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

Page 3 of 8IEEE PES Transactions on Power Systems> REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 3123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960A. ABL SimulationThe ABL simulation was performed under the use ofANSYS CFX computational system [12]. Only four directionof the wind were considered at angles of 45°, 135°, 225° and315° (see Fig. 1). All these simultations were performed usingon the inlet surface (see Fig. 6), a logarithmic boundarycondition with wind speed equal to 1 m/s at 10 m height fromthe ground and neutral atmosphere, i.e. the Froude numberexceeds 1000 (as in (11)). Analysing the numerical results, theset of spans belonging to S ww was identified, i.e., spans withwind speed less than 1 m/s. Of course, many other angles ofincidence could have been considered to precisely identify thespans with lowest wind speed.Fig. 1. ABL simulation for different directions of wind speed.VI. AMPABL METHODOLOGYThe methodology proposed in this paper was developedbased on information of wind speed (obtained from ABLsimulation) and span clearance of the whole transmission line(obtained from the transmission line design). AmpABLmethodology can be summarized in the following set of steps:1) Select the appropriate parameters of the overheadtransmission line to be analysed.2) Select the region of study (by digitalizing the topographicregion containing all spans of the overhead line) anddiscretize it using an appropriate mesh generator.3) Carry out simulations of the ABL as described in SectionV.4) Identify the spans to constitute the set S ww , as described insection IV.5) Identify the spans to compose the set S we , as described inthe Section IV.6) Take the intersection between S ww and S we to have the setS w∩e . Eliminate the dominated spans to have the nondominatedones. Store the identification number of nondominatedspans in a vector S c .7) Calculate the conductor temperature for all spansbelonging to S c , using the iterative method described insection III, considering the corresponding wind speeddetermined in step 4.8) Recalculate the clearances for all spans of S c .9) Identify the critical spans, i.e., least clearance and/orhottest conductor as described in section III.10) Calculate the steady-state thermal rating for the set ofcritical spans identified in step 9.The advantage of AmpABL methodology is to allow theidentification of critical spans without monitoring any spans ofthe whole overhead line. The monitoring and calculation ofthe dynamic rating in real time by conductor temperaturesensors are now possible to be made simply monitoring thecritical spans. The financial cost to supervise them is expectedto be lower if compared to other methodologies.VII. APPLICATION OF AMPABLThe proposed methodology AmpABL was applied indetermining the steady-state thermal rating [10] of a realoverhead line designed for the following parameters:1) Conductor Linnet or 336 MCM2) Line Voltage = 138 kV3) Solar radiation = 1000 W/m 24) Design wind speed of 1 m/s at 10 m height from theground5) Angle between the wind speed direction and theconductor axis equal to 90 degrees6) 1 PU = 510 A7) Ambient temperature = 30 °C8) TN: Normal Design Temperature of Condutor = 70 °C9) TE: Emergency Design Temperature = 90 °CA. Step 1: Parameters of the Overhead LineThe overhead line has 133 spans distributed along 52 km oflength in the region of Acuruí-MG, southeast of Brazil. Theminimum clearances, in all spans, were extracted directly fromthe design or calculated by using PLS-CADD [11]. Forpurposes of illustration one span is shown in Fig. 2.Fig. 2. Range of original profile of the 138 kV overhead line.