Harmonic analysis of power systems in order to network conversion

Conversion of three-Phase Single-Circuit (3PSC) network to three-Phase Double-Circuit (3PDC) and six-Phase Single-Circuit (6PSC) network is a well known method to increase the power transfer capability of the network to meet the increasing energy demand. The most significant constraints maybe used to decide on the optimal alternative, are total loss of the network and desirable voltage limits, while harmonics are omitted. However, harmonic impacts may cause damage to instruments, lead to undesirable power quality and increase total loss of the network. Thereby, in order to obtain the accurate result or adopting an optimal alternative for network conversion, harmonics should be considered. In this paper, harmonic analysis due to conversion of a 3PSC network to 3PDC and 6PSC network is performed. In the study, conversion of entire and one line of the network are analyzed, separately. The results show that suitable alternative for network conversion, with or without considering the effects of harmonics, is different. Also TIF of current is dependent of type of conversion and is different for 3PDC and 6PSC systems; but THD of voltages completely depends on the type of harmonic source in the network. However, analysis of frequency scan results shows that the number of resonances is more in 6PSC conversion than 3PDC counterpart. Also 6PSC conversion leads to less propagation of disturbances along the system during high frequency transients such as lightning surges.