ECE4762011_Lect20 - ECE 476 POWER SYSTEM ANALYSIS Lecture...

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Lecture 20 Symmetrical Components, Unbalanced Fault Analysis Professor Tom Overbye Department of Electrical and Computer Engineering ECE 476 POWER SYSTEM ANALYSIS
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2 Announcements Be reading Chapters 8 and 9 HW 8 is 7.6, 7.13, 7.19, 7.28; due Nov 3 in class. Start working on Design Project. Tentatively due Nov 17 in class Second exam is on Nov 15 in class. Same format as first exam, except you can bring two note sheets (e.g., the one from the first exam and another)
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3 Analysis of Unsymmetric Systems Except for the balanced three-phase fault, faults result in an unbalanced system. The most common types of faults are single line- ground (SLG) and line-line (LL). Other types are double line-ground (DLG), open conductor, and balanced three phase. System is only unbalanced at point of fault! The easiest method to analyze unbalanced system operation due to faults is through the use of symmetrical components
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4 Symmetric Components The key idea of symmetrical component analysis is to decompose the system into three sequence networks. The networks are then coupled only at the point of the unbalance (i.e., the fault) The three sequence networks are known as the positive sequence (this is the one we’ve been using) negative sequence zero sequence
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5 Positive Sequence Sets The positive sequence sets have three phase currents/voltages with equal magnitude, with phase b lagging phase a by 120°, and phase c lagging phase b by 120°. We’ve been studying positive sequence sets Positive sequence sets have zero neutral current
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6 Negative Sequence Sets The negative sequence sets have three phase currents/voltages with equal magnitude, with phase b leading phase a by 120°, and phase c leading phase b by 120°. Negative sequence sets are similar to positive sequence, except the phase order is reversed Negative sequence sets have zero neutral current
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Zero Sequence Sets Zero sequence sets have three values with equal magnitude and angle. Zero sequence sets have neutral current
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ECE4762011_Lect20 - ECE 476 POWER SYSTEM ANALYSIS Lecture...

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