为获得雷电流冲击下110 k V变压器不接地中性点上的过电压,采用线饼模型对110 k V变压器绕组进行建模,并用PSCAD仿真软件对该模型进行仿真计算。利用该模型对广州地区110 k V变压器中性点击穿事故进行仿真分析,结果表明对变压器中性点仅加装放电间隙不足以防止雷电侵害,并且雷电波入侵变压器时中性点故障率高达到0.686次/年,说明需要结合其他防护措施对这一地区变压器中性点进行保护。根据仿真结果提出采用130 mm的间隙并联Y1.5W-72/186避雷器实施改造措施。 相似文献
Although there has been a resurgence of interest in low field magnetic resonance imaging (MRI) systems in recent years, low field MRI is not a new concept. FDA has a long history of evaluating the safety and effectiveness of MRI systems encompassing a wide range of field strengths. Many systems seeking marketing authorization today include new technological features (such as artificial intelligence), but this does not fundamentally change the regulatory paradigm for MR systems. In this review, we discuss some of the US regulatory considerations for low field magnetic resonance imaging (MRI) systems, including applicability of existing laws and regulations and how the U.S. Food and Drug Administration (FDA) evaluates low field MRI systems for market authorization. We also discuss regulatory considerations in the review of low field MRI systems incorporating novel AI technology. We foresee that MRI systems of all field strengths intended for general diagnostic use will continue to be evaluated for marketing clearance by the metric of substantial equivalence set forth in the premarket notification pathway.