Why is harmonic current flow is always indicated as from the non-linear load/s end towards the source end ("backwards" from normal load current flow) ?
The nonlinear load is a source of harmonics. If electrical equivalent circuits are drawn, one for each harmonic frequency, the different frequency sources (harmonic frequency sources) will be located at the nonlinear load location and the harmonic currents will be flowing from it. If the normal power source does not have any harmonics (an ideal case) then the harmonic electrical equivalent diagrams will have no trace of the normal (ideal) power source. If there happen to be used harmonic current mitigators (filters, power line conditioners, etc.), the harmonic current will tend to sink in those.
