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Unformatted text preview: Power Systems I l Overhead Conductor l Overhead Spacer Cable l Underground Cable l ThreeConductor Cable l Service Cables Transmission Lines Power Systems I Overhead Conductors l ACSR Aluminum Conductor with inner Steel Reinforced strands l ACAR Aluminum Conductor with inner Al allow Reinforced strands l ACSR/AW Aluminum Conductor with inner Alumoweld Steel Reiforced strands l Aluminum  current carrying member l Steel  structural support Power Systems I Overhead Cable l Where conductor closep roximity is required l Insulating jacket surrounds each conductor l Plastic spacers keep conductors from coming in contact with one another Power Systems I Cables Power Systems I Cables l Underground transmission and distribution cables l Semiconducting material surrounds the conductor to grade the electric field l Plastic jacket provides insulation and protection l Neutral strands for an outer shell for protection and return currents Power Systems I Transmission Line Parameters l Line resistance u dc resistance u ac resistance n skin effect n at 60 Hz: l Temperature effects u increased resistance at conductor temperature rises u wiring is rated for 65 C, 75 C, or 90 C u ambient temperature is 20 C A l R dc = dc ac R R = 02 . 1 C 228 = + + = Al old new old new T t T t T R R = conductor resistivity l = conductor length A = conductor cross sectional area Power Systems I Review of Magnetics and Inductance Amperes circuital law = = e i d F l H i e H = H = Magnetic Flux Integral of the flux density that is normal to a defined area = = A d a B H B B A B = A = Integral of the scalar product of a closed path and the magnetic field equals the encircled current Power Systems I Review of Magnetics and Inductance Flux Linkage = = N i i 1 Inductance I d I d I I L = = = = a H a B Power Systems I Inductance of a Single Conductor l Conditions: u infinite straight wire is an approximation of a reasonably long wire l Assumptions: u Image the wire to close at +/ infinity, establishing a kind of oneturn coil with the return path at infinity u Straight infinitely long wire of radius r u Uniform current density in the wire. Total current is I x u Flux lines form concentric circles (i.e. H is tangential) u Angular symmetry  it suffices to consider H x Power Systems I Inductance of a Single Conductor l General: l Case 1: Points inside of the conductor ( x < r ) x I H I dl H x x x x 2 2 = = 7 3 4 3 4 2 2 2 2 2 2 2 10 5 . 8 8 2 2 2 2 2 = = = = = = = = = = = = int r x r int x x x x x x x L I x d x r I d dx x r I d r x d xdx r I dx B d x r I B x r I H x I r I Power Systems I Inductance of a Single Conductor l Case 2: Points outside of the conductor ( x > r ) 1 2 7 1 2 ln 10 2 ln 2 1 2 2 2 2 2 1 2 1 D D L D D I x d x I d dx x I d d dx x I dx B d x I H B I I ext D...
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 Spring '11
 THOMASBALDWIN

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