Investigation of VFT surges propagated into transformer and overvoltages applied to winding

Investigations were conducted on the VFT (Very Fast Transient) surges that propagate into a 500‐kV transformer. The disconnector restriking surge and ground fault surged were discussed. It was regarded that a large part of the surge voltage was applied just at the entrance of the transformer winding for the VFT surges. Thus, an equivalent circuit that models the windings was used for the analysis. The overvoltages that appear between the first winding sections at the entrance of the transformer were computed. The following was established. (1) The overvoltage between the first winding sections becomes greater when the magnitude of the voltage change at the transformer terminal is larger. The overvoltage between the first winding sections is not affected by the magnitude of the transformer terminal voltage. (2) For the disconnectors that are not connected directly to the transformer, the voltage change at the transformer terminal is not so large. (3) In the case of a ground fault at the GIS near the transformer, the voltage change at the transformer terminal is the same as that for a disconnector directly connected to the transformer. (4) In actual GIS, the disconnector that is connected directly to the transformer is not usually used. In this situation, the overvoltages that threaten the transformer insulation will not be generated by the restriking of the disconnectors. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(2): 20–26, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10225     

海德汉进给传动精度系列讲座——第4讲 滚珠丝杠长度方向温度分布的影响

除了轴承轴向刚度之外，影响热力学零点最大的因素是丝杠长度方向的温度分布。图1显示的是一根丝杠在相距150mm两点间往复运行几小时之后的热像图。清晰可辨的是，即使是几小时之后，丝杠的发热也几乎仅限于丝杠螺母所运动的区域之内。因此滚珠丝杠发热及伸长是很局域性的。     

NFC — the intuitive contactless technology becomes reality

Near Field Communication (NFC) is opening-up completely new perspectives for the mobile communication industry. It enables contactless peer-to-peer communication, reading/writing of contactless cards and, when combined with a smart card IC, emulation of a contactless card. NFC has taken major steps towards market acceptance: ISO standards are in place for the interface and communication protocols, many leading companies in the field are promoting it within the NFC Forum, and numerous field trials are being deployed around the world. Different architectures are being considered for NFC and security mobile phone architectures. The first Philips cellular system solution integrating NFC hardware and software illustrates a successful implementation of one of these architectures.     

Channel model and capacity for broadband indoor MIMO-WLAN systems based on measurements at 2.4 GHz

This article provides a channel model which is suited for broadband indoor WLAN (wireless local area network) applications. Especially the communication within one room is addressed. These applications are characterized by no or very slow movements of the terminal in conjunction with high data rates requiring high bandwidths for transmission. Present WLAN systems offer data rates up to 108 Mb/s, multiple antenna systems (MIMO systems) are at the beginning of their introduction into the market. Upcoming demand for even higher data rates necessitating higher bandwidth efficiency is almost sure. This requires at first hand a full understanding of the channel in order to make best use of it. The article shows that the channel can be described best by a deterministic model, which needs only few dominant paths. This is underlined by channel sounder measurements and simple calculations. Making use of this deterministic channel model the article shows capacity improvements over a widespread Rayleigh fading model assumption.     

Digital Rights Management

This article presents a selection of Internet links which provide a sound introduction to Digital Rights Management Systems (DRMS). First, links to scientific papers, information portals, organizations companies and consortia are presented to give a general view about DRMS. Then, various aspects about DRMS are presented with a special focus on legal, technological and economical aspect. For each of those further information and links are provided in order to give a better understanding about this topic.