Impact of load modeling on the harmonic impedance seen from the transmission network

Traditionally when studying harmonics at transmission system level the medium and low voltage grid is modeled with either an equivalent short-circuit impedance or a fixed PQ load (based on the powerflow) directly at the secondary side of the transmission transformer. However the recent replacement of conventional loads with electronic loads as well as the extended use of power electronics in LV level will result in reduction of damping and increase of household capacitance which may change the harmonic impedance seen from the upstream network (MV or HV) both in the dominant frequency and magnitude. In this paper a HV feeder is modeled in detail starting from the transmission transformer up to the household equipment to investigate whether changes in the type of load affect the impedance seen from the HV. The simulations are performed using software package PSCAD/EMTDC.