This paper describes the causes of voltage sags in industrial plant, their impacts on equipment operation, and possible solutions. The definition proposed focuses on system faults as the major cause of voltage sags. The sensitivity of different types of industrial equipment; including adjustable speed drive controls, programmable logic controllers, and motor contactors; is analyzed. Available methods of power conditioning for this sensitive equipment are also described.
This paper summarizes the results from a number of different voltage sag investigations. These investigations involve characterizing the voltage sag performance at a customer facility and evaluating equipment sensitivity to different voltage sag magnitudes and durations. Possible solutions to voltage sag sensitivity problems are also described.
Abstmct -Voltage sags, also known as dips, are increasingly important to industrial reliabiliiy. Modern process controls are ojlen sensitive to voltage sags. The combination of a voltage sag and sensitive equipmed may cause s i p 9 c a n t production outages. Less sensitive equipment may be available at a premium price, but the designer must know the sag chamcteristics of the electdc system to make the best choices between reliability and cost. This proposed chapter offers a way to predict vorulge sag pevonnance without h g t e m monitoring and before plants are constructed. The contents of this paper show the analysis technique proposed for a new Chapter 9 in the next revision of IEEE Std 493.characteristics. Difficult calculations should be performed by any of several good computer short circuit analysis programs. These programs allow users to accurately model the electrical network, apply short circuits around the network, and look at the resulting voltage on any bus of interest. These techniques allow engineers to anticipate and possibly prevent voltage sag problems.The ability to predict voltage sag characteristics offers a unique opportunity to evaluate alternate configurations and prevent problems with optimum supply and ride-through specifications. Problems may be avoided by reducing the voltage sag magnitudes, probabilities, and/or duration. Modest changes in equipment specifications can significantly reduce the number of nuisance outages from voltage sags. 9.1 INTRODUCTION 9.2 SOURCE OF VOLTAGE SAGS Momentary voltage sags are very different from service interruptions covered by other chapters of IEEE Std 493.Interruptions are a complete separation from the source of electric energy, normally an electric utility. Momentary voltage sags are a sudden drop in voltage while the load remains connected to the supply. Sags generally last less than one second although a few may last longer.Modem utilization equipment can be very sensitive to voltage sags. There are reports that voltage sags to 85 to 90 % of nominal lasting as short as 16-have triggered immediate outages of critical industrial processes. Equipment in this sensitivity range is likely to be upset by voltage sags an order of magnitude more often than from interruptions. Production employees often notice the lights blink, especially during adverse weather, just when the critical process fails. Many incorrectly conclude the plant experienced an interruption.It is possible to build equipment that will survive even severe voltage sags, but the equipment may be more expensive. Accurate estimates of sag magnitude and duration probabilities help system designers to select appropriate equipment specifications for critical processes. This chapter shows how to combine accepted analysis tools to predict the important voltage sag characteristics. The basic tools include a computer program to calculate unbalanced fault currents and voltages, reliability data, and fault clearing device One paper found that nearly all disruptive voltage sags were due to voltage dr...
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