Analysis of the Behavior of the 5th Harmonic over Power Transmission Lines

With the diffusion in the use of equipment based on power electronics, not only in industry but also and especially in home appliances, harmonic pollution has become a real concern for power systems operation, by including power transmission lines. For addressing this new important issue, analyses through simulations cannot be based on a formerly key simplifying assumption that consists in taking a unique Pi circuit for modelling a transmission line. Thus, based on these concerns, the authors present through examples on a real 230 kV transmission line and with the help of an analytical methodology how to predicting the behavior of power harmonics over the whole length of a line. For its turn, even though many harmonics are supposed to coexist over the line operation, this study is focused on the 5
^th
harmonic due to its importance for being the harmonic of negative sequence with the most likely presence in power transmission systems. Thus, for the solely presence of the 5
^th
harmonic changes in the current amplitude, impedance angle and direction of power flow are performed for showing the consequences in the behavior of the harmonic amplitude of current and voltage over the whole line length. The most significant result is that harmonic analyses can be performed separately from the power frequency and for each of the harmonics with a real ratio of voltage to current. Thus, each of the obtained results can be superimposed to the result at power frequency for giving an overall insight of the influence of power harmonics on the performance ot power transmission line under steady state.