Methodology of Ampacity Calculation for Overhead Line - Technical ...

Page 7 of 8IEEE PES Transactions on Power Systems> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 7123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960TABLE VBOUNDARY CONDICTIONS USED IN SIMPLIFIED CFX MODEL [17]-[18].Boundary u 1 u 2 u 3 K εxu x2 = uref.lnin ⎜ ⎟ ln⎜u 0⎝ x2o⎠ ⎝x2= u3= 02oInlet ( )⎛ x ⎞ ⎛ ⎞22ref⎟⎠∂uOutlet 0∂x1=1∂u∂x2=10∂u∂x31= 0k =2*C µu∂k= 0∂x∂kWall Nonslip conditions couplet with wall functions = 0∂x∂ u 1∂ u2 ∂ u3 Lateral = 0= 0= 0= 0∂x∂x∂xUpper (Symmetry)3u 1= U∞C. Treatment of Vertical Buoyancy StrenghtThe strengh of vertical Buoyancy is considered as a sourceterm S w in the momentum equation (5), which is given by(15).Sg ⋅δρδg ⋅(ρ − ρ )δ0w=2i=2i(15)ρ0ρ0where S w is the source term by unit of fluid density given in(m/s 2 ), g gravity accelaration (m/s 2 ), ρ fluid density (kg/m 3 ),ρ 0 the fluid reference density (kg/m 3 ) and δ is the Kroneckerdelta wich is unity only for i equal to 2 and zero for i = {1,3}.When considering the density variation ∆ρ constant during thesimulation, the Froude number can be calculated by (16).U∞Fr = (16)1( g ⋅ L ⋅δρ ρ ) 20where U ∞ is the wind speed above 500 meters of height (m/s),∆ρ variation between the base of the land to its top (kg/m 3 )and L the height of the simulation domain (m).In this way, the source term on the x 2 direction (height),introduced in the equation of momentum can be written as(17).S2U∞w=2δ2iL⋅Fr2i(17)Finally, the intensity of the strength of buoyancy due tothermal effects of the ground is obtained from values assignedto the Froude number. Table VI shows the relationshipbetween the state of the atmosphere and the range of valuesassigned to the Froude number.TABLE VIGENERAL VALUES OF FROUDE NUMBER - FR.F rType of Atmospheric> 1000 ABL Neutral10 < F r