Contributions on the harmonic analysis of a transmission overhead line - a case study

The increasing need to limit the harmonic pollution of electricity transmission networks, require the use of the harmonic impedance, as a primary tool of analysis. Using the general relations for calculating the harmonic impedance seen along an AC power line deducted under its modeling through a chain of two symmetric passive quadripols built with linear equivalent parameters, uniformly distributed, the article presents the results obtained in a case study that considers an overhead line of 400 kV rated voltage, operating in no load conditions. Sections of the line and respectively the frequencies at which the risk of parallel resonance is maxim are identified. The values obtained with the mathematical model used in Mathcad are confirmed by modeling in Matlab Simulink. The main conclusion drawn from the calculation results is the need to avoid no load operating conditions or operating conditions with very low load of the electricity transmission lines within harmonic polluted power systems.