摘要：1 引言大功率高压电机的起动对电网及设备都有一定的冲击,通过高压变频器进行变频调压,实现电机的软起动, 减少对电网的冲击及设备的磨损。变频调速是通过改变旋转磁场同步转速进行调速的,是无附加转差损耗的高速调速方式,变频调速系统的关键设备是变频器,由它来提供变频电源。高压变频装置是由移相变压器。

摘要：Objective:We longitudinally examined the changes of brachial to ankle distensibility using pulse wave velocity (PWV)-throughout pregnancy and its difference between normal pregnancy and pregnancy-induced hypertension (PIH) groups. Study design:One hundred and eighty-three pregnant women were included in this study. The PWV examinations were performed in a longitudinal way during the first,second,and third trimesters of pregnancy,and immediately and 1 month after delivery. Results:In normal pregnancies,the PWV significantly decreased at the second trimester,increased from the third trimester through immediately after delivery,and decreased again at 1 month after delivery. In PIH patients,it increased in proportion to the progression of gestation. Conclusion:We monitored the longitudinal changes in PWV and constructed a PWV normogram during pregnancy. The predictive value of PWV and blood pressure for PIH was higher than that of blood pressure alone,suggesting the usefulness of measuring PWV to predict PIH.

摘要：本文介绍了专为地铁、轻轨供电而设计制造的牵引变电站用整流器,详细描述了12脉波整流器原理、元件选择、电路保护设计。应用图形编程软件LabVIEW作为与上位计算机的通信软件。

摘要：本文对工业上广泛应用的可控硅变流设备所产生的谐波作了较系统的分析;从母线电压波形畸变的角度,探讨了交流设备的功率和系统短路容量的配合关系。文章在计算了6脉波单桥变流器和12脉波双桥变流器的谐波电压并确定了它们的相位关系之后,导出等值线性谐波网络。建立了用短路比S.C.R.和控制角α表示的母线电压波形畸变因数DF的关系式,并利用电子计算机计算和绘制了便于在工程设计中实际应用的曲线。

摘要：1项目背景天津市某科技有限公司是一家集科研、开发、生产、销售和服务于一体的耐磨材料高新技术企业。公司成立于2011年7月,2012年11月投产。由10 kV双回路供电,其中10 kV I号回路为动力及照明负荷供电,10 kV II号回路为铸造生产线专用回路。铸造生产线分期建设,共规划3台变压器和5套中频炉。一期工程安装1台1 500 kVA12脉波整流变压器和2套2 t中频炉。