thesis-powerquality - On Power Quality and Protection by...

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On Power Quality and Protection by Fan Wang Technical Report No. 372L Submitted to the School of Electrical and Computer Engineering Chalmers University of Technology in Partial Fulfillment of the Requirement for The Degree of Licentiate of Engineering Department of Electric Power Engineering Chalmers University of Technology Göteborg, Sweden March, 2001
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CHALMERS UNIVERSITY OF TECHNOLOGY Department of Electric Power Engineering S-412 96 Göteborg, Sweden Chalmers Bibliotek, Reposervice Göteborg, 2001
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Abstract This project combines knowledge from the power quality field and the protection field. The concept of power quality is extended to the terminals of the protective relay. Disturbances in voltage and/or current, not due to a fault in the zone-to-be-protected, may lead to an incorrect trip of the relay. This phenomenon has been known for a long time, and has its consequences in both the threshold setting of relays and the testing of relays. Future generations of protection relays are expected to be faster, and thus more sensitive to disturbances. This project aims at using power quality data and knowledge for the testing of future relays and protection algorithms. A study was made on the different disturbances that occur in the power system and the way in which they affect protection equipment. Information was obtained from: power quality monitoring surveys, power quality and power system literature; measurements performed in our laboratory. Potential impact was assessed from the transients and non-fundamental frequency components of voltage and current. From the study, it is observed that the relay performance characteristics will be changed due to the existence of power system disturbances. The changes include the variation of setting limits of relays, as almost all the relays are designed to operate under fundamental frequency conditions. Depending on the types of disturbance, as well as the relay operation philosophies, such a variation can be in two opposite directions, either reducing the relay security margin or weakening the relay dependability. The sampling window size of the relay, which stands for the speed of relay decision-making, also plays a key role in determining the severity of the impact. A number of methods were developed for quantifying the potential impact of measured disturbances on the protection. The quantification of the disturbance impact on protective relays can be made in two different ways. The setting- based quantification indicates the potential risk that the relay protection zones could be falsely reached due to the disturbance. The design-based quantification illustrates the severity of impact on relay output performance due to unwanted components in the disturbance signal.
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The quantification diagrams provide intuitive information on the details of the disturbance. By developing criteria on the impact diagrams, the disturbances can be classified according to their impact severity and duration, based on which databases can be set up for relay testing.
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thesis-powerquality - On Power Quality and Protection by...

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