Disturbances on the ac power line are what headaches are made of. Outages, surges, sags, transients: they combine to create an environment that can damage or destroy sensitive load equipment. They can take your system down and leave you with a complicated and expensive repair job. Ensuring that the equipment at your facility receives clean ac power has always been important. But now, with computers integrated into a wide variety of electronic products, the question of ac power quality is more critical than ever.
The computer-based systems prevalent today can garble or lose data because of power-supply disturbances or interruptions. And if the operational problems are not enough, there is the usually difficult task of equipment troubleshooting and repair that follows a utility system fault. This book examines the key elements of ac power use for commercial and industrial customers. The roots of ac power-system problems are identified, and effective solutions are detailed. The book follows a logical progression from generating ac energy to the protection of life and property. General topics include:
• How Much Protection? The degree of protection afforded a facility is generally a compromise between the line abnormalities that will account for most of the expected problems and the amount of money available to spend on that protection. Each installation is unique and requires an assessment of the importance of keeping the system up and running at all times, as well as the threat of disturbances posed by the ac feed to the plant. The author firmly believes that the degree of protection provided a power-distribution system should match the threat of system failure. In this publication, all alternatives are examined with an eye toward deciding how much protection really is needed, and how much money can be justified for ac protection hardware.
• Grounding. The attention given to the design and installation of a facility ground system is a key element in the day-to-day reliability of any plant. A well-planned ground network is invisible to the engineering staff. A marginal ground system, however, will cause problems on a regular basis. Although most engineers view grounding primarily as a method to protect equipment from damage or malfunction, the most important element is operator safety.
The 120 V or 208 V ac line current that powers most equipment can be dangerous — even deadly — if improperly handled. Grounding of equipment and structures provides protection against wiring errors or faults that could endanger human life. Grounding concepts and practices are examined in detail. Clear, step-by-step guidelines are given for designing and installing an effective ground system to achieve good equipment performance, and to provide for operator safety.
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