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Lecture15 - Ampacity Lecture 15 Fundamentals of Power...

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Page 1 Fundamentals of Power Systems Lecture 15 1 Ampacity Fundamentals of Power Systems Lecture 15 2 Geometric Mean Radius (GMR) ' 0 0 1 1 ln ln ln 2 4 2 4 1 r r D D L r r P P P P S S § · § · ± ± ± ¨ ¸ ¨ ¸ © ¹ © ¹ ' 0 1 ln 2 D L GMR P S Inductance of conductor up to a distance of 1 unit (e.g. 1 foot) ' 0 1 ln 2 GMR L GMR P S Per definition the GMR of a specific conductor or conductor arrangement is the radius of an infinitely thin tube with the same internal inductance as the conductor itself out to a 1-foot radius Inductance of conductor in H per meter length with return path at distance D
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Page 2 Fundamentals of Power Systems Lecture 15 3 Alternative Formula used in Practice Substituting ln (base e) by log (base 10) Inserting P 0 = 4 S 10 -7 Vs/Am Expanding 1 mile = 1609.344 m ' 0 0 2 ln 2 60 ln 2 60 2 D f D X f GMR GMR P P S S S S 7 ' 4 10 1609.344 2 60 log 60 2 log( ) f D X e GMR S S S ² in : /mile (per conductor) ' 0.2794 log 60 f D X GMR Fundamentals of Power Systems Lecture 15 4 Example: Line Impedance z
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