ECE4762011_Lect10 - Lecture 10 Transformers, Generators,...

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Unformatted text preview: Lecture 10 Transformers, Generators, Load, Ybus Professor Tom Overbye Department of Electrical and Computer Engineering ECE 476 POWER SYSTEM ANALYSIS 2 Announcements Be reading Chapter 6. HW 3 is due now. HW 4 is 3.4, 3.10, 3.14, 3.19, 3.23, 3.60; due September 29 in class. First exam is October 11 during class. Closed book, closed notes, one note sheet and calculators allowed 3 Load Tap Changing Transformers LTC transformers have tap ratios that can be varied to regulate bus voltages The typical range of variation is 10% from the nominal values, usually in 33 discrete steps (0.0625% per step). Because tap changing is a mechanical process, LTC transformers usually have a 30 second deadband to avoid repeated changes. Unbalanced tap positions can cause "circulating vars" 4 LTCs and Circulating Vars slack 1 1 .0 0 p u 2 3 4 0 .2 M W 4 0 .0 M W 1 .7 M v a r - 0 .0 M v a r 1 .0 0 0 t a p 1 .0 5 6 t a p 2 4 .1 M W 1 2 .8 M v a r 2 4 .0 M W- 1 2 .0 M v a r A MVA 1 .0 5 p u 0 .9 8 p u 2 4 M W 1 2 M v a r 6 4 M W 1 4 M v a r 4 0 M W 0 M v a r 0 .0 M v a r 8 0 % A M V A 5 Phase Shifting Transformers Phase shifting transformers are used to control the phase angle across the transformer Since power flow through the transformer depends upon phase angle, this allows the transformer to regulate the power flow through the transformer Phase shifters can be used to prevent inadvertent "loop flow" and to prevent line overloads. 6...
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ECE4762011_Lect10 - Lecture 10 Transformers, Generators,...

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