Test and evaluation of voltage dip immunity

Abstract

One of the largest power quality problem today is voltage dips. Each year voltage dips cause disturbances in industries, resulting in large economical losses. Today these problems are often solved as they are discovered, and very often the equipment selected for improved immunity are based on experience and opinions rather than a traceable technical analysis. One related problem to voltage dips is that there are no standards covering the complete issue, e.g. there are no descriptions on how to test and present the immunity in a three-phase system. This report presents a structured way of working with voltage dips in order to obtain the voltage dip immunity and related costs. Improving the immunity of a plant must be an ongoing work involving the whole process rather than just separately identified malfunctions. Before deciding to perform a mitigation action, two analyses should be carried out. First, a study of the voltage dip characteristics affecting the site, which will provide information of the voltage dips, types, magnitude, activity, etc. Secondly a work to identify the processes causing the highest cost, and estimating the immunity level of the site has to be done. The proposed method is based on three indices; cost, fault frequency and the interconnection between processes. The different indices will provide knowledge of which process that can have the highest cost assigned due to a voltage dip caused shutdown. Knowing the cost for the voltage dip, evaluation of different mitigation actions can be calculated in order to find them motivated or not. Finally, the report briefly presents some frequent mitigation methods and measurements results from field measurement at the pulp and paper plant Gruvön.