电力系统设计 外文文献.doc

DESIGNING MODERN ELECTRICAL SYSTEMS WITH TRANSFORMERS THAT INHERENTLY REDUCE HARMONIC DISTORTION IN A PC-RICH ENVIRONMENT by Philip J. A. Ling, P.Eng. Cyril J. Eldridge, B. Sc. POWERSMITHS INTERNATIONAL CORP 416-439-1077 ABSTRACT Generally, the electrical community has come to accept the fact that todays office facilities have an abundance of electronic equipment that produce harmonics. Based on the results of hundreds of electrical system surveys we have determined that the predominant harmonics are triplens; however, a high degree of 5th and 7th harmonics are also present and need to be treated for a more comprehensive solution. These harmonic rich environments are known to cause serious operational problems for users as well as building maintenance personnel. Until recently, no cost- effective methods have been proposed that can universally deal with 3rd, 5th and 7th harmonics during the design and specification stage of three phase four wire electrical distribution systems. By integrating phase shifting into an extremely low zero phase sequence impedance transformer with single or multiple outputs, substantial reduction of triplen, 5th and 7th harmonics can be achieved. The net result is that the electrical distribution system predictably becomes electromagnetically compatible with the electronic loads (e.g. personal computers) it has to supply. 1. INTRODUCTION Traditional electrical system design had very little need to deal with harmonics because the loads typically designed for were linear in nature. Over the years, as more and more research and practical experience was gathered with linear loads, the design process became more and more predictable. With the proliferation of variable speed drives, electronic ballasts, personal computers and other electronic equipment, electrical system design strategies need to be adjusted. Because in many cases a major portion of the loads today