corresponding states in a constructed multi-dimensional fault feature space.The distances between the detected feature samples and the cluster centers of the non-fault and the fault states are calculated.If the distance to the fault state is shorter than that to the non-fault state,a fault is detected.Otherwise,the feeder is considered normal.A PSCAD/EMTDC simulator is used to simulate a 35 kV NIEPS under various operating conditions,non-linear loads,and complex fault cases.Results show that the proposed single phase grounding fault protection scheme without threshold setting can protect the system correctly under all kinds of faults.
文摘目的:观察无先兆偏头痛患者(Migraine Without Aura, MWoA)印堂、太阳、大椎、百会、风池、颊车是否存在痛敏现象,并对比经穴针刺与安慰针刺对此穴位的机械痛阈值的影响,探讨针刺对无先兆偏头痛患者痛敏的改善,并为临床治疗提供更科学的依据。方法:将50例MWoA患者随机分为经穴针刺组与安慰针刺组,并纳入25例健康受试者作为对照。研究周期共20周,其中基线期4周,治疗期4周,随访期12周。治疗期间,隔日治疗1次,每周治疗3次,连续治疗12次。主要结局指标为入组0周、4周及随访12周时患者印堂、太阳、大椎、百会、风池、颊车的机械痛阈值;次要结局指标为头痛发作次数、头痛程度、头痛持续时间。结果:MWoA患者百会、大椎、风池机械痛阈值较健康人低,差异具有统计学意义(P<0.05)。治疗4周、随访12周时,经穴针刺组患者风池、大椎机械痛阈值升高,差异具有统计学意义(P<0.05);安慰针刺组在治疗4周后、随访12周时均无明显差异(P>0.05)。经穴针刺组治疗4周、随访12周时头痛发作次数、头痛持续时间、VAS评分均下降,具有统计学意义(P<0.05)。安慰针刺组VAS得分在治疗4周、随访12周时下降;头痛发作次数、头痛持续时间在随访12周时具有差异(P<0.05)。结论:MWoA患者存在一定程度的痛觉敏化,针刺可能通过提高MWoA患者风池、大椎的机械痛域,在一定程度上减轻了患者的疼痛敏感度,改善患者头痛发作情况;且相较安慰针刺具有显著优势,对降低MWoA患者痛觉过敏有一定意义。
