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Unformatted text preview: Page 1 Fundamentals of Power Systems Lecture 15 1 Ampacity Fundamentals of Power Systems Lecture 15 2 Geometric Mean Radius (GMR) ' 1 1 ln ln ln 2 4 2 4 1 r r D D L r r P P P P S S ' 1 ln 2 D L GMR P S Inductance of conductor up to a distance of 1 unit (e.g. 1 foot) ' 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 Page 2 Fundamentals of Power Systems Lecture 15 3 Alternative Formula used in Practice Substituting ln (base e) by log (base 10) Inserting P = 4 S 10-7 Vs/Am Expanding 1 mile = 1609.344 m ' 2 l n 2 6 l n 2 6 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 G M R S S S in : /mile (per conductor) ' 0.2794 log 60 f D X GMR Fundamentals of Power Systems Lecture 15 4 Example: Line Impedance...
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- Spring '08